Wave-driven sediment mobility on the Eastern Brazilian shelf under different weather systems

On micro-tidal continental shelves, waves have been considered the main mechanism responsible for bottom sediment resuspension. In order to study the wave-driven sediment mobility under different weather systems on the Espirito Santo Continental Shelf, located on the Eastern Brazilian shelf, the wave-driven bottom shear stresses were compared to the critical bottom shear stress. While the first was calculated from results obtained by the SWAN wave model, the latter considered the heterogeneity of the sediment grain size. The results showed that waves driven by the local action of Transient Systems and waves driven by remote influence of these systems associated with the local influence of South Atlantic Subtropical Anticyclone are responsible for the highest percentages of sediment mobility on the shelf. These waves are characterized by mean wave direction from the south and southeast, with increased significant wave height and peak periods. Moreover, these waves were associated with higher bottom shear stresses than waves from north, northeast, and east (CM1 and CM4), with the highest differences occurring on the middle and outer shelf, mainly to the south of the Doce River mouth. The spatial distribution of the grain size also strongly influenced sediment mobility patterns, delimiting a less energetic region between the Espirito Santo Bay mouth and the Costa das Algas Marine Protected Area southern limit, and a more energetic region between Costa das Algas Marine Protected Area southern limit and the northern limit of the study area. The findings herein, besides providing information relevant to marine environment management, highlight the importance of including the grain size spatial heterogeneity in studies of sediment resuspension on continental shelves.

Automated summary

The study on the Espirito Santo Continental Shelf in Brazil found that waves driven by the local and remote influences of the South Atlantic Subtropical Anticyclone are responsible for the highest sediment mobility percentages, characterized by waves from the south and southeast with increased wave height and peak periods. The spatial distribution of grain size strongly influences sediment mobility patterns, creating regions of different energy levels on the shelf.