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Marine Chemistry
Volume 98, Issues 2-4, 1 February 2006, Pages 304-314
 
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doi:10.1016/j.marchem.2005.09.006    How to Cite or Link Using DOI (Opens New Window)
Copyright © 2005 Elsevier B.V. All rights reserved.

Raman spectroscopic measurements of synthetic gas hydrates in the ocean

K.C. Hestera, S.N. Whiteb, E.T. Peltzerc, P.G. Brewerc and E.D. Sloana, Corresponding Author Contact Information, E-mail The Corresponding Author

aCenter for Hydrate Research, Colorado School of Mines, Golden, CO 80401, USA bDepartment of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA cMonterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, USA

Received 14 January 2005; 
revised 10 August 2005; 
accepted 12 September 2005. 
Available online 20 December 2005.

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Abstract

A Raman spectrometer extensively modified for deep ocean use was used to measure synthetic hydrates formed in an ocean environment. This was the first time hydrates formed in the ocean have been measured in situ using Raman spectroscopy. Gas hydrates were formed in situ in the Monterey Bay by pressurizing a Pyrex cell with various gas mixtures. Raman spectra were obtained for sI methane hydrate and sII methane + ethane hydrate. Gas occlusion resulting from rapid gas growth of methane hydrate was measured immediately after formation. The Raman shift for methane free gas was coincident with that of methane in the small 512 hydrate cage. The methane Raman peak widths were used to discriminate between methane in the free gas and hydrate phase. Methane + ethane sII hydrate was formed for 43 days on the seafloor. In this case, gas occlusion was not measured when the gas hydrates were allowed to form over an extended time period. Equivalent Raman spectra were obtained for the in situ and laboratory-formed sII methane + ethane hydrates, under similar p, T, and x conditions. With the Raman spectrometer operating in the ocean, seawater contributes to the Raman spectra obtained. Both the Raman bands for the sulfate ion and water were used to qualitatively determine the distribution of water phases measured (hydrate, seawater) in the Raman spectra.

Keywords: Monterey Bay; Gas hydrates; Raman spectroscopy; Structure I; Structure II

Article Outline

1. Introduction
2. Methods
2.1. Field laboratory Raman studies
2.2. Onshore laboratory Raman studies
3. Field experiments and results
3.1. Ventana Dive 2415: August 25th, 2003, midwater at 500–900 m
3.2. Tiburon Dive 641: December 17th, 2003, seafloor at 1024 m
4. Discussion
5. Conclusions
Acknowledgements
References











Marine Chemistry
Volume 98, Issues 2-4, 1 February 2006, Pages 304-314
 
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