Spatial Variability of Antarctic Bottom Water in the Australian Antarctic Basin From 2018–2020 Captured by Deep Argo.

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 multidecade 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% of 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. Plain Language Summary: The dense waters that form along the Antarctic coast and fill the global deep oceans have been warming and freshening over the past three decades. This water is integral to the earth's natural system of temperature regulation. New robotic floats from the Deep Argo program are able to record temperature, salinity, and pressure down to the bottom of the ocean and are capturing variability in the quantity and properties of these dense waters near their formation sites better than ever before. Here we examine data from the first 2 years of float deployments in the Indian sector of the Southern Ocean to quantify the rebound in salinity of dense water from the Ross Sea and study how different varieties of this dense water spread and fill the Australian Antarctic Basin before ultimately flowing out into the Indian and Pacific Oceans. Key Points: A new Deep Argo pilot array improves spatial and temporal resolution of bottom water sampling in the Australian Antarctic BasinThe floats capture the return of high salinity Ross Sea Bottom Water to the region after a period of multi‐decadal fresheningA simple Optimum Multiparameter calculation quantifies the local zonal variation in the new water mass concentrations from 2018 to 2020 [ABSTRACT FROM AUTHOR]