PDFFirst Paragraph
The Amazon shelf is an unusually energetic coastal region. The Amazon River discharges between 80,000 and 250,000 m3 s–1 of fresh water onto the shelf at the equator (Oltman, 1968; Muller-Karger et al., 1988). The resulting surface plume of brackish water extends hundreds of kilometers seaward and northwestward along the coast (e.g., Gibbs, 1970; Milliman et al., 1975; Curtin, 1986a). The North Brazil Current sweeps the waters over the outer shelf and slope northwestward at speeds reaching 1–2 m s–1 (Flagg et al.. 1986; Richardson and Reverdin, 1987). Previous current measurements on the shelf indicate across-shelf tidal velocities of 1–2 m s–1 (Gibbs, 1982; Curtin, 1986b). The persistent trade winds impose a cross-shelf wind stress as large as 1 dyn cm–2 (Picaut et al., 1985). The Amazon River discharge, the North Brazil Current transport, and the trade winds all exhibit strong seasonal cycles (see Figure 3, Nittrouer et al., this issue a). These energetic and highly variable forcing functions result in considerable variability in the hydrographic structure and currents on the Amazon shelf, which in turn lead to marked variations in the transport and fate of sediments and waterborne material. The tremendous flux of suspended sediment is regulated by the structure and energetics of the flow; hence the distribution and deposition of sediments as well as particle-reactive chemicals are intrinsically coupled to the physical oceanographic regime.