Reconstruction of continental mean air temperature across the PETM of IODP Hole 302-M0004A (Appendix A)

The Palaeocene-Eocene Thermal Maximum (PETM; ~55.5 Ma) is a geologically relatively brief episode of extreme warmth. Both deep and surface ocean temperatures increased by up to 5 °C in equatorial waters and up to 8 °C in mid and high latitude waters. From the continents, the annual mean air temperature response during the PETM is still largely unknown, mainly due to a lack of quantitative temperature proxies and sufficient suitable, continuous high resolution records. Recently, a new proxy for continental temperature reconstructions has been proposed, based on the distribution of membrane lipids of bacteria in present-day soils [Weijers et al., 2007, doi:10.1016/j.gca.2006.10.003] and shown to reconstruct annual mean air temperature. In this study we applied this new proxy in an attempt to reconstruct the air temperature in high latitude continental areas during the PETM by analysis of a marine sedimentary sequence obtained from the Lomonosov Ridge in the central Arctic Ocean (Integrated Ocean Drilling Program Expedition 302, Site 004, Hole A). The results indicate a warming of ~8 °C above background values of ~17 °C. This warming is coincident with a similar rise in sea surface temperatures documented earlier. Our results thus further confirm the warm conditions in the Arctic, and point to a strongly reduced latitudinal temperature gradient during the PETM.

古新世-始新世极热事件（Palaeocene-Eocene Thermal Maximum, PETM；约55.5 Ma）是地质历史中相对短暂的极端温暖事件。赤道海域的深海与表层海水温度最高升高5℃，中高纬度海域则最高升高8℃。目前，古新世-始新世极热事件期间大陆年均气温的响应特征仍未明确，这主要源于缺乏定量温度代用指标以及足够优质、连续的高分辨率记录。近期有研究基于现今土壤中细菌膜脂的分布，提出了一种用于大陆温度重建的新型代用指标[Weijers等，2007，doi:10.1016/j.gca.2006.10.003]，并证实其可用于重建年均气温。本研究应用该新型代用指标，通过对北冰洋中部罗蒙诺索夫海岭（Lomonosov Ridge）的海洋沉积序列（综合大洋钻探计划（Integrated Ocean Drilling Program）302航次，004站位A孔）开展分析，尝试重建古新世-始新世极热事件期间高纬度大陆地区的气温。研究结果显示，相较于约17℃的背景值，气温升高了约8℃。此次升温与此前已记录的海表温度上升幅度一致。本研究结果进一步证实了北极地区的极端温暖环境，并表明古新世-始新世极热事件期间全球纬度气温梯度显著降低。