Abstract
Osmium concentrations in corals are very low (<20 ppt) and large isotopic variations (between 2.92 ± 0.05 and 9.01 ± 0.05) are observed indicating sample heterogeneity. These variations are interpreted as a two component mixing for each sample. The unradiogenic component has about the same value for all samples and is of mantle/meteorite composition and concentration. The radiogenic component is interpreted as a composite signal, different for each sample and resulting from the mixing of seawater osmium and continental detrital sediment osmium. Simple calculations show that the micrometeoritic flux of 40 ± 20.10 6 kg/yr is too small by about two orders of magnitude to explain the composition of these samples. In the absence of a potential mantle source for the corals, it is considered that corals, as they filter water for feeding, scavenge meteoritical osmium from seawater.
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