Mathematics – Logic
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996e%26psl.139..497c&link_type=abstract
Earth and Planetary Science Letters, vol. 139, Issue 3-4, pp.497-507
Mathematics
Logic
7
Odp Site 888, Odp Site, Odp Site 892, Bacteria, Gas Hydrates, Elsevier: Odp Site 888, Odp Site 889/(890), Odp Site 892, Bacteria, Gas Hydrates
Scientific paper
Bacterial populations and activity were quantified at three sites in the Cascadia Margin accretionary wedge, off the West Canadian/American coast (ODP Leg 146). At two sites sediments contained gas hydrates, Site had a discrete zone of hydrate approximately 10 m above a bottom simulating reflector (BSR) at 225 m below sea floor (mbsf) and Site 892 had disseminated hydrate in the upper 20 mbsf and a BSR at 74 mbsf. Site 888 was a control site without gas hydrates. The control site (888) and top approximately 90 mbsf of Site had bacterial distributions similar to previous Pacific Ocean sites. In the upper approximately 30 m of Site 892, however, bacterial populations were much lower, suggesting inhibition by the high concentrations of H 2 S within the hydrate zone. Below this depth bacterial populations rose to concentrations consistent with other sites. The control site was dominated by SO 4 reduction and rates of CH 4 oxidation in the top 90 m were low (0.002-0.033 nmol cm -3 d -1 ). At Site bacterial populations and activity were stimulated in the discrete hydrate zone. CH 4 oxidation rates increased in the middle of this zone to 134.5 nmol cm -3 d -1 (ca. 9 times the average rate at other depths), resulting in a significant (× 10) increase in the total bacterial population. The anaerobic process(es) responsible for this oxidation remain unclear, despite SO 4 -reducing bacteria, previously associated with CH 4 oxidation, also being stimulated in this zone. Fluid flux into accretionary wedge sediments may be an important process in providing electron acceptors to maintain these relatively high rates of CH 4 oxidation. This first microbiological study of gas hydrates indicates that bacterial processes are influenced by gas and fluid venting, and they play a major role in geochemical changes within these deep (> 200 mbsf) sediments.
Cragg Barry A.
Fry John C.
John Parkes R.
Maxwell James R.
Rochelle P. A.
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