Mesoscale, Tidal, and Seasonal/Interannual Drivers of the Weddell Sea Overturning Circulation

Abstract

Abstract The Weddell Sea supplies 40%–50% of the Antarctic Bottom Water that fills the global ocean abyss, and therefore exerts significant influence over global circulation and climate. Previous studies have identified a range of different processes that may contribute to dense shelf water (DSW) formation and export on the southern Weddell Sea continental shelf. However, the relative importance of these processes has not been quantified, which hampers prioritization of observational deployments and development of model parameterizations in this region. In this study a high-resolution (1/12°) regional model of the southern Weddell Sea is used to quantify the overturning circulation and decompose it into contributions due to multiannual mean flows, seasonal/interannual variability, tides, and other submonthly variability. It is shown that tides primarily influence the overturning by changing the melt rate of the Filchner–Ronne Ice Shelf (FRIS). The resulting ∼0.2 Sv (1 Sv ≡ 106 m3 s−1) decrease in DSW transport is comparable to the magnitude of the overturning in the FRIS cavity, but small compared to DSW export across the continental shelf break. Seasonal/interannual fluctuations exert a modest influence on the overturning circulation due to the relatively short (8-yr) analysis period. Analysis of the transient energy budget indicates that the nontidal, submonthly variability is primarily baroclinically generated eddies associated with dense overflows. These eddies play a comparable role to the mean flow in exporting dense shelf waters across the continental shelf break, and account for 100% of the transfer of heat onto the continental shelf. The eddy component of the overturning is sensitive to model resolution, decreasing by a factor of ∼2 as the horizontal grid spacing is refined from 1/3° to 1/12°.