Gas hydrate measurements at Hydrate Ridge using
Raman spectroscopy

K.C. Hester,a R.M. Dunk,b S.N. White,c
P.G. Brewer,b E.T. Peltzer,b E.D. Sloan,a,*

a: Center for Hydrate Research, Colorado School of Mines, Golden, CO 80401, USA
b: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, USA
c: Department of Applied Ocean Physics & Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA

* Corresponding author. E-mail address: esloan@mines.edu (E.D. Sloan).

Geochimica et Cosmochimica Acta (2007) 71: 29472959. doi:10.1016/j.gca.2007.03.032

Received: 2006 November 14.
Accepted in revised form: 2007 March 29.
Available online: 2007 April 14.


ABSTRACT

Oceanic gas hydrates have been measured near the seafloor for the first time using a seagoing Raman spectrometer at Hydrate Ridge, Oregon, where extensive layers of hydrates have been found to occur near the seafloor. All of the hydrates analyzed were liberated from the upper meter of the sediment column near active gas venting sites in water depths of 770 780 m. Hydrate properties, such as structure and composition, were measured with significantly less disturbance to the sample than would be realized with core recovery. The natural hydrates measured were sI, with methane as the predominant guest component, and minor/trace amounts of hydrogen sulfide present in three of the twelve samples measured. Methane large-to-small cage occupancy ratios of the hydrates varied from 1.01 to 1.30, in good agreement with measurements of laboratory synthesized and recovered natural hydrates. Although the samples visually appeared to be solid, varying quantities of free methane gas were detected, indicating the possible presence of occluded gas in a hydrate bubble fabric.

© 2007 by Elsevier Ltd. All rights reserved.


Acknowledgements

This work was supported through National Undersea Research Program Grant UAF03-0098. DORISS and PUP development was funded by a grant to MBARI from the David and Lucile Packard Foundation. The authors express their admiration and appreciation to the Captain and crew of the R/V Western Flyer and pilots of the ROV Tiburon. We also thank Patrick Hendra, John Freeman, and Jill Pasteris for helpful discussions about Raman instrumentation. Carolyn Koh is thanked for help with the spectral analysis. Technical assistance was provided by Alana Sherman, Mark Brown, Peter Walz, John Ferreira, and Randy Prickett. We thank editor Robert Burruss, associate editor Alexei Milkov, and the anonymous reviewers for their valuable critique of this work.


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