HR: 1340h
AN: PP43B-0679    [Abstracts]
TI: Seawater Calcium Isotopes Variations Over the Past 24 Million Years From Marine Barite
AU: * Morris, E J
EM: ejmorris@stanford.edu
AF: Stanford University, Department of Geological & Environmental Sciences Bldg. 320 Room 118 , Stanford, CA 94305 United States
AU: Paytan, A
EM: apaytan@stanford.edu
AF: Stanford University, Department of Geological & Environmental Sciences Bldg. 320 Room 118 , Stanford, CA 94305 United States
AU: Bullen, T D
EM: tdbullen@usgs.gov
AF: U. S. Geological Survey, MS 420 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: Carbonate deposition and dissolution significantly affect oceanic alkalinity, atmospheric CO2 and ultimately Earth's climate. Despite over a century's worth of research, we are just beginning to understand the complexity of the carbonate system and elucidate the feedbacks among the processes that control it. The biological precipitation of calcium carbonate largely controls the calcium (Ca) isotope ratio in seawater as a result of the discrimination against heavy isotopes associated with this process. This isotopic fractionation causes seawater to be enriched in the heavier isotopes of Ca relative to its input sources to the ocean, primarily terrigenous and hydrothermal. Reconstructing the seawater Ca isotope ratio over time could be used to quantify the fluctuations in the amount of calcium carbonate deposited in the oceans at any given time assuming some knowledge of the isotopic composition of the sources and sinks. Previously published paleo-seawater Ca isotopic records used bulk marine carbonates, select species of foraminifera, and phosphorites as their source for reconstruction of seawater Ca isotopic composition. However, multiple factors (temperature, precipitation rate, species-specific vital effects and diagenetic alteration) affect the Ca isotope ratio in each of these phases and its preservation of the seawater signal, thus results are complicated to interpret. We present Ca isotope data from marine barite, an inorganic phase precipitated in the water column and extracted from marine sediments. Results from coretop samples indicate marine barite has a constant fractionation from seawater and in not dependent on any environmental paratmeter. We will present the fluctuations in Ca isotopes from marine barite as variations in seawater Ca isotope composition and compare it to previously published results for the past 24 million years at a resolution of approximately one million years from DSDP/ODP cores in the Atlantic and Pacific Oceans.
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4863 Sedimentation (1861)
DE: 4870 Stable isotopes (0454, 1041)
DE: 4875 Trace elements (0489)
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005