Deep-water temperature reconstruction of sediment core MD99-2334@en

Paired measurements of Mg/Ca and delta18O(cc) (calcite delta18O) in benthic foraminifera from a deep-sea core recovered on the Iberian Margin (MD99-2334K; 37°48'N, 10°10'W; 3,146 m) have been performed in parallel with planktonic delta18O(cc) analyses and counts of ice-rafted debris (IRD). The synchrony of temperature changes recorded in the Greenland ice cores and in North Atlantic planktonic delta18O(cc) allows the proxy records from MD99-2334K to be placed confidently on the GISP2 time-scale. This correlation is further corroborated by AMS 14C-dates. Benthic Mg/Ca measurements in MD99-2334K permit the reconstruction of past deep-water temperature (T(dw)) changes since ~34 cal. ka BP (calendar kiloyears before present). Using these T(dw) estimates and parallel benthic delta18O(cc) measurements, a record of deep-water delta18O (delta18O(dw)) has been calculated. Results indicate greatly reduced T(dw) in the deep Northeast Atlantic during the last glaciation until ~15 cal. ka BP, when T(dw) warmed abruptly to near-modern values in parallel with the onset of the Bølling-Allerød interstadial. Subsequently, Tdw reverted to cold glacial values between ~13.4 and ~11.4 cal. ka BP, in parallel with the Younger Dryas cold reversal and the H0 ice-rafting event. Similar millennial-scale T(dw) changes also occurred during the last glaciation. Indeed, throughout the last ~34 cal. ka, millennial delta18O(dw) and T(dw) changes have remained well coupled and are linked with IRD pulses coincident with Heinrich events 3, 2, 1, and the Younger Dryas, when transitions to lower T(dw) and delta18O(dw) conditions occurred. In general, millennial T(dw) and delta18O(dw) variations recorded in MD99-2334K describe an alternation between colder, low-delta18O(dw) and warmer, high delta18O(dw) conditions, which suggests the changing local dominance of northern-sourced North Atlantic Deep Water (NADW) versus southern-sourced Antarctic Bottom Water (AABW). The observed similarity of the T(dw) and GISP2 delta18O(ice) records would therefore suggest a common component of variability resulting from the coupling of NADW formation and Greenland climate. A link between Greenland stadials and the incursion of cold, low-delta18O(dw) AABW in the deep Northeast Atlantic is thus implied, which contributes to the relationship between Greenland climate and the millennial benthic delta18O(cc) signal since ~34 cal. ka BP.采自伊比利亚陆缘（Iberian Margin）的深海岩芯MD99-2334K（坐标：37°48′N，10°10′W；水深3146米）中，研究人员对底栖有孔虫（benthic foraminifera）的Mg/Ca比值与方解石氧同位素δ¹⁸O(cc)（即calcite δ¹⁸O）开展了配对测试分析，同时同步完成了浮游有孔虫（planktonic foraminifera）δ¹⁸O(cc)分析以及冰筏碎屑（ice-rafted debris, IRD）计数。格陵兰冰芯与北大西洋浮游有孔虫δ¹⁸O(cc)所记录的温度变化具有同步性，因此可将MD99-2334K的代用指标记录可靠地锚定至格陵兰冰芯项目2（GISP2）年代标尺之上，该相关性进一步得到加速器质谱碳14测年（AMS ¹⁴C）结果的佐证。MD99-2334K岩芯的底栖有孔虫Mg/Ca比值分析，可重建约34日历千年距今（cal. ka BP，即calendar kiloyears before present）以来的深层海水温度（deep-water temperature, T_dw）变化历史。结合上述深层海水温度估算结果与同步获取的底栖有孔虫δ¹⁸O(cc)数据，可计算得到深层海水氧同位素（δ¹⁸O_dw）记录。研究结果显示，末次冰期期间东北大西洋深层海水温度显著降低，直至约15日历千年距今时，伴随博令-阿勒罗德间冰段（Bølling-Allerød interstadial）的启动，深层海水温度骤升至接近现代的水平。随后在约13.4至11.4日历千年距今期间，深层海水温度回落至冰期寒冷状态，这与新仙女木（Younger Dryas）冷期反转以及H0冰筏事件的发生时间完全吻合。末次冰期期间同样存在类似的千年尺度深层海水温度变化。事实上，在过去约34日历千年的时间里，千年尺度的δ¹⁸O_dw与T_dw变化始终保持良好的耦合关系，且与海因里希事件（Heinrich events）3、2、1以及新仙女木事件期间的冰筏碎屑脉冲事件同步——这些事件均对应着深层海水温度与δ¹⁸O_dw降低的转换阶段。总体而言，MD99-2334K岩芯记录的千年尺度T_dw与δ¹⁸O_dw变化呈现出“寒冷低δ¹⁸O_dw”与“温暖高δ¹⁸O_dw”状态的交替特征，这表明东北大西洋深层水的来源存在区域性转变：即北大西洋深层水（North Atlantic Deep Water, NADW，源自北部）与南极底层水（Antarctic Bottom Water, AABW，源自南部）的相对优势地位发生交替。观测到的深层海水温度与GISP2冰芯δ¹⁸O(ice)记录的相似性，表明二者存在共同的变率驱动因子，该因子源于北大西洋深层水形成过程与格陵兰气候的耦合作用。因此，本研究暗示格陵兰冰期阶地与东北大西洋深层冷性、低δ¹⁸O_dw的南极底层水入侵之间存在关联，这也解释了约34日历千年距今以来格陵兰气候与千年尺度底栖有孔虫δ¹⁸O(cc)信号之间的相关性。