WEATHERING AND GLOBAL DENUDATION

A negative correlation between sediment yield and weathering history, as measured by the chemical alteration (CIA) of the suspended sediment, is observed for many of the world's major rivers and other regions of denudation. The weathering history is a first-order control on the sediment yield of such areas, termed equilibrium denudation regions. For other areas, data scatter with either apparent increases or decreases of sediment yield for given CIA values. These areas are termed nonequilibrium denudation regions. Low sediment yields can be attributed to moderated erosion (either natural or human induced) and/or the incorporation of unweathered glacial debris. Accelerated erosion, resulting in high sediment yield, is primarily human-induced and results from cultivation and other land use. Each of these effects has a profound influence on global sediment discharge from the continents. Pre-human suspended sediment discharge from the continents is estimated to be 12.6 x 10(15) g/yr or about 0.6 the present discharge.