The Ca Isotopic Evolution of the Oceans

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

9909639 DePaolo The proposed research will extend studies of Ca stable isotope variations in nature by determining the 44Ca/40Ca isotopic ratio of seawater and how it has changed over geologic time. Variations of the 44Ca/40Ca ratio in the oceans correspond to changes in the balance between delivery of Ca to the oceans by rivers and its removal into calcareous sediments. The Ca balance in reflects the relationship between weathering and carbonate sedimentation, which control the amount of carbon dioxide in the atmosphere and hence affect global climate. Consequently, this study will improve our understanding of which earth processes have been most influential in determining the global climate of the earth. Previous work shows that the 44Ca/40Ca ratio is shifted as a result of biological processes; the ratio decreases as Ca moves through food chains to higher trophic levels. Because Ca is removed from the oceans mainly by biological processes, there is an effect on the 44Ca/40Ca of the oceans, which produces the relationship between the Ca isotopic composition of the paleo-oceans and the global Ca cycle. The more recent part of the geologic record, back through the age of the oldest ocean floor (about 200 million years) will be the focus of the study. During this part of the geologic record, we can learn the most because we can compare the observed Ca isotopic variations to other indicators of past climate and ocean chemistry. The 44Ca/40Ca ratio will be measured on samples of calcium carbonate. These samples will be obtained from DSDP and ODP cores, from on-land sections in Italy, and other on-land sections. A limited survey of modern marine environments will also be done to investigate variability among modern carbonates and to characterizing the modern sources of Ca in the oceans.