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

East Antarctic coastal polynyas—semi-permanent areas of ice-free ocean—are vital for sea ice production, Antarctic Bottom Water formation, and global heat redistribution. The Dibble Polynya has pronounced sea-ice production, yet the shelf water properties there and its offshore influence have been unclear. Here we show Dense Shelf Water outflow from the polynya that ventilates a lighter variety of local bottom water. Hydrographic records suggest Dense Shelf Water formation has persisted for 50 years, consistent with satellite-derived sea-ice production since the 1990s. Since the 2010s, the downstream cross-slope salinity gradient within bottom water has weakened and the Antarctic Slope Front has been modified, following a sharp decline in sea-ice production in the neighbouring Mertz Polynya after 2010 icescape changes. We infer that reduced denser Antarctic Bottom Water formation upstream weakens the slope current barrier, promoting outflow of not-so-dense shelf water from the Dibble Polynya that efficiently ventilates the abyssal basin.