NRL-led Cruise Discovers Mud-Volcano (Methane Seep) in Greenland-Norwegian Sea

5/13/1996 - 44-96r
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Scientists from the Naval Research Laboratory (NRL) and the University of Bergen, Norway, have used sediment cores, heat flow, and bathymetric measurements to discover an active gas seep and mud volcano. The scientists' studies revealed that a 1-km-diameter circular feature, previously detected by an NRL-led sidescan sonar mapping project on the continental slope northwest of Norway, was a gas seep and mud volcano.

The discovery, the first of this kind in high-latitude (72 degrees north) oceanic areas, was made on an NRL-led research cruise aboard the Norwegian vessel Haakon Mosby, the same ship that had towed the sidescan sonar in prior years. Dr. Peter Vogt, of NRL's Marine Geosciences Division, and Professor Eirik Sundvor, University of Bergen, Norway, were co-chief-scientists.

The circular feature was identified as a "gas seep" because hydrogen sulphide (H2S) and methane hydrate were abundant in the sediment cores, and acoustic returns also suggested gas bubbles in the water column. A new species of worm was recovered and shown to be of the type dependent on chemosynthetic bacteria which utilize methane and/or hydrogen sulphide. The gas seep is at the same time interpreted as a "mud volcano" because of its mound-like shape and the presence of a halo of weak acoustic backscatter material, thought to be sediment oozing out of the mound and flowing into a shallow moat surrounding the mound, according to Dr. Vogt.

The heat flow, measured by Professor Sundvor, is one of the highest ever measured in the world ocean away from active plate boundaries or mid-plate "hotspots" such as Hawaii. Sediment recovered near the heat flow station reeked of H2S, and methane hydrate (clathrate) crystals were observed at the bottom of a 2m-long core. These crystals fizzed away at the ambient atmospheric pressures, but this was the first direct observation of methane hydrate along the continental margin from Norway north to Spitzbergen and the Arctic. In this large region, NRL had previously predicted methane hydrate's existence, and Norwegian scientists had reported seismic reflection evidence for the hydrate from parts of this region.

Further investigations, including deep-tow video, sccheduled for August 1996 aboard a Russian vessel, may find more evidence for this gas venting and chemosynthetic life at the newly identified gas seep and other, similar sidescan sonar features not yet investigated, but now suspected to have a similar origin.

A small portion (50 x 50 cm) of the mud volcano's surface was recovered with a box corer on the recent Mosby expedition. A sample of the mud, containing almost 200 of these vermicelli like pogonophoran tube worms, was later examined by Dr. Roman V. Smirnov of the Zoological Institute, St. Petersburg, Russia. Dr. Smirnov identified these worms as a new species of the genus Sclerolinum. The six previously known Sclerolinum species all hail from Antarctic waters; none are known so far from middle latitudes, notwithstanding the uniformly low temperatures of the deepwater oceans.

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