HR: 1340h
AN: OS43A-0615    [Abstracts]
TI: Authigenic Mineral Fronts as Recorders of Past and Present Methane Fluxes: Offshore Concepcion, Chile
AU: * Novosel, I
EM: novosel@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St., MS 126, Houston, TX 77005 United States
AU: Dickens, G R
EM: jerry@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St., MS 126, Houston, TX 77005 United States
AU: Snyder, G T
EM: gsnyder@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main St., MS 126, Houston, TX 77005 United States
AU: Pohlman, J W
EM: john.pohlman@nrl.navy.mil
AF: Naval Research Lab Code 6114, 4555 Overlook Ave SW, Washington, DC 20375 United States
AU: Pohlman, J W
EM: john.pohlman@nrl.navy.mil
AF: Virginia Institute of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA 23062 United States
AU: Coffin, R B
EM: rcoffin@ccf.nrl.navy.mil
AF: Naval Research Lab Code 6114, 4555 Overlook Ave SW, Washington, DC 20375 United States
AB: It is well documented that upward transport of methane and fluids impacts the authigenic mineralogy and chemistry of marine sediments. However, the significance of long-term preservation of these signals has not been fully acknowledged. For example, while porewater geochemical signatures tell us about the current state of the environment, solid phases may preserve past states in precipitated authigenic mineral fronts. At present, only a few studies have integrated chemical and mineralogical analysis of fluids and solids, in order to constrain the evolution of these phases throughout space and time. This study compares the porewater and solid fraction geochemistry from marine sediment cores recovered along the Chilean continental margin in order to document the changes in methane fluxes and related sulfate-methane transition (SMT). A gas hydrate expedition was conducted in October 2004 off Mid-Chilean margin, west of Concepcion. The overall objective of this survey was to integrate geochemical, geophysical, and microbiological data in order to better understand the relationship between shallow sediment processes and deep hydrate/gas systems. Fifteen piston cores of approximately 5-metre length were collected. Of these, thirteen were located along a NE-SW trending Deep-Tow Acoustics/Geophysics System (DTAGS) survey line that indicated a potential hydrate accumulation. Two additional piston cores containing gas hydrate were collected at the base of a 40-metre high sub-sea mound where chemosynthetic macrofauna commonly associated with increased methane levels at the sediment-water interface were found. The Ca, Mg, Sr, Fe, and S content of the sediments and the pore fluids indicates the formation of authigenic minerals. However, the location of these `authigenic fronts' was not exclusively associated with the location of the present day SMT. Although porewater geochemical profiles show that the anaerobic oxidation of methane (AOM) was occurring at or close to the interface, sediment results suggest the presence of an additional authigenic front above the SMT. These findings suggest that the depth to the SMT has varied through time. The implication is that solid phase geochemical profiles may thus be used as recorders of the changes of methane fluxes through time.
DE: 0460 Marine systems (4800)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1051 Sedimentary geochemistry
DE: 1065 Major and trace element geochemistry
DE: 4851 Oxidation/reduction reactions (0471)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005