Decadal thermal variability of the upper Southern Ocean: Zonal asymmetry

As the major sink of anthropogenic heat, the Southern Ocean has shown quasi -symmetric, deep -reaching warming since the mid -twentieth century. In comparison, the shorter -term heat storage pattern of the Southern Ocean is more complex and has notable impacts on regional climate and marine ecosystems. By analyzing observational datasets and climate model simulations, this study reveals that the Southern Ocean exhibits prominent decadal ( . 8 years) variability extending to ; 700-m depth and is characterized by out -of -phase changes in the Paci fi c and Atlantic - Indian Ocean sectors. Changes in the Paci fi c sector are larger in magnitude than those in the Atlantic - Indian Ocean sectors and dominate the total heat storage of the Southern Ocean on decadal time scales. Instead of heat uptake through surface heat fl uxes, these asymmetric variations arise primarily from wind -driven heat redistribution. Pacemaker and preindustrial simulations of the Community Earth System Model version 1 (CESM1) suggest that these variations in Southern Ocean winds arise primarily from natural variability of the tropical Paci fi c, as represented by the interdecadal Paci fi c oscillation (IPO). Through atmospheric teleconnection, the positive phase of the IPO gives rise to higher -than -normal sea level pressure and anticyclonic wind anomalies in the 50 degrees - 70 degrees S band of the Paci fi c sector. These winds lead to warming of 0 - 700 m by driving the convergence of warm water. The opposite processes, involving cyclonic winds and upper -layer divergence, occur in the Atlantic - Indian Ocean sector. These fi ndings aid our understanding of the time -varying heat storage of the Southern Ocean and provide useful implications on initialized decadal climate prediction.