Feature: "Baked Alaska" Mud Volcano Discovered in North Atlantic
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Researchers on a cruise have confirmed that a hot mud volcano on the sea floor between Greenland and Norway is oozing mud, seeping gas and spewing a gas-laden plume of warm water into the North Atlantic. Frozen methane hydrate caps the volcano, whose slopes are inhabited by a new species of tube worm most closely related to a group found in Antarctica.
The rare juxtaposition of heat vents on the sea floor with a frozen methane cap has led Hunter College geophysicist Kathleen Crane, who studied the feature on a cruise last August, to dub it a "baked Alaska" complex. The methane hydrate is a white, ice-like solid made up of water and gas that can compress a huge amount of gas within its crystal lattice.
Frozen methane has been found within the ocean floor but rarely, as in this case, atop the floor. Methane should dissolve or oxidize in sea water, so its presence suggests that it must be in constant production, according to Naval Research Laboratory geophysicist Peter Vogt, a chief scientist on the cruise. Another theory, however, is that some of the white features are actually bacterial mats.
On the latest cruise to investigate the site, using the Russian vessel Professor Logachev, scientists supported by the National Science Foundation, Naval Research Laboratory, Office of Naval Research and Russian and Norwegian institutions confirmed the existence of the mud volcano, a rare phenomenon in the deep ocean. Located 1250 meters deep, the volcano is about one kilometer in diameter, is encircled by a moat, and has "a gross cowpie shape," according to Vogt. The team, also led by Russian chief scientist Georgy Cherkashev, spotted a similar feature in the area that may be a second volcano.
The flow of heat rising within the volcano (up to one or more watts per square meter) is one of the highest measured in the ocean, apart from the boundaries of tectonic plates or "hot spots" such as Hawaii.
What is generating this heat and setting the gas, fluid, and mud into motion is still a mystery. Vogt suggests that the cause could be the gravitational instability of the marine sediments, which were deposited very rapidly by glaciers; or alternatively, the "dewatering" or extrusion of water by the sediments. Crane, on the other hand, proposes that the volcanism may indicate that an ancient fracture between the Greenland Sea oceanic crust and the Barents Sea continental crust is still active, serving as a crack for heat and fluids to rise up to the seafloor.
Like communities of life at other hydrothermal vents in the oceans, the mud volcano's colonies of vermicelli-like worms ultimately derive their energy not from photosynthesis but from seeping gas.
The matted tangles of tube worms, twisted across the mud like telephone cord, live in association with fish and other life. They are a new species of the genus Sclerolinum, whose six other species live on the other side of the globe in Antarctic waters.
A quill-like tube extends from each worm into the odorous mud. When brought to the surface, mud samples crackle like frying bacon and reek of hydrogen sulfide as gas bubbles are released from decomposing hydrate by the change in pressure. Small bottom-fish resembling salamanders, probably a species of eelpout, appear to be grazing on the tubeworm "lawns."
Carbon isotopes from the worms show that they derive their energy not from "oceanic snow"--dead organic matter sifting down from above, and originally produced by photosynthesis--but rather through chemosynthesis, living off the seeping methane and possibly also the hydrogen sulfide. It is actually the bacteria living in symbiosis inside the worms' cells that appear to "feed" on the gases, providing the energy for the worms to live.
Over recent decades, gas hydrates at the ocean bottom have attracted attention as a potential energy source, twice as extensive as the burnable carbon stored in all other fossil fuels. Scientists also propose that the methane locked up in hydrates, such as the one capping the volcano, could play a role in climate change. If sea level dropped--during an ice age, for example--pressure on this stored gas could ease, ultimately releasing the gas into the atmosphere and causing greenhouse warming.
The scientists hope to visit the site again this year in Russian deep-diving submersibles to sample the biotic community and carry out experiments on the methane-hydrate cap, including research on the possibility that solid hydrate particles float up into the water column.
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