Brøgger Seminar Series
Ophiolite insights into Phanerozoic Ocean Chemistry 

When? 15 February, 14h00 | Where? Nordenskiöldsalen, Geovetenskapens hus


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.


Alexandra Turchyn, Guest seminar at the Department of Geological Sciences, Stockholm UniversityAlexandra Turchyn received her Bachelor from Princeton University and her PhD from Harvard University. She studies the chemical evolution of the ocean over different geological timescales over Earth’s history using stable isotopes and biogeochemical modelling. She is particularly interested in the biogeochemical response to perturbations of Earth’s climate. This has led her to study the interface between geochemistry and microbiology and how these interplay in biogeochemical cycling. One of her current research topics is how chemical alteration in hydrothermal systems provides insights to the chemistry of the past oceans.


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