HR: 0800h
AN: C11A-1060    [Abstracts]
TI: Iodine and Bromine Distributions in Pore Waters: A Comparison Between Permafrost and Marine Gas Hydrate Fields
AU: * Tomaru, H
EM: hitoshi@earth.rochester.edu
AF: Department of Earth & Environmental Sciences, University of Rochester, 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Fehn, U
EM: fehn@earth.rochester.edu
AF: Department of Earth & Environmental Sciences, University of Rochester, 227 Hutchison Hall, Rochester, NY 14627 United States
AU: Lu, Z
EM: luzunli@earth.rochester.edu
AF: Department of Earth & Environmental Sciences, University of Rochester, 227 Hutchison Hall, Rochester, NY 14627 United States
AB: Iodine and, to a lesser degree, bromine are commonly enriched in waters associated with hydrocarbons. The concentrations of these halogens and their ratios can thus be used to identify potential source formations for hydrocarbons such as gas hydrates. While the largest reservoir of gas hydrates is found in marine sediments, permafrost locations are also an important source of gas hydrates. We measured iodine and bromine concentrations in pore waters associated with gas hydrates in the Mallik exploration well, a permafrost location in the Mackenzie delta, Northwest Territory, Canada and compared them to results from gas hydrates in marine sediments. Gas hydrates are found in the Mallik site in two horizons below the permafrost layer which reaches a depth of about 600 m in this location. We measured concentrations in samples collected from depths between 850 and 1150 m. Large sections of the test well have iodine concentrations around 1 μM, but the concentrations increase to values between 10 and 20 μM at the gas hydrate horizons. Bromine concentrations show a similar pattern, with maxima reaching values between 700 and 800 μM. Although iodine concentrations are considerably higher than in seawater (0.4 μM), they are much lower than in marine gas hydrate locations such as Nankai (200 μM); Blake Ridge (2 mM) or Hydrate Ridge (2.5 mM). Bromine concentrations at Mallik do not reach the seawater value (840 μM) in contrast to marine hydrate locations where Br is enriched by factors of four or more compared to seawater. Chlorine concentrations at Mallik are close to that of seawater, in this case similar to the marine hydrate locations. The comparison between marine hydrate locations and Mallik suggests that the organic sources responsible for the methane at Mallik are considerably different from those in marine situations. Since iodine concentrations are generally higher in marine organisms than in terrestrial organisms, the relatively low concentrations of iodine and bromine at Mallik suggest that the source material there is of more terrestrial character than in the marine locations, a observation supported by the presence of several coal seams at Mallik. The large volume of methane in this region suggests that terrestrial sources may play an important role in the accumulation of gas hydrates.
DE: 0702 Permafrost (0475)
DE: 0714 Clathrate
DE: 1009 Geochemical modeling (3610, 8410)
DE: 3004 Gas and hydrate systems
SC: Cryosphere [C]
MN: Fall Meeting 2005