SGER: Seawater Calcium Isotopes and Carbonate Deposition History

Stanford University, Stanford CA

Investigators

Abstract

Seawater Calcium Isotopes and Carbonate Deposition History ABSTRACT Changes in the amount of carbonate precipitation and dissolution have significant effects on oceanic alkalinity, total CO2, and atmospheric CO2, thus climate. Knowledge of the carbonate depositional history is important for understanding the global calcium and carbon cycles and may lead to improved understanding of global biogeochemical cycles operation on Earth on various time scales and the potential feedback mechanisms in these cycles and their effect on climate. The calcium isotope ratio is seawater at any given time is largely controlled by biological precipitation of calcium carbonate, a process that discriminates against heavy isotopes. This fractionation causes seawater to be enriched in heavy calcium relative to the average isotopic ratio of input sources to the ocean. Therefore, reconstruction of seawater Ca isotope ratio could lead to an estimate of the fluctuations in the amount of calcium carbonate deposited in the oceans through time and to better understanding of the calcium and carbon cycles. Accordingly, the main objective of this SGER proposal is to explore the potential of the mineral barite separated from deep-sea sediments to trace the variations in seawater Ca isotope ratios, and to evaluate the use this proxy for reconstruction of the calcium carbonate deposition history. This work fits the criteria for a SGER proposal as it seeks partial support for conducting preliminary work of an untested and novel idea it is a high risk project and applies newly developed tools (so far only two labs in the USA measure Ca isotopes routinely). Results if encouraging will provide a basis to perform further more detailed research that will advance our understanding of the global biogeochemical cycle and its coupling with climate and contribute significantly to the field of paleoceanography and earth history.