The Earth's wet tropical regions form a band around the equator that comprises less than a quarter of the land surface but supplies more than half of the water, particulates, and solutes discharged to the marine environment. Processes operating in the drainage basins and near the mouths of tropical rivers control the quantity and quality of the water, particulates, and solutes that escape to the global ocean. These processes, which can also draw oceanic constituents to coastal areas and trap them, differ from those in temperate and polar settings.
The wet tropics extend about 15° on either side of the equator (Figure 1). Three areas comprise this region: northeastern South America, west-central Africa, and the Indo-Pacific archipelago, including parts of southeast Asia. Geographic differences of these areas influence local coastal processes, but they all experience constantly high precipitation greater than 1500 mm y-1 and temperature above 20°C. The coastal oceans in these locations have other factors in common (Table 1), such as high solar radiation, large freshwater runoff, easterly trade winds, and weak Coriolis force. The enormous water, particulate, and solute discharges also lead to extensive buoyant plumes, large nutrient fluxes, high productivity, and rapid sediment accumulation (Table 1).