Editing Antarctic ice sheet (section)

==Situation during geologic time scales==
[[File:65 Myr Climate Change.png|thumb|upright=1.3|Polar climatic temperature changes throughout the [[Cenozoic]], showing [[glaciation]] of Antarctica toward the end of the [[Eocene]], thawing near the end of the [[Oligocene]] and subsequent [[Miocene]] re-glaciation.]]

The icing of Antarctica began in the  Late Palaeocene or middle [[Eocene]] between 60<ref>{{cite journal |last1=Barr |first1=Iestyn D. |last2=Spagnolo |first2=Matteo |last3=Rea |first3=Brice R. |last4=Bingham |first4=Robert G. |last5=Oien |first5=Rachel P. |last6=Adamson |first6=Kathryn |last7=Ely |first7=Jeremy C. |last8=Mullan |first8=Donal J. |last9=Pellitero |first9=Ramón |last10=Tomkins |first10=Matt D. |title=60 million years of glaciation in the Transantarctic Mountains |journal=Nature Communications |date=21 September 2022 |volume=13 |issue=1 |pages=5526 |doi=10.1038/s41467-022-33310-z |pmid=36130952 |pmc=9492669 |bibcode=2022NatCo..13.5526B |language=en |issn=2041-1723|hdl=2164/19437 |hdl-access=free }}</ref> and 45.5 million years ago<ref>[http://cat.inist.fr/?aModele=afficheN&cpsidt=5254620 Sedimentological evidence for the formation of an East Antarctic ice sheet in Eocene/Oligocene time] {{Webarchive|url=https://web.archive.org/web/20120616100403/http://cat.inist.fr/?aModele=afficheN&cpsidt=5254620 |date=2012-06-16 }} Palaeogeography, palaeoclimatology, & palaeoecology ISSN 0031-0182, 1992, vol. 93, no1-2, pp. 85–112 (3 p.)</ref> and escalated during the [[Eocene–Oligocene extinction event]] about 34 million years ago. CO<sub>2</sub> levels were then about 760 [[parts per million|ppm]]<ref>{{Cite web |title=New CO2 data helps unlock the secrets of Antarctic formation |url=https://phys.org/news/2009-09-co2-secrets-antarctic-formation.html |access-date=2023-06-06 |website=phys.org |language=en|date=September 13, 2009}}</ref> and had been decreasing from earlier levels in the thousands of ppm. Carbon dioxide decrease, with a [[Tipping points in the climate system|tipping point]] of 600 ppm, was the primary agent forcing Antarctic glaciation.<ref>{{cite journal|url=https://www.sciencedaily.com/releases/2011/12/111201174225.htm |title=Drop in carbon dioxide levels led to polar ice sheet, study finds |journal=Science |volume=334 |issue=6060 |pages=1261–1264 |doi=10.1126/science.1203909 |pmid=22144622 |access-date=2014-01-28|bibcode=2011Sci...334.1261P |year=2011 |last1=Pagani |first1=M. |last2=Huber |first2=M. |last3=Liu |first3=Z. |last4=Bohaty |first4=S. M. |last5=Henderiks |first5=J. |last6=Sijp |first6=W. |last7=Krishnan |first7=S. |last8=Deconto |first8=R. M. |s2cid=206533232 |url-access=subscription }}</ref> The glaciation was favored by an interval when the Earth's orbit favored cool summers but [[oxygen isotope ratio cycle]] marker changes were too large to be explained by Antarctic ice-sheet growth alone indicating an [[ice age]] of some size.<ref>{{cite journal | doi = 10.1038/nature03135 | pmid=15635407 | volume=433 | issue=7021 | title=Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific Ocean | year=2005 | journal=Nature | pages=53–57 | last1 = Coxall | first1 = Helen K.| bibcode=2005Natur.433...53C | s2cid=830008 }}</ref> The opening of the [[Drake Passage]] may have played a role as well<ref>{{cite journal | doi = 10.1130/0091-7613(1996)024<0163:EOTITS>2.3.CO;2 | volume=24 | issue=2 | title=Eocene-Oligocene transition in the Southern Ocean: History of water mass circulation and biological productivity | year=1996 | journal=Geology | page=163 | last1 = Diester-Haass | first1 = Liselotte | last2 = Zahn | first2 = Rainer| bibcode=1996Geo....24..163D }}</ref> though models of the changes suggest declining CO<sub>2</sub> levels to have been more important.<ref>{{Cite journal| last1 = DeConto | first1 = Robert M.  | year=2003 | title=Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric CO<sub>2</sub> | journal=Nature | volume=421 | issue = 6920  | pages=245–249 | doi = 10.1038/nature01290 | pmid = 12529638  | bibcode=2003Natur.421..245D | s2cid = 4326971 | url = http://doc.rero.ch/record/16546/files/PAL_E3220.pdf }}</ref>

The Western Antarctic ice sheet declined somewhat during the warm early [[Pliocene]] epoch, approximately five to three million years ago; during this time the [[Ross Sea]] opened up.<ref>{{Cite journal |last1=Naish |first1=Timothy |display-authors=etal |year=2009 |title=Obliquity-paced Pliocene West Antarctic ice sheet oscillations |journal=[[Nature (journal)|Nature]] |volume=458 |issue=7236 |pages=322–328 |bibcode=2009Natur.458..322N |doi=10.1038/nature07867 |pmid=19295607 |s2cid=15213187 |url=https://digitalcommons.unl.edu/cgi/viewcontent.cgi?httpsredir=1&article=1186&context=geosciencefacpub|url-access=subscription }}</ref> But there was no significant decline in the land-based Eastern Antarctic ice sheet.<ref>{{Cite journal|last=Shakun |first=Jeremy D. |display-authors=etal |year=2018 |title=Minimal East Antarctic Ice Sheet retreat onto land during the past eight million years |journal=Nature |volume=558 |issue=7709 |pages=284–287 |doi=10.1038/s41586-018-0155-6 |pmid=29899483 |bibcode=2018Natur.558..284S |osti=1905199 |s2cid=49185845 |url=https://www.osti.gov/biblio/1905199 }}</ref>