Modelling the interannual variability of Maipo and Rapel river plumes off central Chile

Abstract. River plumes have a direct influence on coastal environments, impacting coastal planktonic and benthic communities, including fishery resources. In general, the main drivers of river plume dynamics are the river discharge and the alongshore wind stress, whereas the tides and topography play a secondary role. In the Central parto of Chile, rivers flowing into the eastern Pacific have a relatively short path on the land, with a high slope; further they are characterized by a mixed snow-rain regime. This study aims to understand the interannual variability of the plumes of the Maipo and Rapel rivers in the Coastal/shelf area off Chile and its influence on local ocean dynamics. We used the Coastal and Regional Ocean Community model (CROCO), with 1 km resolution and 20 sigma levels, to simulate the ocean dynamics of the area over the period 2003–2011. The results show that the plume’s area coverage and coastal ocean salinity are strongly correlated to the river discharges. The predominant southwestern wind controls the plumes orientation toward northwest; however, episodes of wind changing direction from northwest in winter can reverse the plumes direction, making them squeezed to the coast and moving southward. Results also show, for the decade under evaluation, a salification trend linked to the severe droughts hitting Central Chile during the studied period. This salification determines a change in local dynamics.