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Geology; February 2006; v. 34; no. 2; p. 117-120; DOI: 10.1130/G22008.1
© 2006 Geological Society of America
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Rise of the base of the gas hydrate zone since the last glacial recorded by rock magnetism

Robert J. Musgrave*,1, Nathan L. Bangs2, Juan Cruz Larrasoaña3, Eulàlia Gràcia4, Jennifer A. Hollamby5 and Marta E. Vega5

1 School of Geosciences, Monash University, Clayton, VIC 3800, Australia
2 University of Texas, Institute for Geophysics, 4412 Spicewood Springs Road, Austin, Texas 78759, USA
3 Laboratori de Paleomagnetisme, Consejo Superior de Investigaciones Científicas, Universitat de Barcelona, Institut de Ciències de la Tierra "Jaume Almera," 08028 Barcelona, Spain
4 Centre Mediterrani d'Investigacions Marines i Ambientals, Unitat de Tecnologia Marina, Consejo Superior de Investigaciones Científicas, Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain
5 La Trobe University, PALM Laboratory, Bundoora, VIC 3086, Australia

Gas hydrate, a clathrate of methane and water widespread on continental margins, has been implicated as a trigger of climate change and submarine slides as a result of methane release when the base of its stability zone moves upward rapidly. Direct tests of these hypotheses are made difficult by the ephemeral record of gas hydrate in sediment. In places, a seismic reflector (double bottom simulating reflector, BSR) appears to mark the old base of the gas hydrate layer, but the occurrence of this feature is patchy and its interpretation is controversial. Microbial activity is stimulated in the presence of gas hydrate, and results in the production of magnetic iron sulfides; the base of the gas hydrate interval is marked by a sharp reduction in the magnetic hysteresis parameter DJH. At Hydrate Ridge on the Cascadia margin, sampled during Ocean Drilling Program Leg 204, this signature occurs between 20 and 65 m below the present-day base of the gas hydrate zone, at a depth consistent with predictions for the base of gas hydrate stability given water depths and bottom-water temperatures appropriate for the last glacial maximum. Seismic evidence for a double BSR over part of Hydrate Ridge corroborates the rock magnetic interpretation.

Key Words: gas hydrates • methane • hysteresis • Ocean Drilling Program • bottom water • last glacial maximum






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