Seasonal and inter-annual dynamics of suspended sediment at the mouth of the Amazon river: The role of continental and oceanic forcing, and implications for coastal geomorphology and mud bank formation. (15th April 2016)

• Record Type: Journal Article
• Authors: Gensac, Erwan; Martinez, Jean-Michel; Vantrepotte, Vincent; Anthony, Edward J.
• Is Part Of: Continental shelf research. Volume 118(2016)
• Page Start: 49
• Page End: 62
• Publication Date: 2016-04-15
• Subjects: MODIS -- Amazon River mouth -- Shallow coastal waters -- Surface suspended sediment concentration -- Mud banks -- Estuarine processes; Continental shelf -- Periodicals; Submarine geology -- Periodicals; 551.41
• DOI: 10.1016/j.csr.2016.02.009
• Languages: English
• ISSNs: 0278-4343

Abstract

Abstract: Fine-grained sediments supplied to the Ocean by the Amazon River and their transport under the influence of continental and oceanic forcing drives the geomorphic change along the 1500 km-long coast northward to the Orinoco River delta. The aim of this study is to give an encompassing view of the sediment dynamics in the shallow coastal waters from the Amazon River mouth to the Capes region (northern part of the Amapa region of Brazil and eastern part of French Guiana), where large mud banks are formed. Mud banks are the overarching features in the dynamics of the Amazon-Orinoco coast. They start migrating northward in the Capes region. Suspended Particulate Matter (SPM) concentrations were calculated from satellite products (MODIS Aqua and Terra) acquired over the period 2000–2013. The Census-X11 decomposition method used to discriminate short-term, seasonal and long-term time components of the SPM variability has rendered possible a robust analysis of the impact of continental and oceanic forcing. Continental forcing agents considered are the Amazon River water discharge, SPM concentration and sediment discharge. Oceanic forcing comprises modelled data of wind speed and direction, wave height and direction, and currents. A 150 km-long area of accretion is detected at Cabo Norte that may be linked with a reported increase in the river's sediment discharge concurrent with the satellite data study period. We also assess the rate of mud bank migration north of Cabo Norte, and highlight its variability. Although we confirm a 2 km y −1 migration rate, in agreement with other authors, we show that this velocity may be up to 5 km y −1 along the Cabo Orange region, and we highlight the effect of water discharge by major rivers debouching on this coastal mud belt in modulating such rates. Finally, we propose a refined sediment transport pattern map of the region based on our results and of previous studies in the area such as the AMASSEDS programme, and discuss the relationship between sediment transport and accumulation patterns and the coastal geomorphology of this region. Highlights: We analyse SPM variability from the Amazon River mouth to French Guiana. We link coastal sediment transport to the sediment dynamics of two major shoals. We highlight the influence of continental and oceanic forcing on shoals. We identify areas of sediment accumulation from 2000 to 2013. We highlight the effect of major rivers in modulating mud bank migration rates.