Synchronous intensification and warming of Antarctic Bottom Water outflow from the Weddell Gyre

Antarctic Bottom Water (AABW), the densest water in the global overturning circulation, has warmed in recent decades, most notably in the Atlantic. Time series recorded within the boundary currents immediately upstream and downstream of the most significant outflow of AABW from the Weddell Sea indicate that raised outflow temperatures are synchronous with stronger boundary current flows. These changes occur rapidly in response to changes in wind forcing, suggesting that barotropic dynamics and the response of the bottom Ekman layer are significant. The observed synchronicity indicates that the previously-detected weakening of the export of the colder forms of AABW from the Weddell Sea need not be associated with a reduction in the total flux of AABW exported via this route. These points need careful consideration when attributing the observed AABW warming in the Atlantic, and when determining its contribution to global heat budgets and sea level rise.

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