Water mass transformation variability in the Weddell Sea in ocean reanalyses

Abstract. This study investigates the variability of water mass transformation (WMT) within Weddell Gyre (WG). The WG serves as a pivotal site for Meridional Overturning Circulation (MOC) and ocean ventilation because it is primary origin largest volume in global ocean: Antarctic Bottom Water (AABW). Recent mooring data suggest substantial seasonal interannual AABW properties exiting WG, studies have linked to large-scale climate forcings affecting wind stress region. However, specific thermodynamic mechanisms that link surface transformations export remain unclear. explores how current state-of-the-art data-assimilating reanalyses can help fill gaps our understanding drivers via WMT budgets derived from Walin's classic framework. three used are following: Estimating Climate Ocean state estimate (ECCOv4), Southern State Estimate (SOSE) Simple Data Assimilation (SODA). From model outputs, we diagnose closed form budget explicitly accounts transport across boundary, forcing, interior mixing numerical mixing. We examine annual mean climatology terms, finally variability. Our finding suggests relatively coarse resolution these models did not realistically capture formation, In ECCO SOSE, see strong budget. find an accelerating loss during 2005–2010, driven largely by changes salt fluxes. shows similar trend 4-year time period starting late 2007 but also reveals such trends be part over much longer period. Overall, provides most useful series processes drive WG. SODA, contrast, displays unphysically large volume, which attribute its assimilation scheme. correlations between indices, including El Niño–Southern Oscillation (ENSO) Annular Mode (SAM), no relationships.