Climate-correlated variations in seawater 187Os/188Os over the past 200,000 yr: Evidence from the Cariaco Basin, Venezuela

A high resolution record of seawater osmium isotopic composition (35 samples over the past 191,000 yr) has been obtained from sediments from Ocean Drilling Program (ODP) Leg 165 Site 1002 in the Cariaco Basin, Venezuela. Strong correlations are observed between 187Os/188Os and both the local and global oxygen isotopic records, with less radiogenic values observed during glacial intervals. In conjunction with previous analyses of sediments from the East Pacific Rise, the Santa Barbara Basin, and the Japan Sea, the data demonstrate conclusively that there have been ocean-wide changes in seawater 187Os/188Os over the Pleistocene. Global seawater excursions to relatively unradiogenic 187Os/188Os, indicating decreased continental inputs, occur during cold intervals, times of increased aridity and increased ice cover of old (radiogenic) continental masses. The data thus indicate a direct climatic control on chemical weathering rates and/or composition of weathering products on a glacial–interglacial timescale.