Editing Pliocene (section)

==Climate==
[[File:Pliocene sst anomaly.png|thumb|left|Mid-Pliocene reconstructed annual sea surface temperature anomaly]]

During the Pliocene epoch (5.3 to 2.6 million years ago (Ma)), the Earth's climate became cooler and drier, as well as more seasonal, marking a transition between the relatively warm [[Miocene]] to the cooler [[Pleistocene]].<ref>{{cite journal |last1=Fauquette |first1=Séverine |last2=Bertini |first2=Adele |date=28 June 2008 |title=Quantification of the northern Italy Pliocene climate from pollen data: evidence for a very peculiar climate pattern |journal=[[Boreas (journal)|Boreas]] |volume=32 |issue=2 |pages=361–369 |doi=10.1111/j.1502-3885.2003.tb01090.x |doi-access=free}}</ref> However, the beginning of the Pliocene was marked by an increase in global temperatures relative to the cooler [[Messinian]]. This increase was related to the 1.2 million year [[Milankovitch cycles|obliquity amplitude modulation cycle]].<ref>{{cite journal |last1=Qin |first1=Jie |last2=Zhang |first2=Rui |last3=Kravchinsky |first3=Vadim A. |last4=Valet |first4=Jean-Pierre |last5=Sagnotti |first5=Leonardo |last6=Li |first6=Jianxing |last7=Xu |first7=Yong |last8=Anwar |first8=Taslima |last9=Yue |first9=Leping |date=2 April 2022 |title=1.2 Myr Band of Earth-Mars Obliquity Modulation on the Evolution of Cold Late Miocene to Warm Early Pliocene Climate |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JB024131 |journal= Journal of Geophysical Research: Solid Earth|volume=127 |issue=4 |doi=10.1029/2022JB024131 |bibcode=2022JGRB..12724131Q |s2cid=247933545 |access-date=24 November 2022}}</ref> By 3.3–3.0 Ma, during the [[Mid-Piacenzian Warm Period]] (mPWP), global average temperature was 2–3&nbsp;°C higher than today,<ref>{{cite journal | last1 = Robinson | first1 = M. | last2 = Dowsett | first2 = H. J. | last3 = Chandler | first3 = M. A. | year = 2008 | title = Pliocene role in assessing future climate impacts | journal = Eos, Transactions, American Geophysical Union | volume = 89 | issue = 49| pages = 501–502 | doi=10.1029/2008eo490001 | bibcode=2008EOSTr..89..501R}}</ref> while carbon dioxide levels were the same as today (400 ppm).<ref>{{cite web|title=Solutions: Responding to Climate Change|url=https://climate.nasa.gov/solutions/adaptation-mitigation/|website=Global Climate Change |date=23 July 2014 |publisher=NASA |access-date=1 September 2016}}</ref> Global sea level was about 25&nbsp;m higher,<ref>{{cite journal | last1 = Dwyer | first1 = G. S. | last2 = Chandler | first2 = M. A. | year = 2009 | title = Mid-Pliocene sea level and continental ice volume based on coupled benthic Mg/Ca palaeotemperatures and oxygen isotopes | journal = Philosophical Transactions of the Royal Society A | volume = 367 | issue = 1886| pages = 157–168 | doi = 10.1098/rsta.2008.0222 | pmid = 18854304 | bibcode = 2009RSPTA.367..157D | hdl = 10161/6586 | s2cid = 3199617 | hdl-access = free }}</ref> though its exact value is uncertain.<ref>{{Cite journal |last1=Raymo |first1=Maureen E. |last2=Kozdon |first2=Reinhard |last3=Evans |first3=David |last4=Lisiecki |first4=Lorraine |last5=Ford |first5=Heather L. |date=February 2018 |title=The accuracy of mid-Pliocene δ18O-based ice volume and sea level reconstructions |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825217305937 |journal=[[Earth-Science Reviews]] |language=en |volume=177 |pages=291–302 |doi=10.1016/j.earscirev.2017.11.022 |access-date=20 July 2024 |via=Elsevier Science Direct|hdl=10023/16606 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Rovere |first1=A. |last2=Hearty |first2=P. J. |last3=Austermann |first3=J. |last4=Mitrovica |first4=J. X. |last5=Gale |first5=J. |last6=Moucha |first6=R. |last7=Forte |first7=A. M. |last8=Raymo |first8=Maureen E. |date=June 2015 |title=Mid-Pliocene shorelines of the US Atlantic Coastal Plain – An improved elevation database with comparison to Earth model predictions |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825215000355 |journal=[[Earth-Science Reviews]] |language=en |volume=145 |pages=117–131 |doi=10.1016/j.earscirev.2015.02.007 |bibcode=2015ESRv..145..117R |access-date=20 July 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> The northern hemisphere ice sheet was ephemeral before the onset of extensive [[glacier|glaciation]] over [[Greenland ice sheet|Greenland]] that occurred in the late Pliocene around 3&nbsp;Ma.<ref>{{cite journal | last1 = Bartoli | first1 = G. |display-authors=etal  | year = 2005 | title = Final closure of Panama and the onset of northern hemisphere glaciation | journal = Earth and Planetary Science Letters | volume = 237 | issue = 1–2| page = 3344 | doi=10.1016/j.epsl.2005.06.020| bibcode = 2005E&PSL.237...33B | doi-access = free }}</ref> The formation of an Arctic [[ice cap]] is signaled by an abrupt shift in [[oxygen]] [[isotope]] ratios and [[ice-rafted]] cobbles in the [[North Atlantic Ocean|North Atlantic]] and [[North Pacific Ocean]] beds.<ref name="VanAndel1994">Van Andel (1994), p. 226.</ref> Mid-latitude glaciation was probably underway before the end of the epoch. The global cooling that occurred during the Pliocene may have accelerated on the disappearance of forests and the spread of grasslands and savannas.<ref>{{cite web |url=http://www.ucmp.berkeley.edu/tertiary/pli.html |title=The Pliocene epoch |work=University of California Museum of Paleontology |access-date=2008-03-25 }}</ref>

During the Pliocene the earth [[climate system]] response shifted from a period of high frequency-low amplitude oscillation dominated by the 41,000-year period of Earth's [[Axial tilt|obliquity]] to one of low-frequency, high-amplitude oscillation dominated by the 100,000-year period of the [[orbital eccentricity]] characteristic of the Pleistocene glacial-interglacial cycles.<ref>{{cite journal |last1=Dowsett |first1=H. J. |last2=Chandler |first2=M. A. |last3=Cronin |first3=T. M. |last4=Dwyer |first4=G. S. |year=2005 |title=Middle Pliocene sea surface temperature variability |url=http://pubs.giss.nasa.gov/docs/2005/2005_Dowsett_etal.pdf |url-status=dead |journal=[[Paleoceanography (journal)|Paleoceanography]] |volume=20 |issue=2 |pages=PA2014 |bibcode=2005PalOc..20.2014D |citeseerx=10.1.1.856.1776 |doi=10.1029/2005PA001133 |archiveurl=https://web.archive.org/web/20111022162030/http://pubs.giss.nasa.gov/docs/2005/2005_Dowsett_etal.pdf |archivedate=2011-10-22}}</ref>

During the late Pliocene and early Pleistocene, 3.6 to 2.6 Ma, the Arctic was much warmer than it is at the present day (with summer temperatures some 8&nbsp;°C warmer than today). That is a key finding of research into a lake-sediment core obtained in Eastern Siberia, which is of exceptional importance because it has provided the longest continuous late Cenozoic land-based sedimentary record thus far.<ref>{{cite web |last=Mason |first=John |title=The last time carbon dioxide concentrations were around 400ppm: a snapshot from Arctic Siberia |url=http://www.skepticalscience.com/pliocene-snapshot.html |access-date=30 January 2014 |publisher=[[Skeptical Science]]}}</ref>

During the late Zanclean, Italy remained relatively warm and humid.<ref>{{Cite journal |last1=Martinetto |first1=Edoardo |last2=Tema |first2=Evdokia |last3=Irace |first3=Andrea |last4=Violanti |first4=Donata |last5=Ciuto |first5=Marco |last6=Zanella |first6=Elena |date=1 May 2018 |title=High-diversity European palaeoflora favoured by early Pliocene warmth: New chronological constraints from the Ca′ Viettone section, NW Italy |url=https://www.sciencedirect.com/science/article/pii/S0031018217310271 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=496 |pages=248–267 |doi=10.1016/j.palaeo.2018.01.042 |bibcode=2018PPP...496..248M |access-date=30 October 2024 |via=Elsevier Science Direct|hdl=2318/1731652 |hdl-access=free }}</ref> [[Central Asia]] became more seasonal during the Pliocene, with colder, drier winters and wetter summers, which contributed to an increase in the abundance of {{C4}} plants across the region.<ref>{{cite journal |last1=Shen |first1=Xingyan |last2=Wan |first2=Shiming |last3=Colin |first3=Christophe |last4=Tada |first4=Ryuji |last5=Shi |first5=Xuefa |last6=Pei |first6=Wenqiang |last7=Tan |first7=Yang |last8=Jiang |first8=Xuejun |last9=Li |first9=Anchun |date=15 November 2018 |title=Increased seasonality and aridity drove the C4 plant expansion in Central Asia since the Miocene–Pliocene boundary |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X18305284 |journal=[[Earth and Planetary Science Letters]] |volume=502 |pages=74–83 |bibcode=2018E&PSL.502...74S |doi=10.1016/j.epsl.2018.08.056 |s2cid=134183141 |access-date=1 January 2023|url-access=subscription }}</ref> In the [[Loess Plateau]], [[δ13C]] values of occluded organic matter increased by 2.5% while those of pedogenic carbonate increased by 5% over the course of the Late Miocene and Pliocene, indicating increased aridification.<ref>{{cite journal |last1=Gallagher |first1=Timothy M. |last2=Serach |first2=Lily |last3=Sekhon |first3=Natasha |last4=Zhang |first4=Hanzhi |last5=Wang |first5=Hanlin |last6=Ji |first6=Shunchuan |last7=Chang |first7=Xi |last8=Lu |first8=Huayu |last9=Breecker |first9=Daniel O. |date=25 November 2021 |title=Regional Patterns in Miocene-Pliocene Aridity Across the Chinese Loess Plateau Revealed by High Resolution Records of Paleosol Carbonate and Occluded Organic Matter |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021PA004344 |journal=[[Paleoceanography and Paleoclimatology]] |volume=32 |issue=12 |bibcode=2021PaPa...36.4344G |doi=10.1029/2021PA004344 |s2cid=244702210 |access-date=1 January 2023|url-access=subscription }}</ref> Further aridification of Central Asia was caused by the development of Northern Hemisphere glaciation during the Late Pliocene.<ref>{{cite journal |last1=Sun |first1=Youbin |last2=An |first2=Zhisheng |date=1 December 2005 |title=Late Pliocene-Pleistocene changes in mass accumulation rates of eolian deposits on the central Chinese Loess Plateau |journal=[[Journal of Geophysical Research]] |volume=110 |issue=D23 |pages=1–8 |bibcode=2005JGRD..11023101S |doi=10.1029/2005JD006064 |doi-access=free}}</ref> A sediment core from the northern South China Sea shows an increase in dust storm activity during the middle Pliocene.<ref>{{cite journal |last1=Süfke |first1=Finn |last2=Kaboth-Barr |first2=Stefanie |last3=Wei |first3=Kuo-Yen |last4=Chuang |first4=Chih-Kai |last5=Gutjahr |first5=Marcus |last6=Pross |first6=Jörg |last7=Friedrich |first7=Oliver |date=15 September 2022 |title=Intensification of Asian dust storms during the Mid-Pliocene Warm Period (3.25–2.96 Ma) documented in a sediment core from the South China Sea |url=https://www.sciencedirect.com/science/article/abs/pii/S0277379122003006 |journal=[[Quaternary Science Reviews]] |volume=292 |bibcode=2022QSRv..29207669S |doi=10.1016/j.quascirev.2022.107669 |s2cid=251426879 |access-date=25 June 2023}}</ref> The South Asian Summer Monsoon (SASM) increased in intensity after 2.95 Ma, likely because of enhanced cross-equatorial pressure caused by the reorganisation of the [[Indonesian Throughflow]].<ref>{{Cite journal |last1=Sarathchandraprasad |first1=T. |last2=Tiwari |first2=Manish |last3=Behera |first3=Padmasini |date=15 July 2021 |title=South Asian Summer Monsoon precipitation variability during late Pliocene: Role of Indonesian Throughflow |url=https://www.sciencedirect.com/science/article/pii/S0031018221002327 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=574 |pages=110447 |doi=10.1016/j.palaeo.2021.110447 |bibcode=2021PPP...57410447S |access-date=30 October 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref>

In the south-central [[Andes]], an arid period occurred from 6.1 to 5.2 Ma, with another occurring from 3.6 to 3.3 Ma. These arid periods are coincident with global cold periods, during which the position of the [[Southern Hemisphere]] [[westerlies]] shifted northward and disrupted the South American Low Level Jet, which brings moisture to southeastern South America.<ref>{{cite journal |last1=Amidon |first1=William H. |last2=Fisher |first2=G. Burch |last3=Burbank |first3=Douglas W. |last4=Ciccioli |first4=Patricia L. |last5=Alonso |first5=Ricardo N. |last6=Gorin |first6=Andrew L. |last7=Silverhart |first7=Perry H. |last8=Kylander-Clark |first8=Andrew R. C. |last9=Christoffersen |first9=Michael S. |display-authors=6 |date=12 June 2017 |title=Mio-Pliocene aridity in the south-central Andes associated with Southern Hemisphere cold periods |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=114 |issue=25 |pages=6474–6479 |bibcode=2017PNAS..114.6474A |doi=10.1073/pnas.1700327114 |pmc=5488932 |pmid=28607045 |doi-access=free}}</ref>

From around 3.8 Ma to about 3.3 Ma, North Africa experienced an extended humid period.<ref>{{Cite journal |last1=Amarathunga |first1=Udara |last2=Rohling |first2=Eelco J. |last3=Grant |first3=Katharine M. |last4=Francke |first4=Alexander |last5=Latimer |first5=James |last6=Klaebe |first6=Robert M. |last7=Heslop |first7=David |last8=Roberts |first8=Andrew P. |last9=Hutchinson |first9=David K. |display-authors=6 |date=24 June 2024 |title=Mid-Pliocene glaciation preceded by a 0.5-million-year North African humid period |url=https://www.nature.com/articles/s41561-024-01472-8 |journal=[[Nature Geoscience]] |language=en |volume=17 |issue=7 |pages=660–666 |doi=10.1038/s41561-024-01472-8 |bibcode=2024NatGe..17..660A |issn=1752-0894 |access-date=30 October 2024}}</ref> In northwestern Africa, tropical forests extended up to Cape Blanc during the Zanclean until around 3.5 Ma. During the Piacenzian, from about 3.5 to 2.6 Ma, the region was forested at irregular intervals and contained a significant Saharan palaeoriver until 3.35 Ma, when trade winds began to dominate over fluvial transport of pollen. Around 3.26 Ma, a strong aridification event that was followed by a return to more humid conditions, which was itself followed by another aridification around 2.7 Ma. From 2.6 to 2.4 Ma, vegetation zones began repeatedly shifting latitudinally in response to glacial-interglacial cycles.<ref>{{cite journal |last1=Leroy |first1=Suzanne |last2=Dupont |first2=Lydie |date=June 1994 |title=Development of vegetation and continental aridity in northwestern Africa during the Late Pliocene: the pollen record of ODP site 658 |url=https://www.sciencedirect.com/science/article/abs/pii/0031018294901813 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=109 |issue=2–4 |pages=295–316 |bibcode=1994PPP...109..295L |doi=10.1016/0031-0182(94)90181-3 |access-date=31 December 2022|url-access=subscription }}</ref>

The climate of eastern Africa was very similar to what it is today. Unexpectedly, the expansion of grasslands in eastern Africa during this epoch appears to have been decoupled from aridification and not caused by it, as evidenced by their asynchrony.<ref>{{cite journal |last1=Blumenthal |first1=Scott A. |last2=Levin |first2=Naomi E. |last3=Brown |first3=Francis H. |last4=Brugal |first4=Jean-Philip |last5=Chritz |first5=Kendra L. |last6=Harris |first6=John M. |last7=Jehle |first7=Glynis E. |last8=Cerling |first8=Thure E. |display-authors=6 |date=26 June 2017 |title=Aridity and hominin environments |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=114 |issue=28 |pages=7331–7336 |bibcode=2017PNAS..114.7331B |doi=10.1073/pnas.1700597114 |pmc=5514716 |pmid=28652366 |doi-access=free}}</ref>

Southwestern Australia hosted [[heathlands]], [[shrubland]]s, and [[woodland]]s with a greater species diversity compared to today during the Middle and Late Pliocene. Three different aridification events occurred around 2.90, 2.59, and 2.56 Ma, and may have been linked to the onset of continental glaciation in the Arctic, suggesting that vegetation changes in Australia during the Pliocene behaved similarly to during the Late Pleistocene and were likely characterised by comparable cycles of aridity and humidity.<ref>{{cite journal |last1=Dodson |first1=J. R. |last2=Macphail |first2=M. K. |date=July 2004 |title=Palynological evidence for aridity events and vegetation change during the Middle Pliocene, a warm period in Southwestern Australia |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818104000153 |journal=[[Global and Planetary Change]] |volume=41 |issue=3–4 |pages=285–307 |bibcode=2004GPC....41..285D |doi=10.1016/j.gloplacha.2004.01.013 |access-date=31 December 2022|url-access=subscription }}</ref>

The equatorial Pacific Ocean [[sea surface temperature]] gradient was considerably lower than it is today. Mean sea surface temperatures in the east were substantially warmer than today but similar in the west. This condition has been described as a permanent [[El Niño]] state, or "El Padre".<ref>{{cite journal |last1=Fedorov |first1=A. V. |display-authors=etal |year=2006 |title=The Pliocene paradox (mechanisms for a permanent El Niño) |journal=[[Science (journal)|Science]] |volume=312 |issue=5779 |pages=1485–1489 |bibcode=2006Sci...312.1485F |citeseerx=10.1.1.143.5772 |doi=10.1126/science.1122666 |pmid=16763140 |s2cid=36446661}}</ref> Several mechanisms have been proposed for this pattern, including [[Cyclonic Niño|increased tropical cyclone activity]].<ref>{{cite journal |last1=Fedorov |first1=Alexey V. |last2=Brierley |first2=Christopher M. |last3=Emanuel |first3=Kerry |date=February 2010 |title=Tropical cyclones and permanent El Niño in the early Pliocene epoch |journal=[[Nature (journal)|Nature]] |language=En |volume=463 |issue=7284 |pages=1066–1070 |bibcode=2010Natur.463.1066F |doi=10.1038/nature08831 |issn=0028-0836 |pmid=20182509 |s2cid=4330367 |hdl-access=free |hdl=1721.1/63099}}</ref>

The extent of the [[West Antarctic Ice Sheet]] oscillated at the 40 [[Kiloannus|kyr]] period of Earth's obliquity. Ice sheet collapse occurred when the global average temperature was 3&nbsp;°C warmer than today and carbon dioxide concentration was at 400 ppmv. This resulted in open waters in the [[Ross Sea]].<ref>{{cite journal |last1=Naish |first1=T. |display-authors=etal |year=2009 |title=Obliquity-paced Pliocene West Antarctic ice sheet oscillations |url=http://digitalcommons.unl.edu/geosciencefacpub/185 |journal=[[Nature (journal)|Nature]] |volume=458 |issue=7236 |pages=322–328 |bibcode=2009Natur.458..322N |doi=10.1038/nature07867 |pmid=19295607 |s2cid=15213187|url-access=subscription }}</ref> Global sea-level fluctuation associated with ice-sheet collapse was probably up to 7 meters for the west Antarctic and 3 meters for the east Antarctic. Model simulations are consistent with reconstructed ice-sheet oscillations and suggest a progression from a smaller to a larger West Antarctic ice sheet in the last 5 million years. Intervals of ice sheet collapse were much more common in the early-mid Pliocene (5 Ma – 3 Ma), after three-million-year intervals with modern or glacial ice volume became longer and collapse occurs only at times when warmer global temperature coincide with strong austral summer insolation anomalies.<ref>{{cite journal |last1=Pollard |first1=D. |last2=DeConto |first2=R. M. |year=2009 |title=Modelling West Antarctic ice sheet growth and collapse through the past five million years |journal=[[Nature (journal)|Nature]] |volume=458 |issue=7236 |pages=329–332 |bibcode=2009Natur.458..329P |doi=10.1038/nature07809 |pmid=19295608 |s2cid=4427715}}</ref>