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2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 20
Presentation Time: 1:30 PM-5:30 PM

MARINE BARITE: A POTENTIAL RECORDER OF SEAWATER CALCIUM ISOTOPE COMPOSITION


MORRIS, Elizabeth J., Geological & Environmental Sciences, Stanford Univ, Building 320, Room 207, Stanford University, Stanford, CA 94305-2115, PAYTAN, Adina, Geological & Environmental Sciences, Stanford University, Building 320, Room 207, Stanford, CA 94305-2115 and BULLEN, Thomas D., Water Resources, U. S. Geologic Survey, 345 Middlefield Rd, MS420, Menlo Park, CA 94025, ejmorris@stanford.edu

Seawater Ca isotope composition is controlled by the oceanic inputs and outputs of calcium and their isotope ratios. The major sink of Ca in the ocean is biogenic precipitation of calcium carbonate, which discriminates against the heavy isotopes resulting in an isotopically heavy ocean. Currently, published records of past variations of oceanic Ca isotope composition are based on carbonate or phosphate phases (Skulan et al., 1997; Zhu and Macdougall, 1998; DeLaRocha and DePaolo, 2000; Schmitt et al., 2003). Interpretation of these records is complicated because one has to assume a constant or known fractionation between the recording phases and seawater. Unknown temperature, growth rate, and other species-specific “vital effects” may however affect the fractionation.

We will evaluate the utility of marine barite as a recorder of seawater Ca isotope composition. Marine barite inorganically precipitates in the water column within micro-environments, thus it has the potential to record the chemical signature of the seawater in which it precipitated. Calcium is incorporated into the crystal structure of barite. The Ca isotope composition of marine barite separated from core top sediments will be presented and compared to the seawater Ca isotope composition.

References:

DeLaRocha, C.L. and DePaolo, D. J. (2000) Isotopic evidence for variations in the marine calcium cycle over the Cenozoic. Science 289, 1176-1178.

Skulan, J., DePaolo, D. J., and Owens, T. L. (1997) Biological control of calcium isotopic abundances in the global calcium cycle. Geochimica et Cosmochimica Acta 61, 2505-2510.

Schmitt, A. D., Stille, P., and Vennemann, T. (2003) Variations of the 44Ca/40Ca ratio in seawater during the past 24 million years: Evidence from d44Ca and d18O values of Miocene phosphates. Gecochimica et Cosmochimica Acta 67, in press.

Zhu, P. and Macdougall, D. J. (1998) Calcium isotopes in the marine environment and the oceanic calcium cycle. Geochimica et Cosmochimica Acta 62, 1691-1698.

Session No. 121--Booth# 129

Paleoclimatology/Paleoceanography (Posters) I
Monday, 3 November 2003: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol. 35, No. 6, September 2003, p.257
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