Variability of the Sub‐Antarctic Mode Water Subduction Rate During the Argo Period

Abstract

AbstractBoth a quasi‐biennial variability and an overall linearly increasing trend are identified in the Sub‐Antarctic Mode Water (SAMW) subduction rate across the Southern Hemisphere ocean, using the Argo data during 2005–2019. The quasi‐biennial variability is mainly due to variability of the mixed layer depth. Variability of wind stress curl in the SAMW formation regions associated with the Southern Annular Mode plays a critical role in generating the quasi‐biennial variability of the mixed layer depth and consequently the SAMW subduction rates. The SAMW subduction rate across the Southern Hemisphere ocean, long‐term mean totaling 56 Sv, has increased at 0.73 ± 0.65 Sv year−1 over the past 15 years. The increase has directly contributed to the observed increase in the total SAMW volume. Much of this increasing trend can be explained by the deepening mixed layers, which in turn are primarily forced by the strengthening westerly winds under an increasing Southern Annular Mode.