Effect of Paleoseawater Composition on Hydrothermal Exchange in Midocean Ridges.

Significance Circulation of seawater through midocean ridges results in large-scale chemical transfer between the solid Earth and oceans. Driven by magmatic heat, seawater undergoes hydrothermal reactions that affect the concentrations of Mg, Ca, SO 4 , and Sr in the oceans over millions of years. Changes in the composition of seawater during the past 500 million years may have previously unrecognized effects on the composition of hydrothermal fluids flowing back into the oceans through time. This work presents a model suggesting that Ca, and Sr exchange in particular, may have been much different in the geologic past, which has important implications for the interpretation of Sr isotope records in paleoseawater and ancient oceanic crust.