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Science 16 December 1977:
Vol. 198. no. 4322, pp. 1149 - 1153
DOI: 10.1126/science.198.4322.1149
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Articles

Submarine Seepage of Natural Gas in Norton Sound, Alaska

JOEL D. CLINE 1 and MARK L. HOLMES 2

1 Pacific Marine Environmental Laboratory, Environmental Research Laboratories, National Oceanic and Atmospheric Administration, Seattle, Washington 98115
2 U.S. Geological Survey, Seattle, Washington 98105

Unusual concentrations of dissolved two- to four-carbon alkanes were observed in the waters in Norton Sound in a localized area approximately 40 kilometers south of Nome, Alaska, in 1976. The hydrocarbons were identified in the near-bottom waters downcurrent for more than 100 kilometers from a sea-floor point source. Preliminary dynamic modeling estimates of the initial gas phase composition predict methanelethane and ethanelpropane ratios of 24 and 1.7, respectively, assuming the hydrocarbons were introduced by bubbles. The low ethanelpropane ratio is indicative of gas from a liquid petroleum source rather than from nonassociated or biogenic natural gas. Preliminary data on the structural geology of Norton Basin lend support to the interpretation based on the hydrocarbon plume. Unconformably truncated strata dip basinward from the seep locus; acoustic anomalies and numerous steeply dipping faults in the immediate vicinity of the seep are corroborating evidence that shallow gas- or petroleum-charged sediments and strata coincide with avenues for migration of mobile hydrocarbons to the sea floor. These factors, taken in concert with the sedimentological regime, the recent revision (increase) of basin depth estimates, and the highly localized hydrocarbon source, strongly suggest a thermogenic rather than a recent biogenic origin for these gaseous compounds.

Submitted on May 24, 1977
Revised on August 22, 1977


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Submarine Seep of Carbon Dioxide in Norton Sound, Alaska.
K. A. Kvenvolden, K. A. KVENVOLDEN, K. WELIKY, H. NELSON, and D. J. D. MARAIS (1979)
Science 205, 1264-1266
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