Schulzki, Tobias G. , Schwarzkopf, Franziska U. and Biastoch, Arne (2024) Atlantic meridional overturning response to increased Southern Ocean wind stress in a climate model with an eddy-rich ocean. Journal of Climate . DOI 10.1175/JCLI-D-23-0727.1.

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Abstract

The Southern Hemisphere westerly winds experienced significant changes over recent decades and are projected to further strengthen, altering ocean hydrography and dynamics. While anomalies of Southern Hemisphere origin are hypothesised to impact the Atlantic Meridional Overturning Circulation (AMOC), many details of this relationship remain unknown as previous modelling studies are limited by the application of forced, coarse resolution ocean models, or a short integration length. Here a coupled, nested climate model configuration, covering the Atlantic Ocean at an eddy-rich 1/10° resolution is applied to study the adjustment of the large-scale circulation to a 30% increase of the Southern Ocean wind stress. The AMOC responds to the stronger wind stress with a strengthening of 0.6 to 1.4 Sv across the entire Atlantic after approximately 80 years. At that time, anomalous watermass transformation mainly occurs at the entry into the Nordic Seas. A density anomaly in the overflow water then induces anomalous sinking in the eastern subpolar gyre, providing a link between AMOC changes in density and depth coordinates. Our study suggests that these watermass changes are caused by northward propagating anomalies and provides a detailed hypothesis for the link between the Indian Ocean inflow via Agulhas leakage and the AMOC. Nevertheless, due to coupled ocean-atmosphere adjustments, anomalies do not simply follow the main volume transport pathways along the western boundary. Mixing between advectively transported and locally forced anomalies leads to an increasingly complex evolution of watermass anomalies and less certainty in the relative contributions of involved mechanisms towards subpolar latitudes.

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