Impact of Antarctic Ice Sheet Melting on the Abyssal Southern Ocean

Abstract:

Antarctic Bottom Water (AABW) is the coldest, densest and deepest water mass of the Global Ocean. Formation and renewal of AABW regulate the lower limb of the global overturning circulation, determining the oceanic ability to sequester heat and carbon in the abyss for centuries. Here we show observations from the entire Southern Ocean collected over multiple decades to study the temporal variability of AABW formation and associated drivers. We show that in "warm regions" (e.g. Amundsen Sea) rapid melting of the Antarctic Ice Sheet prevents AABW formation, generating a positive feedback of warming and freshening. In cold regions (e.g. Ross Sea) decadal variability in ice-sheet melting regulates AABW properties. Our observations provide direct evidence that an increase in Antarctic Ice Sheet melting as projected under sustained anthropogenic forcing can cause a dramatic reduction in AABW formation. Further, our observational results highlight that models coupling ocean and ice sheet are required to predict future changes in the lower limb of the global overturning circulation.