Volume Budget of Subantarctic Mode Water in the Southern Ocean From an Ocean General Circulation Model

Abstract

AbstractThe volume budget of Subantarctic Mode Water (SAMW) in the Southern Ocean (SO) is examined using a 0.1° ocean model output from 1950 to 2017. The results show that air–sea buoyancy fluxes, advective exports, and diapycnal mixing are all important to the SAMW volume budget. A climatological mean analysis finds that, for the SO as a whole, water in the SAMW density range ( kg m−3) is balanced between the following: formation due to air–sea buoyancy fluxes ( Sv), removal due to advective export northward out of the SO ( Sv), destruction due to diapycnal mixing ( Sv), and storage ( Sv). Decadal changes in the SAMW volume in the Indian and Pacific sectors display a two‐layer density structure, in which the volumes of the upper and lower layers vary predominantly out of phase with each other. In addition, the SAMW volume changes in the Indian and Pacific sectors appear to compensate each other on decadal time scales. The volume of SAMW in the SO has increased by ∼11% since the 1950s, and this increase tends to emerge gradually from denser to lighter layers. The increased SAMW volume mainly results from a consistent increase in oceanic buoyancy gain over the outcropping area at approximately 27.1 .