(Table 1) Elemental mean values of the upper Paleocene and lower Eocene in IODP Hole 302-M0004A

We reconstruct the latest Paleocene and early Eocene (~57-50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene-Eocene thermal maximum (PETM) (~55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX86'-reconstructed temperatures of 15°-18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X-ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (~53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.

本研究依托综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）302航次在罗蒙诺索夫海岭（Lomonosov Ridge）获取的岩芯，重建了北冰洋最新古新世至早始新世（约57~50 Ma）的环境演化趋势，并重点聚焦于约55 Ma的古新世-始新世极热事件（Paleocene-Eocene thermal maximum, PETM）。罗蒙诺索夫海岭在最新古新世至早始新世初期仍部分露出海面，早始新世期间逐渐发生沉降。有机甲藻囊孢（organic dinoflagellate cyst, dinocyst）组合指示，整个最新古新世至早始新世的表层水体均为半咸水环境且具有较高初级生产力。此时期的甲藻囊孢组合具有全球广布性，表明当时气候温暖，这一结论得到TEX86'重建的15~18℃古温度数据的佐证。无机地球化学数据整体反映了沉积物内部的还原环境，以及下始新统上部的硫化缺氧环境。频谱分析显示，接近约53 Ma的始新世极热事件2（Eocene thermal maximum 2，其存在已由甲藻囊孢地层学证实）的X射线荧光扫描铁元素数据所记录的沉积旋回性，与岁差周期相关。在古新世-始新世极热事件的下部层位中，各类代用指标均显示当时区域出现了增强的风化作用、地表径流、水体缺氧、初级生产力提升以及海平面上升。基于总有机碳含量与沉积物堆积速率的变化特征，北冰洋内过量的有机碳埋藏似乎对极热事件期间注入碳的固存起到了显著贡献。