Isotope and water temperature measurements of the Atlantic Ocean from ODP Site 172-1056

We use planktonic foraminiferal (Globigerinoides sacculifer and Neogloboquadrina dutertrei) d18O records from subtropical North Atlantic Site 1056 to reconstruct millennial-scale changes in sea surface hydrography during marine isotope stages (MIS) 10 through 12 (340-440 ka). The difference in the d18O records provides a measure of the thermal gradient from the mixed layer to the seasonal thermocline (delta Tml-tc), which we use to constrain upper ocean stratification and infer northward ocean heat transport. Late Holocene G. sacculifer and N. dutertrei d18O values place controls on how the foraminifera record recent ocean conditions at Site 1056. In the down core record we find extreme excursions toward G. sacculifer d18O maxima and delta Tml-tc minima throughout the entire time interval. These cold events have a similar amplitude throughout but are more frequent during the glacial than the interglacial intervals. During interglacial MIS 11 the excursions provide evidence for repeated cooling of the sea surface contributing to existing evidence for relative climate instability during interglacial intervals. During MIS 10, millennial-scale variability in the subtropical record is very similar to that observed in the subpolar North Atlantic at Site 980, perhaps related to a common forcing such as a large Northern Hemisphere ice sheet. Within the limitation of the age models the cold events of MIS 11 are almost synchronous with benthic foraminiferal d13C minima at subtropical North Atlantic Site 1063, which suggests a general surface to deep ocean link via thermohaline circulation during this interval of time.

我们采用北大西洋亚热带1056站位的浮游有孔虫（planktonic foraminifera）——箭射球室虫（Globigerinoides sacculifer）与杜氏新球虫（Neogloboquadrina dutertrei）——的δ¹⁸O记录，重建了海洋同位素阶段（MIS）10至12（距今34万至44万年）期间海水表层水文的千年尺度变化。二者δ¹⁸O记录的差值可用于量化混合层至季节性温跃层的温度梯度（ΔT_ml-tc），以此约束上层海洋层结，并推断北向海洋热输送强度。全新世晚期箭射球室虫与杜氏新球虫的δ¹⁸O值，可用于限定该站位有孔虫对现代海洋环境的记录模式。在岩芯记录中，我们发现整个研究时段内均存在箭射球室虫δ¹⁸O极值与ΔT_ml-tc极小值的极端偏移事件。这类冷事件的振幅整体相近，但冰期阶段的发生频率显著高于间冰期阶段。在间冰期MIS 11阶段，这类偏移事件为海水表层的周期性降温提供了直接证据，进一步佐证了间冰期阶段气候相对不稳定的既有研究结论。MIS 10阶段，亚热带记录的千年尺度变异性与北大西洋亚极地980站位的观测结果高度相似，这可能与共同的气候强迫因子有关，例如北半球大型冰盖活动。在年龄模型的约束范围内，MIS 11阶段的冷事件与北大西洋亚热带1063站位的底栖有孔虫（benthic foraminifera）δ¹³C极小值几乎同步，这表明该时段内通过温盐环流（thermohaline circulation）存在表层与深层海洋的普遍耦合联系。