Editing Cretaceous (section)

==Climate==
{{further|Cool tropics paradox}}
[[Palynology|Palynological]] evidence indicates the Cretaceous climate had three broad phases: a Berriasian–Barremian warm-dry phase, an Aptian–Santonian warm-wet phase, and a Campanian–Maastrichtian cool-dry phase.<ref name="ClimatePalynology">{{cite journal |last1=Wang |first1=Jing-Yu |last2=Li |first2=Xiang-Hui |last3=Li |first3=Li-Qin |last4=Wang |first4=Yong-Dong |date=September 2022 |title=Cretaceous climate variations indicated by palynoflora in South China |url=https://www.sciencedirect.com/science/article/abs/pii/S1871174X21000895 |journal=[[Palaeoworld]] |volume=31 |issue=3 |pages=507–520 |doi=10.1016/j.palwor.2021.11.001 |s2cid=243963376 |access-date=11 December 2022}}</ref> As in the Cenozoic, the 400,000 year eccentricity cycle was the dominant orbital cycle governing carbon flux between different reservoirs and influencing global climate.<ref>{{Cite journal |last1=Giorgioni |first1=Martino |last2=Weissert |first2=Helmut |last3=Bernasconi |first3=Stefano M. |last4=Hochuli |first4=Peter A. |last5=Coccioni |first5=Rodolfo |last6=Keller |first6=Christina E. |date=21 January 2012 |title=Orbital control on carbon cycle and oceanography in the mid-Cretaceous greenhouse: LONG ECCENTRICITY CYCLES IN C-ISOTOPE |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=27 |issue=1 |pages=1–12 |doi=10.1029/2011PA002163 |s2cid=128594924 |doi-access=free }}</ref> The location of the Intertropical Convergence Zone (ITCZ) was roughly the same as in the present.<ref>{{Cite journal |last1=Hofmann |first1=P. |last2=Wagner |first2=T. |date=23 December 2011 |title=ITCZ controls on Late Cretaceous black shale sedimentation in the tropical Atlantic Ocean |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=26 |issue=4 |pages=1–11 |doi=10.1029/2011PA002154 |bibcode=2011PalOc..26.4223H |issn=0883-8305 |doi-access=free }}</ref>

The cooling trend of the last epoch of the Jurassic, the Tithonian, continued into the Berriasian, the first age of the Cretaceous.<ref name="The Berriasian Age" /> The North Atlantic seaway opened and enabled the flow of cool water from the Boreal Ocean into the Tethys.<ref>{{cite journal |last1=Abbink |first1=Oscar |last2=Targarona |first2=Jordi |last3=Brinkhuis |first3=Henk |last4=Visscher |first4=Henk |date=October 2001 |title=Late Jurassic to earliest Cretaceous palaeoclimatic evolution of the southern North Sea |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818101001011 |journal=[[Global and Planetary Change]] |volume=30 |issue=3–4 |pages=231–256 |doi=10.1016/S0921-8181(01)00101-1 |bibcode=2001GPC....30..231A |access-date=17 August 2023}}</ref> There is evidence that snowfalls were common in the higher latitudes during this age, and the tropics became wetter than during the Triassic and Jurassic. Glaciation was restricted to high-[[latitude]] mountains, though seasonal snow may have existed farther from the poles.<ref name="The Berriasian Age">{{cite web|url=http://palaeos.com/mesozoic/cretaceous/berriasian.html|title=Palaeos Mesozoic: Cretaceous: The Berriasian Age|first=M.Alan|last=Kazlev|website=Palaeos.com|access-date=18 October 2017|url-status=dead|archive-url=https://web.archive.org/web/20101220223930/http://palaeos.com/Mesozoic/Cretaceous/Berriasian.html|archive-date=20 December 2010}}</ref> After the end of the first age, however, temperatures began to increase again, with a number of thermal excursions, such as the middle [[Valanginian]] [[Weissert Event|Weissert Thermal Excursion]] (WTX),<ref name="ChristopherScotese" /> which was caused by the Paraná-Etendeka Large Igneous Province's activity.<ref>{{cite journal |last1=Martinez |first1=Mathieu |last2=Aguirre-Urreta |first2=Beatriz |last3=Dera |first3=Guillaume |last4=Lescano |first4=Marina |last5=Omarini |first5=Julieta |last6=Tunik |first6=Maisa |last7=O'Dogherty |first7=Luis |last8=Aguado |first8=Roque |last9=Company |first9=Miguel |last10=Bodin |first10=Stéphane |date=April 2023 |title=Synchrony of carbon cycle fluctuations, volcanism and orbital forcing during the Early Cretaceous |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825223000454 |journal=[[Earth-Science Reviews]] |volume=239 |doi=10.1016/j.earscirev.2023.104356 |bibcode=2023ESRv..23904356M |s2cid=256880421 |access-date=9 August 2023}}</ref> It was followed by the middle [[Hauterivian]] Faraoni Thermal Excursion (FTX) and the early [[Barremian]] Hauptblatterton Thermal Event (HTE). The HTE marked the ultimate end of the Tithonian-early Barremian Cool Interval (TEBCI).<ref name="ChristopherScotese" /> During this interval, precession was the dominant orbital driver of environmental changes in the Vocontian Basin.<ref>{{Cite journal |last=Boulila |first=Slah |last2=Charbonnier |first2=Guillaume |last3=Galbrun |first3=Bruno |last4=Gardin |first4=Silvia |date=1 July 2015 |title=Climatic precession is the main driver of Early Cretaceous sedimentation in the Vocontian Basin (France): Evidence from the Valanginian Orpierre succession |url=https://linkinghub.elsevier.com/retrieve/pii/S0037073815001116 |journal=[[Sedimentary Geology (journal)|Sedimentary Geology]] |language=en |volume=324 |pages=1–11 |doi=10.1016/j.sedgeo.2015.04.014 |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> For much of the TEBCI, northern Gondwana experienced a monsoonal climate.<ref>{{Cite journal |last=Cui |first=Xiaohui |last2=Li |first2=Xin |last3=Aitchison |first3=Jonathan C. |last4=Luo |first4=Hui |date=May 2023 |title=Early Cretaceous monsoonal upwelling along the northern margin of the Gondwana continent: Evidence from radiolarian cherts |url=https://linkinghub.elsevier.com/retrieve/pii/S0377839823000464 |journal=Marine Micropaleontology |language=en |volume=181 |pages=102247 |doi=10.1016/j.marmicro.2023.102247 |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> A shallow thermocline existed in the mid-latitude Tethys.<ref>{{Cite journal |last=Wang |first=Tianyang |last2=Hoffmann |first2=René |last3=He |first3=Songlin |last4=Zhang |first4=Qinghai |last5=Li |first5=Guobiao |last6=Randrianaly |first6=Hasina Nirina |last7=Xie |first7=Jing |last8=Yue |first8=Yahui |last9=Ding |first9=Lin |date=October 2023 |title=Early Cretaceous climate for the southern Tethyan Ocean: Insights from the geochemical and paleoecological analyses of extinct cephalopods |url=https://linkinghub.elsevier.com/retrieve/pii/S0921818123001935 |journal=[[Global and Planetary Change]] |language=en |volume=229 |pages=104220 |doi=10.1016/j.gloplacha.2023.104220 |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> The TEBCI was followed by the Barremian-Aptian Warm Interval (BAWI).<ref name="ChristopherScotese" /> This hot climatic interval coincides with [[Manihiki Plateau|Manihiki]] and [[Ontong Java Plateau]] volcanism and with the [[Selli Event]].<ref>{{Cite journal |last1=Larson |first1=Roger L. |last2=Erba |first2=Elisabetta |date=4 May 2010 |title=Onset of the Mid-Cretaceous greenhouse in the Barremian-Aptian: Igneous events and the biological, sedimentary, and geochemical responses |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=14 |issue=6 |pages=663–678 |doi=10.1029/1999PA900040 |doi-access=free }}</ref> Early Aptian tropical [[sea surface temperature]]s (SSTs) were 27–32&nbsp;°C, based on [[TEX86|TEX<sub>86</sub>]] measurements from the equatorial Pacific.<ref>{{cite journal |last1=Schouten |first1=Stefan |last2=Hopmans |first2=Ellen C. |last3=Forster |first3=Astrid |last4=Van Breugel |first4=Yvonne |last5=Kuypers |first5=Marcel M. M. |last6=Sinninghe Damsté |first6=Jaap S. |date=1 December 2003 |title=Extremely high sea-surface temperatures at low latitudes during the middle Cretaceous as revealed by archaeal membrane lipids |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/31/12/1069/29198/Extremely-high-sea-surface-temperatures-at-low |journal=[[Geology (journal)|Geology]] |volume=31 |issue=12 |pages=1069–1072 |doi=10.1130/G19876.1 |bibcode=2003Geo....31.1069S |hdl=21.11116/0000-0001-D1DF-8 |s2cid=129660048 |access-date=11 May 2023|hdl-access=free }}</ref> During the Aptian, Milankovitch cycles governed the occurrence of anoxic events by modulating the intensity of the hydrological cycle and terrestrial runoff.<ref>{{Cite journal |last1=Behrooz |first1=L. |last2=Naafs |first2=B. D. A. |last3=Dickson |first3=A. J. |last4=Love |first4=G. D. |last5=Batenburg |first5=S. J. |last6=Pancost |first6=R. D. |date=August 2018 |title=Astronomically Driven Variations in Depositional Environments in the South Atlantic During the Early Cretaceous |journal=[[Paleoceanography and Paleoclimatology]] |language=en |volume=33 |issue=8 |pages=894–912 |doi=10.1029/2018PA003338 |bibcode=2018PaPa...33..894B |s2cid=89611847 |issn=2572-4517 |doi-access=free |hdl=1983/dd9ce325-fc6b-44a0-bab0-e0aa68943adc |hdl-access=free }}</ref> The early Aptian was also notable for its millennial scale hyperarid events in the mid-latitudes of Asia.<ref>{{Cite journal |last1=Hasegawa |first1=Hitoshi |last2=Katsuta |first2=Nagayoshi |last3=Muraki |first3=Yasushi |last4=Heimhofer |first4=Ulrich |last5=Ichinnorov |first5=Niiden |last6=Asahi |first6=Hirofumi |last7=Ando |first7=Hisao |last8=Yamamoto |first8=Koshi |last9=Murayama |first9=Masafumi |last10=Ohta |first10=Tohru |last11=Yamamoto |first11=Masanobu |last12=Ikeda |first12=Masayuki |last13=Ishikawa |first13=Kohki |last14=Kuma |first14=Ryusei |last15=Hasegawa |first15=Takashi |last16=Hasebe |first16=Noriko |last17=Nishimoto |first17=Shoji |last18=Yamaguchi |first18=Koichi |last19=Abe |first19=Fumio |last20=Tada |first20=Ryuji |last21=Nakagawa |first21=Takeshi |date=19 December 2022 |title=Decadal–centennial-scale solar-linked climate variations and millennial-scale internal oscillations during the Early Cretaceous |journal=[[Scientific Reports]] |language=en |volume=12 |issue=1 |pages=21894 |doi=10.1038/s41598-022-25815-w |pmid=36536054 |pmc=9763356 |bibcode=2022NatSR..1221894H |issn=2045-2322 }}</ref> The BAWI itself was followed by the Aptian-Albian Cold Snap (AACS) that began about 118 Ma.<ref name="ChristopherScotese" /> A short, relatively minor ice age may have occurred during this so-called "cold snap", as evidenced by glacial [[dropstone]]s in the western parts of the Tethys Ocean<ref>{{cite journal |last1=Rodríguez-López |first1=Juan Pedro |last2=Liesa |first2=Carlos L. |last3=Pardo |first3=Gonzalo |last4=Meléndez |first4=Nieves |last5=Soria |first5=Ana R. |last6=Skilling |first6=Ian |date=15 June 2016 |title=Glacial dropstones in the western Tethys during the late Aptian–early Albian cold snap: Palaeoclimate and palaeogeographic implications for the mid-Cretaceous |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821630058X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=452 |pages=11–27 |doi=10.1016/j.palaeo.2016.04.004 |bibcode=2016PPP...452...11R |access-date=19 March 2023}}</ref> and the expansion of calcareous nannofossils that dwelt in cold water into lower latitudes.<ref>{{cite journal |last1=Mutterlose |first1=Jörg |last2=Bornemann |first2=André |last3=Herrle |first3=Jens |date=May 2009 |title=The Aptian - Albian cold snap: Evidence for "mid" Cretaceous icehouse interludes |url=https://www.researchgate.net/publication/233692068 |journal=[[Neues Jahrbuch für Geologie und Paläontologie]] |volume=252 |issue=2 |pages=217–225 |doi=10.1127/0077-7749/2009/0252-0217 |access-date=18 June 2023}}</ref> The AACS is associated with an arid period in the [[Iberian Peninsula]].<ref>{{cite journal |last1=Diéguez |first1=Carmen |last2=Peyrot |first2=Daniel |last3=Barrón |first3=Eduardo |date=October 2010 |title=Floristic and vegetational changes in the Iberian Peninsula during Jurassic and Cretaceous |url=https://www.sciencedirect.com/science/article/abs/pii/S0034666710001223 |journal=[[Review of Palaeobotany and Palynology]] |volume=162 |issue=3 |pages=325–340 |doi=10.1016/j.revpalbo.2010.06.004 |bibcode=2010RPaPa.162..325D |access-date=18 June 2023}}</ref>

Temperatures increased drastically after the end of the AACS,<ref>{{cite journal |last1=Fletcher |first1=Tamara L. |last2=Greenwood |first2=David R. |last3=Moss |first3=Patrick T. |last4=Salisbury |first4=Steven W. |title=Paleoclimate of the Late Cretaceous (Cenomanian-Turonian) Portion of the Winton Formation, Central-Western Queensland, Australia: New Observations Based on Clamp and Bioclimatic Analysis |date=1 March 2014 |url=https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/29/3/121/146380/PALEOCLIMATE-OF-THE-LATE-CRETACEOUS-CENOMANIAN |journal=[[PALAIOS]] |volume=29 |issue=3–4 |pages=121–128 |doi=10.2110/palo.2013.080 |bibcode=2014Palai..29..121F |s2cid=128403453 |access-date=6 April 2023}}</ref> which ended around 111 Ma with the Paquier/Urbino Thermal Maximum, giving way to the Mid-Cretaceous Hothouse (MKH), which lasted from the early [[Albian]] until the early Campanian.<ref name="ChristopherScotese" /> Faster rates of seafloor spreading and entry of carbon dioxide into the atmosphere are believed to have initiated this period of extreme warmth,<ref>{{cite journal |last1=Leckie |first1=R. Mark |last2=Bralower |first2=Timothy J. |last3=Cashman |first3=Richard |date=23 August 2002 |title=Oceanic anoxic events and plankton evolution: Biotic response to tectonic forcing during the mid-Cretaceous |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001PA000623 |journal=[[Paleoceanography and Paleoclimatology]] |volume=17 |issue=3 |pages=13-1-13-29 |doi=10.1029/2001PA000623 |bibcode=2002PalOc..17.1041L |access-date=19 April 2023}}</ref> along with high flood basalt activity.<ref>{{Cite journal |last=Kerrick |first=Derrill M. |date=1 November 2001 |title=Present and past nonanthropogenic CO 2 degassing from the solid earth |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2001RG000105 |journal=[[Reviews of Geophysics]] |language=en |volume=39 |issue=4 |pages=565–585 |doi=10.1029/2001RG000105 |issn=8755-1209}}</ref> The MKH was punctuated by multiple thermal maxima of extreme warmth. The Leenhardt Thermal Event (LTE) occurred around 110 Ma, followed shortly by the l’Arboudeyesse Thermal Event (ATE) a million years later. Following these two hyperthermals was the [[Amadeus Event|Amadeus Thermal Maximum]] around 106 Ma, during the middle Albian. Then, around a million years after that, occurred the Petite Verol Thermal Event (PVTE). Afterwards, around 102.5 Ma, the Event 6 Thermal Event (EV6) took place; this event was itself followed by the Breistroffer Thermal Maximum around 101 Ma, during the latest Albian. Approximately 94 Ma, the Cenomanian-Turonian Thermal Maximum occurred,<ref name="ChristopherScotese" /> with this hyperthermal being the most extreme hothouse interval of the Cretaceous<ref>{{cite journal |last1=Vandermark |first1=Deborah |last2=Tarduno |first2=John A. |last3=Brinkman |first3=Donald B. |date=May 2007 |title=A fossil champsosaur population from the high Arctic: Implications for Late Cretaceous paleotemperatures |url=https://www.researchgate.net/publication/229407029 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=248 |issue=1–2 |pages=49–59 |doi=10.1016/j.palaeo.2006.11.008 |bibcode=2007PPP...248...49V |access-date=9 June 2023}}</ref><ref>{{cite journal |last1=Forster |first1=Astrid |last2=Schouten |first2=Stephan |last3=Moriya |first3=Kazuyoshi |last4=Wilson |first4=Paul A. |last5=Sinninghe Damsté |first5=Jaap S. |date=14 March 2007 |title=Tropical warming and intermittent cooling during the Cenomanian/Turonian oceanic anoxic event 2: Sea surface temperature records from the equatorial Atlantic |journal=[[Paleoceanography and Paleoclimatology]] |volume=22 |issue=1 |pages=1–14 |doi=10.1029/2006PA001349 |bibcode=2007PalOc..22.1219F |doi-access=free }}</ref><ref>{{cite journal |last1=O'Brien |first1=Charlotte L. |last2=Robinson |first2=Stuart A. |last3=Pancost |first3=Richard D. |last4=Sinninghe Damsté |first4=Jaap S. |last5=Schouten |first5=Stefan |last6=Lunt |first6=Daniel J. |last7=Alsenz |first7=Heiko |last8=Bornemann |first8=André |last9=Bottini |first9=Cinzia |last10=Brassell |first10=Simon C. |last11=Farnsworth |first11=Alexander |last12=Forster |first12=Astrid |last13=Huber |first13=Brian T. |last14=Inglis |first14=Gordon N. |last15=Jenkyns |first15=Hugh C. |last16=Linnert |first16=Christan |last17=Littler |first17=Kate |last18=Markwick |first18=Paul |last19=McAnena |first19=Alison |last20=Mutterlose |first20=Jörg |last21=Naafs |first21=B. David A. |last22=Püttmann |first22=Wilhelm |last23=Sluijs |first23=Appy |last24=Van Helmond |first24=Niels A.G.M. |last25=Wellekoop |first25=Johan |last26=Wagner |first26=Thomas |last27=Wrobel |first27=Neil E. |date=September 2017 |title=Cretaceous sea-surface temperature evolution: Constraints from TEX86 and planktonic foraminiferal oxygen isotopes |journal=[[Earth-Science Reviews]] |volume=172 |pages=224–247 |doi=10.1016/j.earscirev.2017.07.012 |bibcode=2017ESRv..172..224O |s2cid=55405082 |doi-access=free }}</ref> and being associated with a sea level highstand.<ref>{{Cite journal |last1=Püttmann |first1=Tobias |last2=Linnert |first2=Christian |last3=Dölling |first3=Bettina |last4=Mutterlose |first4=Jörg |date=1 July 2018 |title=Deciphering Late Cretaceous (Cenomanian to Campanian) coastline dynamics in the southwestern Münsterland (northwest Germany) by using calcareous nannofossils: Eustasy vs local tectonics |url=https://www.sciencedirect.com/science/article/pii/S0195667117301015 |journal=[[Cretaceous Research]] |series=Advances in Cretaceous palaeontology and stratigraphy – Christopher John Wood Memorial Volume |volume=87 |pages=174–184 |doi=10.1016/j.cretres.2017.07.005 |bibcode=2018CrRes..87..174P |s2cid=134356485 |issn=0195-6671 |access-date=24 November 2023}}</ref> Temperatures cooled down slightly over the next few million years, but then another thermal maximum, the Coniacian Thermal Maximum, happened, with this thermal event being dated to around 87 Ma.<ref name="ChristopherScotese" /> Atmospheric CO<sub>2</sub> levels may have varied by thousands of ppm throughout the MKH.<ref>{{cite journal |last1=Bice |first1=Karen L. |last2=Norris |first2=Richard D. |date=24 December 2002 |title=Possible atmospheric CO2 extremes of the Middle Cretaceous (late Albian–Turonian) |journal=[[Paleoceanography and Paleoclimatology]] |volume=17 |issue=4 |pages=22-1-22-17 |doi=10.1029/2002PA000778 |bibcode=2002PalOc..17.1070B |doi-access=free }}</ref> Mean annual temperatures at the poles during the MKH exceeded 14&nbsp;°C.<ref>{{cite journal |last1=Wang |first1=Yongdong |last2=Huang |first2=Chengmin |last3=Sun |first3=Bainian |last4=Quan |first4=Cheng |last5=Wu |first5=Jingyu |last6=Lin |first6=Zhicheng |date=February 2014 |title=Paleo-CO2 variation trends and the Cretaceous greenhouse climate |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825213001888 |journal=[[Earth-Science Reviews]] |volume=129 |pages=136–147 |doi=10.1016/j.earscirev.2013.11.001 |bibcode=2014ESRv..129..136W |access-date=5 April 2023}}</ref> Such hot temperatures during the MKH resulted in a very gentle [[temperature gradient]] from the [[equator]] to the poles; the latitudinal temperature gradient during the Cenomanian-Turonian Thermal Maximum was 0.54&nbsp;°C per ° latitude for the Southern Hemisphere and 0.49&nbsp;°C per ° latitude for the Northern Hemisphere, in contrast to present day values of 1.07 and 0.69&nbsp;°C per ° latitude for the Southern and Northern hemispheres, respectively.<ref>{{cite journal |last1=Laugié |first1=Marie |last2=Donnadieu |first2=Yannick |last3=Ladant |first3=Jean-Baptiste |last4=Green |first4=J. A. Mattias |last5=Bopp |first5=Laurent |last6=Raisson |first6=François |date=5 June 2020 |title=Stripping back the modern to reveal the Cenomanian–Turonian climate and temperature gradient underneath |url=https://cp.copernicus.org/articles/16/953/2020/ |journal=[[Climate of the Past]] |volume=16 |issue=3 |pages=953–971 |doi=10.5194/cp-16-953-2020 |bibcode=2020CliPa..16..953L |s2cid=219918773 |access-date=19 March 2023 |doi-access=free }}</ref> This meant weaker global winds, which drive the ocean currents, and resulted in less [[upwelling]] and more stagnant [[ocean]]s than today.<ref name="ThermalEvolutionCretaceousTethyanWaters">{{cite journal |last1=Pucéat |first1=Emmanuelle |last2=Lécuyer |first2=Christophe |last3=Sheppard |first3=Simon M. F. |last4=Dromart |first4=Gilles |last5=Reboulet |first5=Stéphane |last6=Grandjean |first6=Patricia |date=3 May 2003 |title=Thermal evolution of Cretaceous Tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels |journal=[[Paleoceanography and Paleoclimatology]] |volume=18 |issue=2 |page=1029 |doi=10.1029/2002PA000823 |bibcode=2003PalOc..18.1029P |doi-access=free }}</ref> This is evidenced by widespread black [[shale]] deposition and frequent [[anoxic event]]s.{{sfn|Stanley|1999|pp=481–482}} Tropical SSTs during the late Albian most likely averaged around 30&nbsp;°C. Despite this high SST, seawater was not hypersaline at this time, as this would have required significantly higher temperatures still.<ref>{{cite journal |last1=Norris |first1=Richard D. |last2=Wilson |first2=Paul A. |date=1 September 1998 |title=Low-latitude sea-surface temperatures for the mid-Cretaceous and the evolution of planktic foraminifera |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/26/9/823/206981/Low-latitude-sea-surface-temperatures-for-the-mid |journal=[[Geology (journal)|Geology]] |volume=26 |issue=9 |pages=823–826 |doi=10.1130/0091-7613(1998)026<0823:LLSSTF>2.3.CO;2 |bibcode=1998Geo....26..823N |access-date=5 April 2023}}</ref> On land, arid zones in the Albian regularly expanded northward in tandem with expansions of subtropical high pressure belts.<ref>{{Cite journal |last1=Hong |first1=Sung Kyung |last2=Yi |first2=Sangheon |last3=Shinn |first3=Young Jae |date=1 July 2020 |title=Middle Albian climate fluctuation recorded in the carbon isotope composition of terrestrial plant matter |url=https://www.sciencedirect.com/science/article/pii/S1367912020301449 |journal=[[Journal of Asian Earth Sciences]] |volume=196 |pages=104363 |doi=10.1016/j.jseaes.2020.104363 |bibcode=2020JAESc.19604363H |s2cid=216375103 |issn=1367-9120 |access-date=19 November 2023}}</ref> The Cedar Mountain Formation's Soap Wash flora indicates a mean annual temperature of between 19 and 26&nbsp;°C in Utah at the Albian-Cenomanian boundary.<ref>{{Cite journal |last=Arens |first=Nan Crystal |last2=Harris |first2=Elisha B. |date=March 2015 |title=Paleoclimatic reconstruction for the Albian–Cenomanian transition based on a dominantly angiosperm flora from the Cedar Mountain Formation, Utah, USA |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667114001943 |journal=[[Cretaceous Research]] |language=en |volume=53 |pages=140–152 |doi=10.1016/j.cretres.2014.11.004 |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> Tropical SSTs during the Cenomanian-Turonian Thermal Maximum were at least 30&nbsp;°C,<ref>{{cite journal |last1=Wilson |first1=Paul A. |last2=Norris |first2=Richard D. |last3=Cooper |first3=Matthew J. |date=1 July 2002 |title=Testing the Cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the Turonian tropics on Demerara Rise |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/30/7/607/191749/Testing-the-Cretaceous-greenhouse-hypothesis-using?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=30 |issue=7 |pages=607–610 |doi=10.1130/0091-7613(2002)030<0607:TTCGHU>2.0.CO;2 |bibcode=2002Geo....30..607W |access-date=5 April 2023}}</ref> though one study estimated them as high as between 33 and 42&nbsp;°C.<ref>{{cite journal |last1=Bice |first1=Karen L. |last2=Birgel |first2=Daniel |last3=Meyers |first3=Philip A. |last4=Dahl |first4=Kristina A. |last5=Hinrichs |first5=Kai-Uwe |last6=Norris |first6=Richard D. |date=8 April 2006 |title=A multiple proxy and model study of Cretaceous upper ocean temperatures and atmospheric CO2 concentrations |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005PA001203 |journal=[[Paleoceanography and Paleoclimatology]] |volume=21 |issue=2 |pages=1–17 |doi=10.1029/2005PA001203 |bibcode=2006PalOc..21.2002B |access-date=5 April 2023|hdl=2027.42/95054 |hdl-access=free }}</ref> An intermediate estimate of ~33-34&nbsp;°C has also been given.<ref>{{cite journal |last1=Norris |first1=Richard D. |last2=Bice |first2=Karen L. |last3=Magno |first3=Elizabeth A. |last4=Wilson |first4=Paul A. |date=1 April 2002 |title=Jiggling the tropical thermostat in the Cretaceous hothouse |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/30/4/299/192373/Jiggling-the-tropical-thermostat-in-the-Cretaceous |journal=[[Geology (journal)|Geology]] |volume=30 |issue=4 |pages=299–302 |doi=10.1130/0091-7613(2002)030<0299:JTTTIT>2.0.CO;2 |bibcode=2002Geo....30..299N |access-date=5 April 2023}}</ref> Meanwhile, deep ocean temperatures were as much as {{convert|15|to|20|C-change|sigfig=2}} warmer than today's<!-- Note that these are differences in temperature -->;{{sfn|Skinner| Porter|1995|p=557}}<!-- "15 higher" or "15 which is higher"? --> one study estimated that deep ocean temperatures were between 12 and 20&nbsp;°C during the MKH.<ref name="FishToothOxygen" /> The poles were so warm that [[ectothermic]] reptiles were able to inhabit them.<ref name="LateCretaceousArcticVertebrates">{{cite journal |last1=Tarduno |first1=J. A. |last2=Brinkman |first2=D. B. |last3=Renne |first3=P. R. |last4=Cottrell |first4=R. D. |last5=Scher |first5=H. |last6=Castillo |first6=P. |date=18 December 1998 |title=Evidence for Extreme Climatic Warmth from Late Cretaceous Arctic Vertebrates |url=https://www.science.org/doi/10.1126/science.282.5397.2241 |journal=[[Science (journal)|Science]] |volume=282 |issue=5397 |pages=2241–2243 |doi=10.1126/science.282.5397.2241 |pmid=9856943 |bibcode=1998Sci...282.2241T |access-date=24 July 2023}}</ref>

Beginning in the Santonian, near the end of the MKH, the global climate began to cool, with this cooling trend continuing across the Campanian.<ref>{{cite journal |last1=Petrizzo |first1=Maria Rose |last2=MacLeod |first2=Kenneth G. |last3=Watkins |first3=David K. |last4=Wolfgring |first4=Erik |last5=Huber |first5=Brian T. |date=27 December 2021 |title=Late Cretaceous Paleoceanographic Evolution and the Onset of Cooling in the Santonian at Southern High Latitudes (IODP Site U1513, SE Indian Ocean) |journal=[[Paleoceanography and Paleoclimatology]] |volume=37 |issue=1 |pages=e2021PA004353 |doi=10.1029/2021PA004353 |pmid=35910494 |pmc=9303530 }}</ref> This period of cooling, driven by falling levels of atmospheric carbon dioxide,<ref name="FishToothOxygen">{{cite journal |last1=Pucéat |first1=Emmanuelle |last2=Lécuyer |first2=Christophe |last3=Donnadieu |first3=Yannick |last4=Naveau |first4=Philippe |last5=Cappetta |first5=Henri |last6=Ramstein |first6=Gilles |last7=Huber |first7=Brian T. |last8=Kriwet |first8=Juergen |date=1 February 2007 |title=Fish tooth δ18O revising Late Cretaceous meridional upper ocean water temperature gradients |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/35/2/107/129762/Fish-tooth-18O-revising-Late-Cretaceous-meridional |journal=[[Geology (journal)|Geology]] |volume=35 |issue=2 |pages=107–110 |doi=10.1130/G23103A.1 |bibcode=2007Geo....35..107P |access-date=19 March 2023}}</ref> caused the end of the MKH and the transition into a cooler climatic interval, known formally as the Late Cretaceous-Early Palaeogene Cool Interval (LKEPCI).<ref name="ChristopherScotese" /> Tropical SSTs declined from around 35&nbsp;°C in the early Campanian to around 28&nbsp;°C in the Maastrichtian.<ref>{{cite journal |last1=Linnert |first1=Christian |last2=Robinson |first2=Stuart A. |last3=Lees |first3=Jackie A. |last4=Bown |first4=Paul R. |last5=Pérez-Rodríguez |first5=Irene |last6=Petrizzo |first6=Maria Rose |last7=Falzoni |first7=Francesca |last8=Littler |first8=Kate |last9=Arz |first9=José Antonio |last10=Russell |first10=Ernest E. |date=17 June 2014 |title=Evidence for global cooling in the Late Cretaceous |journal=[[Nature Communications]] |volume=5 |page=4194 |doi=10.1038/ncomms5194 |pmid=24937202 |pmc=4082635 |bibcode=2014NatCo...5.4194L }}</ref> Deep ocean temperatures declined to 9 to 12&nbsp;°C,<ref name="FishToothOxygen" /> though the shallow temperature gradient between tropical and polar seas remained.<ref>{{cite journal |last1=O'Connor |first1=Lauren K. |last2=Robinson |first2=Stuart A. |last3=Naafs |first3=B. David A. |last4=Jenkyns |first4=Hugh C. |last5=Henson |first5=Sam |last6=Clarke |first6=Madeleine |last7=Pancost |first7=Richard D. |date=27 February 2019 |title=Late Cretaceous Temperature Evolution of the Southern High Latitudes: A TEX86 Perspective |journal=[[Paleoceanography and Paleoclimatology]] |volume=34 |issue=4 |pages=436–454 |doi=10.1029/2018PA003546 |bibcode=2019PaPa...34..436O |s2cid=134095694 |doi-access=free |hdl=1983/9c306756-d31c-4cda-b68e-4ba6f0bf9d44 |hdl-access=free }}</ref> Regional conditions in the [[Western Interior Seaway]] changed little between the MKH and the LKEPCI.<ref>{{cite journal |last1=Wang |first1=Chengshan |last2=Scott |first2=Robert W. |last3=Wan |first3=Xiaoqiao |last4=Graham |first4=Stephan A. |last5=Huang |first5=Yongjian |last6=Wang |first6=Pujun |last7=Wu |first7=Huaichun |last8=Dean |first8=Walter E. |last9=Zhang |first9=Laiming |date=November 2013 |title=Late Cretaceous climate changes recorded in Eastern Asian lacustrine deposits and North American Epieric sea strata |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825213001499 |journal=[[Earth-Science Reviews]] |volume=126 |pages=275–299 |doi=10.1016/j.earscirev.2013.08.016 |bibcode=2013ESRv..126..275W |access-date=19 March 2023}}</ref> During this period of relatively cool temperatures, the ITCZ became narrower,<ref>{{Cite journal |last1=Ma |first1=Mingming |last2=He |first2=Mei |last3=Zhao |first3=Mengting |last4=Peng |first4=Chao |last5=Liu |first5=Xiuming |date=1 April 2021 |title=Evolution of atmospheric circulation across the Cretaceous–Paleogene (K–Pg) boundary interval in low-latitude East Asia |url=https://www.sciencedirect.com/science/article/pii/S0921818121000205 |journal=[[Global and Planetary Change]] |volume=199 |pages=103435 |doi=10.1016/j.gloplacha.2021.103435 |bibcode=2021GPC...19903435M |s2cid=233573257 |issn=0921-8181 |access-date=18 November 2023}}</ref> while the strength of both summer and winter monsoons in East Asia was directly correlated to atmospheric [[Carbon dioxide|CO<sub>2</sub>]] concentrations.<ref>{{Cite journal |last1=Chen |first1=Junming |last2=Zhao |first2=Ping |last3=Wang |first3=Chengshan |last4=Huang |first4=Yongjian |last5=Cao |first5=Ke |date=1 September 2013 |title=Modeling East Asian climate and impacts of atmospheric CO2 concentration during the Late Cretaceous (66Ma) |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |series=Environmental/Climate Change in the Cretaceous Greenhouse World: records from terrestrial scientific drilling of Songliao Basin and adjacent area of China |volume=385 |pages=190–201 |doi=10.1016/j.palaeo.2012.07.017 |bibcode=2013PPP...385..190C |issn=0031-0182 |doi-access=free }}</ref> Laramidia likewise had a seasonal, monsoonal climate.<ref>{{Cite journal |last=Fricke |first=Henry C. |last2=Foreman |first2=Brady Z. |last3=Sewall |first3=Jacob O. |date=15 January 2010 |title=Integrated climate model-oxygen isotope evidence for a North American monsoon during the Late Cretaceous |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X09006177 |journal=[[Earth and Planetary Science Letters]] |language=en |volume=289 |issue=1-2 |pages=11–21 |doi=10.1016/j.epsl.2009.10.018 |access-date=18 July 2024 |via=Elsevier Science Direct}}</ref> The Maastrichtian was a time of chaotic, highly variable climate.<ref>{{Cite journal |last=Barrera |first=Enriqueta |date=1 October 1994 |title=Global environmental changes preceding the Cretaceous-Tertiary boundary: Early-late Maastrichtian transition |url=https://pubs.geoscienceworld.org/geology/article/22/10/877-880/188033 |journal=[[Geology (journal)|Geology]] |language=en |volume=22 |issue=10 |pages=877–880 |doi=10.1130/0091-7613(1994)022<0877:GECPTC>2.3.CO;2 |bibcode=1994Geo....22..877B |issn=0091-7613 |access-date=19 November 2023}}</ref> Two upticks in global temperatures are known to have occurred during the Maastrichtian, bucking the trend of overall cooler temperatures during the LKEPCI. Between 70 and 69 Ma and 66–65 Ma, isotopic ratios indicate elevated atmospheric CO<sub>2</sub> pressures with levels of 1000–1400 ppmV and mean annual temperatures in [[west Texas]] between {{convert|21|and|23|C|F}}. Atmospheric CO<sub>2</sub> and temperature relations indicate a doubling of pCO<sub>2</sub> was accompanied by a ~0.6&nbsp;°C increase in temperature.<ref>{{cite magazine |last1=Nordt |first1=Lee |first2=Stacy |last2=Atchley |first3=Steve |last3=Dworkin |title=Terrestrial Evidence for Two Greenhouse Events in the Latest Cretaceous |magazine=[[GSA Today]] |volume=13 |issue=12 |date= December 2003 |page=4 |doi=10.1130/1052-5173(2003)013<4:TEFTGE>2.0.CO;2}}</ref> The latter warming interval, occurring at the very end of the Cretaceous, was triggered by the activity of the Deccan Traps.<ref>{{cite journal |last1=Gao |first1=Yuan |last2=Ibarra |first2=Daniel E. |last3=Caves Rubenstein |first3=Jeremy K. |last4=Chen |first4=Jiuquan |last5=Kukla |first5=Tyler |last6=Methner |first6=Katharina |last7=Gao |first7=Youfeng |last8=Huang |first8=He |last9=Lin |first9=Zhipeng |last10=Zhang |first10=Laiming |last11=Xi |first11=Dangpeng |last12=Wu |first12=Huaichun |last13=Carroll |first13=Alan R. |last14=Graham |first14=Stephan A. |last15=Chamberlain |first15=C. Page |last16=Wang |first16=Changshan |date=May 2021 |title=Terrestrial climate in mid-latitude East Asia from the latest Cretaceous to the earliest Paleogene: A multiproxy record from the Songliao Basin in northeastern China |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825221000714 |journal=[[Earth-Science Reviews]] |volume=216 |pages=1–29 |doi=10.1016/j.earscirev.2021.103572 |bibcode=2021ESRv..21603572G |s2cid=233918778 |access-date=21 July 2023}}</ref> The LKEPCI lasted into the [[Late Paleocene|Late Palaeocene]], when it gave way to another supergreenhouse interval.<ref name="ChristopherScotese">{{Cite journal |last1=Scotese |first1=Christopher R. |last2=Song |first2=Haijun |last3=Mills |first3=Benjamin J. W. |last4=van der Meer |first4=Douwe G. |date=April 2021 |title=Phanerozoic paleotemperatures: The earth's changing climate during the last 540 million years |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825221000027 |journal=[[Earth-Science Reviews]] |volume=215 |pages=103503 |bibcode=2021ESRv..21503503S |doi=10.1016/j.earscirev.2021.103503 |issn=0012-8252 |archive-url=https://web.archive.org/web/20210108000000/http://dx.doi.org/10.1016/j.earscirev.2021.103503 |archive-date=8 January 2021 |s2cid=233579194 |access-date=18 March 2023}}</ref>

[[File:Cretacico-isotermas-y-mapamundi.svg|thumb|left|A computer-simulated model of surface conditions in Middle Cretaceous, 100 mya, displaying the approximate shoreline and calculated [[Isotherm (contour line)|isotherm]]s]]
The production of large quantities of magma, variously attributed to [[mantle plume]]s or to [[extensional tectonics]],<ref name=Foulger>{{cite book |title=Plates vs. Plumes: A Geological Controversy |author=Foulger, G.R. |url=http://www.wiley.com/WileyCDA/WileyTitle/productCd-1405161485.html |year=2010 |isbn=978-1-4051-6148-0 |publisher=Wiley-Blackwell}}</ref> further pushed sea levels up, so that large areas of the continental crust were covered with shallow seas. The [[Tethys Sea]] connecting the tropical oceans east to west also helped to warm the global climate. Warm-adapted [[plant fossil]]s are known from localities as far north as [[Alaska]] and [[Greenland]], while [[dinosaur]] fossils have been found within 15 degrees of the Cretaceous [[south pole]].{{sfn|Stanley|1999|p=480–482}} It was suggested that there was [[Antarctica|Antarctic]] marine glaciation in the [[Turonian]] Age, based on isotopic evidence.<ref>{{cite journal |last1=Bornemann |first1=Norris R. D. |last2=Friedrich |first2=O. |last3=Beckmann |first3=B. |last4=Schouten |first4=Stefan |last5=Sinnighe Damsté |first5=Jaap S. |last6=Vogel |first6=J. |last7=Hofmann |first7=P. |last8=Wagner |first8=T. |s2cid=206509273 |date=January 2008 |title=Isotopic evidence for glaciation during the Cretaceous supergreenhouse |url=https://www.researchgate.net/publication/5662444 |journal=[[Science (journal)|Science]] |volume=319 |issue=5860 |pages=189–192 |doi=10.1126/science.1148777 |pmid=18187651 |bibcode=2008Sci...319..189B |access-date=18 March 2023}}</ref> However, this has subsequently been suggested to be the result of inconsistent isotopic proxies,<ref>{{Cite journal |last1=Huber |first1=Brian T. |last2=MacLeod |first2=Kenneth G. |last3=Watkins |first3=David K. |last4=Coffin |first4=Millard F. |date=2018-08-01 |title=The rise and fall of the Cretaceous Hot Greenhouse climate |url=http://www.sciencedirect.com/science/article/pii/S0921818117306483 |journal=[[Global and Planetary Change]] |language=en |volume=167 |pages=1–23 |doi=10.1016/j.gloplacha.2018.04.004 |bibcode=2018GPC...167....1H |issn=0921-8181 |hdl=1912/10514 |s2cid=135295956 |hdl-access=free |access-date=18 March 2023}}</ref> with evidence of polar rainforests during this time interval at 82° S.<ref>{{Cite journal|last1=the Science Team of Expedition PS104 |last2=Klages |first2=Johann P. |last3=Salzmann |first3=Ulrich |last4=Bickert |first4=Torsten |last5=Hillenbrand |first5=Claus-Dieter |last6=Gohl |first6=Karsten |last7=Kuhn |first7=Gerhard |last8=Bohaty |first8=Steven M. |last9=Titschack |first9=Jürgen |last10=Müller |first10=Juliane |last11=Frederichs |first11=Thomas |date=April 2020 |title=Temperate rainforests near the South Pole during peak Cretaceous warmth |url=http://www.nature.com/articles/s41586-020-2148-5 |journal=[[Nature (journal)|Nature]] |language=en |volume=580 |issue=7801 |pages=81–86 |doi=10.1038/s41586-020-2148-5 |pmid=32238944 |bibcode=2020Natur.580...81K |s2cid=214736648 |issn=0028-0836 |access-date=18 March 2023}}</ref> Rafting by ice of stones into marine environments occurred during much of the Cretaceous, but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the [[Eromanga Basin]] in southern [[Australia]].<ref>{{Cite journal | last1 = Alley | first1 = N. F. | last2 = Frakes | first2 = L. A. | doi = 10.1046/j.1440-0952.2003.00984.x | title = First known Cretaceous glaciation: Livingston Tillite Member of the Cadna-owie Formation, South Australia | journal = [[Australian Journal of Earth Sciences]] | volume = 50 | issue = 2 | pages = 139–144 | year = 2003 |bibcode = 2003AuJES..50..139A | s2cid = 128739024 }}</ref><ref>{{Cite journal | last1 = Frakes | first1 = L. A. | last2 = Francis | first2 = J. E. | doi = 10.1038/333547a0 | title = A guide to Phanerozoic cold polar climates from high-latitude ice-rafting in the Cretaceous | journal = [[Nature (journal)|Nature]] | volume = 333 | issue = 6173 | pages = 547–549 | year = 1988 |bibcode = 1988Natur.333..547F | s2cid = 4344903 }}</ref>