Oral

IAPSO

JMP04 - Antarctic Bottom Water formation, variability and trends

Emerging outflow of not-so-dense shelf water from an East Antarctic polynya

East Antarctic coastal polynyas play a vital role in Antarctic Bottom Water (AABW) formation, redistributing heat and carbon globally. The Dibble Polynya, off Wilkes Land, has significant sea ice production yet the characteristics of shelf water here, and its influence on offshore AABW, have not been reported. We present the first observational evidence of Dense Shelf Water (DSW) outflow from the Dibble Polynya, which ventilates a lighter variety of local AABW. Hydrographic data show DSW formation has persisted for more than 30 years, consistent with stable sea ice production based on satellite measurements. The cross-slope AABW salinity gradient off the Dibble Polynya has decreased since the 2010s, following a significant drop in sea ice production in the eastern Mertz Polynya due to major icescape changes. Concurrently, the westward velocity of the Antarctic Slope Current off the Mertz Polynya has reduced. These findings suggest that recent DSW outflows from the Dibble Polynya are advantaged by the reduction in upstream AABW, which decreases momentum input to the Antarctic Slope Current. Changing shelf water outflows from mid-sized polynyas warrant particular attention since the densest layers of AABW are diminishing in a warming climate.