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Researchers explore ocean floor with rare instrument

By Tony Fitzpatrick

In collaboration with oceanographers and engineers at the Monterey Bay Aquarium Research Institute (MBARI), a team of University geologists is using a rare instrument on the ocean floor — more than two miles beneath the surface — just west of California.

One of the group's earliest projects was to see if it's possible to capture carbon dioxide from the atmosphere and store it on the ocean floor. The research is supported by the Department of Energy.

The geologists, headed by Jill Pasteris, Ph.D., professor of earth and planetary sciences in Arts & Sciences, and their MBARI colleagues are the first to deploy a Raman spectrometer on the ocean floor. The instrument combines a portable focusing lens with a potent laser to examine minerals, gases and liquids — even seawater itself.

A fish on the ocean floor off California gazes at a sight no human has seen first-hand: a modified Raman spectrometer gathering data on a carbon dioxide sample. Jill Pasteris, Ph.D., professor of earth and planetary sciences in Arts & Sciences, heads the University group collaborating with researchers at the Monterey Bay Aquarium Research Institute to determine the feasibility of storing the greenhouse gas carbon dioxide on the ocean floor. The Raman spectrometer is the first-ever deployed on the ocean floor.

Courtesy photo - MBARI

A fish on the ocean floor off California gazes at a sight no human has seen first-hand: a modified Raman spectrometer gathering data on a carbon dioxide sample. Jill Pasteris, Ph.D., professor of earth and planetary sciences in Arts & Sciences, heads the University group collaborating with researchers at the Monterey Bay Aquarium Research Institute to determine the feasibility of storing the greenhouse gas carbon dioxide on the ocean floor. The Raman spectrometer is the first-ever deployed on the ocean floor.

The University team comprises Pasteris and John Freeman, Ph.D., and Brigitte Wopenka, Ph.D., research scientists in earth and planetary sciences. They and their MBARI colleagues are using Raman spectroscopy to see what carbon dioxide in either a pure liquid or a complex solid phase will do on the sea floor.

They are also examining the feasibility of synthetically trapping carbon dioxide in solids called clathrate hydrates — ice-like solids that form a cage around gas molecules, such as methane, trapping them and storing them. Such solids occur naturally on the ocean floor.

The hope is that someday carbon dioxide can be trapped in a similar way.

"It's a remotely controlled laboratory on the ocean floor manipulated by a robot and controlled from the research ship above," Pasteris said. "The Raman signals so far are telling us that we can track the carbon dioxide and tell the different types — gas or liquid — and the spectra also can distinguish clathrate hydrates."

Carbon dioxide is the major gas that contributes to global warming. It is primarily the result of burning fossil fuels, and while there are ways to reduce its levels in the atmosphere, scientists are researching new methods to capture it and store it. The ocean floor is chief among alternative sites being studied.

"The ocean floor is still a mysterious place," Pasteris said. "You can't get scientists directly on the floor, so you either send them down in miniature subs or operate remotely, as the MBARI group does.

"Ultimately, we want to get more expertise on the mineralogy of the sea floor, and we believe the Raman spectrometer is the best thing going to give on-the-spot analysis and identification."

Pasteris explained her collaborative research at the Geological Society of America annual meeting held last month in Seattle.

In the past, Pasteris' team has analyzed the kind of sulfur that unusual bacteria oxidize on the ocean floor for MBARI scientists, again using their specialty, Raman spectroscopy.

In the carbon sequestration research, MBARI scientists have dismantled the Raman spectrometer system and placed its components in three pressure-resistant cylinders connected by fiber-optic cables. A robotic arm controlled from the research ship manipulates the probe head containing the laser.

The laser excites various effects in samples, including what is called the Raman effect. The same lens system used to focus the laser then captures backscattered radiation and routes it to the cylinder with the electronics instrument for analysis.

"The emergence of global positioning systems and remotely operated vehicles such as MBARI employs make the use of our instrumentation in extreme environments more and more feasible," Pasteris said. "We expect to get valuable data on the growth of carbon dioxide clathrate hydrate, the formation of secondary solid and dissolved species, the formation of carbon dioxide-saturated boundary layers in ocean water, and the dissolution of sea-floor minerals, among other information, in future deployments."

She said that hydrothermal vents on the sea floor — a possible site for the origin of life on Earth — and their attendant bacterial colonies are possible future candidates for DORISS, the deep-ocean Raman in-situ spectrometer system. MBARI scientists are studying ways of downsizing the Raman instrument package so that other instruments can piggyback together with it on the robotic vehicles that are sent to the sea floor.

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