Variations of Subpolar Ocean Gyres Observed by the GRACE Time-Variable Gravity: Antarctic Ross/Weddell and Arctic Beaufort Gyres

The mesoscale ocean gyres within polar oceans, including Ross Gyre (RG), Weddell Gyre (WG) and Beaufort Gyre (BG), are important features of the polar climate and ocean systems. However, they are not well observed by satellite altimetry because of their high latitudes and wintertime sea-ice coverage. We employ the GRACE satellite’s time-variable gravity (TVG) dataset from the Centre National d'Etudes Spatiales/Groupe de Recherches de Géodésie Spatiale (CNES/GRGS) Release 03 solutions at nominal 10-day sampling between July 2002 to June 2016, to investigate the non-seasonal and high-frequency variations of the three gyres, a feat demonstrated in a previous work by Yu and Chao (2018) for studying the Argentine Gyre. We solve the empirical orthogonal functions (EOF) and confirm their barotropic structure and find the sea level variations in the RG and WG are strongly correlated with the Antarctic Oscillation (AAO) and the El Nino-Southern Oscillation (ENSO), and that in the BG is correlated with salinity changes and ENSO. Different from the Argentine Gyre, there are no short-period oscillations of dipole pattern within the three subpolar gyres based on the complex EOF (CEOF) analysis from GRACE data. The fact that GRACE does observe these signals, while the de-aliasing background ocean model (whose predictions were removed before-hand in the employed GRACE data) fails to, ascertains that GRACE TVG data can shed light on the ocean gyre variabilities unavailable by satellite altimetry and at spatial and temporal resolutions higher than practiced hitherto.