Development of a laser Raman spectrometer for deep-ocean science

P.G. Brewer,a G. Malby,a J.D. Pasteris,b S.N. White,a E.T. Peltzer,a B. Wopenka,b J. Freeman,b and M.O. Browna
a: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing CA 95039-9644, USA
b: Department of Earth and Planetary Sciences, Washington University, Campus Box 1169, St. Louis, MO 63130-4899, USA

Deep-Sea Research I (2004) 51: 739753. doi:10.1016/j.dsr.2003.11.005.

Received: 2003 June 19.
Revision received: 2003 November 26.
Accepted: 2003 November 26.


ABSTRACT

We have extensively modified and successfully used a laser Raman spectrometer (DORISS, deep-ocean Raman in situ spectrometer) for geochemical studies in the deep ocean. The initial instrument, from Kaiser Optical, was separated into three components: an optical head, a laser-power supply telemetry unit, and the spectrometer. These components were modified to fit into custom designed pressure housings, and connected by deep-sea cables and optical penetrators designed to minimize signal loss. The instrument ensemble has been field deployed on remotely operated vehicles (ROVs) for a variety of experiments and observations, with successful operation at 1.6°C, 3600&nbp;m depth. Power supply, instrument control, and signal telemetry are provided through the ROV tether, which contains copper conductors and single mode optical fibers. The optical head is deployable by the ROV robotic arm for sample analysis; the remaining components are fixed within the vehicle tool-sled. Challenges of system calibration at depth, temperature and pressure artifacts, and system control through over 4 km of cable were successfully overcome. We present exemplary spectra obtained in situ of gas, liquid, and solid specimens, and of the ubiquitous signal of sea water itself. Future challenges include weight and size reduction, and advances in precise beam positioning on mineral targets on the sea floor..

© 2004 Elsevier Ltd. All rights reserved.


Acknowledgements

We thank the officers and crew of the RVs Point Lobos and Western Flyer, and the ROV teams of Ventana and Tiburon, for their skill and support at sea. We acknowledge the skilled work of D. Cline in implementing the software for system operation. We thank D. Clague and R. Kleinberg for helpful comments on the manuscript. Funding was provided by a grant to MBARI from the David and Lucile Packard Foundation, and by the US Dept. of Energy Ocean Carbon Sequestration Program (Grants No. DE-FC26-00NT40929 and DE-FC03-01ER6305).


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