Germanium and silicon in rivers of the Orinoco drainage basin

Abstract

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 silicon^2–5. 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.