| Summary: | The global ocean plays a major role in moderating atmospheric temperature rise, thereby buffering climate change. Amongst the various oceanic regions undergoing warming, the Southern Ocean is a primary heat sink in the climate system. Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) are the dominant water masses in the upper Southern Ocean, and play a fundamental role in ocean ventilation and the uptake of heat and carbon into the ocean interior. This talk will first focus on understanding the geographic variability in the formation of SAMW and AAIW in the Southern Ocean based on a volume budget analysis, as well as the advection of heat and freshwater by SAMW and AAIW along the Antarctic Circumpolar Current (ACC), using observationally based hydrographic and eddy diffusivity datasets. Our results suggest that the distribution of SAMW and AAIW is set by their formation due to subduction and mesoscale and small-scale turbulent mixing, which shows strong regional variability with hotspots of large subduction and water-mass transformation. Their circulation eastward along the ACC transports temperature and salinity anomalies and preconditions the mixed-layer formation further downstream in the ACC. To better understand how and where the anthropogenic heat is stored in the world ocean, we further analyzed the warming of a set of regional mode and intermediate waters over the subtropical oceans and in the Southern Ocean. Warming of these mode and intermediate waters explains nearly half net global ocean warming during the Argo era, despite occupying just 24% of the total ocean volume.
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