Driving mechanisms of the variability and long-term trend of the Brazil-Malvinas confluence during the 21st century

Over the last decade, several studies have identified a southward drift of the mean meridional position of the Brazil-Malvinas confluence (BMC). Although this trend has been ascribed to different mechanisms, the most recent study found a reduction of the Malvinas current (MC) as the main reason behind it. It is unclear, however, how this mechanism would persist in the face of global warming and under projected increased winds over the Southern Ocean, as the response of the Antarctic Circumpolar Current (ACC) varies within different Earth System Models (ESM), ultimately impacting the MC. We ran a high-resolution (1/12 degrees) ocean model driven with results from the Max-Planck-Institute-ESM to verify how the confluence will respond to anthropogenic climate change, by downscaling results from the pre-industrial control and RCP8.5 scenarios. Our results show that the southward confluence shift is only persistent under anthropogenic forcing and is led by a reduction of the MC volume transport. This reduction of the Malvinas transport is induced by a shift of the main ACC flow closer to Antarctica's shelf, in response to a southward movement of the westerlies band, even if no long-term changes on the total ACC transport can be found. Our results corroborate previous evidence regarding the MC as the main responsible behind the observed BMC southward shift in the recent past but points toward anthropogenic climate change as the triggering mechanism, with various effects cascading from its impact on the Southern Ocean. This also has consequences for the BMC variability, whose amplitude reduces as we approach the end of the 21st century.