Nearshore transport processes in San José Gulf, Southwestern Atlantic

Abstract

This paper reports on the occurrence of coastal processes in the San José Gulf (SJG), a semi-enclosed basin in the Southwest Atlantic Ocean. A topographic front divides the SJG into two hydrographic domains: western (vertically homogeneous) and eastern (stratified) during the austral spring and summer. Associated with this area, the processes that transport plankton and nutrients nearshore were analyzed using seawater temperature data recorded at different depths, wind and tidal height time series. The analyzed processes include small-scale upwelling and downwelling, and internal waves, all of which contribute to water mass advection and exchange within the gulf. To detect upwelling and downwelling events, surface and bottom temperatures were recorded in the eastern domain of the gulf during the summer of 2015?2016. Internal waves were identified using moorings, each with eight thermistors. The wind plays a key role in the movements of coastal water masses. Small-scale downwelling and upwelling events were associated with southerly and northerly winds, respectively, leading to warming or cooling of the water column within a matter of hours. High-frequency internal waves were often associated with changes in wind intensity or direction; however, during periods of low winds, some internal wave events were observed during flood tides. The coupling between wind and tides may perturb the thermocline and trigger the generation and propagation of internal waves, highlighting the potential role in the transport of plankton and nutrients into the eastern domain.