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Abstract

The Southern Hemisphere supergyre connects the Atlantic, Pacific, and Indian basins and is a key pathway in the global overturning circulation. The supergyre properties are investigated in the historical simulation of CMIP6 models and compared to the ECCO reanalysis product. The vertical structure of the supergyre is assessed by calculating strength and position metrics as a function of depth. The study aims to identify how the supergyre metrics at intermediate depths influence the properties and circulation of Antarctic Intermediate Water (AAIW). Results suggest that the connectivity of the supergyre across basins varies strongly with depth and across models. In CMIP6 models, the supergyre appears well-connected through all basins at the surface, via the Indonesian Throughflow and Tasman Leakage. At intermediate depths, CMIP6 models differ, with some CMIP6 models showing a connected supergyre in all three basins whereas other models present a disconnected Pacific basin. In all CMIP6 models, the supergyre becomes increasingly more disconnected with depth. The properties of AAIW (depth, salinity, temperature and density) are calculated at its core location, defined as the position of the vertical salinity minimum. Linkages between AAIW properties and the supergyre at intermediate depths were identified, with the deepest values of AAIW found at the centre of the supergyre. AAIW core properties present reduced variability within the supergyre compared to outside the supergyre. Results suggest that the heterogeneity of AAIW core properties within the supergyre depend on the models representation of the supergyre at intermediate depths.