Abstract
<b>We review the rapid progress made in the applications of Raman spectroscopy
to deep-ocean science. This is made possible by deployment of instrumentation on
remotely operated vehicles used for providing power and data flow and for
precise positioning on targets of interest. Early prototype systems have now
been replaced by compact and robust units that have been deployed well over 100
times on an expeditionary basis over a very wide range of ocean depths without
failure. Real-time access to the spectra obtained in the vehicle control room
allows for expedition decision making. Quantification of some of the solutes in
seawater or pore waters observed in the spectra is made possible by
self-referencing to the ubiquitous ν<sub>2</sub> water bending peak. The
applications include detection of the structure and composition of complex
thermogenic gas hydrates both occurring naturally on the sea floor and in
controlled sea floor experiments designed to simulate the growth of such natural
systems. New developments in the ability to probe the chemistry of sediment pore
waters in situ, long thought impossible candidates for Raman study due to
fluorescence observed in recovered samples, have occurred. This permits accurate
measurement of the abundance of dissolved methane and sulfide in sediment pore
waters. In areas where a high gas flux is observed coming out of the sediments a
difference of about ×30 between in situ Raman measurement and the quantity
observed in recovered cores has been found. New applications under development
include the ability to address deep-sea biological processes and the ability to
survey the sea floor chemical conditions associated with potential sub-sea
geologic CO<sub>2</sub> disposal in abandoned oil and gas fields.</b>
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