Editing Ice core (section)

=== Antarctica deep cores ===
[[File:Co2 glacial cycles 800k.png|thumb|Composite data for Dome C, CO<sub>2</sub> levels (ppm) going back nearly 800,000 years, and related glacial cycles.|left|alt=Graph showing CO<sub>2</sub> levels, highlit to indicate glacial cycles|300x300px]]

[[Soviet Union|Soviet]] ice drilling projects began in the 1950s, in [[Franz Josef Land]], the [[Urals]], [[Novaya Zemlya]], and at [[Mirny Station|Mirny]] and Vostok in the Antarctic; not all these early holes retrieved cores.<ref>{{harvnb|Ueda|Talalay|2007}}, pp. 3–5.</ref> Over the following decades work continued at multiple locations in Asia.<ref>{{harvnb|Ueda|Talalay|2007}}, pp. 50–58.</ref> Drilling in the Antarctic focused mostly on Mirny and Vostok, with a series of deep holes at Vostok begun in 1970.<ref>{{harvnb|Ueda|Talalay|2007}}, pp. 3–26.</ref> The first deep hole at Vostok reached 506.9&nbsp;m in April 1970; by 1973 a depth of 952&nbsp;m had been reached.  A subsequent hole, Vostok 2, drilled from 1971 to 1976, reached 450&nbsp;m, and Vostok 3 reached 2202&nbsp;m in 1985 after six drilling seasons.<ref>{{harvnb|Ueda|Talalay|2007}}, p. 11.</ref> Vostok 3 was the first core to retrieve ice from the previous glacial period, 150,000 years ago.<ref name="Jouzel-2013-2" /> Drilling was interrupted by a fire at the camp in 1982, but further drilling began in 1984, eventually reaching 2546&nbsp;m in 1989. A fifth Vostok core was begun in 1990, reached 3661&nbsp;m in 2007, and was later extended to 3769&nbsp;m.<ref name="Jouzel-2013-1">{{harvnb|Jouzel|2013}}, p. 2527.</ref><ref name="Jouzel-2013-2" /> The estimated age of the ice is 420,000 years at 3310&nbsp;m depth; below that point it is difficult to interpret the data reliably because of mixing of the ice.<ref name="Jouzel-2013-3">{{harvnb|Jouzel|2013}}, p. 2529.</ref>

[[File:EPICA delta D plot.svg|thumb|The EPICA Dome C and Vostok ice cores compared|400px]]

[[EPICA]], 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&nbsp;m in only two seasons of drilling, but which took another four years to reach bedrock at 3260 m; and one at [[Kohnen Station]], which reached bedrock at 2760&nbsp;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.<ref name="Jouzel-2013-3" />

Other deep Antarctic cores included a Japanese project at [[Dome F]], which reached 2503&nbsp;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&nbsp;m in 2006, estimated to reach ice 720,000 years old.<ref name="Jouzel-2013-3" /> US teams drilled at [[McMurdo Station]] in the 1990s, and at [[Taylor Dome]] (554&nbsp;m in 1994) and [[Siple Dome]] (1004&nbsp;m in 1999), with both cores reaching ice from the last glacial period.<ref name="Jouzel-2013-3" /><ref>{{Cite journal|last1=Bentley|first1=Charles R.|last2=Koci|first2=Bruce R.|year=2007|title=Drilling to the beds of the Greenland and Antarctic ice sheets: a review|journal=Annals of Glaciology|volume=47|issue=1|pages=3–4|doi=10.3189/172756407786857695|bibcode=2007AnGla..47....1B|doi-access=free}}</ref> The [[West Antarctic Ice Sheet]] (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.<ref name="Jouzel-2013-4">{{harvnb|Jouzel|2013}}, p. 2530.</ref> A 948&nbsp;m core was drilled at [[Berkner Island]] by a project managed by the [[British Antarctic Survey]] from 2002 to 2005, extending into the last glacial period;<ref name="Jouzel-2013-4" /> and an Italian-managed [[ITASE]] project completed a 1620&nbsp;m core at [[Talos Dome]] in 2007.<ref name="Jouzel-2013-4" /><ref>{{Cite web|url=http://www.taldice.org/site/index.php|title=TALos Dome Ice CorE – TALDICE|last=Iaccarino|first=Tony|publisher=Talos Dome Ice Core|access-date=28 May 2017}}</ref>

In 2016, cores were retrieved from the [[Allan Hills]] 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.<ref>{{Cite news|url=https://www.science.org/content/article/record-shattering-27-million-year-old-ice-core-reveals-start-ice-ages|title=Record-shattering 2.7-million-year-old ice core reveals start of the ice ages|date=14 August 2017|work=Science |publisher= AAAS|access-date=30 August 2017|language=en}}</ref>