Property balances in the Scotia Sea as deduced from inverse modelling

Abstract

An inverse model (Machín et al., 2006; Wunsch, 1996) is applied to the Scotia Sea (Naveira Garabato et al., 2003) in order to assess the balances of heat, salt, mass and biogeochemical properties in the upper 2000 m of the Antarctic Circumpolar Current (ACC). The circulation model is constructed using hydrographic profiles at the boundaries of the region as obtained from several datasets: SODB (Orsi & Whitworth, 1998), MEOP (Roquet et al., 2014), ESASSI and Argo. The reference velocities at 1000 m are calculated from the drifting of the Argo floats and conditioned with the freshwater fluxes and wind-driven Ekman transports. The model results reveal that the upper Scotia Sea circulation pattem consists mainly of water inputs in the Drake, Phillip and South Scotia Ridge Passages, and outputs through the North Scotia Ridge and Georgia Passages, dominated by the circumpolar deep waters. The ACC mass transports through the different passages are as follows: 154.5±1.6 Sv for the Drake, 105.8 ± 1.4 Sv for the North Sotia Ridge, 53.9±1 Sv for Georgia, 10.8±1.4 Sv for the South Scotia Ridge and 0.9±0.7 Sv for the Phillip. Moreover, the Biogeochemical Southem Ocean State Estimate (B-SOSE) (Verdy & Mazloff, 2017) is used for establishing the dissolved oxygen, nitrate and phosphate concentrations at the boundaries. The fluxes of these properties are hence obtained as the product of velocity times concentration. Using this methodology, the inverse model shows fairly good biogeochemical balances, with total transport inputs of 37021 kmol s-1 for dissolved oxygen, 5007 kmol s-1 for nitrates and 349 kmol s-1 for phosphates, and output transports through the remaining passages of 35779 kmol s-1, 4804 kmol s-1 and 333 kmol s-1, respectively.