The isotopic composition of leachable osmium from river sediments

The 187Os186Os ratios of acidic hydrogen peroxide leaches of river sediments are inferred to be representative of the isotopic composition of Os delivered to sea water from the continents. The 187Os186Os values for river sediment leaches from the eastern and central U.S., the Ganges River, and the Rio Maipo range from 10.1 to 21.5. These results suggest that the 187Os186Os of the soluble river load delivered from the major continental areas to the oceans is, on average, more radiogenic than average currently eroding continental crust (10.5). Sediment leaches from three rivers from the western U.S. that drain ophiolitic peridotites have distinctly lower 187Os186Os values, 1.4–7.1; such rivers may be significant contributors to sea water of the relatively unradiogenic osmium required to yield the contemporary oceanic 187Os186Os of 8.6.