Sources and sinks of sediment to the Amazon margin: The Amapa coast

Modern and Holocene muddy strata were studied along the shoreline adjacent to the Amazon river mouth using sedimentological, radiochemical, physical, and seismic methods. The present paper is a synthesis of the results, collected during the AmasSeds project, that is used to outline a regional shoreline sediment budget. Erosion of relict Amazon muds in southern Amapa supplies 10(6) tons yr(-1) to the Amazon advective mud stream. Local rivers are sediment-poor (total suspended discharge similar to 1 x 10(6) tons yr(-1)), but form depositional sandflats on the shoreface downdrift of the river mouths. Mudflat accumulation in northern Amapa sequesters 10(6)-10(7) tons yr(-1) by tidal-flat aggradation, alongshore mudcape accretion, and sediment trapping by mangroves. The processes temporarily store 1.5 x 10(8) tons of Amazon mud in January-June.