Abstract
THE strontium isotope ratio in sea water is influenced by climate, tectonics, weathering and hydrothermal activity at ocean ridges1–4. Its evolution through time, determined primarily by measuring the strontium isotope composition of marine carbonates, holds information about variations in these processes, and is also useful for stratigraphic correlation and dating5–7. Carbonates are absent from some marine sediments such as siliceous oozes and red clays, and can be significantly diagenetically altered in others, especially in Eocene and older sediments. Here we show that marine barite is an effective alternative monitor of seawater 87Sr/86Sr. We find that microcrystals of marine barite separated from Holocene Pacific, Atlantic and Indian Ocean sediments all record the modern seawater 87Sr/86Sr value. Moreover, the 87Sr/86Sr of barite from 25 sediment samples spanning the past 35 Myr falls within the range of published data for carbonates over this time period. We conclude that marine barite reliably records both present and past variations in seawater strontium isotope composition.
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