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

East Antarctic coastal polynyas are vital for Antarctic Bottom Water (AABW) formation, thereby redistributing heat and carbon globally. The Dibble Polynya, off Wilkes Land, is recognised for its pronounced sea ice production, yet the properties of shelf water there and its influence on offshore AABW have not been reported. Here we show the first observational evidence of Dense Shelf Water (DSW) outflow from the Dibble Polynya, ventilating a lighter variety of local AABW (28.27–28.30 kg m⁻³ γn). Hydrographic records show DSW formation has persisted for over 50 years, consistent with steady satellite-derived sea ice production since the 1990s. Since the 2010s, cross-slope salinity gradient in AABW downstream of the Dibble Polynya has distinctly weakened, with the nearby Antarctic Slope Front structure modified concurrently. This followed a sharp decline in sea ice production in the neighbouring Mertz Polynya caused by post-2010 icescape changes. Our results suggest DSW outflow recently emerged from the Dibble Polynya is advantaged by the reduction of denser AABW upstream, potentially weakening the Antarctic Slope Current and its barrier to the cross-slope exchange. As the densest AABW layers are rapidly diminishing in a warming climate, not-so-dense shelf water from the mid-sized polynya efficiently ventilates the abyssal basin.