SGER: Seawater Calcium Isotopes and Carbonate Deposition History

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.