Effects of Holocene Climatic Change on some Tropical Geomorphic Processes

Abstract

Man's interference with the landscape process places him in the role of a “paraglacial” agent: He tends to duplicate ice-age stresses such as deforestation, accelerated erosion, and climate alteration. Against a background climatic control dictated by the Milankovich mechanisms, the 10,000-year history of the Holocene has seen very large secondary modulations that must be better understood so that they may be distinguished from anthropogenic effects. If they are exogenetically controlled, as it seems, then they are probably predictable from astronomic data. Four geomorphic type areas are selected for demonstrating Holocene changes in tropical regions, because they have been somewhat neglected within the framework of Quaternary science and because they include some of the most fragile and easily disrupted environments: lakes, semiarid desert margins, coastlines, and coral reefs. In a nutshell, the tropical Holocene has seen three major changes: (a) the evolution from the hyperaridity of the last pleniglacial stage to the “postglacial pluvial”; (b) the “climatic optimum,” which was highly diachronous and strongly retarded as it shifted from low latitudes to high; (c) the postoptimum “deterioration” that has involved desiccation of lakes, readvances of the deserts, fall of sea level, and truncation of coral reefs. While this deterioration is predictable in terms of an interglacial-glacial climatic transition, strong natural climatic oscillations, not yet well understood, together with man's activities, make the future a cause for concern.