Sedimentology, planktonic foraminifera distribution and stable isotope composition during marine isotope stage 3 of ODP Site 172-1060 in the West Atlantic

We have studied Ocean Drilling Program Site 1060 on the Blake Outer Ridge, which lies beneath the Gulf Stream. We focus on marine isotope stage 3, 60-25 thousand years before present (ka). Sea surface temperatures (SSTs) inferred both from foraminiferal fauna and alkenone ratios, as well as counts of iceberg melt-out debris and benthic stable isotope analyses, enable our record to be interpreted in terms of regional hydrographic changes as well as changing thermohaline circulation (THC). The observed SST record is consistent with the air temperature record from the Greenland ice cores. However, Site 1060 exhibits important differences in detail compared with the ice core record, and when compared to other sites within the North Atlantic, significant longitudinal differences emerge. At Site 1060 in the western Atlantic, all Greenland stadials (GS) whether associated with Heinrich events (HEs) or not, show a similar small amplitude of cooling; mean faunal-based SSTaug during GS is only 1.5°C colder than during Greenland interstadials (GIS). In addition, during GS the coldest SSTs are limited to apparently brief events. This is in contrast to several eastern Atlantic sites where HE stadials exhibit coolings that are enhanced by 2°C compared to other GS and where cold conditions are not restricted to cold pulses but cover 2 ka-long intervals. Furthermore, Site 1060 SSTs remained warm right through each interstadial, in contrast to the sustained and uniform cooling trend through interstadials that is consistently observed in Greenland, indicated by measurements of delta18O in ice.

我们针对位于湾流（Gulf Stream）下方的布雷克外海岭的大洋钻探计划（Ocean Drilling Program, ODP）1060站位展开研究，聚焦于距今60至25千年（ka）的海洋同位素第3阶段（marine isotope stage 3）。通过有孔虫动物群与烯酮比值反演得到的海表温度（Sea Surface Temperatures, SSTs）、冰山融出碎屑计数以及底栖稳定同位素分析，我们得以基于区域水文变化与温盐环流（thermohaline circulation, THC）的演化对该记录进行解译。观测得到的海表温度记录与格陵兰冰芯的气温记录具有一致性，但1060站位的细节特征与冰芯记录存在显著差异；若与北大西洋其他站位对比，则可发现显著的经向差异。在西大西洋的1060站位，所有格陵兰冰阶（Greenland stadials, GS）——无论是否伴随海因里希事件（Heinrich events, HEs）——均呈现出相似的小幅降温特征：冰阶期间基于动物群反演的SST_aug仅比格陵兰冰间阶（Greenland interstadials, GIS）低1.5℃。此外，冰阶期间的最低海表温度仅局限于短暂的事件中。这与大西洋东部多个站位的特征形成鲜明对比：后者的海因里希冰阶降温幅度较其他冰阶高出2℃，且寒冷环境并非仅局限于冷脉冲事件，而是覆盖了长达2千年的时段。进一步而言，1060站位的海表温度在整个冰间阶期间始终维持温暖状态，这与格陵兰通过冰芯氧同位素（δ¹⁸O）测量所观测到的、贯穿冰间阶的持续且均匀的降温趋势截然不同。