Magma that heats seafloor mud could help pump large amounts of heat-trapping greenhouse gases into the oceans, enriching what may be a new kind of ecosystem and potentially contributing to shifts in climate, a new study finds.
Researchers analyzed photographs and seismic and sonar data of the seafloor of Guaymas basin in the Gulf of California, near where the ocean bottom rifts. They unexpectedly saw hot magma flowing under seafloor mud for up to 30 miles (48 kilometers) on both sides of the 34-mile-long (55 km) rift. This is 10 times farther than magma flow seen in ridges without sediment cover, probably because such mud blankets — some 0.6 to 1.2 miles (1 to 2 km) thick — keep seawater from cooling and solidifying the molten rock.
The molten rock apparently heated up the seafloor mud, prompting the organic material-rich sediments to release carbon dioxide and methane, greenhouse gases that trap heat from the sun and contribute to global warming. This methane seemed to help support a seafloor community of bacteria, tubeworms and other life.
These "may represent a distinct type of ecosystem," said researcher Daniel Lizarralde, a geophysicist at Woods Hole Oceanographic Institution in Massachusetts. The newfound ecosystem is potentially home to species adapted to the unique thermal and chemical gradients found at such "warm seeps."
The researchers estimate that such heating at this site could release as much as 88,000 tons (80,000 metric tons) of carbon annually.
More seep sites
There are probably quite a few more sites like Guaymas around the world, such as in the South China Sea, the Philippine Sea, the Red Sea, the Aegean Sea and the Lau Basin (by the Tonga Islands in the southwest Pacific).
In total, such rifts probably extend thousands of miles and release thousands of times more carbon than seen at Guaymas, Lizarralde said.
"These may represent a whole vast region where you can have this distinct type of 'warm seep' community that hasn't been explored yet," Lizarralde told OurAmazingPlanet.
Greenhouse gas release
Hot rock pumped into sedimentary basins has been linked to huge natural pulses of methane that may have generated dramatic shifts in global climate in the past, such as at the Karoo basin in South Africa 183 million years ago and at the Norwegian margin 55 million years ago. Still, the amount of carbon the Guaymas site pumps out pales in comparison to fossil fuel combustion, which now surpasses 9 billion tons (8 billion metric tons) of carbon released per year. It also remains uncertain as to how much of this carbon might ultimately escape into the atmosphere and how much the seafloor organisms capture.
Although the carbon from these rifts probably has little direct impact on current global warming concerns, "our results may help understand the past, which is useful for trying to predict the future," Lizarralde said.
In addition, while rifts can release global warming gases, scientists have suggested they could also serve as sites where people could bury such gases and help fight climate change. Some rifts are linked with a moderate to large amount of magma, and Lizarralde advised it would be a bad idea to try to dump carbon in these kinds of systems. However, other rifts are very magma-poor, and a potentially useful rock from the mantle known as peridotite is exposed.
"As it turns out, exposed mantle rocks alter in such a way as to absorb a lot of carbon," he explained. One approach to sequestering man-made greenhouse gases "that has received a good bit of attention is the fracturing of exposed peridotite to increase the surface area of these rocks so that they can absorb more carbon."
The scientists detailed their findings online Nov. 14 in the journal Nature Geoscience.
This article was provided by OurAmazingPlanet, a sister site of Live Science.
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