Subsurface heat storage and transport in the tropical Atlantic during the last Deglaciation

大西洋经向翻转环流（AMOC）强度的波动强烈影响海洋中热、盐和碳的分布，从而影响全球气候。大量证据表明，AMOC强度在晚更新世和全新世期间变化较大，在海因里希冰期和新仙女木期变化最为剧烈，此时海洋翻转严重减弱。由于在未来的全球变暖情景下，预计AMOC将明显放缓，因此评估AMOC放缓对全球热收支的影响至关重要。数值模型预测，在AMOC减弱期间，半球间海洋热输送减少将导致南大西洋地下大量热量积累，并在巴西东部附近形成一个“热点”。这些温暖的地下水也可能对AMOC的恢复起关键作用，因为它们的高盐度和密度当平流到北大西洋深水形成的位置时。然而，来自西热带大西洋地表下最大变暖区域的古数据仍然缺失，但这对模型结果的真实性至关重要。这种模型测试是迫切需要的，因为即使是最先进的模型，在模拟主要边界流（例如南大西洋的巴西流）的水团运输的复杂动力学以及通过大规模涡流（所谓的“阿古拉斯泄漏”）从印度洋到南大西洋（亚）表面的热量和盐转移的能力方面也是有限的。因此，本研究的重点是重建AMOC扰动期间南大西洋的地下热盐收支。为此，将利用巴西东部的M125-35-3核心，该核心位于响应弱AMOC的模式预测的最大地下暖异常范围内。通过对深埋有孔虫Globorotalia inflata的Mg/Ca和d18O测量，获得了其地下温度和盐度记录。这些数据将以高分辨率覆盖最后一次冰期，包括海因里希第一次冰期和新仙女木期（海因里希第一次冰期可达50年）。这些数据将与大西洋盆地现有的地下记录进行比较，以生成最后一次消冰期间地下热量和盐输送的综合图像。与捕获Agulhas泄漏强度的记录的相关性将进一步用于评估Agulhas泄漏对南大西洋去冰地下热量和盐收支的重要性。

Fluctuations of the Atlantic Meridional Overturning Circulation (AMOC) strength strongly impact the distribution of heat, salt, and carbon in the ocean, thus affecting global climate. Abundant evidence exists that AMOC strength varied considerably during the Late Pleistocene and Holocene, most drastically during Heinrich Stadials and the Younger Dryas when oceanic overturning was severely reduced. As a distinct AMOC slow-down is predicted under future global warming scenarios, it is pivotal to assess the effect that a sluggish AMOC will exert on the global heat budget. Numerical models predict that reduced interhemispheric oceanic heat transport during a weakened AMOC will lead to massive heat accumulation in the subsurface of the South Atlantic with a “hot spot” off East Brazil. These warm subsurface waters might also play a pivotal role for the resumption of the AMOC due to their high salinity and hence density when advected to the loci of deep water formation in the North Atlantic. However, paleo-data from the proposed area of maximum subsurface warming in the western tropical Atlantic are yet missing but crucial to ground-truth the fidelity of the model results. Such model-testing is urgently needed as even state-of-the art models are limited in their capability to simulate the complex dynamics of water mass transport by major boundary currents (e.g. the Brazil Current in the South Atlantic) as well as the heat and salt transfer from the Indian Ocean into the (sub)surface of the South Atlantic via large-scale Eddies (the so-called “Agulhas Leakage”). Focus of this proposal is therefore to reconstruct the subsurface heat and salt budget in the South Atlantic during periods of AMOC disturbance. For this purpose, Core M125-35-3 from off East Brazil will be utilized, which locates within the maximum of the subsurface warm anomaly predicted by models in response to a weak AMOC. Subsurface temperature and salinity records will be obtained by combined Mg/Ca and d18O measurements on the deep dwelling foraminifera Globorotalia inflata. The data will cover the last Deglaciation, including Heinrich Stadial 1 and the Younger Dryas, in high resolution (up to 50 yrs for Heinrich Stadial 1). This data will be compared to existing subsurface records from across the Atlantic Basin to generate a comprehensive picture of subsurface heat and salt transport during the last deglaciation. Correlation with records capturing Agulhas Leakage strength will be further used to assess the importance of Agulhas Leakage for the deglacial subsurface heat and salt budget of the South Atlantic.