What Controls the Formation of Antarctic Bottom Water at Cape Darnley, East Antarctica?

Abstract Antarctic Bottom Water (AABW), formed from Dense Shelf Water (DSW) in Antarctic coastal polynyas, partly drives the global overturning circulation. Cape Darnley Polynya in East Antarctica, the most recently‐identified AABW formation site, remains poorly understood. We present simulations of the Cape Darnley region quantifying the main processes responsible for forming DSW and identify two key, opposing influences. Wintertime DSW export from Cape Darnley—mean of m 3 s −1 (0.28 Sv)—is suppressed by basal melting of the Amery Ice Shelf, but enhanced by cold, saline preconditioning from Mackenzie Polynya. A doubling of Amery Ice Shelf melting reduces export to 0.26 Sv (7.0% decrease), while a shutdown of Mackenzie Polynya reduces DSW export to 0.18 Sv (a 36% decrease). Our findings reveal the sensitivity of DSW formation at Cape Darnley to oceanic and glaciological conditions, with implications for future AABW production, the global overturning circulation, and climate.