(Table 1) Geochemistry of the ETM-2 section from IODP Hole 302-M0004A

During the early Eocene, a series of short-term global warming events ("hyperthermals”) occurred in response to the rapid release of carbon into the oceans and atmosphere. In order to investigate the response of ocean redox to global warming, we have determined the molybdenum isotope compositions (d98/95Mo) of samples spanning one such hyperthermal (Eocene Thermal Maximum 2 (ETM-2, 54.1 Ma)), from Integrated Ocean Drilling Program Expedition 302 Site M0004A in the Arctic Ocean. The highest d98/95Mo in our sample set (2.00 ± 0.11 per mil) corresponds to the development of local euxinia at Site M0004A during the peak of ETM-2, which we interpret as recording the global seawater d98/95Mo at that time. The ETM-2 seawater d98/95Mo is indistinguishable from a recent estimate of seawater d98/95Mo from an earlier hyperthermal (Paleocene Eocene Thermal Maximum (PETM, 55.9 Ma), d98/95Mo = 2.08 ± 0.11 per mil). We argue that the similarity in seawater d98/95Mo during ETM-2 and the PETM was caused by the development of transient euxinia in the Arctic Ocean during each hyperthermal that allowed sediments accumulating in this basin to capture the long-term d98/95Mo of early Eocene seawater. Our new data therefore place a minimum constraint on the magnitude of transient global seafloor deoxygenation during early Eocene hyperthermals.

始新世早期，随着碳被快速释放进入海洋与大气，一系列短期全球变暖事件（hyperthermals）就此发生。为探究海洋氧化还原状态对全球变暖的响应，我们对取自北冰洋综合大洋钻探计划（Integrated Ocean Drilling Program）第302航次M0004A站位的样品进行了分析，测定了横跨其中一次极热事件——始新世热事件2（Eocene Thermal Maximum 2, ETM-2, 54.1 Ma）——的钼同位素组成（δ98/95Mo）。本数据集样品中最高的δ98/95Mo值为2.00 ± 0.11 ‰，对应ETM-2峰值期M0004A站位局域硫化缺氧环境的形成；我们将该值解读为当时全球海水δ98/95Mo的直接记录。本次测得的ETM-2时期海水δ98/95Mo值，与早前针对另一极热事件——古新世-始新世极热事件（Paleocene Eocene Thermal Maximum, PETM, 55.9 Ma）——估算的海水δ98/95Mo值（2.08 ± 0.11 ‰）并无显著差异。我们认为，ETM-2与PETM时期海水δ98/95Mo值的相似性，源于两次极热事件期间北冰洋均出现了暂时性硫化缺氧环境，使得该盆地沉积的沉积物能够捕获始新世早期海水长期的δ98/95Mo组成。因此，本研究的新数据为始新世早期极热事件期间暂时性全球海底缺氧化的强度限定了最低下限。