Dynamics of riverplumes in the South Brazilian Bight and South Brazil

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إنجليزي. The plumes from the rivers of the South Brazilian Bight (SBB) and South Brazil (SB) were studied using a realistic modelconfiguration. River plume variability on continental shelves is driven by the input of river runoff into the shelf, by windvariability, and also by ambient currents and its seasonal variability, especially the Brazil Current, which are realisticallymodelled in this study. It is presented a simulation of 4 years using a nested configuration, which allows resolving the regionaround Florianopolis with very high resolution ( ´ ∼150 m). The dispersion of river plumes was assessed not only with thehydrodynamical model results but also by using passive tracers whose dynamics was analyzed seasonally. Several dyes werereleased together with the river discharges. This approach allowed calculating the depths of the riverine freshwater, andthe resulting regions affected by the plumes. Northward intrusions of waters from the southern region, under the potentialinfluence of the distant La Plata river plume, were evaluated with a Lagrangian approach. The local river plumes are confinedto the inner shelf, except south of 30◦S where discharges from Lagoa dos Patos disperse over the shelf in the spring andsummer. The Brazil Current flowing southward over the slope prevents the river plumes from interaction with oceanicmesoscale dynamics. The river plumes are, thus, mainly controlled by the wind forcing. The plumes from SBB are able todisperse until SB following the southward wind regime typical of the summer. And both the SB and La Plata river plumesare also able to reach SBB, forced by the northward wind typical of the winter season, until the latitude of 25.5◦S. A lowsalinity belt (below 35) is present along the coastal region of SB and SBB year-round, supported by contributions from boththe large and small rivers. The interaction between the different plumes influences the dispersion patterns, shielding theFlorianpolis coastal region from plumes of distant rivers, and dispersing the plume of SBB rivers away from Santa Catarina ´Island as it disperses southward during the summer months