HR: 17:00h
AN: PP14A-05    [Abstracts]
TI: Barium Cycling During the Paleocene-Eocene Thermal Maximum: Evidence From Ba/Ca in Foraminifera
AU: * Hall, J M
EM: jenney.hall@yale.edu
AF: Yale University, Department of Geology and Geophysics, P.O. Box 208109, New Haven, CT 06521 United States
AU: Zachos, J C
EM: jzachos@es.ucsc.edu
AF: University of California, Santa Cruz, Earth Sciences Department, EMZ Building, Santa Cruz, CA 95064 United States
AU: Turekian, K K
EM: karl.turekian@yale.edu
AF: Yale University, Department of Geology and Geophysics, P.O. Box 208109, New Haven, CT 06521 United States
AB: The Paleocene-Eocene thermal maximum (PETM) around 55 Ma reflects short-term, rapid climate change during a period of intense greenhouse climate. This interval is characterized by a negative carbon isotopic shift, interpreted as a release of methane from seafloor gas hydrate reservoirs. This perturbation of the carbon cycle is accompanied by significantly greater rates of euhedral barite accumulation in deep sea sediment commonly believed to be a reflection of elevated primary productivity in surface waters. An interpretation of higher productivity during the PETM, however, is contrary to microfossil assemblage data which indicates a decrease in primary productivity. It has also been suggested that the increase in barite accumulation during the PETM may have been the result of an increase in dissolved barium concentrations in the deep ocean coeval with methane release. This supposition has support from the fact that modern gas hydrate reservoirs are surrounded by pore waters with dissolved barium concentrations considerably higher than that of seawater. This investigation utilizes the barium content of foraminifera as a proxy to reconstruct changes in the barium concentration of the ocean. At 55 Ma, Ba/Ca decreases between 25 to 28% in the planktic foraminifer \textit{Morozovella velascoensis}, indicating a decrease in the barium concentration of the surface ocean. These results bolster the theory that there was increased biogenic barite precipitation during the PETM. Changes in surface water temperature and pH may have altered species assemblages such that celestite (SrSO$_4$) precipitating organisms enriched in barium as BaSO$_4$ (possibly acantharia) were dominant, modifying the barite precipitation pathways, which affected water column barite cycling. Ba/Ca and Cd/Ca measurements on benthic foraminifera show a positive correlation with Mn/Ca, indicating contamination of manganese oxide coatings. This contamination is in part due to the greater surface to volume ratio of benthic foraminifera, which are smaller than planktic species. Additionally, smaller quantities of benthics were available for analysis, which limited the intensity of pre-treatment to remove these coatings. After correcting for this coating contamination, no significant change in benthic Ba/Ca could be discerned through this interval. Taken together, the planktic and benthic foraminiferal Ba/Ca data suggests that enhanced biogenic barite accumulation during the PETM was primarily due to increased export from the surface waters.
DE: 1030 Geochemical cycles (0330)
DE: 1065 Trace elements (3670)
DE: 1635 Oceans (4203)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting