早始新世气候适宜期形成机制探讨

The driving mechanisms for the Early Eocene Climatic Optimum

早始新世气候适宜期发生在53—51 Ma,是新生代早期一段气候持续温暖时期。与中中新世气候适宜期和上新世气候适宜期相比,早始新世气候适宜期更加温暖。对于该时期驱动机制的理解有助于深入认识未来温暖气候状况的变化。本文总结了前人提出的构造尺度气候变化的假说,推断出早始新世气候适宜期可能是由于板块构造活动变化导致的温室气体变化所造成,而星际暗物质变化对早始新世气候适宜期的影响有待进一步评估。

Background,aim,and scope Superimposed on a progressive cooling trend of Cenozoic Earth,there are three sustained warm intervals:The Early Eocene Climatic Optimum(EECO),the Middle Miocene Climatic Optimum(MMCO),and the Pliocene Climatic Optimum(PCO).In comparison with the MMCO and the PCO,the EECO is much warmer,with atmospheric CO2 content between 600μmol∙mol−1 and 2000μmol∙mol−1.Understanding the climatic and environmental variations during the EECO and their driving mechanisms can help understand future warming and how climate and environment will respond to future warming.In this paper,we provide a brief review for the potential driving mechanisms for the EECO.Materials and methods There will be no new data presented and we instead use data compilation and synthesis as our main approach.Results Based on the benthic oxygen isotopic records,EECO spans the interval from 53 Ma to 51 Ma.The available driving mechanism hypotheses for the EECO include uplift-weathering hypothesis,BLAG hypothesis,dissociation of oceanic methane hydrate,and effect of dark matters.Discussion Based on a comparison of several records including seafloor spreading rate,greenhouse gas content,geomagnetic reversal frequency,we infer that CO2 increase associated with faster seafloor spreading,together with lack of high plateau,are the main reasons for the EECO.It remains to be tested whether dark matters in galaxies could be responsible for the EECO.Conclusions Plate tectonics-driven fast greenhouse gas release is the most likely forcing for the EECO.Recommendations and perspectives Further studies should target on testing whether dark matters exist in the galaxies.Moreover,due to the scarcity of high-resolution terrestrial records covering the EECO,it remains unclear how the climate change on orbital-timescales during the EECO.Future work should also focus on generating high-resolution terrestrial paleoclimate records covering the EECO so that the terrestrial records can be compared more rigorously with the marine records.