Editing Eocene (section)

=== Late Eocene ===

At the end of the MECO, the MLEC resumed.<ref name="ChristopherRobertScotese" /> Cooling and the carbon dioxide drawdown continued through the late Eocene and into the Eocene–Oligocene transition around 34 Ma.<ref>{{cite journal |last1=Cappelli |first1=C. |last2=Bown |first2=P. R. |last3=Westerhold |first3=T. |last4=Bohaty |first4=S. M. |last5=De Riu |first5=M. |last6=Loba |first6=V. |last7=Yamamoto |first7=Y. |last8=Agnini |first8=C. |date=15 November 2019 |title=The Early to Middle Eocene Transition: An Integrated Calcareous Nannofossil and Stable Isotope Record From the Northwest Atlantic Ocean (Integrated Ocean Drilling Program Site U1410) |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019PA003686 |journal=[[Paleoceanography and Paleoclimatology]] |volume=34 |issue=12 |pages=1913–1930 |bibcode=2019PaPa...34.1913C |doi=10.1029/2019PA003686 |s2cid=210245165 |access-date=17 March 2023}}</ref> The post-MECO cooling brought with it a major aridification trend in Asia,<ref>{{cite journal |last1=Bosboom |first1=Roderic E. |last2=Abels |first2=Hemmo A. |last3=Hoorn |first3=Carina |last4=Van den Berg |first4=Bas C. J. |last5=Guo |first5=Zhaojie |last6=Dupont-Nivet |first6=Guillaume |date=1 March 2014 |title=Aridification in continental Asia after the Middle Eocene Climatic Optimum (MECO) |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X13007206 |journal=[[Earth and Planetary Science Letters]] |volume=389 |pages=34–42 |doi=10.1016/j.epsl.2013.12.014 |bibcode=2014E&PSL.389...34B |access-date=18 May 2023}}</ref> enhanced by retreating seas.<ref>{{Cite journal |last1=Bosboom |first1=Roderic |last2=Dupont-Nivet |first2=Guillaume |last3=Grothe |first3=Arjen |last4=Brinkhuis |first4=Henk |last5=Villa |first5=Giuliana |last6=Mandic |first6=Oleg |last7=Stoica |first7=Marius |last8=Kouwenhoven |first8=Tanja |last9=Huang |first9=Wentao |last10=Yang |first10=Wei |last11=Guo |first11=ZhaoJie |date=1 June 2014 |title=Timing, cause and impact of the late Eocene stepwise sea retreat from the Tarim Basin (west China) |url=https://www.sciencedirect.com/science/article/pii/S0031018214001709 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=403 |pages=101–118 |doi=10.1016/j.palaeo.2014.03.035 |bibcode=2014PPP...403..101B |issn=0031-0182 |access-date=26 December 2023 |via=Elsevier Science Direct}}</ref> A monsoonal climate remained predominant in East Asia.<ref>{{Cite journal |last1=Li |first1=Qijia |last2=Utescher |first2=Torsten |last3=Liu |first3=Yusheng (Christopher) |last4=Ferguson |first4=David |last5=Jia |first5=Hui |last6=Quan |first6=Cheng |date=1 September 2022 |title=Monsoonal climate of East Asia in Eocene times inferred from an analysis of plant functional types |url=https://linkinghub.elsevier.com/retrieve/pii/S003101822200308X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=601 |pages=111138 |doi=10.1016/j.palaeo.2022.111138 |bibcode=2022PPP...60111138L |access-date=20 July 2024 |via=Elsevier Science Direct}}</ref> The cooling during the initial stages of the opening of the Drake Passage ~38.5 Ma was not global, as evidenced by an absence of cooling in the North Atlantic.<ref>{{cite journal |last1=Borrelli |first1=Chiara |last2=Cramer |first2=Benjamin S. |last3=Katz |first3=Miriam E. |date=27 March 2014 |title=Bipolar Atlantic deepwater circulation in the middle-late Eocene: Effects of Southern Ocean gateway openings |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2012PA002444 |journal=[[Paleoceanography and Paleoclimatology]] |volume=29 |issue=4 |pages=308–327 |doi=10.1002/2012PA002444 |bibcode=2014PalOc..29..308B |access-date=7 April 2023}}</ref> During the cooling period, benthic oxygen isotopes show the possibility of ice creation and ice increase during this later cooling.<ref name="Pearson4" /> The end of the Eocene and beginning of the Oligocene is marked with the massive expansion of area of the Antarctic ice sheet that was a major step into the icehouse climate.<ref name="Lear11" /> Multiple proxies, such as oxygen isotopes and [[alkenone]]s, indicate that at the Eocene–Oligocene transition, the atmospheric carbon dioxide concentration had decreased to around 750–800 ppm, approximately twice that of [[Atmosphere of Earth|present levels]].<ref name="Pagani10" /><ref name="Lear11" /> Along with the decrease of atmospheric carbon dioxide reducing the global temperature, orbital factors in ice creation can be seen with 100,000-year and 400,000-year fluctuations in benthic oxygen isotope records.<ref name="Diester23" /> Another major contribution to the expansion of the ice sheet was the creation of the [[Antarctic Circumpolar Current]].<ref name="Barker24" /> The creation of the Antarctic circumpolar current would isolate the cold water around the Antarctic, which would reduce heat transport to the Antarctic<ref name="Huber25" /> along with creating [[ocean gyre]]s that result in the [[upwelling]] of colder bottom waters.<ref name="Barker24" /> The issue with this hypothesis of the consideration of this being a factor for the Eocene-Oligocene transition is the timing of the creation of the circulation is uncertain.<ref name="Barker26" /> For [[Drake Passage]], sediments indicate the opening occurred ~41 Ma while tectonics indicate that this occurred ~32 Ma.{{citation needed|date=February 2022}} Solar activity did not change significantly during the greenhouse-icehouse transition across the Eocene-Oligocene boundary.<ref>{{Cite journal |last1=Shi |first1=Juye |last2=Jin |first2=Zhijun |last3=Liu |first3=Quanyou |last4=Fan |first4=Tailiang |last5=Gao |first5=Zhiqian |date=1 October 2021 |title=Sunspot cycles recorded in Eocene lacustrine fine-grained sedimentary rocks in the Bohai Bay Basin, eastern China |url=https://www.sciencedirect.com/science/article/pii/S0921818121001995 |journal=[[Global and Planetary Change]] |volume=205 |pages=103614 |doi=10.1016/j.gloplacha.2021.103614 |bibcode=2021GPC...20503614S |issn=0921-8181 |access-date=26 December 2023 |via=Elsevier Science Direct}}</ref>