早始新世极热事件的陆相高分辨率记录及机制研究

The Eocene hyperthermals (including PETM, H1, H2, I1, and I2) are a series of geologically abrupt global warming events superimposed on the long-term warming trend of the early Eocene. These events are generally interpreted to have been caused by a massive input of 13C-depleted carbon into the external carbon reservoir. It has been suggested that the total carbon addition to the ocean-atmosphere system during each event is comparable in magnitude to that which could occur through the 21st century, and these events have thus served as significant geological analogues for the future warming trend and environmental effects. To date, however, there are still several first-order controversies concerning the carbon injection. These include the sources and injection pattern of isotopically light carbon, and potential feedbacks. The current debate is mainly attributable to the ambiguity of the details in δ13C and the coupling relation between carbon isotope excursion and temperature for each hyperthermal. To address this, we plan to reconstruct the high-resolution δ13C time series of micritic carbonate, total organic carbon and black carbon for each hyperthermal based on the lacustrine sedimentary from the Nanyang Basin; and then, we intend to reconstruct the high-resolution temperature records for each hyperthermal based on branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) analysis; finally, in combination with orbital-tuned age model, we will further clarify the timing relation among the δ13C, orbital forcing, and temperature in order to test the existing mechanisms and exploring carbon cycle-climate dynamics and potential feedbacks.

始新世极热事件（包括PETM、H1、H2、I1和I2），是指发生在早始新世全球持续增温背景下，由巨量13C亏损的CO2加入到外生碳库所引发的一系列历时短暂的快速增温事件。据估算，极热事件时期加入到海-气系统中的总碳量与工业革命至本世纪末的人为排放量是可对比的。因此，这类事件被视为预估今后增温趋势和环境效应的重要基础。但迄今为止，涉及巨量碳的来源、释放方式及反馈过程等问题，争议颇大。其主要原因是各事件δ13C变化细节及其与温度之间的耦合关系仍不清楚。为此，本项目拟选取南阳盆地湖相沉积物为研究载体，通过高分辨率微晶碳酸盐、有机碳和黑碳δ13C时间序列的重建，识别出各极热事件；在此基础上，利用甘油二烷基甘油四醚（GDGTs）重建各事件温度演化历史，并结合轨道旋回地层学，厘清δ13C变化与轨道强迫、温度之间的时间演变关系，以期检验现有机制、探索碳循环-气候动力学过程及气候系统的潜在反馈机制。

早始新世发生了一系列由大气CO2浓度增加所诱发的快速增温事件（即极热事件）。这些事件被学术界视为评估人类碳排放导致环境变化的重要地质实例。本项目选取中国东部大陆陆相沉积物为研究载体，通过沉积相和地球化学等研究手段，重点研究了早始新世高温期气候环境记录，初步取得如下进展：（1）确立了南阳盆地早新生代地层年代框架，并指出始新世大暖期中国大陆表现为一个相对湿润的环境；（2）首次从湖相地层中识别出H1、H2、I1和I2四个极热事件；（3）通过有机碳同位素分析，在江汉盆地确立了PETM事件；（4）PETM时期，中国东部大陆降雨量整体加强，但高纬度地区相对低纬度地区降雨增加更多。这些认识为评估未来人为变暖的气候环境效应提供了地质依据。