Sr isotopic data from DSDP Sites 575 and 590

By taking this shift into account we reconstruct the original 87Sr/86Sr of each increment of carbonate sampled, which when plotted as a function of age becomes our best estimate of the Sr isotopic evolution of seawater. Because Sr is very well mixed in the ocean, at any given time there is a single worldwide value of seawater 87Sr/86Sr. Therefore, if we are quantitatively accounting for the effect Sr exchange, we should find the same seawater evolution curve regardless of what DSDP Site is used.

When we compare the observed bulk carbonate 87Sr/86Sr vs. age at the two sites they are seen to differ by amounts that are sometimes large compared to the analytical uncertainties of the measurements. However, when these data are corrected for the post-depositional Sr isotopic shifts predicted by our diagenetic model, we find almost perfect agreement. This agreement suggests that we have made a realistic determination of the rate of Sr exchange and its consequences in terms of shifting the 87Sr/86Sr of the bulk carbonate, and more importantly, that Sr isotopes can be used to correlate marine sediments with an accuracy comparable to the very small analytical uncertainties of modern isotopic measurements.