Regionalisation of the physical and biogeochemical environment in the Southern Indian Ocean

Physical regionalisations have been previously performed at the global scale to define biogeochemical provinces from surface data or in the mesopelagic zone. However, these regionalisations often lack finer-scale separations as they do not always consider regional patterns such as island effects or physically dynamic zones. Our study aimed to overcome these limitations by defining coherent bio-physical regions within the Southern Indian Ocean (20°W-160°E; 30°S-60°S), considering both spatial and temporal dynamics of environmental parameters. For this purpose, two complementary approaches have been used: one focusing on surface environmental data, and the other considering their vertical profiles. The first method, based on multivariate analyses, allowed us to delineate regions latitudinally due to the existing temperature and oxygen concentration gradient and revealed finer-scale structures such as regions of high turbulence or productive areas. The second approach used functional analyses and provided an additional subdivision in the subtropical zone driven by the mesopelagic domain. This subdivision results from temperature differences. It separates longitudinally the subtropical region with warmer waters found in the western area, likely transported from lower latitudes by the Agulhas Return Current.