Coastal plumes contribution to the suspended sediment transport in the Southwest Atlantic inner continental shelf

Global coastal zones are constantly changing due to the actions of various physical forces. Recent studies show that the supply of suspended sediment of continental origin plays an important role in these changes. Once in the coastal region, this sediment significantly influences the sedimentation process on the inner shelf. Thus, understanding the transport and destination of these suspended sediments is crucial to interpret the morphodynamic evolution of the seabed and biogeochemical processes in the ocean. The Southwest Atlantic Shelf is the largest continental shelf in the Southern Hemisphere and one of the most important in biological production, because of the great continental contribution exercised by both Río de la Plata and Patos Lagoon. Studies in the region showed that these effluents are significantly affected by the El Niño–Southern Oscillation (ENSO) effect, which can interfere with the availability of suspended material inserted into the coastal region. Despite the great efforts of several authors to understand these changes and their interactions with the environment, some questions remain unanswered. Thus, this work aims to fill this gap by answering questions related to the contribution of suspended sediment of continental origin and its behaviour on the Southwest Atlantic Inner Shelf. The behaviour of suspended sediment was investigated in two distinct periods using the hydro-morphodynamic model TELEMAC-3D: one representing normal years, that is, without the effect of ENSO (2005–2006) and the other experiencing the effect of ENSO (2008–2009).The model was calibrated and validated using field data for both studied periods. R esults were based on statistical analysis, such as wavelet and empirical orthogonal function (EOF) analysis, in addition to time series analysis. Results showed that the Southwest Atlantic Inner Shelf is mainly influenced by the fluvial discharge of Río de la Plata and Patos Lagoon, and by the local wind. Río de la Plata is the largest exporter of suspended sediment in the region, with an approximate rate of 1.2 × 10⁸ tons.year^-1 in neutral (normal) years and 3.0 × 10⁸ tons.year^-1 in years under the influence of ENSO. The Patos Lagoon, on the other hand, exports approximately 1.25 × 10⁷ tons.year^-1 in the period without the ENSO effect and 1.35 × 10⁷ tons.year^-1 in the period influenced by ENSO. Results also showed that the fluvial discharge interacts with the suspended sediment in seasonal to interannual scales, while the wind contributes to the concentration of suspended sediment on synoptic scales. Still on the wind regime, results show that the local wind regime gains importance particularly when the suspended sediment reaches the coastal region.