Water-Mass Transformation in the Weddell Gyre

Antarctic Bottom Water (AABW) formation plays a key role in the climate system as it provides a pathway for ventilation of abyssal water and transport of nutrients. Recent mooring data suggest substantial seasonal and interannual variability of AABW properties exiting the Weddell Gyre (WG). It is hypothesized that these variabilities are linked to the coupling of large-scale climate forcings, ENSO and SAM, through wind stress variability that leads to the variability in the WG strength and its density structure. However, the precise thermodynamic mechanisms that link variability in surface forcings to AABW export remains unclear.

This study aims to investigate the dynamics and thermodynamics of temporal variability in AABW production through the use of ocean models. Ocean models are a useful tool in studying regions that lack consistent observations, and for investigating physical mechanisms. This study uses the SOSE and ECCOv4 state estimates, which provide a physically consistent solution that is a best fit with available observations. The water-mass-transformation (WMT) framework allows us to attribute changes in water-mass volume to inflow/outflow fluxes and transformation. Transformation can be further decomposed into various components of surface forcing and interior mixing.

Recent observations establishes a connection between the variability of ENSO and SAM coupling, and the variability in AABW export in the WG region. We use time-dependent water-mass budgets constructed from ocean models to assess the mechanisms responsible for seasonal and interannual AABW export variability, and analyze their relationships to climate forcings. We examine correlations between the variability of the WMT and the climate indices, helping to determine what physical mechanisms are responsible for variations in AABW production.