Water Mass Transformations Within Antarctic Coastal Polynyas of Prydz Bay from Clustered Drifters

Antarctic Bottom Water (AABW) forms the deepest limb of the meridional overturning circulation (MOC) and is a key control on global exchanges of heat, freshwater, and carbon. Density differences that drive the MOC have their origin, in part, in coastal polynyas. Prydz Bay polynyas in East Antarctica are a key source of Dense Shelf Water (DSW) that feeds AABW to the Atlantic and Indian Oceans. However, several poorly understood mechanisms influence the pathways and change water mass properties of the DSW on its way to the abyss. To better understand these mechanisms, we release Lagrangian particles in a 10 km resolution simulation of the Whole Antarctic Ocean Model and analyze the resulting tracks using novel cluster analysis. Our results highlight the role of mixing with other water masses on the shelf in controlling the fate of DSW and its eventual contribution to AABW. When advected beneath the ice shelf, DSW can mix with fresh Ice Shelf Water (ISW), becoming less dense and making future AABW formation less likely. This study confirms that towards the shelf break along the Antarctic Slope Current, mixing with circumpolar deep water (CDW) forms modified circumpolar deep water (mCDW) and influences DSW export as AABW. Our findings indicate that the pathway from DSW to AABW is sensitive to mixing with ambient waters on the shelf. An important implication is that with future increase in ice shelf melt and CDW warming, AABW production is likely to decline, even if DSW production in coastal polynyas remains constant.