Benthic foraminifers, isotopes and varimax factors at DSDP Holes 72-517 and 72-518

Pliocene changes in the vertical water mass structure of the western South Atlantic are inferred from changes in benthic foraminiferal assemblages and stable isotopes from DSDP Holes 516A, 517, and 518. Factor analysis of 34 samples from Site 518 reveals three distinct benthic foraminiferal assemblages that have been associated with specific subsurface water masses in the modern ocean. These include a Nuttalides umbonifera assemblage (Factor 1) associated with Antarctic Bottom Water (AABW), a Globocassidulina subglobosa-Uvigerina peregrina assemblage (Factor 2) associated with Circumpolar Deep Water (CPDW), and an Oridorsalis umbonatus-Epistominella exigua assemblage associated with North Atlantic Deep Water (NADW). Bathymetric gradients in d13C between Holes 516A (1313 m), 517 (2963 m), and 518 (3944 m) are calculated whenever possible to monitor the degree of similarity and/or difference in the apparent oxygen utilization (AOU) of water masses located at these depths during the Pliocene. Changes in bathymetric d13C gradients coupled with benthic foraminiferal assemblages record fundamental changes in the vertical water mass structure of the Vema Channel during the Pliocene from 4.1 to 2.7 Ma. […]

本研究通过分析深海钻探计划（Deep Sea Drilling Project, DSDP）516A、517与518孔的底栖有孔虫组合及稳定同位素记录，重建了南大西洋西部上新世时期的水体垂直结构演化。对518站位34个样品开展的因子分析显示，存在3种特征鲜明的底栖有孔虫组合，这些组合可对应现代海洋中的特定深水水团：与南极底层水（Antarctic Bottom Water, AABW）相关的*Nuttalides umbonifera*组合（因子1）、与环极深层水（Circumpolar Deep Water, CPDW）相关的*Globocassidulina subglobosa*-*Uvigerina peregrina*组合（因子2），以及与北大西洋深层水（North Atlantic Deep Water, NADW）相关的*Oridorsalis umbonatus*-*Epistominella exigua*组合。本研究尽可能对516A孔（水深1313 m）、517孔（2963 m）与518孔（3944 m）的δ¹³C水深梯度进行计算，以监测上新世时期各深度水体的表观耗氧量（apparent oxygen utilization, AOU）的异同程度。δ¹³C水深梯度的变化结合底栖有孔虫组合记录，揭示了4.1 Ma至2.7 Ma上新世时期维马海峡（Vema Channel）的水体垂直结构发生的根本性演化。[…]