Planktonic foraminiferal 87Sr/86Sr ratios of sediment cores from the Pacific and Indian Ocean

To investigate these potential fluctuations we present very high precision (13 ppm) 87Sr/86Sr measurements on planktonic foraminifera from Indian Ocean and Pacific cores. 87Sr/86Sr ratios from three different foraminiferal species are indistinguishable from one another in both core-top and 50 ka samples, demonstrating that changes due to diagenesis or contamination do not influence the measurements.

Average 87Sr/86Sr ratios for Pacific Ocean and Indian Ocean samples are also indistinguishable at three intervals (core-top, 50 ka and 300-370 ka), demonstrating that the oceans have remained well mixed with respect to Sr. Also, 87Sr/86Sr ratios are not affected by changes in the precleaning of samples. Measurements from Pacific core V28-238, that used in the study of Dia et al. (1992, doi:10.1038/356786a0), do not reproduce the cycles seen in the previous study and are statistically well explained by a linear increase in the seawater 87Sr/86Sr ratio.