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vector-toc-toggle"> Toggle Coring subsection </button> <ul id="toc-Coring-sublist" class="vector-toc-list"> <li id="toc-Large_coring_projects" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Large_coring_projects"> <div class="vector-toc-text"> 2.1 Large coring projects </div> </a> <ul id="toc-Large_coring_projects-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Core_processing" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Core_processing"> <div class="vector-toc-text"> 3 Core processing </div> </a> <button aria-controls="toc-Core_processing-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle Core processing subsection </button> <ul id="toc-Core_processing-sublist" class="vector-toc-list"> <li id="toc-Brittle_ice" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Brittle_ice"> <div class="vector-toc-text"> 3.1 Brittle ice </div> </a> <ul id="toc-Brittle_ice-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Ice_core_data" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Ice_core_data"> <div class="vector-toc-text"> 4 Ice core data </div> </a> <button aria-controls="toc-Ice_core_data-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle Ice core data subsection </button> <ul id="toc-Ice_core_data-sublist" class="vector-toc-list"> <li id="toc-Dating" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Dating"> <div class="vector-toc-text"> 4.1 Dating </div> </a> <ul id="toc-Dating-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Visual_analysis" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Visual_analysis"> <div class="vector-toc-text"> 4.2 Visual analysis </div> </a> <ul id="toc-Visual_analysis-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Isotopic_analysis" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Isotopic_analysis"> <div class="vector-toc-text"> 4.3 Isotopic analysis </div> </a> <ul id="toc-Isotopic_analysis-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Palaeoatmospheric_sampling" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Palaeoatmospheric_sampling"> <div class="vector-toc-text"> 4.4 Palaeoatmospheric sampling </div> </a> <ul id="toc-Palaeoatmospheric_sampling-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Glaciochemistry" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Glaciochemistry"> <div class="vector-toc-text"> 4.5 Glaciochemistry </div> </a> <ul id="toc-Glaciochemistry-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Radionuclides" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Radionuclides"> <div class="vector-toc-text"> 4.6 Radionuclides </div> </a> <ul id="toc-Radionuclides-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Other_inclusions" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Other_inclusions"> <div class="vector-toc-text"> 4.7 Other inclusions </div> </a> <ul id="toc-Other_inclusions-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Physical_properties" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Physical_properties"> <div class="vector-toc-text"> 4.8 Physical properties </div> </a> <ul id="toc-Physical_properties-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-History" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#History"> <div class="vector-toc-text"> 5 History </div> </a> <button aria-controls="toc-History-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> Toggle History subsection </button> <ul id="toc-History-sublist" class="vector-toc-list"> <li id="toc-Early_years" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Early_years"> <div class="vector-toc-text"> 5.1 Early years </div> </a> <ul id="toc-Early_years-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Antarctica_deep_cores" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Antarctica_deep_cores"> <div class="vector-toc-text"> 5.2 Antarctica deep cores </div> </a> <ul id="toc-Antarctica_deep_cores-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Greenland_deep_cores" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Greenland_deep_cores"> <div class="vector-toc-text"> 5.3 Greenland deep cores </div> </a> <ul id="toc-Greenland_deep_cores-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Non-polar_cores" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Non-polar_cores"> <div class="vector-toc-text"> 5.4 Non-polar cores </div> </a> <ul id="toc-Non-polar_cores-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Future_plans" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Future_plans"> <div class="vector-toc-text"> 6 Future plans </div> </a> <ul id="toc-Future_plans-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> 7 See also </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> 8 References </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Sources" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Sources"> <div class="vector-toc-text"> 9 Sources </div> </a> <ul id="toc-Sources-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> 10 External links </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" > Toggle the table of contents </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading">Ice core</h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" 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Available in 31 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-31" aria-hidden="true" > 31 languages </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%B9%D9%8A%D9%86%D8%A9_%D9%84%D8%A8%D9%8A%D8%A9_%D8%AC%D9%84%D9%8A%D8%AF%D9%8A%D8%A9" title="عينة لبية جليدية – Arabic" lang="ar" hreflang="ar" data-title="عينة لبية جليدية" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target">العربية</a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Testimoni_de_gel" title="Testimoni de gel – Catalan" lang="ca" hreflang="ca" data-title="Testimoni de gel" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target">Català</a></li><li class="interlanguage-link interwiki-cy mw-list-item"><a href="https://cy.wikipedia.org/wiki/Craidd_ia" title="Craidd ia – Welsh" lang="cy" hreflang="cy" data-title="Craidd ia" data-language-autonym="Cymraeg" data-language-local-name="Welsh" class="interlanguage-link-target">Cymraeg</a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/Iskerne" title="Iskerne – Danish" lang="da" hreflang="da" data-title="Iskerne" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target">Dansk</a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Eisbohrkern" title="Eisbohrkern – German" lang="de" hreflang="de" data-title="Eisbohrkern" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target">Deutsch</a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/J%C3%A4%C3%A4puurs%C3%BCdamik" title="Jääpuursüdamik – Estonian" lang="et" hreflang="et" data-title="Jääpuursüdamik" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target">Eesti</a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Testigo_de_hielo" title="Testigo de hielo – Spanish" lang="es" hreflang="es" data-title="Testigo de hielo" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target">Español</a></li><li class="interlanguage-link interwiki-eo mw-list-item"><a href="https://eo.wikipedia.org/wiki/Glacikerno" title="Glacikerno – Esperanto" lang="eo" hreflang="eo" data-title="Glacikerno" data-language-autonym="Esperanto" data-language-local-name="Esperanto" class="interlanguage-link-target">Esperanto</a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%85%D8%BA%D8%B2%D9%87_%DB%8C%D8%AE%DB%8C" title="مغزه یخی – Persian" lang="fa" hreflang="fa" data-title="مغزه یخی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target">فارسی</a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/Carotte_de_glace" title="Carotte de glace – French" lang="fr" hreflang="fr" data-title="Carotte de glace" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target">Français</a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/%EB%B9%99%ED%95%98_%EC%BD%94%EC%96%B4" title="빙하 코어 – Korean" lang="ko" hreflang="ko" data-title="빙하 코어" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target">한국어</a></li><li class="interlanguage-link interwiki-hy mw-list-item"><a href="https://hy.wikipedia.org/wiki/%D5%8D%D5%A1%D5%BC%D6%81%D5%A1%D5%B5%D5%AB%D5%B6_%D5%AF%D5%A5%D5%BC%D5%B6" title="Սառցային կեռն – Armenian" lang="hy" hreflang="hy" data-title="Սառցային կեռն" data-language-autonym="Հայերեն" data-language-local-name="Armenian" class="interlanguage-link-target">Հայերեն</a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Carota_di_ghiaccio" title="Carota di ghiaccio – Italian" lang="it" hreflang="it" data-title="Carota di ghiaccio" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target">Italiano</a></li><li class="interlanguage-link interwiki-he badge-Q17437796 badge-featuredarticle mw-list-item" title="featured article badge"><a href="https://he.wikipedia.org/wiki/%D7%9C%D7%99%D7%91%D7%AA_%D7%A7%D7%A8%D7%97" title="ליבת קרח – Hebrew" lang="he" hreflang="he" data-title="ליבת קרח" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target">עברית</a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/Ledus_dzi%C4%BCurbums" title="Ledus dziļurbums – Latvian" lang="lv" hreflang="lv" data-title="Ledus dziļurbums" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target">Latviešu</a></li><li class="interlanguage-link interwiki-lt mw-list-item"><a href="https://lt.wikipedia.org/wiki/Ledo_kernas" title="Ledo kernas – Lithuanian" lang="lt" hreflang="lt" data-title="Ledo kernas" data-language-autonym="Lietuvių" data-language-local-name="Lithuanian" class="interlanguage-link-target">Lietuvių</a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/J%C3%A9gmag" title="Jégmag – Hungarian" lang="hu" hreflang="hu" data-title="Jégmag" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target">Magyar</a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/Teras_ais" title="Teras ais – Malay" lang="ms" hreflang="ms" data-title="Teras ais" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target">Bahasa Melayu</a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/IJskern" title="IJskern – Dutch" lang="nl" hreflang="nl" data-title="IJskern" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target">Nederlands</a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E6%B0%B7%E5%BA%8A%E3%82%B3%E3%82%A2" title="氷床コア – Japanese" lang="ja" hreflang="ja" data-title="氷床コア" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target">日本語</a></li><li class="interlanguage-link interwiki-no mw-list-item"><a href="https://no.wikipedia.org/wiki/Iskjernepr%C3%B8ve" title="Iskjerneprøve – Norwegian Bokmål" lang="nb" hreflang="nb" data-title="Iskjerneprøve" data-language-autonym="Norsk bokmål" data-language-local-name="Norwegian Bokmål" class="interlanguage-link-target">Norsk bokmål</a></li><li class="interlanguage-link interwiki-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/Iskjerne" title="Iskjerne – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="Iskjerne" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target">Norsk nynorsk</a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Rdze%C5%84_lodowy" title="Rdzeń lodowy – Polish" lang="pl" hreflang="pl" data-title="Rdzeń lodowy" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target">Polski</a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Testemunho_de_gelo" title="Testemunho de gelo – Portuguese" lang="pt" hreflang="pt" data-title="Testemunho de gelo" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target">Português</a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/%D0%9B%D0%B5%D0%B4%D1%8F%D0%BD%D1%8B%D0%B5_%D0%BA%D0%B5%D1%80%D0%BD%D1%8B" title="Ледяные керны – Russian" lang="ru" hreflang="ru" data-title="Ледяные керны" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target">Русский</a></li><li class="interlanguage-link interwiki-simple mw-list-item"><a href="https://simple.wikipedia.org/wiki/Ice_core" title="Ice core – Simple English" lang="en-simple" hreflang="en-simple" data-title="Ice core" data-language-autonym="Simple English" data-language-local-name="Simple English" class="interlanguage-link-target">Simple English</a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/J%C3%A4%C3%A4kairausn%C3%A4yte" title="Jääkairausnäyte – Finnish" lang="fi" hreflang="fi" data-title="Jääkairausnäyte" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target">Suomi</a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/Isk%C3%A4rna" title="Iskärna – Swedish" lang="sv" hreflang="sv" data-title="Iskärna" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target">Svenska</a></li><li class="interlanguage-link interwiki-ta mw-list-item"><a href="https://ta.wikipedia.org/wiki/%E0%AE%AA%E0%AE%A9%E0%AE%BF_%E0%AE%89%E0%AE%B3%E0%AF%8D%E0%AE%B3%E0%AE%95%E0%AE%AE%E0%AF%8D" title="பனி உள்ளகம் – Tamil" lang="ta" hreflang="ta" data-title="பனி உள்ளகம்" data-language-autonym="தமிழ்" data-language-local-name="Tamil" class="interlanguage-link-target">தமிழ்</a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/Buz_%C3%A7ekirde%C4%9Fi" title="Buz çekirdeği – Turkish" lang="tr" hreflang="tr" data-title="Buz çekirdeği" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target">Türkçe</a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/%D0%9B%D1%8C%D0%BE%D0%B4%D0%BE%D0%B2%D0%B8%D0%BA%D0%BE%D0%B2%D1%96_%D0%BA%D0%B5%D1%80%D0%BD%D0%B8" title="Льодовикові керни – Ukrainian" lang="uk" hreflang="uk" data-title="Льодовикові керни" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target">Українська</a></li> </ul> <div class="after-portlet after-portlet-lang"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q258914#sitelinks-wikipedia" title="Edit 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Click here for more information."><img alt="Featured article" src="//upload.wikimedia.org/wikipedia/en/thumb/e/e7/Cscr-featured.svg/20px-Cscr-featured.svg.png" decoding="async" width="20" height="19" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/e/e7/Cscr-featured.svg/30px-Cscr-featured.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/e/e7/Cscr-featured.svg/40px-Cscr-featured.svg.png 2x" data-file-width="466" data-file-height="443" /></a></div></div> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Cylindrical sample drilled from an ice sheet</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Icecore_4.jpg" class="mw-file-description"><img alt="An ice core being slid out of a drill barrel sideways" src="//upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Icecore_4.jpg/220px-Icecore_4.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Icecore_4.jpg/330px-Icecore_4.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Icecore_4.jpg/440px-Icecore_4.jpg 2x" data-file-width="864" data-file-height="576" /></a><figcaption>Ice core sample taken from drill</figcaption></figure> An ice core is a <a href="/wiki/Core_sample" title="Core sample">core sample</a> that is typically removed from an <a href="/wiki/Ice_sheet" title="Ice sheet">ice sheet</a> or a high mountain <a href="/wiki/Glacier" title="Glacier">glacier</a>. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains ice formed over a range of years. Cores are <a href="/wiki/Ice_drilling" title="Ice drilling">drilled</a> with hand <a href="/wiki/Auger_(drill)" class="mw-redirect" title="Auger (drill)">augers</a> (for shallow holes) or powered drills; they can reach depths of over two miles (3.2 km), and contain ice up to 800,000 years old. The physical properties of the ice and of material trapped in it can be used to reconstruct the climate over the age range of the core. The proportions of different oxygen and hydrogen <a href="/wiki/Isotope" title="Isotope">isotopes</a> provide information about <a href="/wiki/Paleothermometer" title="Paleothermometer">ancient temperatures</a>, and the <a href="/wiki/Atmosphere_of_Earth" title="Atmosphere of Earth">air</a> trapped in tiny bubbles can be analysed to determine the level of atmospheric gases such as <a href="/wiki/Carbon_dioxide" title="Carbon dioxide">carbon dioxide</a>. Since <a href="/wiki/Heat_transfer" title="Heat transfer">heat flow</a> in a large ice sheet is very slow, the borehole temperature is another indicator of temperature in the past. This data can be combined to find the <a href="/wiki/Climate_model" title="Climate model">climate model</a> that best fits all the available data. Impurities in ice cores may depend on location. Coastal areas are more likely to include material of marine origin, such as sea salt <a href="/wiki/Ion" title="Ion">ions</a>. <a href="/wiki/Greenland" title="Greenland">Greenland</a> ice cores contain layers of <a href="/wiki/Loess" title="Loess">wind-blown dust</a> that correlate with cold, dry periods in the past, when cold deserts were scoured by wind. <a href="/wiki/Radioactivity" class="mw-redirect" title="Radioactivity">Radioactive</a> elements, either of natural origin or created by <a href="/wiki/Nuclear_weapons_testing" title="Nuclear weapons testing">nuclear testing</a>, can be used to date the layers of ice. Some volcanic events that were sufficiently powerful to send material around the globe have left a signature in many different cores that can be used to synchronise their time scales. Ice cores have been studied since the early 20th century, and several cores were drilled as a result of the <a href="/wiki/International_Geophysical_Year" title="International Geophysical Year">International Geophysical Year</a> (1957–1958). Depths of over 400 m were reached, a record which was extended in the 1960s to 2164 m at <a href="/wiki/Byrd_Station" title="Byrd Station">Byrd Station</a> in Antarctica. <a href="/wiki/Soviet_Union" title="Soviet Union">Soviet</a> ice drilling projects in Antarctica include decades of work at <a href="/wiki/Vostok_Station" title="Vostok Station">Vostok Station</a>, with the deepest core reaching 3769 m. Numerous other deep cores in the Antarctic have been completed over the years, including the <a href="/wiki/West_Antarctic_Ice_Sheet" title="West Antarctic Ice Sheet">West Antarctic Ice Sheet</a> project, and cores managed by the <a href="/wiki/British_Antarctic_Survey" title="British Antarctic Survey">British Antarctic Survey</a> and the <a href="/wiki/ITASE" title="ITASE">International Trans-Antarctic Scientific Expedition</a>. In Greenland, a sequence of collaborative projects began in the 1970s with the <a href="/wiki/Greenland_Ice_Sheet_Project" title="Greenland Ice Sheet Project">Greenland Ice Sheet Project</a>; there have been multiple follow-up projects, with the most recent, the <a href="/wiki/East_Greenland_Ice-Core_Project" title="East Greenland Ice-Core Project">East Greenland Ice-Core Project</a>, originally expected to complete a deep core in east Greenland in 2020 but since postponed.<a href="#cite_note-corona-1">[1]</a> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Structure_of_ice_sheets_and_cores">Structure of ice sheets and cores</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=1" title="Edit section: Structure of ice sheets and cores">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Ice-sheet_dynamics" class="mw-redirect" title="Ice-sheet dynamics">Ice-sheet dynamics</a></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Taku_glacier_firn_ice_sampling.png" class="mw-file-description"><img alt="A scientist in a pit of snow" src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e9/Taku_glacier_firn_ice_sampling.png/220px-Taku_glacier_firn_ice_sampling.png" decoding="async" width="220" height="149" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e9/Taku_glacier_firn_ice_sampling.png/330px-Taku_glacier_firn_ice_sampling.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e9/Taku_glacier_firn_ice_sampling.png/440px-Taku_glacier_firn_ice_sampling.png 2x" data-file-width="519" data-file-height="352" /></a><figcaption>Sampling the surface of <a href="/wiki/Taku_Glacier" title="Taku Glacier">Taku Glacier</a> in Alaska. There is increasingly dense <a href="/wiki/Firn" title="Firn">firn</a> between surface snow and blue glacier ice.</figcaption></figure> An ice core is a vertical column through a glacier, sampling the layers that formed through an annual cycle of snowfall and melt.<a href="#cite_note-Alley-2000-2-2">[2]</a> As snow accumulates, each layer presses on lower layers, making them denser until they turn into <a href="/wiki/Firn" title="Firn">firn</a>. Firn is not dense enough to prevent air from escaping; but at a density of about 830 kg/m3 it turns to ice, and the air within is sealed into bubbles that capture the composition of the atmosphere at the time the ice formed.<a href="#cite_note-Alley-2000-3">[3]</a> The depth at which this occurs varies with location, but in Greenland and the Antarctic it ranges from 64 m to 115 m.<a href="#cite_note-Talalay-2016-6-4">[4]</a> Because the rate of snowfall varies from site to site, the age of the firn when it turns to ice varies a great deal. At <a href="/wiki/Summit_Camp" title="Summit Camp">Summit Camp</a> in Greenland, the depth is 77 m and the ice is 230 years old; at <a href="/wiki/Dome_C" title="Dome C">Dome C</a> in Antarctica the depth is 95 m and the age 2500 years.<a href="#cite_note-5">[5]</a> As further layers build up, the pressure increases, and at about 1500 m the <a href="/wiki/Crystal_structure" title="Crystal structure">crystal structure</a> of the ice changes from hexagonal to cubic, allowing air molecules to move into the cubic crystals and form a <a href="/wiki/Clathrate" class="mw-redirect" title="Clathrate">clathrate</a>. The bubbles disappear and the ice becomes more transparent.<a href="#cite_note-Alley-2000-3">[3]</a> Two or three feet of snow may turn into less than a foot of ice.<a href="#cite_note-Alley-2000-3">[3]</a> The weight above makes deeper layers of ice thin and flow outwards. Ice is lost at the edges of the glacier to <a href="/wiki/Icebergs" class="mw-redirect" title="Icebergs">icebergs</a>, or to summer melting, and the overall shape of the glacier does not change much with time.<a href="#cite_note-6">[6]</a> The outward flow can distort the layers, so it is desirable to drill deep ice cores at places where there is very little flow. These can be located using maps of the flow lines.<a href="#cite_note-7">[7]</a> Impurities in the ice provide information on the environment from when they were deposited. These include soot, ash, and other types of particle from <a href="/wiki/Wildfire" title="Wildfire">forest fires</a> and <a href="/wiki/Volcano" title="Volcano">volcanoes</a>; isotopes such as <a href="/wiki/Beryllium-10" title="Beryllium-10">beryllium-10</a> created by <a href="/wiki/Cosmic_ray" title="Cosmic ray">cosmic rays</a>; <a href="/wiki/Micrometeorite" title="Micrometeorite">micrometeorites</a>; and <a href="/wiki/Pollen" title="Pollen">pollen</a>.<a href="#cite_note-Alley-2000-2-2">[2]</a> The lowest layer of a glacier, called basal ice, is frequently formed of subglacial meltwater that has refrozen. It can be up to about 20 m thick, and though it has scientific value (for example, it may contain subglacial microbial populations),<a href="#cite_note-8">[8]</a> it often does not retain stratigraphic information.<a href="#cite_note-9">[9]</a> Cores are often drilled in areas such as Antarctica and central Greenland where the temperature is almost never warm enough to cause melting, but the summer sunlight can still alter the snow. In polar areas, the Sun is visible day and night during the local summer and invisible all winter. It can make some snow <a href="/wiki/Sublimation_(phase_transition)" title="Sublimation (phase transition)">sublimate</a>, leaving the top inch or so less dense. When the Sun approaches its lowest point in the sky, the temperature drops and <a href="/wiki/Hoar_frost" class="mw-redirect" title="Hoar frost">hoar frost</a> forms on the top layer. Buried under the snow of following years, the coarse-grained hoar frost compresses into lighter layers than the winter snow. As a result, alternating bands of lighter and darker ice can be seen in an ice core.<a href="#cite_note-10">[10]</a> <div class="mw-heading mw-heading2"><h2 id="Coring">Coring</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=2" title="Edit section: Coring">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Ice_drilling" title="Ice drilling">Ice drilling</a></div> <figure class="mw-default-size mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Brooks_ice_auger_patent_drawings_1932-retouched.png" class="mw-file-description"><img alt="Drawing of a cylinder with two helical flanges around it and cutting teeth at the bottom" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/af/Brooks_ice_auger_patent_drawings_1932-retouched.png/220px-Brooks_ice_auger_patent_drawings_1932-retouched.png" decoding="async" width="220" height="559" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/a/af/Brooks_ice_auger_patent_drawings_1932-retouched.png 1.5x" data-file-width="287" data-file-height="729" /></a><figcaption>Ice auger patented in 1932; the design is very similar to modern augers used for shallow drilling.<a href="#cite_note-Talalay-2016-2-11">[11]</a></figcaption></figure> Ice cores are collected by cutting around a cylinder of ice in a way that enables it to be brought to the surface. Early cores were often collected with hand <a href="/wiki/Auger_(drill)" class="mw-redirect" title="Auger (drill)">augers</a> and they are still used for short holes. A design for ice core augers was patented in 1932 and they have changed little since. An auger is essentially a cylinder with <a href="/wiki/Helix" title="Helix">helical</a> metal ribs (known as flights) wrapped around the outside, at the lower end of which are cutting blades. Hand augers can be rotated by a <a href="/wiki/T-handle" class="mw-redirect" title="T-handle">T handle</a> or a <a href="/wiki/Brace_(tool)" title="Brace (tool)">brace handle</a>, and some can be attached to handheld <a href="/wiki/Electric_drill" class="mw-redirect" title="Electric drill">electric drills</a> to power the rotation. With the aid of a <a href="/wiki/Tripod" title="Tripod">tripod</a> for lowering and raising the auger, cores up to 50 m deep can be retrieved, but the practical limit is about 30 m for engine-powered augers, and less for hand augers. Below this depth, electromechanical or thermal drills are used.<a href="#cite_note-Talalay-2016-2-11">[11]</a> The cutting apparatus of a drill is on the bottom end of a drill barrel, the tube that surrounds the core as the drill cuts downward. The <a href="/wiki/Drill_cuttings" title="Drill cuttings">cuttings</a> (chips of ice cut away by the drill) must be drawn up the hole and disposed of or they will reduce the cutting efficiency of the drill.<a href="#cite_note-Talalay-2016-3-12">[12]</a> They can be removed by compacting them into the walls of the hole or into the core, by air circulation (dry drilling),<a href="#cite_note-Talalay-2016-3-12">[12]</a><a href="#cite_note-Talalay_2016-13">[13]</a> or by the use of a <a href="/wiki/Drilling_fluid" title="Drilling fluid">drilling fluid</a> (wet drilling).<a href="#cite_note-Talalay-2016-4-14">[14]</a> Dry drilling is limited to about 400 m depth, since below that point a hole would close up as the ice deforms from the weight of the ice above.<a href="#cite_note-15">[15]</a> Drilling fluids are chosen to balance the pressure so that the hole remains stable.<a href="#cite_note-Talalay_2016-13">[13]</a> The fluid must have a low kinematic <a href="/wiki/Viscosity" title="Viscosity">viscosity</a> to reduce <a href="/wiki/Tripping_(pipe)" title="Tripping (pipe)">tripping</a> time (the time taken to pull the drilling equipment out of the hole and return it to the bottom of the hole). Since retrieval of each segment of core requires tripping, a slower speed of travel through the drilling fluid could add significant time to a project—a year or more for a deep hole. The fluid must contaminate the ice as little as possible; it must have low <a href="/wiki/Toxicity" title="Toxicity">toxicity</a>, for safety and to minimize the effect on the environment; it must be available at a reasonable cost; and it must be relatively easy to transport.<a href="#cite_note-16">[16]</a> Historically, there have been three main types of ice drilling fluids: two-component fluids based on <a href="/wiki/Kerosene" title="Kerosene">kerosene</a>-like products mixed with <a href="/wiki/Fluorocarbon" title="Fluorocarbon">fluorocarbons</a> to increase density; alcohol compounds, including aqueous <a href="/wiki/Ethylene_glycol" title="Ethylene glycol">ethylene glycol</a> and <a href="/wiki/Ethanol" title="Ethanol">ethanol</a> solutions; and <a href="/wiki/Ester" title="Ester">esters</a>, including <a href="/wiki/N-Butyl_acetate" class="mw-redirect" title="N-Butyl acetate">n-butyl acetate</a>. Newer fluids have been proposed, including new ester-based fluids, low-molecular weight <a href="/wiki/Dimethylsiloxane" class="mw-redirect" title="Dimethylsiloxane">dimethyl siloxane</a> oils, <a href="/wiki/Fatty_acid_ester" title="Fatty acid ester">fatty-acid esters</a>, and kerosene-based fluids mixed with foam-expansion agents.<a href="#cite_note-17">[17]</a> Rotary drilling is the main method of drilling for minerals and it has also been used for ice drilling. It uses a <a href="/wiki/Drill_string" title="Drill string">string of drill pipe</a> rotated from the top, and drilling fluid is pumped down through the pipe and back up around it. The cuttings are removed from the fluid at the top of the hole and the fluid is then pumped back down.<a href="#cite_note-Talalay-2016-4-14">[14]</a> This approach requires long trip times, since the entire drill string must be hoisted out of the hole, and each length of pipe must be separately disconnected, and then reconnected when the drill string is reinserted.<a href="#cite_note-Talalay-2016-3-12">[12]</a><a href="#cite_note-Talalay-2016-5-18">[18]</a> Along with the logistical difficulties associated with bringing heavy equipment to ice sheets, this makes traditional rotary drills unattractive.<a href="#cite_note-Talalay-2016-3-12">[12]</a> In contrast, <a href="/wiki/Wireline_(cabling)" title="Wireline (cabling)">wireline</a> drills allow the removal of the core barrel from the drill assembly while it is still at the bottom of the borehole. The core barrel is hoisted to the surface, and the core removed; the barrel is lowered again and reconnected to the drill assembly.<a href="#cite_note-19">[19]</a> Another alternative is flexible drill-stem rigs, in which the <a href="/wiki/Drill_string" title="Drill string">drill string</a> is flexible enough to be coiled when at the surface. This eliminates the need to disconnect and reconnect the pipes during a trip.<a href="#cite_note-Talalay-2016-5-18">[18]</a><figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Drilling_mechanical-drill-head.jpg" class="mw-file-description"><img alt="The bottom of an ice drill" src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Drilling_mechanical-drill-head.jpg/220px-Drilling_mechanical-drill-head.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Drilling_mechanical-drill-head.jpg/330px-Drilling_mechanical-drill-head.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Drilling_mechanical-drill-head.jpg/440px-Drilling_mechanical-drill-head.jpg 2x" data-file-width="2400" data-file-height="1600" /></a><figcaption>Mechanical drill head, showing cutting teeth</figcaption></figure> The need for a string of drillpipe that extends from the surface to the bottom of the borehole can be eliminated by suspending the entire downhole assembly on an armoured cable that conveys power to the downhole motor. These cable-suspended drills can be used for both shallow and deep holes; they require an anti-torque device, such as <a href="/wiki/Leaf_spring" title="Leaf spring">leaf-springs</a> that press against the borehole, to prevent the drill assembly rotating around the drillhead as it cuts the core.<a href="#cite_note-20">[20]</a> The drilling fluid is usually circulated down around the outside of the drill and back up between the core and core barrel; the cuttings are stored in the downhole assembly, in a chamber above the core. When the core is retrieved, the cuttings chamber is emptied for the next run. Some drills have been designed to retrieve a second annular core outside the central core, and in these drills the space between the two cores can be used for circulation. Cable-suspended drills have proved to be the most reliable design for deep ice drilling.<a href="#cite_note-21">[21]</a><a href="#cite_note-22">[22]</a> Thermal drills, which cut ice by electrically heating the drill head, can also be used, but they have some disadvantages. Some have been designed for working in cold ice; they have high power consumption and the heat they produce can degrade the quality of the retrieved ice core. Early thermal drills, designed for use without drilling fluid, were limited in depth as a result; later versions were modified to work in fluid-filled holes but this slowed down trip times, and these drills retained the problems of the earlier models. In addition, thermal drills are typically bulky and can be impractical to use in areas where there are logistical difficulties. More recent modifications include the use of <a href="/wiki/Antifreeze" title="Antifreeze">antifreeze</a>, which eliminates the need for heating the drill assembly and hence reduces the power needs of the drill.<a href="#cite_note-23">[23]</a> Hot-water drills use jets of hot water at the drill head to melt the water around the core. The drawbacks are that it is difficult to accurately control the dimensions of the borehole, the core cannot easily be kept sterile, and the heat may cause <a href="/wiki/Thermal_shock" title="Thermal shock">thermal shock</a> to the core.<a href="#cite_note-24">[24]</a> When drilling in temperate ice, thermal drills have an advantage over electromechanical (EM) drills: ice melted by pressure can refreeze on EM drill bits, reducing cutting efficiency, and can clog other parts of the mechanism. EM drills are also more likely to fracture ice cores where the ice is under high stress.<a href="#cite_note-25">[25]</a> When drilling deep holes, which require drilling fluid, the hole must be <a href="/wiki/Casing_(borehole)" title="Casing (borehole)">cased</a> (fitted with a cylindrical lining), since otherwise the drilling fluid will be absorbed by the snow and firn. The casing has to reach down to the impermeable ice layers. To install casing a shallow auger can be used to create a pilot hole, which is then <a href="/wiki/Reaming" class="mw-redirect" title="Reaming">reamed</a> (expanded) until it is wide enough to accept the casing; a large diameter auger can also be used, avoiding the need for reaming. An alternative to casing is to use water in the borehole to saturate the porous snow and firn; the water eventually turns to ice.<a href="#cite_note-Talalay-2016-6-4">[4]</a> Ice cores from different depths are not all equally in demand by scientific investigators, which can lead to a shortage of ice cores at certain depths. To address this, work has been done on technology to drill replicate cores: additional cores, retrieved by drilling into the sidewall of the borehole, at depths of particular interest. Replicate cores were successfully retrieved at WAIS divide in the 2012–2013 drilling season, at four different depths.<a href="#cite_note-26">[26]</a> <div class="mw-heading mw-heading3"><h3 id="Large_coring_projects">Large coring projects</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=3" title="Edit section: Large coring projects">edit</a>]</div> The logistics of any coring project are complex because the locations are usually difficult to reach, and may be at high altitude. The largest projects require years of planning and years to execute, and are usually run as international consortiums. The <a href="/wiki/East_Greenland_Ice-Core_Project" title="East Greenland Ice-Core Project">EastGRIP</a> project, for example, which as of 2017 is drilling in eastern Greenland, is run by the <a href="/w/index.php?title=Centre_for_Ice_and_Climate&action=edit&redlink=1" class="new" title="Centre for Ice and Climate (page does not exist)">Centre for Ice and Climate</a> (<a href="/wiki/Niels_Bohr_Institute" title="Niels Bohr Institute">Niels Bohr Institute</a>, <a href="/wiki/University_of_Copenhagen" title="University of Copenhagen">University of Copenhagen</a>) in <a href="/wiki/Denmark" title="Denmark">Denmark</a>,<a href="#cite_note-27">[27]</a> and includes representatives from 12 countries on its steering committee.<a href="#cite_note-28">[28]</a> Over the course of a drilling season, scores of people work at the camp,<a href="#cite_note-29">[29]</a> and logistics support includes airlift capabilities provided by the <a href="/wiki/Air_National_Guard" title="Air National Guard">US Air National Guard</a>, using <a href="/wiki/Lockheed_C-130_Hercules" title="Lockheed C-130 Hercules">Hercules transport planes</a> owned by the <a href="/wiki/National_Science_Foundation" title="National Science Foundation">National Science Foundation</a>.<a href="#cite_note-30">[30]</a> In 2015 the EastGRIP team moved the camp facilities from <a href="/w/index.php?title=North_Greenland_Eemian_Ice_Drilling&action=edit&redlink=1" class="new" title="North Greenland Eemian Ice Drilling (page does not exist)">NEEM</a>, a previous Greenland ice core drilling site, to the EastGRIP site.<a href="#cite_note-31">[31]</a> Drilling is expected to continue until at least 2020.<a href="#cite_note-32">[32]</a> <div class="mw-heading mw-heading2"><h2 id="Core_processing">Core processing</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=4" title="Edit section: Core processing">edit</a>]</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Gripsaw.jpg" class="mw-file-description"><img alt="Scientist standing at a bench, sawing an ice core" src="//upload.wikimedia.org/wikipedia/commons/thumb/2/29/Gripsaw.jpg/220px-Gripsaw.jpg" decoding="async" width="220" height="147" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/29/Gripsaw.jpg/330px-Gripsaw.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/29/Gripsaw.jpg/440px-Gripsaw.jpg 2x" data-file-width="900" data-file-height="600" /></a><figcaption>Sawing the <a href="/wiki/Greenland_ice_core_project" title="Greenland ice core project">GRIP</a> core</figcaption></figure> With some variation between projects, the following steps must occur between drilling and final storage of the ice core.<a href="#cite_note-UNH-33">[33]</a> The drill removes an annulus of ice around the core but does not cut under it. A spring-loaded lever arm called a core dog can break off the core and hold it in place while it is brought to the surface. The core is then extracted from the drill barrel, usually by laying it out flat so that the core can slide out onto a prepared surface.<a href="#cite_note-UNH-33">[33]</a> The core must be cleaned of drilling fluid as it is slid out; for the <a href="/wiki/WAIS_Divide" title="WAIS Divide">WAIS Divide</a> coring project, a vacuuming system was set up to facilitate this. The surface that receives the core should be aligned as accurately as possible with the drill barrel to minimise mechanical stress on the core, which can easily break. The ambient temperature is kept well below freezing to avoid thermal shock.<a href="#cite_note-Souney-2014-1-34">[34]</a> A log is kept with information about the core, including its length and the depth it was retrieved from, and the core may be marked to show its orientation. It is usually cut into shorter sections, the standard length in the US being one metre. The cores are then stored on site, usually in a space below snow level to simplify temperature maintenance, though additional refrigeration can be used. If more drilling fluid must be removed, air may be blown over the cores. Any samples needed for preliminary analysis are taken. The core is then bagged, often in <a href="/wiki/Polythene" class="mw-redirect" title="Polythene">polythene</a>, and stored for shipment. Additional packing, including padding material, is added. When the cores are flown from the drilling site, the aircraft's flight deck is unheated to help maintain a low temperature; when they are transported by ship they must be kept in a refrigeration unit.<a href="#cite_note-Souney-2014-1-34">[34]</a> There are several locations around the world that store ice cores, such as the <a href="/wiki/National_Ice_Core_Laboratory" class="mw-redirect" title="National Ice Core Laboratory">National Ice Core Laboratory</a> in the US. These locations make samples available for testing. A substantial fraction of each core is archived for future analyses.<a href="#cite_note-Souney-2014-1-34">[34]</a><a href="#cite_note-35">[35]</a> <div class="mw-heading mw-heading3"><h3 id="Brittle_ice">Brittle ice</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=5" title="Edit section: Brittle ice">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1273380762/mw-parser-output/.tmulti">.mw-parser-output .tmulti .multiimageinner{display:flex;flex-direction:column}.mw-parser-output .tmulti .trow{display:flex;flex-direction:row;clear:left;flex-wrap:wrap;width:100%;box-sizing:border-box}.mw-parser-output .tmulti .tsingle{margin:1px;float:left}.mw-parser-output .tmulti .theader{clear:both;font-weight:bold;text-align:center;align-self:center;background-color:transparent;width:100%}.mw-parser-output .tmulti .thumbcaption{background-color:transparent}.mw-parser-output .tmulti .text-align-left{text-align:left}.mw-parser-output .tmulti .text-align-right{text-align:right}.mw-parser-output .tmulti .text-align-center{text-align:center}@media all and (max-width:720px){.mw-parser-output .tmulti .thumbinner{width:100%!important;box-sizing:border-box;max-width:none!important;align-items:center}.mw-parser-output .tmulti .trow{justify-content:center}.mw-parser-output .tmulti .tsingle{float:none!important;max-width:100%!important;box-sizing:border-box;text-align:center}.mw-parser-output .tmulti .tsingle .thumbcaption{text-align:left}.mw-parser-output .tmulti .trow>.thumbcaption{text-align:center}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .tmulti .multiimageinner span:not(.skin-invert-image):not(.skin-invert):not(.bg-transparent) img{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .tmulti .multiimageinner span:not(.skin-invert-image):not(.skin-invert):not(.bg-transparent) img{background-color:white}}</style><div class="thumb tmulti tleft"><div class="thumbinner multiimageinner" style="width:308px;max-width:308px"><div class="trow"><div class="tsingle" style="width:152px;max-width:152px"><div class="thumbimage"><a href="/wiki/File:CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/2/22/CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg/150px-CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg" decoding="async" width="150" height="103" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/22/CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg/225px-CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/22/CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg/300px-CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg 2x" data-file-width="2464" data-file-height="1686" /></a></div><div class="thumbcaption">Bubbles in an Antarctic ice sample. Illuminated with polarised light</div></div><div class="tsingle" style="width:152px;max-width:152px"><div class="thumbimage"><a href="/wiki/File:CSIRO_ScienceImage_521_Bubbles_in_Ice.jpg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/d/d0/CSIRO_ScienceImage_521_Bubbles_in_Ice.jpg/150px-CSIRO_ScienceImage_521_Bubbles_in_Ice.jpg" decoding="async" width="150" height="99" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/d0/CSIRO_ScienceImage_521_Bubbles_in_Ice.jpg/225px-CSIRO_ScienceImage_521_Bubbles_in_Ice.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/d0/CSIRO_ScienceImage_521_Bubbles_in_Ice.jpg/300px-CSIRO_ScienceImage_521_Bubbles_in_Ice.jpg 2x" data-file-width="2543" data-file-height="1681" /></a></div><div class="thumbcaption">Sliver of Antarctic ice showing trapped bubbles. Images from <a href="/wiki/CSIRO" title="CSIRO">CSIRO</a>.</div></div></div></div></div> Over a depth range known as the <a href="/w/index.php?title=Brittle_ice&action=edit&redlink=1" class="new" title="Brittle ice (page does not exist)">brittle ice</a> zone, bubbles of air are trapped in the ice under great pressure. When the core is brought to the surface, the bubbles can exert a stress that exceeds the tensile strength of the ice, resulting in cracks and <a href="/wiki/Spall" title="Spall">spall</a>.<a href="#cite_note-Souney-2014-2-36">[36]</a> At greater depths, the air disappears into clathrates and the ice becomes stable again.<a href="#cite_note-Souney-2014-2-36">[36]</a><a href="#cite_note-37">[37]</a> At the WAIS Divide site, the brittle ice zone was from 520 m to 1340 m depth.<a href="#cite_note-Souney-2014-2-36">[36]</a> The brittle ice zone typically returns poorer quality samples than for the rest of the core. Some steps can be taken to alleviate the problem. Liners can be placed inside the drill barrel to enclose the core before it is brought to the surface, but this makes it difficult to clean off the drilling fluid. In mineral drilling, special machinery can bring core samples to the surface at bottom-hole pressure, but this is too expensive for the inaccessible locations of most drilling sites. Keeping the processing facilities at very low temperatures limits thermal shocks. Cores are most brittle at the surface, so another approach is to break them into 1 m lengths in the hole. Extruding the core from the drill barrel into a net helps keep it together if it shatters. Brittle cores are also often allowed to rest in storage at the drill site for some time, up to a full year between drilling seasons, to let the ice gradually relax.<a href="#cite_note-Souney-2014-2-36">[36]</a><a href="#cite_note-38">[38]</a> <div class="mw-heading mw-heading2"><h2 id="Ice_core_data">Ice core data</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=6" title="Edit section: Ice core data">edit</a>]</div> <div class="mw-heading mw-heading3"><h3 id="Dating">Dating</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=7" title="Edit section: Dating">edit</a>]</div> Many different kinds of analysis are performed on ice cores, including visual layer counting, tests for <a href="/wiki/Electrical_resistivity_and_conductivity" title="Electrical resistivity and conductivity">electrical conductivity</a> and physical properties, and assays for inclusion of gases, particles, <a href="/wiki/Radionuclide" title="Radionuclide">radionuclides</a>, and various molecular <a href="/wiki/Chemical_species" title="Chemical species">species</a>. For the results of these tests to be useful in the reconstruction of <a href="/wiki/Paleoenvironment" class="mw-redirect" title="Paleoenvironment">palaeoenvironments</a>, there has to be a way to determine the relationship between depth and age of the ice. The simplest approach is to count layers of ice that correspond to the original annual layers of snow, but this is not always possible. An alternative is to model the ice accumulation and flow to predict how long it takes a given snowfall to reach a particular depth. Another method is to correlate radionuclides or trace atmospheric gases with other timescales such as periodicities in the earth's <a href="/wiki/Orbital_parameter" class="mw-redirect" title="Orbital parameter">orbital parameters</a>.<a href="#cite_note-39">[39]</a> A difficulty in ice core dating is that gases can <a href="/wiki/Diffusion" title="Diffusion">diffuse</a> through firn, so the ice at a given depth may be substantially older than the gases trapped in it. As a result, there are two chronologies for a given ice core: one for the ice, and one for the trapped gases. To determine the relationship between the two, models have been developed for the depth at which gases are trapped for a given location, but their predictions have not always proved reliable.<a href="#cite_note-40">[40]</a><a href="#cite_note-41">[41]</a> At locations with very low snowfall, such as <a href="/wiki/Vostok_Station" title="Vostok Station">Vostok</a>, the uncertainty in the difference between ages of ice and gas can be over 1,000 years.<a href="#cite_note-42">[42]</a> The density and size of the bubbles trapped in ice provide an indication of crystal size at the time they formed. The size of a crystal is related to its growth rate, which in turn depends on the temperature, so the properties of the bubbles can be combined with information on accumulation rates and firn density to calculate the temperature when the firn formed.<a href="#cite_note-Alley-2010-43">[43]</a> <a href="/wiki/Radiocarbon_dating" title="Radiocarbon dating">Radiocarbon dating</a> can be used on the carbon in trapped CO 2. In the polar ice sheets there is about 15–20 μg of carbon in the form of CO 2 in each kilogram of ice, and there may also be <a href="/wiki/Carbonate" title="Carbonate">carbonate</a> particles from wind-blown dust (<a href="/wiki/Loess" title="Loess">loess</a>). The CO 2 can be isolated by subliming the ice in a vacuum, keeping the temperature low enough to avoid the loess giving up any carbon. The results have to be corrected for the presence of <a href="/wiki/Carbon-14" title="Carbon-14">14 C</a> produced directly in the ice by cosmic rays, and the amount of correction depends strongly on the location of the ice core. Corrections for 14 C produced by nuclear testing have much less impact on the results.<a href="#cite_note-44">[44]</a> Carbon in <a href="/wiki/Particulates" title="Particulates">particulates</a> can also be dated by separating and testing the water-insoluble <a href="/wiki/Organic_chemistry" title="Organic chemistry">organic</a> components of dust. The very small quantities typically found require at least 300 g of ice to be used, limiting the ability of the technique to precisely assign an age to core depths.<a href="#cite_note-45">[45]</a> Timescales for ice cores from the same hemisphere can usually be synchronised using layers that include material from volcanic events. It is more difficult to connect the timescales in different hemispheres. The <a href="/wiki/Laschamp_event" title="Laschamp event">Laschamp event</a>, a <a href="/wiki/Geomagnetic_reversal" title="Geomagnetic reversal">geomagnetic reversal</a> about 40,000 years ago, can be identified in cores;<a href="#cite_note-46">[46]</a><a href="#cite_note-47">[47]</a> away from that point, measurements of gases such as CH 4 (<a href="/wiki/Methane" title="Methane">methane</a>) can be used to connect the chronology of a Greenland core (for example) with an Antarctic core.<a href="#cite_note-48">[48]</a><a href="#cite_note-49">[49]</a> In cases where volcanic <a href="/wiki/Tephra" title="Tephra">tephra</a> is interspersed with ice, it can be dated using <a href="/wiki/Argon%E2%80%93argon_dating" title="Argon–argon dating">argon/argon dating</a> and hence provide fixed points for dating the ice.<a href="#cite_note-Landais-2012-50">[50]</a><a href="#cite_note-51">[51]</a> <a href="/wiki/Uranium_series_dating" class="mw-redirect" title="Uranium series dating">Uranium decay</a> has also been used to date ice cores.<a href="#cite_note-Landais-2012-50">[50]</a><a href="#cite_note-52">[52]</a> Another approach is to use <a href="/wiki/Bayesian_probability" title="Bayesian probability">Bayesian probability</a> techniques to find the optimal combination of multiple independent records. This approach was developed in 2010 and has since been turned into a software tool, DatIce.<a href="#cite_note-53">[53]</a><a href="#cite_note-54">[54]</a> The boundary between the <a href="/wiki/Quaternary_extinction_event" class="mw-redirect" title="Quaternary extinction event">Pleistocene</a> and the <a href="/wiki/Holocene" title="Holocene">Holocene</a>, about 11,700 years ago, is now formally defined with reference to data on Greenland ice cores. Formal definitions of stratigraphic boundaries allow scientists in different locations to correlate their findings. These often involve fossil records, which are not present in ice cores, but cores have extremely precise <a href="/wiki/Paleoclimatology" title="Paleoclimatology">palaeoclimatic</a> information that can be correlated with other climate proxies.<a href="#cite_note-55">[55]</a> The dating of ice sheets has proved to be a key element in providing dates for palaeoclimatic records. According to <a href="/wiki/Richard_Alley" title="Richard Alley">Richard Alley</a>, "In many ways, ice cores are the 'rosetta stones' that allow development of a global network of accurately dated paleoclimatic records using the best ages determined anywhere on the planet".<a href="#cite_note-Alley-2010-43">[43]</a> <div class="mw-heading mw-heading3"><h3 id="Visual_analysis">Visual analysis</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=8" title="Edit section: Visual analysis">edit</a>]</div> <figure class="mw-default-size mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:GISP2_1855m_ice_core_layers.png" class="mw-file-description"><img alt="A series of dark and light bands, with arrows identifying the lighter bands" src="//upload.wikimedia.org/wikipedia/commons/thumb/3/31/GISP2_1855m_ice_core_layers.png/220px-GISP2_1855m_ice_core_layers.png" decoding="async" width="220" height="99" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/31/GISP2_1855m_ice_core_layers.png/330px-GISP2_1855m_ice_core_layers.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/31/GISP2_1855m_ice_core_layers.png/440px-GISP2_1855m_ice_core_layers.png 2x" data-file-width="741" data-file-height="335" /></a><figcaption>19 cm long section of GISP 2 ice core from 1855 m showing annual layer structure illuminated from below by a fibre optic source. Section contains 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers.<a href="#cite_note-56">[56]</a></figcaption></figure> Cores show visible layers, which correspond to annual snowfall at the core site. If a pair of pits is dug in fresh snow with a thin wall between them and one of the pits is roofed over, an observer in the roofed pit will see the layers revealed by sunlight shining through. A six-foot pit may show anything from less than a year of snow to several years of snow, depending on the location. Poles left in the snow from year to year show the amount of accumulated snow each year, and this can be used to verify that the visible layer in a snow pit corresponds to a single year's snowfall.<a href="#cite_note-57">[57]</a> In central Greenland a typical year might produce two or three feet of winter snow, plus a few inches of summer snow. When this turns to ice, the two layers will make up no more than a foot of ice. The layers corresponding to the summer snow will contain bigger bubbles than the winter layers, so the alternating layers remain visible, which makes it possible to count down a core and determine the age of each layer.<a href="#cite_note-58">[58]</a> As the depth increases to the point where the ice structure changes to a clathrate, the bubbles are no longer visible, and the layers can no longer be seen. Dust layers may now become visible. Ice from Greenland cores contains dust carried by wind; the dust appears most strongly in late winter, and appears as cloudy grey layers. These layers are stronger and easier to see at times in the past when the Earth's climate was cold, dry, and windy.<a href="#cite_note-59">[59]</a> Any method of counting layers eventually runs into difficulties as the flow of the ice causes the layers to become thinner and harder to see with increasing depth.<a href="#cite_note-60">[60]</a> The problem is more acute at locations where accumulation is high; low accumulation sites, such as central Antarctica, must be dated by other methods.<a href="#cite_note-Jouzel-2013-4-61">[61]</a> For example, at Vostok, layer counting is only possible down to an age of 55,000 years.<a href="#cite_note-Ruddiman-62">[62]</a> When there is summer melting, the melted snow refreezes lower in the snow and firn, and the resulting layer of ice has very few bubbles so is easy to recognise in a visual examination of a core. Identification of these layers, both visually and by measuring density of the core against depth, allows the calculation of a melt-feature percentage (MF): an MF of 100% would mean that every year's deposit of snow showed evidence of melting. MF calculations are averaged over multiple sites or long time periods in order to smooth the data. Plots of MF data over time reveal variations in the climate, and have shown that since the late 20th century melting rates have been increasing.<a href="#cite_note-63">[63]</a><a href="#cite_note-64">[64]</a> In addition to manual inspection and logging of features identified in a visual inspection, cores can be optically scanned so that a digital visual record is available. This requires the core to be cut lengthwise, so that a flat surface is created.<a href="#cite_note-65">[65]</a> <div class="mw-heading mw-heading3"><h3 id="Isotopic_analysis">Isotopic analysis</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=9" title="Edit section: Isotopic analysis">edit</a>]</div> The isotopic composition of the oxygen in a core can be used to model the temperature history of the ice sheet. Oxygen has three stable isotopes, <a href="/wiki/Oxygen-16" title="Oxygen-16">16 O</a>, <a href="/wiki/Oxygen-17" title="Oxygen-17">17 O</a> and <a href="/wiki/Oxygen-18" title="Oxygen-18">18 O</a>.<a href="#cite_note-66">[66]</a> The ratio between 18 O and 16 O indicates the temperature when the snow fell.<a href="#cite_note-Lowe-2014-67">[67]</a> Because 16 O is lighter than 18 O, water containing 16 O is slightly more likely to turn into vapour, and water containing 18 O is slightly more likely to condense from vapour into rain or snow crystals. At lower temperatures, the difference is more pronounced. The standard method of recording the 18 O/16 O ratio is to subtract the ratio in a standard known as <a href="/wiki/Standard_Mean_Ocean_Water" class="mw-redirect" title="Standard Mean Ocean Water">standard mean ocean water</a> (SMOW):<a href="#cite_note-Lowe-2014-67">[67]</a> <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {\delta ^{18}O} ={\Biggl (}\mathrm {\frac {{\bigl (}{\frac {^{18}O}{^{16}O}}{\bigr )}_{sample}}{{\bigl (}{\frac {^{18}O}{^{16}O}}{\bigr )}_{SMOW}}} -1{\Biggr )}\times 1000\ ^{o}\!/\!_{oo},}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <msup> <mi>δ</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>18</mn> </mrow> </msup> <mi mathvariant="normal">O</mi> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-OPEN"> <mo maxsize="2.470em" minsize="2.470em">(</mo> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-OPEN"> <mo maxsize="1.2em" minsize="1.2em">(</mo> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <msup> <mi></mi> <mrow class="MJX-TeXAtom-ORD"> <mn>18</mn> </mrow> </msup> <mi mathvariant="normal">O</mi> </mrow> <mrow> <msup> <mi></mi> <mrow class="MJX-TeXAtom-ORD"> <mn>16</mn> </mrow> </msup> <mi mathvariant="normal">O</mi> </mrow> </mfrac> </mrow> <msub> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-CLOSE"> <mo maxsize="1.2em" minsize="1.2em">)</mo> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">s</mi> <mi mathvariant="normal">a</mi> <mi mathvariant="normal">m</mi> <mi mathvariant="normal">p</mi> <mi mathvariant="normal">l</mi> <mi mathvariant="normal">e</mi> </mrow> </msub> </mrow> <mrow> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-OPEN"> <mo maxsize="1.2em" minsize="1.2em">(</mo> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <msup> <mi></mi> <mrow class="MJX-TeXAtom-ORD"> <mn>18</mn> </mrow> </msup> <mi mathvariant="normal">O</mi> </mrow> <mrow> <msup> <mi></mi> <mrow class="MJX-TeXAtom-ORD"> <mn>16</mn> </mrow> </msup> <mi mathvariant="normal">O</mi> </mrow> </mfrac> </mrow> <msub> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-CLOSE"> <mo maxsize="1.2em" minsize="1.2em">)</mo> </mrow> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">S</mi> <mi mathvariant="normal">M</mi> <mi mathvariant="normal">O</mi> <mi mathvariant="normal">W</mi> </mrow> </msub> </mrow> </mfrac> </mrow> <mo>−</mo> <mn>1</mn> <mrow class="MJX-TeXAtom-ORD"> <mrow class="MJX-TeXAtom-CLOSE"> <mo maxsize="2.470em" minsize="2.470em">)</mo> </mrow> </mrow> <mo>×</mo> <mn>1000</mn> <msup> <mtext> </mtext> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> </mrow> </msup> <mspace width="negativethinmathspace"></mspace> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <msub> <mspace width="negativethinmathspace"></mspace> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>o</mi> </mrow> </msub> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathrm {\delta ^{18}O} ={\Biggl (}\mathrm {\frac {{\bigl (}{\frac {^{18}O}{^{16}O}}{\bigr )}_{sample}}{{\bigl (}{\frac {^{18}O}{^{16}O}}{\bigr )}_{SMOW}}} -1{\Biggr )}\times 1000\ ^{o}\!/\!_{oo},}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/e2a57b00208b0420b0f09071f2b9c54f337e4d26" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -4.005ex; width:39.683ex; height:9.343ex;" alt="{\displaystyle \mathrm {\delta ^{18}O} ={\Biggl (}\mathrm {\frac {{\bigl (}{\frac {^{18}O}{^{16}O}}{\bigr )}_{sample}}{{\bigl (}{\frac {^{18}O}{^{16}O}}{\bigr )}_{SMOW}}} -1{\Biggr )}\times 1000\ ^{o}\!/\!_{oo},}" /> where the ‰ sign indicates <a href="/wiki/Parts_per_thousand" class="mw-redirect" title="Parts per thousand">parts per thousand</a>.<a href="#cite_note-Lowe-2014-67">[67]</a> A sample with the same 18 O/16 O ratio as SMOW has a δ18O of 0‰; a sample that is depleted in 18 O has a negative δ18O.<a href="#cite_note-Lowe-2014-67">[67]</a> Combining the δ18O measurements of an ice core sample with the borehole temperature at the depth it came from provides additional information, in some cases leading to significant corrections to the temperatures deduced from the δ18O data.<a href="#cite_note-68">[68]</a><a href="#cite_note-Jouzel-2013-5-69">[69]</a> Not all boreholes can be used in these analyses. If the site has experienced significant melting in the past, the borehole will no longer preserve an accurate temperature record.<a href="#cite_note-70">[70]</a> Hydrogen ratios can also be used to calculate a temperature history. <a href="/wiki/Deuterium" title="Deuterium">Deuterium</a> (2 H, or D) is heavier than hydrogen (1 H) and makes water more likely to condense and less likely to evaporate. A <a href="/wiki/%CE%94D" class="mw-redirect" title="ΔD">δD</a> ratio can be defined in the same way as δ18O.<a href="#cite_note-71">[71]</a><a href="#cite_note-72">[72]</a> There is a linear relationship between δ18O and δD:<a href="#cite_note-Jouzel-2013-6-73">[73]</a> <math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {\delta D} =8\times \mathrm {\delta ^{18}O} +\mathrm {d} ,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mi>δ</mi> <mi mathvariant="normal">D</mi> </mrow> <mo>=</mo> <mn>8</mn> <mo>×</mo> <mrow class="MJX-TeXAtom-ORD"> <msup> <mi>δ</mi> <mrow class="MJX-TeXAtom-ORD"> <mn>18</mn> </mrow> </msup> <mi mathvariant="normal">O</mi> </mrow> <mo>+</mo> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">d</mi> </mrow> <mo>,</mo> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathrm {\delta D} =8\times \mathrm {\delta ^{18}O} +\mathrm {d} ,}</annotation> </semantics> </math><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a507c0636f80889bbe008a59c8c8a1f2c458c969" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:19.443ex; height:3.009ex;" alt="{\displaystyle \mathrm {\delta D} =8\times \mathrm {\delta ^{18}O} +\mathrm {d} ,}" /> where d is the deuterium excess. It was once thought that this meant it was unnecessary to measure both ratios in a given core, but in 1979 Merlivat and <a href="/wiki/Jean_Jouzel" title="Jean Jouzel">Jouzel</a> showed that the deuterium excess reflects the temperature, relative humidity, and wind speed of the ocean where the moisture originated. Since then it has been customary to measure both.<a href="#cite_note-Jouzel-2013-6-73">[73]</a> Water isotope records, analyzed in cores from <a href="/wiki/Camp_Century" title="Camp Century">Camp Century</a> and <a href="/wiki/Dye_3" title="Dye 3">Dye 3</a> in Greenland, were instrumental in the discovery of <a href="/wiki/Dansgaard%E2%80%93Oeschger_event" title="Dansgaard–Oeschger event">Dansgaard-Oeschger events</a>—rapid warming at the onset of an <a href="/wiki/Interglacial" title="Interglacial">interglacial</a>, followed by slower cooling.<a href="#cite_note-74">[74]</a> Other isotopic ratios have been studied, for example, the ratio between 13 C and 12 C can provide information about past changes in the <a href="/wiki/Carbon_cycle" title="Carbon cycle">carbon cycle</a>. Combining this information with records of carbon dioxide levels, also obtained from ice cores, provides information about the mechanisms behind changes in CO 2 over time.<a href="#cite_note-75">[75]</a> <div class="mw-heading mw-heading3"><h3 id="Palaeoatmospheric_sampling">Palaeoatmospheric sampling</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=10" title="Edit section: Palaeoatmospheric sampling">edit</a>]</div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Vostok_Petit_data.svg" class="mw-file-description"><img alt="Three graphs laid out one above the other; the CO2 and temperature can be visually seen to be correlated; the dust graph is inversely correlated with the other two" src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b8/Vostok_Petit_data.svg/300px-Vostok_Petit_data.svg.png" decoding="async" width="300" height="225" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b8/Vostok_Petit_data.svg/450px-Vostok_Petit_data.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b8/Vostok_Petit_data.svg/600px-Vostok_Petit_data.svg.png 2x" data-file-width="1024" data-file-height="768" /></a><figcaption>Graph of CO2 (green), reconstructed temperature (blue) and dust (red) from the <a href="/wiki/Vostok_Station#Ice_core_drilling" title="Vostok Station">Vostok ice core</a> for the past 420,000 years</figcaption></figure> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Greenland_firn_CFCs.png" class="mw-file-description"><img alt="Graph showing the relationship between depth below surface, and fraction of surface concentration at the surface, for multiple gases" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Greenland_firn_CFCs.png/268px-Greenland_firn_CFCs.png" decoding="async" width="268" height="300" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/6f/Greenland_firn_CFCs.png/403px-Greenland_firn_CFCs.png 1.5x, //upload.wikimedia.org/wikipedia/commons/6/6f/Greenland_firn_CFCs.png 2x" data-file-width="450" data-file-height="503" /></a><figcaption>Ozone-depleting gases in Greenland firn.<a href="#cite_note-76">[76]</a></figcaption></figure> It was understood in the 1960s that analyzing the air trapped in ice cores would provide useful information on the <a href="/wiki/Paleoatmosphere" title="Paleoatmosphere">paleoatmosphere</a>, but it was not until the late 1970s that a reliable extraction method was developed. Early results included a demonstration that the CO 2 concentration was 30% less at the <a href="/wiki/Last_Glacial_Maximum" title="Last Glacial Maximum">last glacial maximum</a> than just before the start of the industrial age. Further research has demonstrated a reliable correlation between CO 2 levels and the temperature calculated from ice isotope data.<a href="#cite_note-Jouzel-2013-7-77">[77]</a> Because CH 4 (methane) is produced in lakes and <a href="/wiki/Wetland" title="Wetland">wetlands</a>, the amount in the atmosphere is correlated with the strength of <a href="/wiki/Monsoon" title="Monsoon">monsoons</a>, which are in turn correlated with the strength of <a href="/wiki/Tropics" title="Tropics">low-latitude</a> summer <a href="/wiki/Solar_irradiance" title="Solar irradiance">insolation</a>. Since insolation depends on <a href="/wiki/Milankovitch_cycles" title="Milankovitch cycles">orbital cycles</a>, for which a timescale is available from other sources, CH 4 can be used to determine the relationship between core depth and age.<a href="#cite_note-Jouzel-2013-4-61">[61]</a><a href="#cite_note-Ruddiman-62">[62]</a> N 2O (nitrous oxide) levels are also correlated with glacial cycles, though at low temperatures the graph differs somewhat from the CO 2 and CH 4 graphs.<a href="#cite_note-Jouzel-2013-7-77">[77]</a><a href="#cite_note-78">[78]</a> Similarly, the ratio between N 2 (nitrogen) and O 2 (oxygen) can be used to date ice cores: as air is gradually trapped by the snow turning to firn and then ice, O 2 is lost more easily than N 2, and the relative amount of O 2 correlates with the strength of local summer insolation. This means that the trapped air retains, in the ratio of O 2 to N 2, a record of the summer insolation, and hence combining this data with orbital cycle data establishes an ice core dating scheme.<a href="#cite_note-Jouzel-2013-4-61">[61]</a><a href="#cite_note-79">[79]</a> <a href="/wiki/Diffusion" title="Diffusion">Diffusion</a> within the firn layer causes other changes that can be measured. Gravity causes heavier molecules to be enriched at the bottom of a gas column, with the amount of enrichment depending on the difference in mass between the molecules. Colder temperatures cause heavier molecules to be more enriched at the bottom of a column. These <a href="/wiki/Fractionation" title="Fractionation">fractionation</a> processes in trapped air, determined by the measurement of the 15 N/14 N ratio and of <a href="/wiki/Neon" title="Neon">neon</a>, <a href="/wiki/Krypton" title="Krypton">krypton</a> and <a href="/wiki/Xenon" title="Xenon">xenon</a>, have been used to infer the thickness of the firn layer, and determine other palaeoclimatic information such as past mean ocean temperatures.<a href="#cite_note-Jouzel-2013-5-69">[69]</a> Some gases such as <a href="/wiki/Helium" title="Helium">helium</a> can rapidly diffuse through ice, so it may be necessary to test for these "fugitive gases" within minutes of the core being retrieved to obtain accurate data.<a href="#cite_note-Souney-2014-1-34">[34]</a> <a href="/wiki/Chlorofluorocarbon" title="Chlorofluorocarbon">Chlorofluorocarbons</a> (CFCs), which contribute to the <a href="/wiki/Greenhouse_effect" title="Greenhouse effect">greenhouse effect</a> and also cause <a href="/wiki/Ozone_depletion" title="Ozone depletion">ozone loss</a> in the <a href="/wiki/Stratosphere" title="Stratosphere">stratosphere</a>,<a href="#cite_note-Neelin-2010-80">[80]</a> can be detected in ice cores after about 1950; almost all CFCs in the atmosphere were created by human activity.<a href="#cite_note-Neelin-2010-80">[80]</a><a href="#cite_note-81">[81]</a> Greenland cores, during times of climatic transition, may show excess CO2 in air bubbles when analysed, due to CO2 production by acidic and alkaline impurities.<a href="#cite_note-82">[82]</a> <div style="clear:both;" class=""></div> <div class="mw-heading mw-heading3"><h3 id="Glaciochemistry">Glaciochemistry</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=11" title="Edit section: Glaciochemistry">edit</a>]</div> Summer snow in Greenland contains some sea salt, blown from the surrounding waters; there is less of it in winter, when much of the sea surface is covered by pack ice. Similarly, <a href="/wiki/Hydrogen_peroxide" title="Hydrogen peroxide">hydrogen peroxide</a> appears only in summer snow because its production in the atmosphere requires sunlight. These seasonal changes can be detected because they lead to changes in the <a href="/wiki/Electrical_conductivity" class="mw-redirect" title="Electrical conductivity">electrical conductivity</a> of the ice. Placing two <a href="/wiki/Electrode" title="Electrode">electrodes</a> with a high voltage between them on the surface of the ice core gives a measurement of the conductivity at that point. Dragging them down the length of the core, and recording the conductivity at each point, gives a graph that shows an annual periodicity. Such graphs also identify chemical changes caused by non-seasonal events such as forest fires and major volcanic eruptions. When a known volcanic event, such as the <a href="/wiki/Laki#1783_eruption" title="Laki">eruption of Laki</a> in Iceland in 1783, can be identified in the ice core record, it provides a cross-check on the age determined by layer counting.<a href="#cite_note-83">[83]</a> Material from Laki can be identified in Greenland ice cores, but did not spread as far as Antarctica; the 1815 eruption of <a href="/wiki/Mount_Tambora" title="Mount Tambora">Tambora</a> in Indonesia injected material into the stratosphere, and can be identified in both Greenland and Antarctic ice cores. If the date of the eruption is not known, but it can be identified in multiple cores, then dating the ice can in turn give a date for the eruption, which can then be used as a reference layer.<a href="#cite_note-Legrand-1997-3-84">[84]</a> This was done, for example, in an analysis of the climate for the period from 535 to 550 AD, which was thought to be influenced by an otherwise unknown tropical eruption in about 533 AD; but which turned out to be caused by two eruptions, one in 535 or early 536 AD, and a second one in 539 or 540 AD.<a href="#cite_note-85">[85]</a> There are also more ancient reference points, such as the eruption of <a href="/wiki/Lake_Toba" title="Lake Toba">Toba</a> about 72,000 years ago.<a href="#cite_note-Legrand-1997-3-84">[84]</a> Many other elements and molecules have been detected in ice cores.<a href="#cite_note-Legrand-1997-1-86">[86]</a> In 1969, it was discovered that <a href="/wiki/Lead" title="Lead">lead</a> levels in Greenland ice had increased by a factor of over 200 since pre-industrial times, and increases in other elements produced by industrial processes, such as <a href="/wiki/Copper" title="Copper">copper</a>, <a href="/wiki/Cadmium" title="Cadmium">cadmium</a>, and <a href="/wiki/Zinc" title="Zinc">zinc</a>, have also been recorded.<a href="#cite_note-87">[87]</a> The presence of nitric and sulfuric acid (<a href="/wiki/Nitric_acid" title="Nitric acid">HNO 3</a> and <a href="/wiki/Sulfuric_acid" title="Sulfuric acid">H 2SO 4</a>) in precipitation can be shown to correlate with increasing fuel <a href="/wiki/Combustion" title="Combustion">combustion</a> over time. <a href="/wiki/Mesylate" title="Mesylate">Methanesulfonate</a> (MSA) (CH 3SO− 3) is produced in the atmosphere by marine organisms, so ice core records of MSA provide information on the history of the oceanic environment. Both hydrogen peroxide (<a href="/wiki/Hydrogen_peroxide" title="Hydrogen peroxide">H 2O 2</a>) and formaldehyde (<a href="/wiki/Formaldehyde" title="Formaldehyde">HCHO</a>) have been studied, along with organic molecules such as <a href="/wiki/Carbon_black" title="Carbon black">carbon black</a> that are linked to vegetation emissions and forest fires.<a href="#cite_note-Legrand-1997-1-86">[86]</a> Some species, such as <a href="/wiki/Calcium" title="Calcium">calcium</a> and <a href="/wiki/Ammonium" title="Ammonium">ammonium</a>, show strong seasonal variation. In some cases there are contributions from more than one source to a given species: for example, Ca++ comes from dust as well as from marine sources; the marine input is much greater than the dust input and so although the two sources peak at different times of the year, the overall signal shows a peak in the winter, when the marine input is at a maximum.<a href="#cite_note-88">[88]</a> Seasonal signals can be erased at sites where the accumulation is low, by surface winds; in these cases it is not possible to date individual layers of ice between two reference layers.<a href="#cite_note-Legrand-1997-2-89">[89]</a> Some of the deposited chemical species may interact with the ice, so what is detected in an ice core is not necessarily what was originally deposited. Examples include HCHO and H 2O 2. Another complication is that in areas with low accumulation rates, deposition from fog can increase the concentration in the snow, sometimes to the point where the atmospheric concentration could be overestimated by a factor of two.<a href="#cite_note-90">[90]</a> <table class="wikitable"> <caption>Soluble impurities found in ice cores<a href="#cite_note-91">[91]</a> </caption> <tbody><tr> <th>Source </th> <th>Via </th> <th>Measured in polar ice </th></tr> <tr> <td>Oceans </td> <td>Waves and wind </td> <td>Sea salt: Na+ , Cl− , Mg2+ , Ca2+ , SO2− 4, K+ </td></tr> <tr> <td>Land </td> <td>Aridity and wind </td> <td>Terrestrial salts: Mg2+ , Ca2+ , CO2− 3, SO2− 4, <a href="/wiki/Aluminosilicate" title="Aluminosilicate">aluminosilicates</a> </td></tr> <tr> <td>Human and biological gas emissions: SO 2, (CH 3) 2S, H 2S, COS, NO x, NH 3, <a href="/wiki/Hydrocarbon" title="Hydrocarbon">hydrocarbons</a> and <a href="/wiki/Halocarbon" title="Halocarbon">halocarbons</a> </td> <td>Atmospheric chemistry: O 3, H 2O 2, OH, <a href="/wiki/Organic_peroxide" class="mw-redirect" title="Organic peroxide">RO 2</a>, NO 3, </td> <td>H+ , NH+ 4, Cl− , NO− 3, SO2− 4, CH 3SO− 3, F− , HCOO− , other organic compounds </td></tr></tbody></table> <div class="mw-heading mw-heading3"><h3 id="Radionuclides">Radionuclides</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=12" title="Edit section: Radionuclides">edit</a>]</div> <figure typeof="mw:File/Thumb"><a href="/wiki/File:Upper_Fremont_glacier_ice_cl36.gif" class="mw-file-description"><img alt="Graph showing abundance of 36Cl against snow depth, showing a spike at the time of above-ground nuclear testing" src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Upper_Fremont_glacier_ice_cl36.gif/300px-Upper_Fremont_glacier_ice_cl36.gif" decoding="async" width="300" height="219" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Upper_Fremont_glacier_ice_cl36.gif/450px-Upper_Fremont_glacier_ice_cl36.gif 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Upper_Fremont_glacier_ice_cl36.gif/600px-Upper_Fremont_glacier_ice_cl36.gif 2x" data-file-width="952" data-file-height="694" /></a><figcaption><a href="/wiki/Chlorine" title="Chlorine">36Cl</a> from 1960s nuclear testing in US glacier ice.</figcaption></figure> <a href="/wiki/Galactic_cosmic_rays" class="mw-redirect" title="Galactic cosmic rays">Galactic cosmic rays</a> produce 10 Be in the atmosphere at a rate that depends on the solar magnetic field. The strength of the field is related to the intensity of <a href="/wiki/Solar_radiation" class="mw-redirect" title="Solar radiation">solar radiation</a>, so the level of 10 Be in the atmosphere is a <a href="/wiki/Proxy_(climate)" title="Proxy (climate)">proxy</a> for climate. <a href="/wiki/Accelerator_mass_spectrometry" title="Accelerator mass spectrometry">Accelerator mass spectrometry</a> can detect the low levels of 10 Be in ice cores, about 10,000 atoms in a gram of ice, and these can be used to provide long-term records of solar activity.<a href="#cite_note-92">[92]</a> <a href="/wiki/Tritium_radioluminescence" title="Tritium radioluminescence">Tritium</a> (3 H), created by nuclear weapons testing in the 1950s and 1960s, has been identified in ice cores,<a href="#cite_note-93">[93]</a> and both <a href="/wiki/Chlorine-36" title="Chlorine-36">36Cl</a> and <a href="/wiki/Plutonium-239" title="Plutonium-239">239 Pu</a> have been found in ice cores in Antarctica and Greenland.<a href="#cite_note-94">[94]</a><a href="#cite_note-95">[95]</a><a href="#cite_note-96">[96]</a> Chlorine-36, which has a half-life of 301,000 years, has been used to date cores, as have krypton (<a href="/wiki/Krypton-85" title="Krypton-85">85 Kr</a>, with a half-life of 11 years), lead (<a href="/wiki/Lead-210" class="mw-redirect" title="Lead-210">210 Pb</a>, 22 years), and silicon (<a href="/wiki/Silicon-32" class="mw-redirect" title="Silicon-32">32 Si</a>, 172 years).<a href="#cite_note-Legrand-1997-2-89">[89]</a> <div class="mw-heading mw-heading3"><h3 id="Other_inclusions">Other inclusions</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=13" title="Edit section: Other inclusions">edit</a>]</div> Meteorites and micrometeorites that land on polar ice are sometimes concentrated by local environmental processes. For example, there are places in Antarctica where winds evaporate surface ice, concentrating the solids that are left behind, including meteorites. Meltwater ponds can also contain meteorites. At the <a href="/wiki/South_Pole_Station" class="mw-redirect" title="South Pole Station">South Pole Station</a>, ice in a well is melted to provide a water supply, leaving micrometeorites behind. These have been collected by a robotic "vacuum cleaner" and examined, leading to improved estimates of their flux and mass distribution.<a href="#cite_note-97">[97]</a> The well is not an ice core, but the age of the ice that was melted is known, so the age of the recovered particles can be determined. The well becomes about 10 m deeper each year, so micrometeorites collected in a given year are about 100 years older than those from the previous year.<a href="#cite_note-98">[98]</a> <a href="/wiki/Pollen" title="Pollen">Pollen</a>, an important component of sediment cores, can also be found in ice cores. It provides information on changes in vegetation.<a href="#cite_note-99">[99]</a> <div class="mw-heading mw-heading3"><h3 id="Physical_properties">Physical properties</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=14" title="Edit section: Physical properties">edit</a>]</div> In addition to the impurities in a core and the isotopic composition of the water, the physical properties of the ice are examined. Features such as crystal size and <a href="/wiki/Crystal_axis" class="mw-redirect" title="Crystal axis">axis</a> orientation can reveal the history of ice flow patterns in the ice sheet. The crystal size can also be used to determine dates, though only in shallow cores.<a href="#cite_note-100">[100]</a> <div class="mw-heading mw-heading2"><h2 id="History">History</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=15" title="Edit section: History">edit</a>]</div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/History_of_scientific_ice_drilling" class="mw-redirect" title="History of scientific ice drilling">History of scientific ice drilling</a></div> <div class="mw-heading mw-heading3"><h3 id="Early_years">Early years</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=16" title="Edit section: Early years">edit</a>]</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:2000_core-repository02_hg.jpg" class="mw-file-description"><img alt="A man on a walkway between two high shelf racks loaded with ice core samples" src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b7/2000_core-repository02_hg.jpg/220px-2000_core-repository02_hg.jpg" decoding="async" width="220" height="220" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b7/2000_core-repository02_hg.jpg/330px-2000_core-repository02_hg.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b7/2000_core-repository02_hg.jpg/440px-2000_core-repository02_hg.jpg 2x" data-file-width="1714" data-file-height="1714" /></a><figcaption>A store of core samples</figcaption></figure> In 1841 and 1842, <a href="/wiki/Louis_Agassiz" title="Louis Agassiz">Louis Agassiz</a> drilled holes in the <a href="/wiki/Unteraargletscher" title="Unteraargletscher">Unteraargletscher</a> in the <a href="/wiki/Alps" title="Alps">Alps</a>; these were drilled with iron rods and did not produce cores. The deepest hole achieved was 60 m. On <a href="/wiki/Erich_von_Drygalski" title="Erich von Drygalski">Erich von Drygalski</a>'s Antarctic expedition in 1902 and 1903, 30 m holes were drilled in an iceberg south of the Kerguelen Islands and temperature readings were taken. The first scientist to create a snow sampling tool was <a href="/wiki/James_E._Church" title="James E. Church">James E. Church</a>, described by <a href="/wiki/Pavel_Talalay" title="Pavel Talalay">Pavel Talalay</a> as "the father of modern snow surveying". In the winter of 1908–1909, Church constructed steel tubes with slots and cutting heads to retrieve cores of snow up to 3 m long. Similar devices are in use today, modified to allow sampling to a depth of about 9 m. They are simply pushed into the snow and rotated by hand.<a href="#cite_note-101">[101]</a> The first systematic study of snow and firn layers was by Ernst Sorge, who was part of the <a href="/wiki/Alfred_Wegener" title="Alfred Wegener">Alfred Wegener</a> Expedition to central Greenland in 1930–1931. Sorge dug a 15 m pit to examine the snow layers, and his results were later formalized into Sorge's Law of Densification by Henri Bader, who went on to do additional coring work in northwest Greenland in 1933.<a href="#cite_note-102">[102]</a> In the early 1950s, a <a href="/wiki/SIPRE" class="mw-redirect" title="SIPRE">SIPRE</a> expedition took pit samples over much of the Greenland ice sheet, obtaining early oxygen isotope ratio data. Three other expeditions in the 1950s began ice coring work: a joint <a href="/wiki/Norwegian-British-Swedish_Antarctic_Expedition" class="mw-redirect" title="Norwegian-British-Swedish Antarctic Expedition">Norwegian-British-Swedish Antarctic Expedition</a> (NBSAE), in <a href="/wiki/Queen_Maud_Land" title="Queen Maud Land">Queen Maud Land</a> in Antarctica; the <a href="/w/index.php?title=Juneau_Ice_Field_Research_Project&action=edit&redlink=1" class="new" title="Juneau Ice Field Research Project (page does not exist)">Juneau Ice Field Research Project</a> (JIRP), in <a href="/wiki/Alaska" title="Alaska">Alaska</a>; and <a href="/w/index.php?title=Exp%C3%A9ditions_Polaires_Fran%C3%A7aises&action=edit&redlink=1" class="new" title="Expéditions Polaires Françaises (page does not exist)">Expéditions Polaires Françaises</a>, in central Greenland. Core quality was poor, but some scientific work was done on the retrieved ice.<a href="#cite_note-103">[103]</a> The <a href="/wiki/International_Geophysical_Year" title="International Geophysical Year">International Geophysical Year</a> (1957–1958) saw increased <a href="/wiki/Glaciology" title="Glaciology">glaciology</a> research around the world, with one of the high priority research targets being deep cores in polar regions. SIPRE conducted pilot drilling trials in 1956 (to 305 m) and 1957 (to 411 m) at Site 2 in Greenland; the second core, with the benefit of the previous year's drilling experience, was retrieved in much better condition, with fewer gaps.<a href="#cite_note-104">[104]</a> In Antarctica, a 307 m core was drilled at <a href="/wiki/Byrd_Station" title="Byrd Station">Byrd Station</a> in 1957–1958, and a 264 m core at <a href="/wiki/Little_America_V" class="mw-redirect" title="Little America V">Little America V</a>, on the <a href="/wiki/Ross_Ice_Shelf" title="Ross Ice Shelf">Ross Ice Shelf</a>, the following year.<a href="#cite_note-105">[105]</a> The success of the IGY core drilling led to increased interest in improving ice coring capabilities, and was followed by a <a href="/wiki/CRREL" class="mw-redirect" title="CRREL">CRREL</a> project at Camp Century, where in the early 1960s three holes were drilled, the deepest reaching the base of the ice sheet at 1387 m in July 1966.<a href="#cite_note-106">[106]</a> The drill used at Camp Century then went to Byrd Station, where a 2164 m hole was drilled to bedrock before the drill was frozen into the borehole by sub-ice meltwater and had to be abandoned.<a href="#cite_note-107">[107]</a> French, Australian and Canadian projects from the 1960s and 1970s include a 905 m core at <a href="/wiki/Dome_C" title="Dome C">Dome C</a> in Antarctica, drilled by <a href="/wiki/Centre_national_de_la_recherche_scientifique" class="mw-redirect" title="Centre national de la recherche scientifique">CNRS</a>; cores at <a href="/wiki/Law_Dome" title="Law Dome">Law Dome</a> drilled by <a href="/wiki/Australian_National_Antarctic_Research_Expeditions" title="Australian National Antarctic Research Expeditions">ANARE</a>, starting in 1969 with a 382 m core; and <a href="/wiki/Devon_Ice_Cap" title="Devon Ice Cap">Devon Ice Cap</a> cores recovered by a Canadian team in the 1970s.<a href="#cite_note-Jouzel-2013-1-108">[108]</a> <div class="mw-heading mw-heading3"><h3 id="Antarctica_deep_cores">Antarctica deep cores</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=17" title="Edit section: Antarctica deep cores">edit</a>]</div> <figure class="mw-halign-left" typeof="mw:File/Thumb"><a href="/wiki/File:Co2_glacial_cycles_800k.png" class="mw-file-description"><img alt="Graph showing CO2 levels, highlit to indicate glacial cycles" src="//upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Co2_glacial_cycles_800k.png/300px-Co2_glacial_cycles_800k.png" decoding="async" width="300" height="213" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Co2_glacial_cycles_800k.png/450px-Co2_glacial_cycles_800k.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Co2_glacial_cycles_800k.png/600px-Co2_glacial_cycles_800k.png 2x" data-file-width="818" data-file-height="580" /></a><figcaption>Composite data for Dome C, CO2 levels (ppm) going back nearly 800,000 years, and related glacial cycles.</figcaption></figure> <a href="/wiki/Soviet_Union" title="Soviet Union">Soviet</a> ice drilling projects began in the 1950s, in <a href="/wiki/Franz_Josef_Land" title="Franz Josef Land">Franz Josef Land</a>, the <a href="/wiki/Urals" class="mw-redirect" title="Urals">Urals</a>, <a href="/wiki/Novaya_Zemlya" title="Novaya Zemlya">Novaya Zemlya</a>, and at <a href="/wiki/Mirny_Station" title="Mirny Station">Mirny</a> and Vostok in the Antarctic; not all these early holes retrieved cores.<a href="#cite_note-109">[109]</a> Over the following decades work continued at multiple locations in Asia.<a href="#cite_note-110">[110]</a> Drilling in the Antarctic focused mostly on Mirny and Vostok, with a series of deep holes at Vostok begun in 1970.<a href="#cite_note-111">[111]</a> The first deep hole at Vostok reached 506.9 m in April 1970; by 1973 a depth of 952 m had been reached. A subsequent hole, Vostok 2, drilled from 1971 to 1976, reached 450 m, and Vostok 3 reached 2202 m in 1985 after six drilling seasons.<a href="#cite_note-112">[112]</a> Vostok 3 was the first core to retrieve ice from the previous glacial period, 150,000 years ago.<a href="#cite_note-Jouzel-2013-2-113">[113]</a> Drilling was interrupted by a fire at the camp in 1982, but further drilling began in 1984, eventually reaching 2546 m in 1989. A fifth Vostok core was begun in 1990, reached 3661 m in 2007, and was later extended to 3769 m.<a href="#cite_note-Jouzel-2013-1-108">[108]</a><a href="#cite_note-Jouzel-2013-2-113">[113]</a> The estimated age of the ice is 420,000 years at 3310 m depth; below that point it is difficult to interpret the data reliably because of mixing of the ice.<a href="#cite_note-Jouzel-2013-3-114">[114]</a> <figure typeof="mw:File/Thumb"><a href="/wiki/File:EPICA_delta_D_plot.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1e/EPICA_delta_D_plot.svg/400px-EPICA_delta_D_plot.svg.png" decoding="async" width="400" height="300" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1e/EPICA_delta_D_plot.svg/600px-EPICA_delta_D_plot.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1e/EPICA_delta_D_plot.svg/800px-EPICA_delta_D_plot.svg.png 2x" data-file-width="1024" data-file-height="768" /></a><figcaption>The EPICA Dome C and Vostok ice cores compared</figcaption></figure> <a href="/wiki/EPICA" class="mw-redirect" title="EPICA">EPICA</a>, a European ice coring collaboration, was formed in the 1990s, and two holes were drilled in East Antarctica: one at Dome C, which reached 2871 m in only two seasons of drilling, but which took another four years to reach bedrock at 3260 m; and one at <a href="/wiki/Kohnen_Station" title="Kohnen Station">Kohnen Station</a>, which reached bedrock at 2760 m in 2006. The Dome C core had very low accumulation rates, which mean that the climate record extended a long way; by the end of the project the usable data extended to 800,000 years ago.<a href="#cite_note-Jouzel-2013-3-114">[114]</a> Other deep Antarctic cores included a Japanese project at <a href="/wiki/Dome_F" title="Dome F">Dome F</a>, which reached 2503 m in 1996, with an estimated age of 330,000 years for the bottom of the core; and a subsequent hole at the same site which reached 3035 m in 2006, estimated to reach ice 720,000 years old.<a href="#cite_note-Jouzel-2013-3-114">[114]</a> US teams drilled at <a href="/wiki/McMurdo_Station" title="McMurdo Station">McMurdo Station</a> in the 1990s, and at <a href="/wiki/Taylor_Dome" class="mw-redirect" title="Taylor Dome">Taylor Dome</a> (554 m in 1994) and <a href="/wiki/Siple_Dome" title="Siple Dome">Siple Dome</a> (1004 m in 1999), with both cores reaching ice from the last glacial period.<a href="#cite_note-Jouzel-2013-3-114">[114]</a><a href="#cite_note-115">[115]</a> The <a href="/wiki/West_Antarctic_Ice_Sheet" title="West Antarctic Ice Sheet">West Antarctic Ice Sheet</a> (WAIS) project, completed in 2011, reached 3405 m; the site has high snow accumulation so the ice only extends back 62,000 years, but as a consequence, the core provides high resolution data for the period it covers.<a href="#cite_note-Jouzel-2013-4-61">[61]</a> A 948 m core was drilled at <a href="/wiki/Berkner_Island" title="Berkner Island">Berkner Island</a> by a project managed by the <a href="/wiki/British_Antarctic_Survey" title="British Antarctic Survey">British Antarctic Survey</a> from 2002 to 2005, extending into the last glacial period;<a href="#cite_note-Jouzel-2013-4-61">[61]</a> and an Italian-managed <a href="/wiki/ITASE" title="ITASE">ITASE</a> project completed a 1620 m core at <a href="/wiki/Talos_Dome" title="Talos Dome">Talos Dome</a> in 2007.<a href="#cite_note-Jouzel-2013-4-61">[61]</a><a href="#cite_note-116">[116]</a> In 2016, cores were retrieved from the <a href="/wiki/Allan_Hills" title="Allan Hills">Allan Hills</a> in Antarctica in an area where old ice lay near the surface. The cores were dated by potassium-argon dating; traditional ice core dating is not possible as not all layers were present. The oldest core was found to include ice from 2.7 million years ago—by far the oldest ice yet dated from a core.<a href="#cite_note-117">[117]</a> <div class="mw-heading mw-heading3"><h3 id="Greenland_deep_cores">Greenland deep cores</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=18" title="Edit section: Greenland deep cores">edit</a>]</div> In 1970, scientific discussions began which resulted in the <a href="/wiki/Greenland_Ice_Sheet_Project" title="Greenland Ice Sheet Project">Greenland Ice Sheet Project</a> (GISP), a multinational investigation into the Greenland ice sheet that lasted until 1981. Years of field work were required to determine the ideal location for a deep core; the field work included several intermediate-depth cores, at Dye 3 (372 m in 1971), Milcent (398 m in 1973) and Crete (405 m in 1974), among others. A location in north-central Greenland was selected as ideal, but financial constraints forced the group to drill at Dye 3 instead, beginning in 1979. The hole reached bedrock at 2037 m, in 1981. Two holes, 30 km apart, were eventually drilled at the north-central location in the early 1990s by two groups: <a href="/wiki/Greenland_Ice_Core_Project" class="mw-redirect" title="Greenland Ice Core Project">GRIP</a>, a European consortium, and GISP-2, a group of US universities. GRIP reached bedrock at 3029 m in 1992, and GISP-2 reached bedrock at 3053 m the following year.<a href="#cite_note-118">[118]</a> Both cores were limited to about 100,000 years of climatic information, and since this was thought to be connected to the topography of the rock underlying the ice sheet at the drill sites, a new site was selected 200 km north of GRIP, and a new project, <a href="/wiki/North_Greenland_Ice_Core_Project" title="North Greenland Ice Core Project">NorthGRIP</a>, was launched as an international consortium led by Denmark. Drilling began in 1996; the first hole had to be abandoned at 1400 m in 1997, and a new hole was begun in 1999, reaching 3085 m in 2003. The hole did not reach bedrock, but terminated at a subglacial river. The core provided climatic data back to 123,000 years ago, which covered part of the last interglacial period. The subsequent North Greenland Eemian (<a href="/wiki/NEEM_Camp" title="NEEM Camp">NEEM</a>) project retrieved a 2537 m core in 2010 from a site further north, extending the climatic record to 128,500 years ago;<a href="#cite_note-Jouzel-2013-2-113">[113]</a> NEEM was followed by <a href="/wiki/East_Greenland_Ice-Core_Project" title="East Greenland Ice-Core Project">EastGRIP</a>, which began in 2015 in east Greenland and was planned to be completed in 2020.<a href="#cite_note-119">[119]</a> In March 2020, the 2020 EGRIP field campaign was cancelled due to the ongoing <a href="/wiki/COVID-19_pandemic" title="COVID-19 pandemic">COVID-19 pandemic</a>. EastGRIP reopened for field work in 2022, where the CryoEgg reached new depths in the ice, under pressures in excess of 200 bar and temperatures of around -30c.<a href="#cite_note-120">[120]</a><a href="#cite_note-121">[121]</a> <div class="mw-heading mw-heading3"><h3 id="Non-polar_cores">Non-polar cores</h3>[<a href="/w/index.php?title=Ice_core&action=edit&section=19" title="Edit section: Non-polar cores">edit</a>]</div> Ice cores have been drilled at locations away from the poles, notably in the <a href="/wiki/Himalayas" title="Himalayas">Himalayas</a> and the <a href="/wiki/Andes" title="Andes">Andes</a>. Some of these cores reach back to the last glacial period, but they are more important as records of <a href="/wiki/El_Ni%C3%B1o" class="mw-redirect" title="El Niño">El Niño</a> events and of <a href="/wiki/Monsoon_season" class="mw-redirect" title="Monsoon season">monsoon seasons</a> in south Asia.<a href="#cite_note-Jouzel-2013-4-61">[61]</a> Cores have also been drilled on <a href="/wiki/Mount_Kilimanjaro" title="Mount Kilimanjaro">Mount Kilimanjaro</a>,<a href="#cite_note-Jouzel-2013-4-61">[61]</a> in the Alps,<a href="#cite_note-Jouzel-2013-4-61">[61]</a> and in Indonesia,<a href="#cite_note-122">[122]</a> New Zealand,<a href="#cite_note-123">[123]</a> Iceland,<a href="#cite_note-124">[124]</a> Scandinavia,<a href="#cite_note-125">[125]</a> Canada,<a href="#cite_note-126">[126]</a> and the US.<a href="#cite_note-127">[127]</a> <div class="mw-heading mw-heading2"><h2 id="Future_plans">Future plans</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=20" title="Edit section: Future plans">edit</a>]</div> <a href="/w/index.php?title=IPICS&action=edit&redlink=1" class="new" title="IPICS (page does not exist)">IPICS</a> (International Partnerships in Ice Core Sciences) has produced a series of white papers outlining future challenges and scientific goals for the ice core science community. These include plans to:<a href="#cite_note-128">[128]</a> <ul><li>Retrieve ice cores that reach back over 1.2 million years, in order to obtain multiple iterations of ice core record for the 40,000-year long climate cycles known to have operated at that time. Current cores reach back over 800,000 years, and show 100,000-year cycles.</li> <li>Improve ice core chronologies, including connecting chronologies of multiple cores.</li> <li>Identify additional proxies from ice cores, for example for sea ice, marine biological productivity, or forest fires.</li> <li>Drill additional cores to provide high-resolution data for the last 2,000 years, to use as input for detailed climate modelling.</li> <li>Identify an improved drilling fluid</li> <li>Improve the ability to handle brittle ice, both while drilling and in transport and storage</li> <li>Find a way to handle cores which have pressurised water at bedrock</li> <li>Come up with a standardised lightweight drill capable of drilling both wet and dry holes, and able to reach depths of up to 1000 m.</li> <li>Improve core handling to maximise the information that can be obtained from each core.</li></ul> A <a href="/wiki/Climate_change" title="Climate change">warming climate</a> is found to create glacial meltwater that washes away temporally ordered layers of trapped aerosols that researchers use as an historical record of environmental events.<a href="#cite_note-PopSci_20240714-129">[129]</a> The <a href="/wiki/Ice_Memory#Ice_Memory_Foundation" title="Ice Memory">Ice Memory Foundation</a> plans to store additional <a href="/wiki/Ice_cores" class="mw-redirect" title="Ice cores">ice cores</a> in Antarctica in advance of this impending loss of data.<a href="#cite_note-PopSci_20240714-129">[129]</a> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=21" title="Edit section: See also">edit</a>]</div> <ul><li><a href="/wiki/List_of_ice_cores" title="List of ice cores">List of ice cores</a></li> <li><a href="/wiki/Ice_drilling" title="Ice drilling">Ice drilling</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=22" title="Edit section: References">edit</a>]</div> <div class="mw-references-wrap mw-references-columns"><ol class="references"> <li id="cite_note-corona-1"><a href="#cite_ref-corona_1-0">^</a> <style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFBerwyn2020" class="citation web cs1">Berwyn, Bob (27 March 2020). <a rel="nofollow" class="external text" href="https://insideclimatenews.org/news/26032020/coronavirus-climate-science-research-impact">"Coronavirus Already Hindering Climate Science, But the Worst Disruptions Are Likely Yet to Come"</a>. 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(2016). Mechanical Ice Drilling Technology. Beijing: Springer. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-7-116-09172-6" title="Special:BookSources/978-7-116-09172-6"><bdi>978-7-116-09172-6</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Mechanical+Ice+Drilling+Technology&rft.place=Beijing&rft.pub=Springer&rft.date=2016&rft.isbn=978-7-116-09172-6&rft.aulast=Talalay&rft.aufirst=Pavel+G.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIce+core" class="Z3988"></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFUedaTalalay2007" class="citation report cs1">Ueda, Herbert T.; Talalay, Pavel G. (October 2007). <a rel="nofollow" class="external text" href="https://apps.dtic.mil/sti/pdfs/ADA472548.pdf">Fifty Years of Soviet and Russian Drilling Activity in Polar and Non-Polar Ice</a> (PDF) (Report). ERDC/CRREL. TR-07-02. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20170420234732/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA472548">Archived</a> from the original on 20 April 2017. Retrieved 14 September 2017.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=report&rft.btitle=Fifty+Years+of+Soviet+and+Russian+Drilling+Activity+in+Polar+and+Non-Polar+Ice&rft.pub=ERDC%2FCRREL&rft.date=2007-10&rft.aulast=Ueda&rft.aufirst=Herbert+T.&rft.au=Talalay%2C+Pavel+G.&rft_id=https%3A%2F%2Fapps.dtic.mil%2Fsti%2Fpdfs%2FADA472548.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIce+core" class="Z3988"></li></ul> </div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2>[<a href="/w/index.php?title=Ice_core&action=edit&section=24" title="Edit section: External links">edit</a>]</div> <style data-mw-deduplicate="TemplateStyles:r1235681985">.mw-parser-output .side-box{margin:4px 0;box-sizing:border-box;border:1px solid #aaa;font-size:88%;line-height:1.25em;background-color:var(--background-color-interactive-subtle,#f8f9fa);display:flow-root}.mw-parser-output .side-box-abovebelow,.mw-parser-output .side-box-text{padding:0.25em 0.9em}.mw-parser-output .side-box-image{padding:2px 0 2px 0.9em;text-align:center}.mw-parser-output .side-box-imageright{padding:2px 0.9em 2px 0;text-align:center}@media(min-width:500px){.mw-parser-output .side-box-flex{display:flex;align-items:center}.mw-parser-output .side-box-text{flex:1;min-width:0}}@media(min-width:720px){.mw-parser-output .side-box{width:238px}.mw-parser-output .side-box-right{clear:right;float:right;margin-left:1em}.mw-parser-output .side-box-left{margin-right:1em}}</style><style data-mw-deduplicate="TemplateStyles:r1237033735">@media print{body.ns-0 .mw-parser-output .sistersitebox{display:none!important}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}</style><div 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class="side-box-text plainlist">The Wikibook <a href="https://en.wikibooks.org/wiki/Historical_Geology" class="extiw" title="wikibooks:Historical Geology">Historical Geology</a> has a page on the topic of: <a href="https://en.wikibooks.org/wiki/Historical_Geology/Ice_cores" class="extiw" title="wikibooks:Historical Geology/Ice cores">Ice cores</a></div></div> </div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1235681985" /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1237033735" /><div class="side-box side-box-right plainlinks sistersitebox"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1126788409" /> <div class="side-box-flex"> <div class="side-box-image"><a href="/wiki/File:Commons-logo.svg" class="mw-file-description"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png" decoding="async" width="30" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/45px-Commons-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/59px-Commons-logo.svg.png 2x" data-file-width="1024" data-file-height="1376" /></a></div> <div class="side-box-text plainlist">Wikimedia Commons has media related to <a href="https://commons.wikimedia.org/wiki/Category:Ice_cores" class="extiw" title="commons:Category:Ice cores">Ice cores</a>.</div></div> </div> <ul><li><a rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=JS2PhRd_5NA">US National Ice Core Laboratory video showing storage and processing of cores</a></li> <li><a rel="nofollow" class="external text" href="http://www.ncdc.noaa.gov/paleo/icgate.html">Ice Core Gateway</a></li> <li><a rel="nofollow" class="external text" href="http://www-bprc.mps.ohio-state.edu/Icecore/">Byrd Polar Research Center – Ice Core Paleoclimatology Research Group</a></li> <li><a rel="nofollow" class="external text" href="https://www.carbonbrief.org/factcheck-what-greenland-ice-cores-say-about-past-and-present-climate-change">A misleading graph has been circling the internet since at least 2010</a></li> <li><a rel="nofollow" class="external text" href="https://www.science.org/content/article/world-s-oldest-ice-core-could-solve-mystery-flipped-ice-age-cycles">A 2.7 million year old core</a></li> <li><a rel="nofollow" class="external text" href="https://www.livescience.com/65188-antarctica-drilling-oldest-ice.html">Beyond EPICA-Oldest Ice mission</a></li> <li><a rel="nofollow" class="external text" href="https://www.sciencedaily.com/releases/2017/12/171213104607.htm">Third Pole ice</a></li></ul> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist 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.navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Chronology" title="Template:Chronology"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Chronology" title="Template talk:Chronology"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Chronology" title="Special:EditPage/Template:Chronology"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Chronology382" style="font-size:114%;margin:0 4em"><a href="/wiki/Chronology" title="Chronology">Chronology</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;">Key topics</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Archaeology" title="Archaeology">Archaeology</a></li> <li><a href="/wiki/Astronomy" title="Astronomy">Astronomy</a></li> <li><a href="/wiki/Geology" title="Geology">Geology</a></li> <li><a href="/wiki/History" title="History">History</a> <ul><li><a href="/wiki/Big_History" title="Big History">Big History</a></li></ul></li> <li><a href="/wiki/Paleontology" title="Paleontology">Paleontology</a></li> <li><a href="/wiki/Time" title="Time">Time</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><div class="hlist"><ul><li><a href="/wiki/Periodization" title="Periodization">Periods</a></li><li><a href="/wiki/Era" title="Era">Eras</a></li><li><a href="/wiki/Epoch_(reference_date)" class="mw-redirect" title="Epoch (reference date)">Epochs</a></li></ul></div></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Calendar_era" title="Calendar era">Calendar eras</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Holocene_calendar" title="Holocene calendar">Human Era</a></li> <li><a href="/wiki/Ab_urbe_condita" title="Ab urbe condita">Ab urbe condita</a></li> <li><a href="/wiki/Anno_Domini" title="Anno Domini">Anno Domini</a> / <a href="/wiki/Common_Era" title="Common Era">Common Era</a></li> <li><a href="/wiki/Anno_Mundi" title="Anno Mundi">Anno Mundi</a></li> <li><a href="/wiki/Bosporan_era" title="Bosporan era">Bosporan era</a></li> <li><a href="/wiki/Bostran_era" title="Bostran era">Bostran era</a></li> <li><a href="/wiki/Byzantine_calendar" title="Byzantine calendar">Byzantine era</a></li> <li><a href="/wiki/Seleucid_era" title="Seleucid era">Seleucid era</a></li> <li><a href="/wiki/Era_of_Caesar_(Iberian_Peninsula)" class="mw-redirect" title="Era of Caesar (Iberian Peninsula)">Era of Caesar (Iberia)</a></li> <li><a href="/wiki/Before_present" class="mw-redirect" title="Before present">Before present</a></li> <li><a href="/wiki/Islamic_calendar" title="Islamic calendar">Hijri</a></li> <li><a href="/wiki/Egyptian_chronology" title="Egyptian chronology">Egyptian</a></li> <li><a href="/wiki/Sothic_cycle" title="Sothic cycle">Sothic cycle</a></li> <li><a href="/wiki/Hindu_units_of_time" title="Hindu units of time">Hindu units of time</a> (<a href="/wiki/Yuga" title="Yuga">Yuga</a>)</li> <li><a href="/wiki/Mesoamerican_calendars" title="Mesoamerican calendars">Mesoamerican</a> <ul><li><a href="/wiki/Mesoamerican_Long_Count_calendar" title="Mesoamerican Long Count calendar">Long Count</a></li> <li><a href="/wiki/Maya_calendar#Short_Count" title="Maya calendar">Short Count</a></li> <li><a href="/wiki/Tzolk%27in" class="mw-redirect" title="Tzolk'in">Tzolk'in</a></li> <li><a href="/wiki/Haab%27" class="mw-redirect" title="Haab'">Haab'</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Regnal_year" title="Regnal year">Regnal year</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Anka_year" title="Anka year">Anka year</a></li> <li><a href="/wiki/Canon_of_Kings" title="Canon of Kings">Canon of Kings</a></li> <li><a href="/wiki/Regnal_years_of_English_and_British_monarchs" title="Regnal years of English and British monarchs">English and British regnal year</a></li> <li><a href="/wiki/Category:Regnal_lists" title="Category:Regnal lists">Lists of kings</a></li> <li><a href="/wiki/Limmu" title="Limmu">Limmu</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Regnal_year" title="Regnal year">Era names</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chinese_era_name" title="Chinese era name">Chinese</a></li> <li><a href="/wiki/Japanese_era_name" title="Japanese era name">Japanese</a></li> <li><a href="/wiki/Korean_era_name" title="Korean era name">Korean</a></li> <li><a href="/wiki/Vietnamese_era_name" title="Vietnamese era name">Vietnamese</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><a href="/wiki/Calendar" title="Calendar">Calendars</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Pre-Julian / Julian</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Roman_calendar" title="Roman calendar">Pre-Julian Roman</a></li> <li><a href="/wiki/Julian_calendar" title="Julian calendar">Original Julian</a></li> <li><a href="/wiki/Proleptic_Julian_calendar" title="Proleptic Julian calendar">Proleptic Julian</a></li> <li><a href="/wiki/Revised_Julian_calendar" title="Revised Julian calendar">Revised Julian</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Gregorian</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Gregorian_calendar" title="Gregorian calendar">Gregorian</a></li> <li><a href="/wiki/Proleptic_Gregorian_calendar" title="Proleptic Gregorian calendar">Proleptic Gregorian</a></li> <li><a href="/wiki/Old_Style_and_New_Style_dates" title="Old Style and New Style dates">Old Style and New Style dates</a></li> <li><a href="/wiki/Adoption_of_the_Gregorian_calendar" title="Adoption of the Gregorian calendar">Adoption of the Gregorian calendar</a></li> <li><a href="/wiki/Dual_dating" title="Dual dating">Dual dating</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Astronomical</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Lunisolar_calendar" title="Lunisolar calendar">Lunisolar</a> (<a href="/wiki/Hebrew_calendar" title="Hebrew calendar">Hebrew</a>, <a href="/wiki/Hindu_calendar" title="Hindu calendar">Hindu</a>)</li> <li><a href="/wiki/Solar_calendar" title="Solar calendar">Solar</a></li> <li><a href="/wiki/Lunar_calendar" title="Lunar calendar">Lunar</a> (<a href="/wiki/Islamic_calendar" title="Islamic calendar">Islamic</a>)</li> <li><a href="/wiki/Astronomical_year_numbering" title="Astronomical year numbering">Astronomical year numbering</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Others</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Sexagenary_cycle" title="Sexagenary cycle">Chinese sexagenary cycle</a></li> <li><a href="/wiki/Geologic_Calendar" title="Geologic Calendar">Geologic Calendar</a></li> <li><a href="/wiki/Iranian_calendars" title="Iranian calendars">Iranian</a></li> <li><a href="/wiki/ISO_week_date" title="ISO week date">ISO week date</a></li> <li><a href="/wiki/Mesoamerican_calendars" title="Mesoamerican calendars">Mesoamerican</a> <ul><li><a href="/wiki/Maya_calendar" title="Maya calendar">Maya</a></li> <li><a href="/wiki/Aztec_calendar" title="Aztec calendar">Aztec</a></li></ul></li> <li><a href="/wiki/Winter_count" title="Winter count">Winter count</a></li> <li><a href="/wiki/New_Earth_Time" title="New Earth Time">New Earth Time</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><a href="/wiki/Astronomical_chronology" title="Astronomical chronology">Astronomic time</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0;background:#fff;"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Cosmic_Calendar" title="Cosmic Calendar">Cosmic Calendar</a></li> <li><a href="/wiki/Ephemeris" title="Ephemeris">Ephemeris</a></li> <li><a href="/wiki/Galactic_year" title="Galactic year">Galactic year</a></li> <li><a href="/wiki/Metonic_cycle" title="Metonic cycle">Metonic cycle</a></li> <li><a href="/wiki/Milankovitch_cycles" title="Milankovitch cycles">Milankovitch cycles</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><a href="/wiki/Geologic_time_scale" title="Geologic time scale">Geologic time</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Concepts</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Deep_time" title="Deep time">Deep time</a></li> <li><a href="/wiki/Geological_history_of_Earth" title="Geological history of Earth">Geological history of Earth</a></li> <li><a href="/wiki/Geologic_time_scale#Terminology" title="Geologic time scale">Geological time units</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Standards</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Global_Standard_Stratigraphic_Age" title="Global Standard Stratigraphic Age">Global Standard Stratigraphic Age (GSSA)</a></li> <li><a href="/wiki/Global_Boundary_Stratotype_Section_and_Point" title="Global Boundary Stratotype Section and Point">Global Boundary Stratotype Section and Point (GSSP)</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;">Methods</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronostratigraphy" title="Chronostratigraphy">Chronostratigraphy</a></li> <li><a href="/wiki/Geochronology" title="Geochronology">Geochronology</a></li> <li><a href="/wiki/Isotope_geochemistry" title="Isotope geochemistry">Isotope geochemistry</a></li> <li><a href="/wiki/Law_of_superposition" title="Law of superposition">Law of superposition</a></li> <li><a href="/wiki/Luminescence_dating" title="Luminescence dating">Luminescence dating</a></li> <li><a href="/wiki/Samarium%E2%80%93neodymium_dating" title="Samarium–neodymium dating">Samarium–neodymium dating</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;"><a href="/wiki/Chronological_dating" title="Chronological dating">Chronological dating</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Absolute_dating" title="Absolute dating">Absolute dating</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Amino_acid_dating" title="Amino acid dating">Amino acid racemisation</a></li> <li><a href="/wiki/Archaeomagnetic_dating" title="Archaeomagnetic dating">Archaeomagnetic dating</a></li> <li><a href="/wiki/Dendrochronology" title="Dendrochronology">Dendrochronology</a></li> <li><a class="mw-selflink selflink">Ice core</a></li> <li><a href="/wiki/Incremental_dating" title="Incremental dating">Incremental dating</a></li> <li><a href="/wiki/Lichenometry" title="Lichenometry">Lichenometry</a></li> <li><a href="/wiki/Paleomagnetism" title="Paleomagnetism">Paleomagnetism</a></li> <li><a href="/wiki/Radiometric_dating" title="Radiometric dating">Radiometric dating</a> <ul><li><a href="/wiki/Lead%E2%80%93lead_dating" title="Lead–lead dating">Lead–lead</a></li> <li><a href="/wiki/K%E2%80%93Ar_dating" title="K–Ar dating">Potassium–argon</a></li> <li><a href="/wiki/Radiocarbon_dating" title="Radiocarbon dating">Radiocarbon</a></li> <li><a href="/wiki/Uranium%E2%80%93lead_dating" title="Uranium–lead dating">Uranium–lead</a></li></ul></li> <li><a href="/wiki/Tephrochronology" title="Tephrochronology">Tephrochronology</a></li> <li><a href="/wiki/Luminescence_dating" title="Luminescence dating">Luminescence dating</a></li> <li><a href="/wiki/Thermoluminescence_dating" title="Thermoluminescence dating">Thermoluminescence dating</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:8.0em;font-weight:normal;background:#cc9;"><a href="/wiki/Relative_dating" title="Relative dating">Relative dating</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Fluorine_absorption_dating" title="Fluorine absorption dating">Fluorine absorption</a></li> <li><a href="/wiki/Nitrogen_dating" title="Nitrogen dating">Nitrogen dating</a></li> <li><a href="/wiki/Obsidian_hydration_dating" title="Obsidian hydration dating">Obsidian hydration</a></li> <li><a href="/wiki/Seriation_(archaeology)" title="Seriation (archaeology)">Seriation</a></li> <li><a href="/wiki/Stratigraphy_(archaeology)" title="Stratigraphy (archaeology)">Stratigraphy</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;">Genetic methods</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Molecular_clock" title="Molecular clock">Molecular clock</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;">Linguistic methods</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Glottochronology" title="Glottochronology">Glottochronology</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;line-height:1.2em;background:#cc9;">Related topics</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Chronicle" title="Chronicle">Chronicle</a></li> <li><a href="/wiki/New_Chronology_(Fomenko)" class="mw-redirect" title="New Chronology (Fomenko)">New Chronology</a></li> <li><a href="/wiki/Synchronoptic_view" title="Synchronoptic view">Synchronoptic view</a></li> <li><a href="/wiki/Timeline" title="Timeline">Timeline</a></li> <li><a href="/wiki/Year_zero" title="Year zero">Year zero</a></li> <li><a href="/wiki/Floruit" title="Floruit">Floruit</a></li> <li><a href="/wiki/Terminus_post_quem" title="Terminus post quem">Terminus post quem</a></li> <li><a href="/wiki/ASPRO_chronology" title="ASPRO chronology">ASPRO chronology</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374" /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235" /></div><div role="navigation" class="navbox" aria-labelledby="Glaciers217" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374" /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1239400231" /><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Glaciers" title="Template:Glaciers"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Glaciers" title="Template talk:Glaciers"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Glaciers" title="Special:EditPage/Template:Glaciers"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Glaciers217" style="font-size:114%;margin:0 4em"><a href="/wiki/Glacier" title="Glacier">Glaciers</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Types</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Aufeis" title="Aufeis">Aufeis</a></li> <li><a href="/wiki/Cirque" title="Cirque">Cirque</a></li> <li><a href="/wiki/Glacieret" title="Glacieret">Glacieret</a></li> <li><a href="/wiki/Ice_cap" title="Ice cap">Ice cap</a></li> <li><a href="/wiki/Ice_field" title="Ice field">Ice field</a></li> <li><a href="/wiki/Ice_sheet" title="Ice sheet">Ice sheet</a></li> <li><a href="/wiki/Ice_shelf" title="Ice shelf">Ice shelf</a></li> <li><a href="/wiki/Ice_stream" title="Ice stream">Ice stream</a></li> <li><a href="/wiki/Ledoyom" title="Ledoyom">Ledoyom</a></li> <li><a href="/wiki/Outlet_glacier" class="mw-redirect" title="Outlet glacier">Outlet glacier</a></li> <li><a href="/wiki/Piedmont_glacier" class="mw-redirect" title="Piedmont glacier">Piedmont glacier</a></li> <li><a href="/wiki/Rock_glacier" title="Rock glacier">Rock glacier</a></li> <li><a href="/wiki/Valley_glacier" class="mw-redirect" title="Valley glacier">Valley glacier</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Anatomy</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ablation_zone" title="Ablation zone">Ablation zone</a></li> <li><a href="/wiki/Accumulation_zone" title="Accumulation zone">Accumulation zone</a></li> <li><a href="/wiki/Bergschrund" title="Bergschrund">Bergschrund</a></li> <li><a href="/wiki/Blue_ice_(glacial)" title="Blue ice (glacial)">Blue ice</a></li> <li><a href="/wiki/Crevasse" title="Crevasse">Crevasse</a></li> <li><a href="/wiki/Dirt_cone" title="Dirt cone">Dirt cone</a></li> <li><a href="/wiki/Firn" title="Firn">Firn</a></li> <li><a href="/wiki/Glacier_cave" title="Glacier cave">Glacier cave</a></li> <li><a href="/wiki/Glacier_head" title="Glacier head">Glacier head</a></li> <li><a href="/wiki/Ice_divide" title="Ice divide">Ice divide</a></li> <li><a href="/wiki/Glacier_tongue" class="mw-redirect" title="Glacier tongue">Glacier tongue</a></li> <li><a href="/wiki/Icefall" title="Icefall">Icefall</a></li> <li><a href="/wiki/Lateral_moraine" class="mw-redirect" title="Lateral moraine">Lateral moraine</a></li> <li><a href="/wiki/Medial_moraine" class="mw-redirect" title="Medial moraine">Medial moraine</a></li> <li><a href="/wiki/Moraine" title="Moraine">Moraine</a></li> <li><a href="/wiki/Moulin_(geomorphology)" title="Moulin (geomorphology)">Moulin</a></li> <li><a href="/wiki/Penitente_(snow_formation)" title="Penitente (snow formation)">Penitente</a></li> <li><a href="/wiki/Randkluft" title="Randkluft">Randkluft</a></li> <li><a href="/wiki/Serac" title="Serac">Sérac</a></li> <li><a href="/wiki/Glacier_terminus" title="Glacier terminus">Terminus</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Processes</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ablation" title="Ablation">Ablation</a></li> <li><a href="/wiki/Glacier_ice_accumulation" title="Glacier ice accumulation">Accumulation</a></li> <li><a href="/wiki/Basal_sliding" title="Basal sliding">Basal sliding</a></li> <li><a href="/wiki/Ice_calving" title="Ice calving">Calving</a></li> <li><a href="/wiki/Creep_(deformation)" title="Creep (deformation)">Creep</a></li> <li><a href="/wiki/Glacial_motion" title="Glacial motion">Motion</a></li> <li><a href="/wiki/Glacial_lake_outburst_flood" title="Glacial lake outburst flood">Outburst flood</a></li> <li><a href="/wiki/Overdeepening" title="Overdeepening">Overdeepening</a></li> <li><a href="/wiki/Periglaciation" title="Periglaciation">Periglaciation</a></li> <li><a href="/wiki/Plucking_(glaciation)" title="Plucking (glaciation)">Plucking</a></li> <li><a href="/wiki/Retreat_of_glaciers_since_1850" title="Retreat of glaciers since 1850">Retreat</a></li> <li><a href="/wiki/Starvation_(glaciology)" title="Starvation (glaciology)">Starvation</a></li> <li><a href="/wiki/Surge_(glacier)" title="Surge (glacier)">Surge</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Measurements</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a class="mw-selflink selflink">Ice core</a></li> <li><a href="/wiki/Glacier_mass_balance" title="Glacier mass balance">Mass balance</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Volcanic relations</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/J%C3%B6kulhlaup" title="Jökulhlaup">Jökulhlaup</a></li> <li><a href="/wiki/Subglacial_eruption" title="Subglacial eruption">Subglacial eruption</a></li> <li><a href="/wiki/Subglacial_volcano" title="Subglacial volcano">Subglacial volcano</a></li> <li><a href="/wiki/Tuya" title="Tuya">Tuya</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Glacial_landform" title="Glacial landform">Landforms</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%">Erosional</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Ar%C3%AAte" title="Arête">Arête</a></li> <li><a href="/wiki/Cirque" title="Cirque">Cirque</a></li> <li><a href="/wiki/Cirque_stairway" title="Cirque stairway">Cirque stairway</a></li> <li><a href="/wiki/Crag_and_tail" title="Crag and tail">Crag and tail</a></li> <li><a href="/wiki/Finger_lake" title="Finger lake">Finger lake</a></li> <li><a href="/wiki/Fjord" title="Fjord">Fjord</a></li> <li><a href="/wiki/Pyramidal_peak" title="Pyramidal peak">Glacial horn</a></li> <li><a href="/wiki/Glacial_lake" title="Glacial lake">Glacial lake</a></li> <li><a href="/wiki/Glacial_striation" title="Glacial striation">Glacial striae</a></li> <li><a href="/wiki/Hanging_valley" class="mw-redirect" title="Hanging valley">Hanging valley</a></li> <li><a href="/wiki/Nunatak" title="Nunatak">Nunatak</a></li> <li><a href="/wiki/P-form_(geology)" title="P-form (geology)">P-form</a></li> <li><a href="/wiki/Ribbon_lake" title="Ribbon lake">Ribbon lake</a></li> <li><a href="/wiki/Roche_moutonn%C3%A9e" title="Roche moutonnée">Roche moutonnée</a></li> <li><a href="/wiki/Suncup_(snow)" title="Suncup (snow)">Suncup</a></li> <li><a href="/wiki/Tarn_(lake)" title="Tarn (lake)">Tarn</a></li> <li><a href="/wiki/Finger_lake" title="Finger lake">Trough lake</a></li> <li><a href="/wiki/Trough_valley" class="mw-redirect" title="Trough valley">Trough valley</a></li> <li><a href="/wiki/Tunnel_valley" title="Tunnel valley">Tunnel valley</a></li> <li><a href="/wiki/Valley#Glacial_valleys" title="Valley">U-valley</a></li> <li><a href="/wiki/Valley_step" title="Valley step">Valley step</a></li> <li><a href="/wiki/Zungenbecken" title="Zungenbecken">Zungenbecken</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Depositional</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Drumlin" title="Drumlin">Drumlin</a></li> <li><a href="/wiki/Glacial_erratic" title="Glacial erratic">Erratic block</a></li> <li><a href="/wiki/Moraine" title="Moraine">Moraine</a></li> <li><a href="/wiki/Moraine-dammed_lake" title="Moraine-dammed lake">Moraine-dammed lake</a></li> <li><a href="/wiki/Pulju_moraine" title="Pulju moraine">Pulju moraine</a></li> <li><a href="/wiki/Rogen_moraine" title="Rogen moraine">Rogen moraine</a></li> <li><a href="/wiki/Sevetti_moraine" title="Sevetti moraine">Sevetti moraine</a></li> <li><a href="/wiki/Terminal_moraine" title="Terminal moraine">Terminal moraine</a></li> <li><a href="/wiki/Till_plain" title="Till plain">Till plain</a></li> <li><a href="/wiki/Veiki_moraine" title="Veiki moraine">Veiki moraine</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="/wiki/Glaciofluvial_deposits" class="mw-redirect" title="Glaciofluvial deposits">Glaciofluvial</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Alpentor" title="Alpentor">Alpentor</a></li> <li><a href="/wiki/Diluvium" title="Diluvium">Diluvium</a></li> <li><a href="/wiki/Esker" title="Esker">Esker</a></li> <li><a href="/wiki/Giant_current_ripples" title="Giant current ripples">Giant current ripples</a></li> <li><a href="/wiki/Kame" title="Kame">Kame</a></li> <li><a href="/wiki/Kame_delta" title="Kame delta">Kame delta</a></li> <li><a href="/wiki/Kettle_(landform)" title="Kettle (landform)">Kettle hole</a></li> <li><a href="/wiki/Outwash_fan" title="Outwash fan">Outwash fan</a></li> <li><a href="/wiki/Outwash_plain" title="Outwash plain">Sandur</a></li> <li><a href="/wiki/Urstromtal" title="Urstromtal">Urstromtal</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Related</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Glaciers_on_Mars" title="Glaciers on Mars">Glaciers on Mars</a></li></ul> </div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><a href="/wiki/Glaciology" title="Glaciology">Glaciology</a></li> <li><a href="/wiki/Category:Glaciers" title="Category:Glaciers">Category</a></li> <li><a href="/wiki/List_of_glaciers" title="List of glaciers">List</a></li> <li><a href="/wiki/Template:Periglacial_environment" title="Template:Periglacial environment">Template:Periglacial environment</a></li></ul> </div></td></tr></tbody></table></div> <div class="navbox-styles"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374" /><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236075235" /></div><div role="navigation" class="navbox authority-control" aria-label="Navbox507" style="padding:3px"><table class="nowraplinks hlist navbox-inner" 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