Interannual Variability of the Outflow of Weddell Sea Bottom Water

Arnold L Gordon,Bruce A Huber,E Povl Abrahamsen

doi:10.1029/2020gl087014

Abstract

AbstractThe Weddell Sea Bottom Water (WSBW) export from 1999 to 2019 displays distinct seasonal and interannual variability. From 2014 into 2017 a marked salinity decrease was recorded, with the lowest salinity, 34.615, attained in early 2016. The reduced salinity is derived from the V‐shaped trough formed by a double front along the shelf break of the Weddell Gyre's western boundary, which is filled with a blend of surface water and modified Weddell Deep Water. We estimate that when the V‐shaped apex attains a depth of greater than ~700 m, the thermobaric effect promotes its descent into the WSBW. We propose that this occurred during anomalously strong cyclonic wind stress curl over the Weddell Gyre from 2014 into 2017, which increased the intensity of the gyre and its western boundary current, deepening the V‐shape trough. The WSBW salinity increased to its prior to 2014 values as the wind stress relaxed in 2018.

Highlights

The Southern Ocean circulation is far from zonally symmetric, since the Antarctic Circumpolar Current (ACC) shifts in latitude in response to the wind patterns and to sea floor morphology, as it encircles Antarctica
The ACC northward displacement is greatest in the Atlantic Ocean sector, which enables the development of the large cyclonic Weddell Gyre, driven by the wind stress curl induced by the westerlies near the ACC and the easterlies along the Antarctic margin (Vernet et al, 2019)
Warm, salty Circumpolar Deep Water of the ACC enters the eastern limb of the Weddell Gyre, forming Weddell Deep Water (WDW), capped by the AASW

Summary

Introduction

The Southern Ocean circulation is far from zonally symmetric, since the Antarctic Circumpolar Current (ACC) shifts in latitude in response to the wind patterns and to sea floor morphology, as it encircles Antarctica. At various sites along margins of Antarctica dense shelf water feeds into the Antarctic Bottom Water (AABW) spreading into the world ocean (Legg et al, 2009; Orsi et al, 1999, 2001, 2002; Purkey & Johnson, 2013; Purkey et al, 2018; Stewart & Thompson, 2013). Warm, salty Circumpolar Deep Water of the ACC enters the eastern limb of the Weddell Gyre, forming Weddell Deep Water (WDW), capped by the AASW. Through various pathways the WDW feeds into the formation of dense precursors of AABW along the continental margins of the Weddell Sea through processes including heat and freshwater exchange with the atmosphere and ice shelves.

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