On the relationship between the Weddell Polynya and Antarctic Bottom Water trends

Abstract

Satellite microwave observations of Antarctic sea ice started in 1973, just in time to capture a massive open water area enclosed in winter sea ice in the Weddell Sea, known as the Weddell Polynya. This polynya was roughly the size of the United Kingdom and it lasted through the winters of 1974–76 with observed ocean mixed layer depths exceeding 3000 m. This study evaluates the impacts of the 1970s Weddell Polynya on Antarctic Bottom Water trends and volume transports. We use two global ocean simulations at eddying resolutions to create polynyas similar in size and duration to the Weddell Polynya. These are initiated with a brief, localized wind perturbation near Maud Rise. A comparison of simulated water-mass trends to available full-depth hydrographic data reveals that warming and oxygen decline in the bottom layers in the Weddell and Scotia Seas can be explained by a multidecadal recovery from the Weddell Polynya that continues today. The observed decline of Antarctic Bottom Water (AABW) outflow from the Scotia Sea since the 1990s can also be attributed to the multidecadal recovery from a large spike in abyssal transport created by the polynya. However, the model simulations do not show a substantial change in the Antarctic Circumpolar Current transport or lower cell overturning transports north of the South Scotia Ridge, and the water-mass trends do not substantially propagate north of ∼55°S in the Atlantic sector. Recently observed bottom water trends in the Pacific and East Indian sector of the Southern Ocean are likely controlled by factors other than the Weddell Polynya, such as increased glacial melt.

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ORCID for Alessandro Silvano: orcid.org/0000-0002-6441-1496

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