Lagrangian tracking of Pleuragramma antarctica in the Ross Sea using a circulation model of the Southern Ocean (PARSOM)

As part of the BIOCLEVER project and of the IPSODES project of the Progetto Nazionale di Ricerche in Antartide (PNRA), the sigma-coordinate ocean circulation model Parthenope University Southern Ocean Model (PARSOM) is coupled with a Lagrangian particle tracking algorithm to perform forward and backward mode simulations in the summer season to determine the possible path of the different stages of Pleuragramma antarctica sampled at 22 stations located between Terranova Bay and Whale Bay in the Ross Sea (RS). The RS is the second largest source of Antarctic Bottom Water (AABW) that supplies the lower limb of the global overturning circulation and ventilates the abyssal ocean. Dense Shelf Waters, precursor of the AABW, form on the RS continental shelf in winter by cooling and brine releasing during sea ice formation processes. The local circulation is influenced by the Ross Gyre, which regulates the proximity of the relatively warm waters of the Antarctic Circumpolar Current to the continental shelf. PARSOM the includes the whole Southern Ocean with a latitudinal extension ranging from 30° S to 80° S, so that no spurious lateral boundaries affect the RS internal response. The bathymetry is derived from the GEBCO dataset, the momentum flux and total heat fluxes (i.e. the sum of the latent and sensible heat and long wave radiation fluxes) are provided by the ECMWF ERA5 reanalysis and the initialization and relaxation to climatology are based on the World Ocean Atlas 2009 dataset.

PARSOM simulates the dynamics of the RG, and the results show a significant weakening during the summer of 2015. We investigate the relationships with local wind-driven and large-scale circulation. It was found that, in 2015, the northern branch of the RG, which interacts with the ACC, showed intensification, leading to a reduction in both the intensity and the eastward extension of the gyre itself.