Laser Raman Spectrometer for In Situ Deep-Sea Studies
Sheri N White, Peter G Brewer, Edward T Peltzer III, William J. Kirkwood
MBARI, 7700 Sandholdt Rd., Moss Landing, CA 95039
Laser Raman spectrometry is a powerful tool for obtaining chemical and structural compositional information from solids, liquids, and gaseous species. It is a non-destructive technique which requires no sample preparation. Thus, it is well suited for making in situ measurements in the deep ocean.
We have modified a laser Raman spectrometer (LRS) for use in the deep ocean. The LRS uses a 532 nm laser to excite a sample of interest and then records a spectrum of the Raman (inelastically) scattered light. The frequency shift of the Raman scattered light is due to the characteristic molecular vibrations of the molecule. So the Raman spectrum serves as a kind of “fingerprint” of a substance based on both composition and molecular structure. Raman spectroscopy can be used to study gases (e.g., CO2, CH4), liquids and dissolved species (e.g., isopropanol, and CO2 or SO4 in seawater), solids (e.g., precipitates, particles, minerals), and phase transitions (gas/liquid, and gas/solid are spectrally distinct).
We have successfully deployed our LRS to depths up to 3600 m, and have obtained quality spectra from solid minerals, liquids, and gases. Although we have primarily used the LRS for studies of CO2 sequestration and gas hydrates, it is applicable to a number of other fields. These areas include mineralogy and fluid chemistry of hydrothermal systems, the CO2 system in the ocean, and bacterial mats.