Exchange of mass and heat between the different components of circulation of the Southern Ocean and the role of the Straits (ACC-Agulhas Leakage-ITF System).

We propose to study the heat and mass transport regimes in the system composed by the Southern Atlantic-Indian Ocean passage (Agulhas Leakage, AL in the following), the Indonesian throughflow (ITF) and their possible link to the Antarctic Circumpolar Current (ACC) variability. Recently it was found that the enhanced heat uptake by the Pacific Ocean has been compensated by an increased heat transport from the Pacific Ocean to the Indian Ocean, carried by the Indonesian throughflow. Moreover the pronounced strengthening in Pacific trade winds over the past two decades is sufficient to account for the cooling of the tropical Pacific and a substantial slowdown in surface warming through increased subsurface ocean heat uptake. The net effect of these anomalous winds is a cooling in the 2012 global average surface air temperature of 0.1-0.2 C, which may account for much of the hiatus on surface temperature warming observed since 2001. The transport of warm and salty Indian Ocean waters into the Atlantic Ocean--the Agulhas leakage--has a crucial role in the global oceanic circulation and thus in the evolution of future climate. At present these waters provide the main source of heat and salt for the surface branch of the Atlantic Meridional Overturning Circulation (AMOC). There is evidence from past glacial-to-interglacial variations in foraminiferal assemblages and model studies that the amount of Agulhas leakage and its corresponding effect on the AMOC have been subject to substantial change, potentially linked to latitudinal shifts in the Southern Hemisphere westerlies. Indeed, a progressive poleward migration of the westerlies has been observed during the past two to three decades and linked to anthropogenic forcing via increase in GHGs and stratospheric ozone depletion, but because of the sparse observational records it has not been possible to determine whether there has been a concomitant response of Agulhas leakage. Recent results from a high-resolution ocean general circulation model show that the transport of Indian Ocean waters into the South Atlantic via the Agulhas leakage has increased during the past decades in response to the change in wind forcing. Both model and historic measurements off South America suggest that the additional Indian Ocean waters have begun to invade the North Atlantic, with potential implications for the future evolution of the AMOC. By using satellite data, lagrangian drifters, and the analysis of global Earth System Models, we investigate and set hypothesis regarding the criticality of the ACC-AL-ITF system. In particular, focus on how this system affect the ACC and the acceleration of the melting of Antarctic ice, as well as the ice melting along the peninsula Antarctica, beside the understanding of the 3D transport regimes using the drifters and Argo buoys.