Dark Ocean Carbon Absorption Not Enough To Restrict Global Warming
September 6, 2013

Dark Ocean Carbon Absorption Not Enough To Restrict Global Warming

April Flowers for redOrbit.com - Your Universe Online

A new study led by the University of Iowa shows that although microbes that live below 600 feet where light doesn’t penetrate – the so called “dark ocean”-- might not absorb enough carbon to curtail global warming, they do absorb considerable amounts of carbon, meriting further study. The findings of this study were published in the International Society of Microbial Ecology Journal.

While many people are familiar with the concept of trees and grass absorbing carbon from the air, Tim Mattes, associate professor of civil and environmental engineering at the University of Iowa, said that bacteria and ancient single-celled organisms called “archaea” in the dark ocean hold between 300 million and 1.3 billion tons of carbon.

“A significant amount of carbon fixation occurs in the dark ocean,” says Mattes. “What might make this surprising is that carbon fixation is typically linked to organisms using sunlight as the energy source.”

Dark ocean organisms might not require sunlight to lock up carbon, but they do require an energy source.

“In the dark ocean, carbon fixation can occur with reduced chemical energy sources such as sulfur, methane, and ferrous iron,” Mattes says. “The hotspots are hydrothermal vents that generate plumes rich in chemical energy sources that stimulate the growth of microorganisms forming the foundation for deep sea ecosystems.”

Mattes and his colleagues studied hydrothermal vents in a volcanic caldera at Axial Seamount, an active volcano approximately 5000 feet underwater in the Pacific Ocean and about 300 miles west of Cannon Beach, Oregon. During a 2011 cruise, sponsored by the National Science Foundation (NSF), Mattes’ colleague Robert Morris gathered data and collected samples used in the study.

“Using protein-based techniques, we observed that sulfur-oxidizing microorganisms were numerically dominant in this particular hydrothermal vent plume and also converting carbon dioxide to biomass, as suggested by the title of our paper: ‘Sulfur oxidizers dominate carbon fixation at a biogeochemical hot spot in the dark ocean,’” said Mattes, who conducted the research at the University of Washington School of Oceanography while on leave from UI.

Because carbon fixation occurs on such a large scale in the dark ocean, scientists question the contribution of such activity to offsetting carbon emissions that contribute to global warming. The research team says that such speculation needs further study.

“While it is true that these microbes are incorporating carbon dioxide into their cells in the deep ocean and thus having an impact on the global carbon cycle, there is no evidence to suggest that they could play any role in mitigating global warming,” he says.

The primary value of the investigation, according to Mattes, is to better understand how microorganisms function in the dark ocean and to increase fundamental knowledge of global biogeochemical cycles.