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的热、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很大，在Heinrich Stadials和年轻仙女木时期变化最大，当时海洋倾覆严重减少。由于在未来全球变暖的情景下，预测到明显的AMOC减速，评估AMOC的迟缓将对全球热量收支产生的影响是至关重要的。数值模型预测，在减弱的AMOC过程中，半球间海洋热量输送的减少将导致南大西洋次表层的大量热量积累，该次表层是巴西东部附近的一个热点。这些温暖的次表层水由于盐度高，因此在平流到北大西洋深水形成地点时的密度很高，因此也可能对AMOC的恢复起到关键作用。然而，来自热带大西洋西部最大次表层变暖区域的古数据仍然缺失，但对地面真相模型结果的保真度至关重要。迫切需要进行这种模型测试，因为即使是最先进的模型也无法模拟主要边界流(例如南大西洋的巴西流)造成的水团输送的复杂动态，以及通过大尺度涡流将热量和盐分从印度洋转移到南大西洋(次)表面的过程(所谓的“阿古拉泄漏”)。因此，这项提议的重点是重建南大西洋在AMOC扰动期间的次表层热量和盐分收支。为此，将使用来自巴西东部海域的M125-35-3岩芯，该岩芯位于响应弱AMOC的模型预测的次表层暖异常的最大值范围内。深层有孔虫Globorotalia flata的温度和盐度记录将通过联合测量镁/钙和d18O来获得。这些数据将涵盖最后一次冰川消融，包括海因里希·斯塔迪尔1号和年轻的仙女木，分辨率高(海因里希·斯塔迪尔1号冰川消融时间长达50年)。这些数据将与大西洋盆地现有的地下记录进行比较，以生成最后一次冰川消融期间地下热量和盐分运输的综合图景。将进一步利用记录阿古拉什渗漏强度的记录来评估阿古拉什渗漏对南大西洋去冰川次表层热量和盐分收支的重要性。

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.