The Weddell Sea, a semi-enclosed basin to the east of the Antarctic Peninsula, plays a crucial role in the global climate system as it hosts some of the most important sites of Antarctic Bottom Water formation. Dense bottom waters fill ocean abyss and are thought to influence the ocean circulation over timescales from centuries to millennia. Approximately 60% of bottom water is formed in the Weddell basin. The rate at which this dense water is exported to the open ocean is controlled by the strength of the Weddell Gyre, a cyclonic circulation that dense waters must traverse if they are to escape their formation regions.

To date, a large number of studies have sought to show that the observed seasonal variability of the Weddell gyre is controlled by variations in surface wind forcing. Here, we take a contrary view and provide evidence from a relatively new and unprecedented  database of under-ice hydrographic observations that Weddell gyre variability is potentially controlled by surface buoyancy fluxes, particularly salt and freshwater fluxes likely associated with  seasonal sea ice formation and melt. Our results imply that complex interactions between oceans, sea ice and the atmosphere are capable of driving significant ocean circulation variability with implications for the climate system.