The Todos os Santos Bay (TSB) is the second largest coastal bay in Brazil, with an area of approximately 1270 km 2. The tides in the bay are semidiurnal, with a mean range of 2 m, and a slight distortion that favors stronger ebb-tidal currents. The bay average depth, volume and tidal prism are 5.2 m, 12.5 x 109 m3, 3.36 x109 m3, respectively, and average fresh water input from all catchments is calculated as 111.10 m3/s. Fresh water discharge is three orders of magnitude smaller than the estimated average spring-tidal discharge at the bay mouth (1.30 x 105 m3/s). Under these circumstances, mixing of the water column appears to be effective throughout the year. Based on a massive data collection campaigns during two different seasons (summer and winter), a characterization of the circulation of TSB and its interaction with the associated continental shelf is provided. The hydrographic data collected during each season includes 17 current-meter stations (involving the deployment of 27 mechanical and electromagnetic current meters, as well as 2 ADCPs), 8 tide-gauging stations, 3 wind-gauging stations and 12 water-column profiling stations (CTD samplings during 1 spring and 1 neap tidal cycle).
Currents inside the TSB are tidal driven, with average values between 10-30 cm/s, and residual velocities varying from 1-4 cm/s. The residual currents directed landward in the low water column may help to explain an extensive deposition of a several meters thick layer of mud in the shallower, inner half of the bay, where a turbidity maximum zone might exist. Outside the TSB, the inner shelf stations show higher values of residual velocities (4-14 cm/s) as well as a change in direction depending on the season, which indicates the influence of other forcing mechanisms in the area. Temperature and salinity gradients between the adjacent shelf and the innermost region of TSB can be as high as 2.7ZC and 3.6 psu respectively and according to the season.
Based on all the data available, the Princeton Ocean Model was run in its three-dimensional model, and a comparison of the results from the in situ data and the numerical simulations is presented as part of this oceanographic characterization. |
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