Mid-Pleistocene planktonic foraminiferal composition and IRD content in ODP Sites 162-980 and 162-984

We investigated surface and deep ocean variability in the subpolar North Atlantic from 1000 to 500 thousand years ago (ka) based on two Ocean Drilling Program (ODP) sites, Feni drift site 980 (55°29'N, 14°42'W) and Bjorn drift site 984 (61°25'N, 24°04'W). Benthic foraminiferal stable isotope data, planktic foraminiferal faunas, ice-rafted debris data, and faunally based sea-surface temperature estimates help test the hypothesis that oceanographic changes in the North Atlantic region were associated with the onset of the 100-kyr world during the mid-Pleistocene revolution. Based on percentage of Neogloboquadrina pachyderma (s) records from both sites, surface waters during interglacials and glacials were cooler in the mid-Pleistocene than during marine isotope stages (MIS) 5 and 6. In particular, interglaciations at Bjorn drift site 984 were significantly cooler. Faunal evidence suggests that the interglacial Arctic front shifted from a position between the two sites to a position northwest of Bjorn drift site 984 after ca. 610 ka. As during the late Pleistocene, we find faunal evidence for lagging surface warmth at most of the glacial initiations during the mid-Pleistocene. Each initiation is associated with high benthic d13C values that are maintained into the succeeding glaciation, which we term “lagging NADW production.” These findings indicate that lagging warmth and lagging NADW production are robust features of the regional climate system that persist in the middle to late Pleistocene.

本研究基于两个大洋钻探计划（Ocean Drilling Program, ODP）站位——芬伊漂移区980站位（55°29'N，14°42'W）与比约恩漂移区984站位（61°25'N，24°04'W），对100万至50万年前（千年，ka）的亚极地北大西洋海域表层与深层海洋变化展开了系统调查。本研究采用底栖有孔虫稳定同位素数据、浮游有孔虫群落组成、冰筏碎屑数据以及基于群落的海表温度估算结果，对"北大西洋区域海洋学变化与中更新世革命期间10万年尺度气候周期（100-kyr world）的启动存在关联"这一假说进行了检验。基于两个站位的厚壁新方球虫（Neogloboquadrina pachyderma (s)）占比记录，中更新世冰期与间冰期的表层海水温度，均较海洋同位素阶段（Marine Isotope Stages, MIS）5和6时期更为偏低。尤为值得注意的是，比约恩漂移区984站位的间冰期表层海水温度偏低幅度更为显著。群落学证据显示，约61万年前（ca. 610 ka）之后，间冰期的北极锋面从两个站位之间的区域，迁移至比约恩漂移区984站位的西北侧海域。与晚更新世的情况一致，本研究在中更新世多数冰期启动事件中，均发现了表层海水增温滞后的群落学证据。每一次冰期启动事件均伴随高值底栖δ¹³C特征，且该特征会持续至后续冰期阶段，我们将这一现象定义为"北大西洋深层水（North Atlantic Deep Water, NADW）生成滞后"。上述研究结果表明，表层增温滞后与北大西洋深层水生成滞后，是贯穿中晚更新世区域气候系统的稳定特征。