Deep ocean instrument to look at chemistry of seismically-active sea floor

University of Hawaiʻi at Mānoa
Contact:
Tara Hicks Johnson, (808) 956-3151
Gary McMurty, (808) 956-6858
School of Ocean & Earth Science & Technology
Posted: Jun 27, 2005


San Jose, Costa Rica - University of Hawaii scientists Gary McMurtry and Lloyd French, have deployed the first long-term, deep-ocean time-series experiment using an underwater mass spectrometer off the coast of Costa Rica. The goal of the project is to gather chemical information about the natural variability of the subsurface seafloor in this extremely active region. The use of a mass spectrometer permits for very sensitive multi-component characterization simultaneously on the ocean floor, allowing for many compounds to be measured in quantities ranging from percent to ppb (parts per billion) levels.

The spectrometer is being deployed off of the Woods Hole Oceanographic Institution‘s research vessel Atlantis. The research team also consists of Bernhard Chapligin, a geoecology graduate student trainee from the University of Karlsruhe.

The Deep-Ocean Mass Spectrometer (DOMS) was lowered to the seafloor at greater than 1000 m water depth and will remain there sampling the fluid chemistry of cold seep vents for at least four months duration. The DOMS, its large external battery, and a Continuous Aqueous Transport (CAT) system that can also measure fluid flow rates and the chemistry of fluids stored over the deployment period, are part of a combined underwater mainframe assembly. It was placed over active venting areas on mounds denoted by bacterial mats and associated vent fauna, using the Alvin manned submersible. After the planned four-month deployment, the assembly will be retrieved from the seafloor by the Quest Remotely Operated Vehicle, operated from the German research ship Meteor.

"This seafloor area off the Pacific coast of Costa Rica was chosen for study because of the extremely active collision of the Cocos tectonic plate with the Caribbean plate, and due to previous marine surveys done in this area," says McMurtry. "The Costa Rica area is similar to the active Sumatran collision zone that caused the devastating tsunami of December 26, 2004. Although initially recording the data internally, the promise of the DOMS is multi-compound chemical characterization that can be relayed in real time from the seafloor."

The DOMS uses membrane introduction mass spectrometry to measure dissolved gases and volatile organic compounds, and is optimized for low-power, long-duration sampling at high pressure (greater than 400 bars or 4000 m water depth) and low temperature (4 to 5 C). These data, in combination with other physical parameters such as seep water flow rates, background seismicity, and earthquakes, will lead to a better understanding of the subseafloor processes in active margins and will perhaps someday lead to earthquake and tsunami prediction.

"The whole idea is to obtain a time series so we can begin to see the natural variability. That in turn may reflect subseafloor processes such as response to regional stress changes or to bottom water temperature changes, tidal forcing, etc. This is basic, exploratory research, with an endurance test of novel equipment thrown in," explains McMurtry. "The promise is to correlate the chemical data obtained with geophysical parameters (e.g., seismicity, fluid flow) and augment our knowledge base about these active seafloor regions."

The study is part of a larger collaborative research effort funded by the U.S. National Science Foundation and was conducted with scientist colleagues from Scripps Institution of Oceanography, the Monterey Bay Research Institute, GEOMAR and Karlsruhe University of Germany, and the University of Costa Rica.

High resolution images available for download at http://www.soest.hawaii.edu/SOEST_News/PressReleases/McMurtry/.

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About the School of Ocean and Earth Science and Technology
The School of Ocean and Earth Science and Technology (SOEST) was established by the Board of Regents of the University of Hawaii in 1988. SOEST brings together in a single focused ocean, earth sciences and technology group, some of the nation‘s highest quality academic departments, research institutes, federal cooperative programs, and support facilities to meet challenges in the ocean and earth sciences. Scientists at SOEST are supported by both state and federal funds as they endeavor to understand the subtle and complex interrelations of the seas, the atmosphere, and the earth.

For more information, visit: http://www.soest.hawaii.edu/oceanography