Using MODIS True-Color 250 m Remote Sensing Data to Assess Interannual Variability of Suspended Matter over Southeastern Brazilian Continental Shelf

Abstract:

Continental shelf is the final destination of terrigenous sediments drained by rivers and estuaries, forming a mass of water drifting over the shelf due to its differential density from underlaying salty oceanic waters, forming a coastal plume. On the Southeastern Brazilian Continental Shelf, Cabo Frio region represents the limit between Santos and Campos basin oil reserves. The continental drainage in this area is not expressive, nevertheless presents a complex interaction between the western boundary Brazil Current (BC) and shelf border mechanisms providing amid-shelf intrusion and a coastal upwelling of South Atlantic Central Water (SACW) over the shelf. Satellite images of the region shows expressive shelf plumes with sedimentary contributions from Paraiba do Sul river located approximately 180 km northward of Cabo Frio, as well as from Guanabara bay, located 150 km westward of Cabo Frio. In order to understand the role of plumes in sedimentary processes over the continental shelf, this study analyzed 10 years of MODIS true-color 250 m remote sensing data in order to understand the temporal variability of the shelf front and the area of plumes. The remote data were obtained from the Aerosol Robotic Network and USDA Foreign Agricultural Service subsets. Selected 17% of daily images were cloud-free to allow shelf plumes to be delimited and processed to enhancement of features as well as land masking, geo-referencing, and daily area calculation on pixel basis. During austral winter (dry season) the plumes get its maximum extension in area over the shelf, suggesting that the mechanism of sediment transport is connected with high energetic wave-wind interactions on the coast followed by wind-driven dispersion less than continental drainage. The interannual pattern shows a general decreasing trend, mainly in the last 4 years, associated with sediment availability on the inner shelf, which is driven by river discharge during the austral summer (rain season). We also calculated the spatial probability function of the plume front on the shelf showing the areas were high contrast between clear oceanic waters and sediment rich plume waters can be found. The region corresponds to deposition centers of fine sedimentary material on the shelf, which corroborates our hypothesis.