Trapping Carbon Dioxide In An Icy Cage: Researchers Explore The Ocean Floor With Rare Instrument

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. Pasteris' group 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 also are 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," explained Pasteris. "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.

"The ocean floor is still a mysterious place. 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 Nov. 2-5 in Seattle.

Pasteris and her colleagues John Freeman, Ph.D., and Brigitte Wopenka, Ph.D., Washington University research scientists, are collaborators with oceanographers and engineers at MBARI. In the past they have 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.