Spatial and temporal variability of deep water-mass properties within the Australian Antarctic Basin captured by Deep Argo

The formation and distribution of Antarctic Bottom Water is a crucial component of the Global Thermohaline Circulation. Antarctic Bottom Water within the Australian Antarctic Basin, formed along the adjacent Adelie and George V Land coast and in the more remote Ross Shelf, has experienced both warming and freshening over the past three decades. In early 2018, five new Deep Argo floats were deployed in the Australian Antarctic Basin. These floats are equipped with Seabird SBE-61 CTD sensors, are capable of profiling down to 6000 m, and sample all year round, including under ice in the winter. Three of the floats have stayed close to two GO-SHIP tracks, SR03 and S4I, with ship-based, full-depth, high quality, repeated hydrographic occupations going back to 1991. Here we explore the spatial and temporal variability found in data from this new observational platform and compare it to the GO-SHIP repeat hydrography tracks. The floats reveal small spatial variability in deep ocean salinity and temperature distribution and provide full depth profiles up onto the continental shelf under the ice during the winter of 2018, with float position inferred from bottom bathymetry and known profile depth. In addition, the floats capture the recent return of salty bottom water to the region. Deep Argo shows the potential to drastically change how we understand bottom water formation and export.