Neodymium isotope record of late Paleocene to eraly Eocene fish teeth

High-resolution, fish tooth Nd isotopic records for eight Deep Sea Drilling Project and Ocean Drilling Program sites were used to reconstruct the nature of late Paleocene-early Eocene deep-water circulation. The goal of this reconstruction was to test the hypothesis that a change in thermohaline circulation patterns caused the abrupt 4-5°C warming of deep and bottom waters at the Paleocene/Eocene boundary - the Paleocene-Eocene thermal maximum (PETM) event. The combined set of records indicates a deep-water mass common to the North and South Atlantic, Southern and Indian oceans characterized by mean epsilon-Nd values of ~-8.7, and different water masses found in the central Pacific Ocean (epsilon-Nd ~-4.3) and Caribbean Sea (epsilon-Nd ~1.2). The geographic pattern of Nd isotopic values before and during the PETM suggests a Southern Ocean deep-water formation site for deep and bottom waters in the Atlantic and Indian ocean basins. The Nd data do not contain evidence for a change in the composition of deep waters prior to the onset of the PETM. This finding is consistent with the pattern of warming established by recently published stable isotope records, suggesting that deep- and bottom-water warming during the PETM was gradual and the consequence of surface-water warming in regions of downwelling.本研究采用8个深海钻探计划（Deep Sea Drilling Project, DSDP）与大洋钻探计划（Ocean Drilling Program, ODP）站位的高分辨率鱼牙钕（Nd）同位素记录，重建了古新世晚期至始新世早期的深水环流特征。本次重建的核心目标为验证下述假说：热盐环流（thermohaline circulation）模式的变化，是引发古新世/始新世界线处深层与底层海水发生4~5℃突发性增温的原因——该事件即古新世-始新世极热事件（Paleocene-Eocene thermal maximum, PETM）。综合全部记录的分析结果表明，北大西洋、南大西洋、南大洋与印度洋共享一个平均ε-Nd（epsilon-Nd）值约为-8.7的深水水团；而中太平洋（ε-Nd约-4.3）与加勒比海（ε-Nd约1.2）则分布有特征迥异的水团。古新世-始新世极热事件前后钕同位素值的空间分布格局显示，大西洋与印度洋盆地的深层、底层海水的形成源区位于南大洋。钕同位素数据未发现古新世-始新世极热事件爆发前，深水水团组成发生改变的相关证据。这一发现与近期发表的稳定同位素记录所揭示的增温格局一致，表明古新世-始新世极热事件期间的深层与底层海水增温为渐进过程，其驱动机制为下降流区域的表层海水增温。