Attributing low-frequency variations in ocean water mass redistribution during 2002-2020

Studying how ocean water mass is redistributed can help with a better understanding of the regional sea level change. This study investigates the roles of the different physical processes involved in low-frequency ocean water mass, including the sea level fingerprint and the dynamic ocean mass change, from regional to global scales over the period 2004-2021. Global water mass redistribution data from the GRACE and GRACE-FO satellites were used, as well as surface wind and sea surface temperature data from the ERA5 reanalysis. The sea-level equation is used to simulate the sea level fingerprint, and the maximum covariance analysis is used to extract possible signals of the wind-forcing and temperature-gradient-forcing ocean mass redistribution. The results show that the low-frequency ocean water mass is dominated by the long-term trend and the decadal-like fluctuation. Sea level fingerprint significantly contributes to the open ocean. Compared with temperature gradients, wind forcing plays a more important role in dynamic ocean mass redistribution. The wind-forcing dynamic processes significantly drive the anomalies near the North Indian Ocean, North Atlantic Ocean, South Pacific Ocean, and some marginal seas. After removing the sea level fingerprint and ocean dynamics, some non-negligible noise, located in seismic zones, was also found, suggesting the misestimation of seafloor deformation resulting from earthquakes in the GRACE/GRACE-FO data processing. These findings may improve our understanding of the long-term anomalies in regional and global sea levels.