The Early Eocene Climatic Optimum (EECO), also referred to as the Early Eocene Thermal Maximum (EETM),[1] was a period of extremely warm greenhouse climatic conditions during the Eocene epoch. The EECO represented the hottest sustained interval of the Cenozoic era and one of the hottest periods in all of Earth's history.[2]

Duration

The EECO lasted from about 54 to 49 Ma.[1] The EECO's onset is signified by a major geochemical enrichment in isotopically light carbon, commonly known as a negative δ13C excursion, that demarcates the hyperthermal Eocene Thermal Maximum 3 (ETM3).[3]

Climate

Following some climate models, the EECO was marked by an extremely high global mean surface temperature,[1] which has been estimated to be anywhere between 23.2 and 29.7 °C, with the mean estimate being around 27.0 °C.[4] In North America, the mean annual temperature was 23.0 °C.[2] The mean annual temperature range (MATR) of North America may have been as low as 47 °C or as high as 61 °C, while the MATR of Asia was anywhere from 51 to 60 °C.[5] Mean annual precipitation in North America was about 150 cm/yr.[2] The high elevation areas of Asia, Africa, and Antarctica saw elevation dependent warming (EDW), while those in North America and India saw elevation dependent cooling (EDC).[6]

Although sea surface temperatures (SSTs) are often believed to have had a shallow latitudinal temperature gradient, this is likely to be an artefact of burial-induced oxygen isotope reequilibration in fossilised benthic foraminifera.[7]

Climate modelling simulations point to a carbon dioxide concentration in the atmosphere of about 1,680 ppm to reproduce the observed hothouse conditions of the EECO,[8] although geochemical proxies suggest only 700-900 ppm.[9] Additionally, methane concentrations in the Early Eocene may have been significantly higher than in the present day.[10]

Causes

The EECO was preceded by a major long-term warming trend in the Late Palaeocene and Early Eocene.[11] It was initiated by a series of intense hyperthermal events in the Early Eocene, including Eocene Thermal Maximum 2 (ETM2) and ETM3.[12]

The emplacement of the Pana Formation, a volcanic rock formation in southern Tibet that may represent the product of a supereruption, has also been proposed as a source of excess carbon flux into the atmosphere that drove the EECO.[13]

Biotic effects

The final phase of the Angiosperm Terrestrial Revolution occurred during the EECO.[14] The supergreenhouse climate of the EECO fostered extensive floral diversification and increased habitat complexity in North American terrestrial biomes.[2]

The euryhaline dinoflagellate Homotryblium became superabundant at the site of Waipara in New Zealand during the early and middle EECO, reflecting the occurrence of significant stratification of surficial waters as well as increased salinity.[15]

Comparison to present global warming

Because the pCO2 values of the EECO could potentially be reached if anthropogenic greenhouse gas emissions continue unabated for three centuries, the EECO has been used as an analogue for high-end projections of the Earth's future climate that would result from humanity's burning of fossil fuels.[16] Based on the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario, by 2150 CE, the climates across much of the world would resemble conditions during the EECO.[17]

See also

References

  1. 1 2 3 Scotese, Christopher R.; Song, Haijun; Mills, Benjamin J.W.; van der Meer, Douwe G. (1 April 2021). "Phanerozoic paleotemperatures: The earth's changing climate during the last 540 million years". Earth-Science Reviews. 215: 103503. Bibcode:2021ESRv..21503503S. doi:10.1016/j.earscirev.2021.103503. S2CID 233579194. Retrieved 24 December 2023 – via Elsevier Science Direct.
  2. 1 2 3 4 Woodburne, Michael O.; Gunnell, Gregg F.; Stucky, Richard K. (11 August 2009). "Climate directly influences Eocene mammal faunal dynamics in North America". Proceedings of the National Academy of Sciences of the United States of America. 106 (32): 13399–13403. Bibcode:2009PNAS..10613399W. doi:10.1073/pnas.0906802106. ISSN 0027-8424. PMC 2726358. PMID 19666605.
  3. ↑ Slotnick, B. S.; Dickens, G. R.; Hollis, C. J.; Crampton, J. S.; Strong, C. Percy; Phillips, A. (17 September 2015). "The onset of the Early Eocene Climatic Optimum at Branch Stream, Clarence River valley, New Zealand". New Zealand Journal of Geology and Geophysics. 58 (3): 262–280. Bibcode:2015NZJGG..58..262S. doi:10.1080/00288306.2015.1063514. S2CID 130982094.
  4. ↑ Inglis, Gordon N.; Bragg, Fran; Burls, Natalie J.; Cramwinckel, Margot J.; Evans, David; Foster, Gavin L.; Huber, Matthew; Lunt, Daniel J.; Siler, Nicholas; Steinig, Sebastian; Tierney, Jessica E.; Wilkinson, Richard; Anagnostou, Eleni; de Boer, Agatha M.; Dunkley Jones, Tom; Edgar, Kirsty M.; Hollis, Christopher J.; Hutchinson, David K.; Pancost, Richard D. (26 October 2020). "Global mean surface temperature and climate sensitivity of the early Eocene Climatic Optimum (EECO), Paleocene–Eocene Thermal Maximum (PETM), and latest Paleocene". Climate of the Past. 16 (5): 1953–1968. Bibcode:2020CliPa..16.1953I. doi:10.5194/cp-16-1953-2020. hdl:1983/24a30f12-51a6-4544-9db8-b2009e33c02a. ISSN 1814-9332. Retrieved 24 December 2023.
  5. ↑ Sloan, L.Cirbus; Morrill, C (15 November 1998). "Orbital forcing and Eocene continental temperatures". Palaeogeography, Palaeoclimatology, Palaeoecology. 144 (1–2): 21–35. Bibcode:1998PPP...144...21S. doi:10.1016/S0031-0182(98)00091-1. Retrieved 24 December 2023 – via Elsevier Science Direct.
  6. ↑ Kad, Pratik; Blau, Manuel Tobias; Ha, Kyung-Ja; Zhu, Jiang (1 November 2022). "Elevation-dependent temperature response in early Eocene using paleoclimate model experiment". Environmental Research Letters. 17 (11): 114038. doi:10.1088/1748-9326/ac9c74. ISSN 1748-9326. Retrieved 30 December 2023.
  7. ↑ Bernard, S.; Daval, D.; Ackerer, P.; Pont, S.; Meibom, A. (26 October 2017). "Burial-induced oxygen-isotope re-equilibration of fossil foraminifera explains ocean paleotemperature paradoxes". Nature Communications. 8 (1): 1134. doi:10.1038/s41467-017-01225-9. ISSN 2041-1723. PMC 5656689. Retrieved 30 December 2023.
  8. ↑ Goudsmit-Harzevoort, Barbara; Lansu, Angelique; Baatsen, Michiel L. J.; von der Heydt, Anna S.; de Winter, Niels J.; Zhang, Yurui; Abe-Ouchi, Ayako; de Boer, Agatha; Chan, Wing-Le; Donnadieu, Yannick; Hutchinson, David K.; Knorr, Gregor; Ladant, Jean-Baptiste; Morozova, Polina; Niezgodzki, Igor; Steinig, Sebastian; Tripati, Aradhna; Zhang, Zhongshi; Zhu, Jiang; Ziegler, Martin (17 February 2023). "The Relationship Between the Global Mean Deep-Sea and Surface Temperature During the Early Eocene". Paleoceanography and Paleoclimatology. 38 (3): 1–18. Bibcode:2023PaPa...38.4532G. doi:10.1029/2022PA004532. ISSN 2572-4517. Retrieved 24 September 2023.
  9. ↑ Pearson, Paul N.; Palmer, Martin R. (17 August 2000). "Atmospheric carbon dioxide concentrations over the past 60 million years". Nature. 406 (6797): 695–699. Bibcode:2000Natur.406..695P. doi:10.1038/35021000. ISSN 1476-4687. PMID 10963587. S2CID 205008176. Retrieved 24 December 2023.
  10. ↑ Sloan, L. Cirbus; Walker, James C. G.; Moore, T. C.; Rea, David K.; Zachos, James C. (28 May 1992). "Possible methane-induced polar warming in the early Eocene". Nature. 357 (6376): 320–322. Bibcode:1992Natur.357..320S. doi:10.1038/357320a0. hdl:2027.42/62963. ISSN 0028-0836. PMID 11536496. S2CID 4348331. Retrieved 24 December 2023.
  11. ↑ Zachos, James; Pagani, Mark; Sloan, Lisa; Thomas, Ellen; Billups, Katharina (27 April 2001). "Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present". Science. 292 (5517): 686–693. Bibcode:2001Sci...292..686Z. doi:10.1126/science.1059412. ISSN 0036-8075. PMID 11326091. S2CID 2365991. Retrieved 24 December 2023.
  12. ↑ Lauretano, V.; Littler, K.; Polling, M.; Zachos, J. C.; Lourens, L. J. (7 October 2015). "Frequency, magnitude and character of hyperthermal events at the onset of the Early Eocene Climatic Optimum". Climate of the Past. 11 (10): 1313–1324. Bibcode:2015CliPa..11.1313L. doi:10.5194/cp-11-1313-2015. ISSN 1814-9332. Retrieved 24 December 2023.
  13. ↑ Zhang, Shao-Hua; Ji, Wei-Qiang; Chen, Hou-Bin; Kirstein, Linda A.; Wu, Fu-Yuan (June 2023). "Linking rapid eruption of the Linzizong volcanic rocks and Early Eocene Climatic Optimum (EECO): Constraints from the Pana Formation in the Linzhou and Pangduo basins, southern Tibet". Lithos. 446–447: 107159. Bibcode:2023Litho.44607159Z. doi:10.1016/j.lithos.2023.107159. hdl:20.500.11820/5605da8a-33fd-42ee-8d54-68590a4e12f8. S2CID 257848801. Retrieved 24 December 2023 – via Elsevier Science Direct.
  14. ↑ Benton, Michael James; Wilf, Peter; Sauquet, Hervé (26 October 2021). "The Angiosperm Terrestrial Revolution and the origins of modern biodiversity". New Phytologist. 233 (5): 2017–2035. doi:10.1111/nph.17822. hdl:1983/82a09075-31f4-423e-98b9-3bb2c215e04b. PMID 34699613. S2CID 240000207. Retrieved 24 November 2022.
  15. ↑ Crouch, E. M.; Shepherd, C. L.; Morgans, H. E. G.; Naafs, B. D. A.; Dallanave, E.; Phillips, A.; Hollis, C. J.; Pancost, R. D. (1 January 2020). "Climatic and environmental changes across the early Eocene climatic optimum at mid-Waipara River, Canterbury Basin, New Zealand". Earth-Science Reviews. 200: 102961. Bibcode:2020ESRv..20002961C. doi:10.1016/j.earscirev.2019.102961. hdl:1983/aedc04cc-bba8-44c6-8f9d-ba398bb24607. ISSN 0012-8252. S2CID 210618370. Retrieved 11 September 2023.
  16. ↑ Zachos, James C.; Dickens, Gerald R.; Zeebe, Richard E. (16 January 2008). "An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics". Nature. 451 (7176): 279–283. Bibcode:2008Natur.451..279Z. doi:10.1038/nature06588. ISSN 1476-4687. PMID 18202643. Retrieved 24 December 2023.
  17. ↑ Burke, K. D.; Williams, J. W.; Chandler, M. A.; Haywood, A. M.; Lunt, D. J.; Otto-Bliesner, B. L. (26 December 2018). "Pliocene and Eocene provide best analogs for near-future climates". Proceedings of the National Academy of Sciences of the United States of America. 115 (52): 13288–13293. Bibcode:2018PNAS..11513288B. doi:10.1073/pnas.1809600115. ISSN 0027-8424. PMC 6310841. PMID 30530685.
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