Geochemical behavior of inorganic germanium in an unperturbed estuary

Eleven monthly estuarine profiles of dissolved inorganic germanium (Ge i) and silica (Si) in a natural, pristine river/bay system demonstrate that Ge-removal and -input parallel the seasonal silica cycle, reflecting Ge-uptake by and -dissolution from diatoms. The Ge/Si atom ratio of the river is 0.6 ± 0.15 × 10 −6, which is near the average value for continental granites and for uncontaminated, remote, natural rivers (0.7 ± 0.3 × 10 −6). The Ge Si ratio escaping this estuary to the ocean is 0.8 × 10 −6, reflecting some estuarine enhancement of the fluvial Ge-flux, probably due to release of Ge i from fluvial particulates. Nevertheless, the post-estuarine Ge Si ratio is not significantly different from the continental crustal ratio but is very different from the ratio in sea-floor hot springs and mid-ocean ridge hydrothermal plumes (4 ± 2 × 10 −6) and in oceanic basalts (2.6 × 10 −6). Thus natural estuarine processes do not obscure the contrasting Ge Si signatures entering the ocean from dissolution of continental and sea-floor silicates.