Warm surface waters increase Antarctic ice shelf melt and delay dense water formation

Melting ice shelves around Antarctica control the massive input of freshwater into the ocean and play an intricate role in global heat redistribution. The Amery Ice Shelf regulates wintertime sea-ice growth and dense shelf water formation. We investigated the role of warm Antarctic Surface Water in ice shelf melting and its impact on dense shelf water. Here we show that the coastal ocean in summer 2016/17 was almost sea-ice free, leading to higher surface water temperatures. The glacial meltwater fraction in surface water was the highest on record, hypothesised to be attributable to anomalous ice shelf melting. The excess heat and freshwater in early 2017 delayed the seasonal evolution of dense shelf water. Focused on ice shelf melting at depth, the importance and impacts of warming surface waters has been overlooked. In a warming climate, increased surface water heating will reduce coastal sea-ice production and potentially Antarctic Bottom Water formation. Excessively warm and fresh surface water along the Amery Ice Shelf, Antarctica, in 2017 led to more ice melt and delayed dense water formation, according to analyses of in situ observations.

Automated summary

Melting ice shelves play a crucial role in the input of freshwater into the ocean and global heat redistribution. In summer 2016/17, the coastal ocean around Antarctica had almost no sea-ice, resulting in higher surface water temperatures. The glacial meltwater fraction in surface water reached a record high, likely due to abnormal ice shelf melting. The excess heat and freshwater delayed the seasonal formation of dense shelf water in early 2017.