Isotopic evidence for an intensified hydrological cycle in the Indian sector of the Southern Ocean

Abstract The hydrological cycle is expected to intensify in a warming climate. However, observational evidence of such changes in the Southern Ocean is difficult to obtain due to sparse measurements and a complex superposition of changes in precipitation, sea ice, and glacial meltwater. We here disentangle these signals using a unique dataset of salinity and seawater oxygen isotope observations collected in the Indian sector of the Southern Ocean. Our results show that the atmospheric water cycle has intensified in this region between 1993 and 2021, increasing the salinity in subtropical surface waters by 0.07 g kg-1 per decade, and decreasing it in subpolar surface waters by -0.028 g kg-1 per decade. In the subpolar region, this salinity decrease is countered by a salinity increase of 0.008 g kg-1 per decade from reduced sea ice melt, and enhanced by a salinity decrease of -0.005 g kg-1 per decade from increased glacial melt. These changes extend the growing evidence for an acceleration of the atmospheric water cycle and a melting cryosphere that can be expected from global warming.