UC San Diego

There are two varieties of Antarctic Bottom Water present in the Australian Antarctic Basin (AAB): locally-produced Adélie Land Bottom Water (ALBW) and distantly-produced Ross Sea Bottom Water (RSBW). Between 2014 and 2018, RSBW has rebounded from a multi-decade freshening trend. The return of the salty RSBW to the AAB is revealed by six Deep Argo floats that have occupied the region from January of 2018 to March of 2020. The floats depict a zonal variation in temperature and salinity in the bottom waters of the AAB, driven by the inflow of RSBW. A simple Optimum Multiparameter Analysis based on potential temperature and salinity gives a sense of scale to the composition of the bottom waters, which are nearly 80% the new, salty RSBW in the south-east corner of the basin by 2019, and generally less than 40% to the west closer to the ALBW outflow region and the abyssal plain.