Age determination and stable carbon oxygen isotopes of sediment core MD99-2334

A sequence of accelerator mass spectrometry (AMS) 14C dates performed on benthic and planktonic foraminifera from a northeast Atlantic deep-sea core (MD99-2334K; 37°48'N, 10°10'W; 3146 m) permit the reconstruction of deep water “14C ventilation ages” across the last deglaciation. The records from MD99-2334K have been placed on the GISP2 timescale via the synchrony of temperature changes recorded in the Greenland ice cores and in North Atlantic planktonic delta18O(cc) (calcite delta18O). On the basis of a range of estimates for past source water Delta14C, this permits the estimation of 14C projection ventilation ages for comparison with benthic-planktonic 14C age differences. Although the accurate estimation of past ventilation ages is precluded by unknown deep water Delta14C source signatures, and by uncertainty regarding the extent of deep water mixing, it is clear that deep water ventilation in the northeast Atlantic was significantly reduced during the last glaciation, increased abruptly coincident with the Bølling-Allerød warming, and rapidly became reduced again during the Younger Dryas cold reversal. The character of these changes is consistent with a varying dominance of North Atlantic Deep Water (NADW) versus Antarctic Bottom Water (AABW). Parallel benthic delta13C, deep water temperature (T(dw)), and deep water delta18O (delta18O(dw)) estimates support this inference. The fact that deglacial changes in the deep water radiocarbon content of the northeast Atlantic run parallel to opposite changes in atmospheric radiocarbon content, and in parallel with Greenland temperature fluctuations, unequivocally implicates changes in ocean circulation in deglacial climate evolution and illustrates the capacity for the deep ocean to respond and contribute to abrupt climate change.本研究对东北大西洋深海岩芯MD99-2334K（坐标：37°48'N，10°10'W；水深3146米）中的底栖与浮游有孔虫开展了一系列加速器质谱法（accelerator mass spectrometry, AMS）¹⁴C测年，据此重建了末次冰消期以来的深层水¹⁴C通风年龄序列。该岩芯的记录已通过格陵兰冰芯与北大西洋浮游有孔虫方解石δ¹⁸O（cc, calcite δ¹⁸O）所记录的温度变化同步性，锚定至GISP2年代标尺。基于一系列过去源水Δ¹⁴C的估算值，本研究可推导¹⁴C投影通风年龄，以与底栖-浮游有孔虫¹⁴C年龄差进行对比。尽管未知的深层水Δ¹⁴C源信号以及深层水混合范围的不确定性，制约了过去通风年龄的精准估算，但现有结果清晰表明：东北大西洋深层水通风作用在末次冰期显著减弱，在博林-阿勒罗德（Bølling-Allerød）暖期出现突发性增强，随后在新仙女木（Younger Dryas）冷反转事件期间再度快速减弱。这些变化的特征与北大西洋深层水（North Atlantic Deep Water, NADW）相较于南极底层水（Antarctic Bottom Water, AABW）的主导地位变化相一致。同步获得的底栖δ¹³C、深层水温（T_dw）以及深层水δ¹⁸O（δ¹⁸O_dw）估算结果支持了这一推论。东北大西洋深层水放射性碳含量的冰消期变化与大气放射性碳含量的反向变化、以及格陵兰温度波动均呈同步趋势，这一现象明确表明海洋环流变化在冰消期气候演化中起到关键作用，同时也印证了深海能够响应并参与突发性气候变迁。