HR: 09:15h
AN: OS11C-06    [Abstracts]
TI: The iodine release during organic matter degradation at Northern Cascadia Margin: a numerical approach
AU: * Lu, Z
EM: luzunli@earth.rochester.edu
AF: University of Rochester, 227 Hutchison Hall Dept. of Earth and Env. Sci., Rochester, NY 14627, United States
AU: Hensen, C
EM: chensen@ifm-geomar.de
AF: Leibniz-Institut fur Meereswissenschaften, IFM-GEOMAR,Wischhofstr. 1-3, Kiel, 24148, Germany
AU: Fehn, U
EM: fehn@earth.rochester.edu
AF: University of Rochester, 227 Hutchison Hall Dept. of Earth and Env. Sci., Rochester, NY 14627, United States
AB: Iodine is dominated by organic material decomposition and transports with fluids in reducing environments such as deep marine sediments. It is often strongly concentrated in the pore waters associated with gas hydrates, with enrichment factors up to a few thousands comparing to seawater. The organic source of iodine very likely is also responsible for the large amount of methane in the hydrates. Once iodine is released from organic matter, it migrates with fluids and is rarely involved in diagenetic processes. We apply a Mathematica-based, one dimensional model to the drilling sites of IODP 311 at northern Cascadia Margin, in order to simulate the transport of deep-sourced old iodine and the in-situ release of younger iodine by microbial activity. In the model, iodine in the sediments is assumed to be associated only with organic materials and is released by particulate organic carbon (POC) degradation into the ambient pore waters. Depth profiles of dissolved iodide, bromide concentrations, and sediment-bounded iodine concentrations are calculated by the model to fit the analytical data. Modeling results suggest that the rates of POC degradation in these sediment cores can only account for a small amount of iodine, much lower than the level observed. The dominant organic source for iodine must be the deeper sediment layers. This is consistent with the old source age (~30 Ma) indicated by iodine isotope results. For comparison, we also applied the model to Site 1230, ODP 201 at Peru Margin and obtained similar results. The results demonstrate that iodine in gas hydrate locations is predominantly derived from deep, old sources with only small contributions from local organic material. Because iodine and methane commonly are transported together, the results suggest that a major part of methane in gas hydrate occurrences is also derived from distant sources.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 3002 Continental shelf and slope processes (4219)
DE: 3004 Gas and hydrate systems
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting