Thermal rejuvenation along the
Barents Sea Margin:
Implications for the production and release of methane into the Northern Oceans

Kathleen Crane
Hunter College, New York

Monday, August 17, 1998
3:00 p.m.—Pacific Forum

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A warm methane-rich vent has recently been located in a sedimentary environment on the Bear Island Fan adjacent to an ancient fracture zone, marking the boundary between the Barents and Norwegian-Greenland Sea. In contrast to most sediment-covered vents, which are cold seeps, the Haakon Mosby mud volcano is characterized by extremely high thermal gradients >10,000 K/km. Directly above the central region, a thermal and methane-enriched broad plume was detected up to 80 meters above bottom. In 1998, samples collected from the seafloor revealed extensive bacterial mats living on top of a thin layer of surface hydrates.

Cores collected from the mud volcano contained gaseous hydrogen sulfide, methane hydrates and gas in the upper 2 m of sediment, as well as two types of pogonophoran worms (both new species). In addition, recovered gas hydrate crystals are associated with both very high heat flow and anomalous acoustic patterns in the water column up to 100m above the seafloor, which we interpret to be possible gas bubble exhalations.

Heat flow data suggest that the upwelling fluid migration may be stimulated by deep magmatic intrusions into or adjacent to the Senja Fracture Zone, which traverses the seafloor from northern Norway to Spitsbergen and beyond. The cause of the heat release may be a consequence of the reorganization of the unstable Knipovich-Mohns Ridge plate boundary leading to an underplating of the Barents seafloor by deep-seated mantle material. Underplating would be manifested by a broad swath of seismic activity and it would cause rapid uplift of the crust, rapid erosion rates, high heat flow emanating from any pre-existing, deep-seated structure, and even recent volcanism—all of which are observed in the region of the eastern Norwegian-Greenland and western Barents Seas. Thus the amount of methane naturally arising from the seafloor fracture zones onto the margin of the Barents Sea may be a function of the geographic range of mantle underplating in this area.

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