GERMANIUM AND SILICON IN RIVERS OF THE ORINOCO DRAINAGE-BASIN

CONTINENTAL weathering and mid-ocean-ridge hydrothermal circulation are the two main processes that release dissolved silicon to the ocean. It has been hypothesized1 that temporal variations in the relative strengths of these two processes might be estimated from the Ge/Si ratio of opal in marine sediments, because the chemistry of germanium is similar to that of silicon2-5. We analysed river water from the Orinoco basin and soils from Venezuela and Panama for germanium and silicon, to determine the relationship between river Ge/Si ratios, drainage basin lithology and chemical-weathering intensity. Our results, presented here, indicate that chemical-weathering intensity, defined as the fraction of original bedrock silicon dissolved during continental weathering, is related to the Ge/Si ratio in river water and is inversely related to river silicon concentrations. Changes in global climate, sea level or patterns of plate-tectonic interactions could change chemical-weathering intensity and complicate the interpretation of the marine opal Ge/Si record. © 1990 Nature Publishing Group.