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

George Thomas,Sarah G Purkey,Dean Roemmich,Annie Foppert,Stephen R Rintoul

doi:10.1029/2020gl089467

Abstract

AbstractThere 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.

Highlights

Introduction and Background1.1 Antarctic Bottom WaterOver the past three decades Antarctic Bottom Water (AABW) has played a crucial role in mitigating the increase of anthropogenic atmospheric warming through the sequestration of heat into the abyssal ocean
We describe the properties and sources of AABW found in the southern Antarctic Basin (AAB) and quantify the return of salty Ross Sea Bottom Water (RSBW) spreading into the AAB from the east, as observed by Deep Argo floats from January of 2018 to March of 2020
The six Deep Argo floats measured the spatial distribution of bottom properties in the southeastern AAB, providing insight into the general flow paths of Adélie Land Bottom Water (ALBW) and RSBW into the region (Figure 1; blue and red arrows, respectively)

Summary

Introduction

Introduction and Background1.1 Antarctic Bottom WaterOver the past three decades Antarctic Bottom Water (AABW) has played a crucial role in mitigating the increase of anthropogenic atmospheric warming through the sequestration of heat into the abyssal (greater than 4,000 m depth) ocean. Decadal occupations of hydrographic sections gridding the deep ocean conducted by the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP; Talley et al, 2016) have shown that the abyssal ocean has warmed significantly throughout the globe (Aoki et al, 2017; Desbruyeres et al, 2016; Johnson et al, 2019; Kobayashi, 2018; Kouketsu et al, 2011; Purkey & Johnson, 2010). There they feed the bottom limb of the Meridional Overturning Circulation (MOC; Ganachaud & Wunsch, 2000; Lumpkin & Speer, 2007; Sloyan & Rintoul, 2001; Talley, 2003) and fill the bottom half of the global ocean (Johnson, 2008)

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