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Undersea Methane Could be a Source of Ancient Carbon in Oceans

A North Carolina State University researcher is part of a team that has found methane is converted into dissolved organic matter within “cold seeps” – undersea areas where fluids bubble up through sediments at the bottom of the ocean.  This material
could be a significant source of ancient organic matter in the oceans and may
have contributed to the ocean acidification during prior climate change events.

Oceanic microbes consume dissolved organic carbon (DOC) and methane. A byproduct of this consumption is CO2 – carbon dioxide – which increased the acidity of seawater. Microbial processing of the methane-dervied DOC could have contributed to increased CO2 in the deep ocean and thus to ocean acidification in the geologic past.

Dr. Chris Osburn, assistant professor of marine science at NC State, and a research team led by geologists from the U.S. Geological Survey found high levels of methane-derived DOC in the deep water over cold seeps in two areas of the Pacific Ocean. Their findings appear online in Nature Geoscience.

“Normally, DOC primarily comes from the degradation of phytoplankton (algae), or from river discharge into the ocean,” Osburn says. “Finding DOC that comes from methane is a new part of the carbon cycle that hasn’t really been accounted for.”

Now that they have found methane-derived DOC, the researchers need to determine if it is found in other cold seeps worldwide, and whether or not it is labile, or easily used by the microorganisms that survive on DOC.  “Based on what we found, up to 30 percent of the Pacific Ocean’s deep water DOC could be methane-derived,” Osburn says. “If it is utilized by marine microorganisms, methane-derived DOC could be an important component of deep ocean ecosystems.”

The research was funded by grants from the National Science Foundation, the Natural Sciences and Engineering Research Council of Canada, and the U.S. Geological Survey, and included researchers from the Ohio State University and the University of Victoria (Canada). The Department of Marine, Earth and Atmospheric Sciences is part of NC State’s College of Physical and Mathematical Sciences.