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

• Applicant: Privatdozent Dr. André Bahr
• Subject Area: Geology
• Term: from 2021 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 457847783

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.

• DFG Programme: Research Grants