In situ Raman analyses of deep-sea hydrothermal and cold
seep systems (Gorda Ridge and Hydrate Ridge)

S.N. White,a,+ R.M. Dunk,a E.T. Peltzer,a J.J. Freemanb and P.G. Brewera
a: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, California 95039-9644, USA
b: Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri 63130-4899, USA

+: Now at Woods Hole Oceanographic Institution, Blake 209, MS#7, Woods Hold, Massachusetts 02543, USA

Geochemistry, Geophysics & Geosystems (2006) 7 Q05023 doi:10.1029/2005GC001204.

Received: 2005 November 29.
Revised: 2006 March 17.
Accepted: 2006 March 30.
Published: 2006 May 25.


ABSTRACT

The Deep Ocean Raman In Situ Spectrometer (DORISS) instrument was deployed at the Sea Cliff Hydrothermal Field and Hydrate Ridge in July 2004. The first in situ Raman spectra of hydrothermal minerals, fluids, and bacterial mats were obtained. These spectra were analyzed and compared to laboratory Raman measurements of standards and samples collected from the site. Spectra of vent fluid (~294°C at the orifice) at ~2700 m depth were collected with noncontact and immersion sampling optics. Compared to spectra of ambient (~2°C) seawater, the vent fluid spectra show changes in the intensity and positions of the water O-H stretch bands due to the elevated temperature. The sulfate band observed in seawater spectra is reduced in vent fluid spectra as sulfate is removed from vent fluid in the subseafloor. Additional components of hydrothermal fluid are present in concentrations too low to be detected with the current Raman system. A precision underwater positioner (PUP) was used to focus the laser spot on opaque samples such as minerals and bacterial mats. Spectra were obtained of anhydrite from actively venting chimneys, and of barite deposits in hydrothermal crusts. Laboratory analysis of rock samples collected in the vent field also detected the presence of gypsum. Spectra of bacterial mats revealed the presence of elemental sulfur (S8) and the carotenoid beta-carotene. Challenges encountered include strong fluorescence from minerals and organics and insufficient sensitivity of the instrument. The next generation DORISS instrument addresses some of these challenges and holds great potential for use in deep-sea vent environments.

© 2006 by the American Geophysical Union.


Acknowledgements

We thank the captain and crew of the R/V Western Flyer and the pilots of the ROV Tiburon. This project benefited greatly from the engineering expertise of Alana Sherman, Mark Brown, and John Ferreira. Funding was provided by the David & Lucile Packard Foundation.


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