2020 Articles

Interannual variability of the outflow of Weddell Sea Bottom Water

Gordon, Arnold L.; Huber, Bruce A.; Abrahamsen, E. Povi

The 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.

Plain Language Summary: The Weddell Sea Bottom Water (WSBW) emanating from the western Weddell Sea impacts the characteristics of the Antarctic Bottom Water that ventilates the deep ocean. From 2014 to 2017 the WSBW attained its lowest salinity values since we began monitoring the outflow in 1999. We present evidence that the change was a consequence of a wind‐induced spin‐up of the Weddell Gyre, which increased intensity of the western boundary current of the Weddell Sea enabled relatively low salinity winter surface layer water to descend into the bottom layer, through the thermobaric effect. Since 2017 the salinity of the WSBW returned to the long‐term average, as the wind stress forcing relaxed.