Exposure time and connectivity in the Baía de Todos os Santos, Brazil

Abstract

We applied the Regional Ocean Modeling System (ROMS) to simulate the circulation within Baía de Todos os Santos (BTS). Using lagrangian particle tracking, we performed sensitive studies to compare the importance of the winds (W), tides (T) and fresh water and heat fluxes (FWHF) to the exposure time and connectivity in BTS. We added tracking particles to three sectors of the bay (upper, middle and entrance) and tracked the trajectories for 330 days. The circulation forced exclusively by tides (T) or by winds (W) did not flush all particles from the bay after 330 days. The simultaneous effect of tides and winds (T+W) resulted in an exposure time of 210 days, with particles from the entrance, the middle and the upper sections leaving the bay after 30, 60 and 110 days, respectively. When we added fresh water and heat fluxes plus the riverine discharge to the model (W+T+FW+HF+RV) the exposure time was reduced to 115 days. The interconnection between the entrance and the bay head is small, with less than 10% of the particles released from the entrance reaching the upper bay. Most of the particles released within the bay are advected to the continental shelf southwest of the BTS. Our results show that, differently from what has been previously described, the baroclinic circulation is important for reducing the exposure time. It is expected that the insights gained from this simulation will also be applicable to transport studies of inorganic and organic loads from small bays and river discharges within the BTS.