Abstract

One of the most enigmatic questions in paleoceanography is whether there has been secular variation in the oxygen isotope composition of the ocean over the last 550 million years. Well preserved carbonate rocks and fossils suggest early Phanerozoic oceans that may have been as much as 4-5‰ lower than today, but many models and other mineral proxies have failed to reproduce this. In this talk I will discuss an attempt made to address this issue by using paired vein mineral analysis to reconstruct the oxygen isotope composition of hydrothermal vent fluid in the late Cambrian (500 million years ago) from ophiolites in Newfoundland. The data is considered in both a stagnant (water/rock ratio) and reactive transport context, and the results are enigmatic. Water-rock interaction in hydrothermal systems may be a function of the major ion chemistry of the ocean over the course of Earth history, which may offer new insight into the modulation of chemical fluxes within hydrothermal systems.