Rapid Variability of Seawater Chemistry Over the Past 130 Million Years

Abstract

More than a Dash of Sea Salt The cycling of major elements, such as sulfur, in the oceans depends on a number of processes, from bacterial respiration of organic matter to venting of gases from hydrothermal vents on the seafloor. Over geologic time, sediment deposited on the seafloor preserves chemical records of major changes in sulfur cycling and seawater chemistry (see the Perspective by Hurtgen ). Halevy et al. (p. 331 ) observed swings in sulfur isotopes in a stratigraphic database covering North America and the Caribbean that, when modeled, corresponded to variable evaporite preservation and high turnover of sedimentary pyrite. Wortmann and Paytan (p. 334 ) modeled the two most recent major swings in sedimentary sulfur isotopes over the last 130 million years and suggest that short periods of rapid fluxes in sulfur cycling were at least in part caused by the growth and dissolution of evaporite deposits.