Osmium Isotopes as a Paleoweathering Tracer

Broecker 9314674 The potential of osmium isotopic ratios of marine sediments as a geochemical tracer was demonstrated by Pegram et. al. (1992). They showed that there has been a large increase in the 187 Os/186 Os ratio of osmium leached from Pacific red clays over the past 58 million years. They proposed that the leachable osmium is hydrogenous in origin, and reflects the isotopic composition of sea water at the time of precipitation. The observed change in 187 Os/186 Os was attributed to changes in continental weathering rates; higher values corresponding to increased supply of radiogenic 187 Os via rivers. The presumed short residence time of osmium in sea water potentially allows it to respond to rapid (