Heterogeneous seawater 187Os/188Os during the Late Pleistocene glaciations

We report high temporal resolution osmium isotopes records of bulk sediment and sediment leachates from DSDP Site 480 (Gulf of California) over the last 30 ka; from ODP Site 849 (Eastern equatorial Pacific) from the last 200 ka and from ODP Site 1002C (Cariaco Basin) across the 9–17 ka time interval in order to critically evaluate claims of a global 10% shift in the 187Os/188Os of seawater from glacial to interglacial intervals. We use organic-rich continental margin sites and carbonate-rich pelagic sites to isolate the temporal variations of the osmium seawater isotopic composition. Our results reveal that variations in 187Os/188Os fail to correlate with global changes in temperature across glacials/interglacials cycles as previously claimed. Instead, these results indicate differences of a few percent in the measured 187Os/188Os between each oceanic basin. We argue that these differences strongly suggest that seawater is not well homogenized with respect to its Os isotope composition.

► Seawater 187Os/188Os show minima at glacial maxima.
► These minima are thought to result from reduced chemical weathering fluxes.
► We analyzed seawater 187Os/188Os in additional sites.
► We failed to corroborate 187Os/188Os minima.
► We suggest a heterogeneous ocean with respect to its osmium isotopic composition.