Search

A large and diverse dataset has been compiled and analysed in the Barents Sea and Finnmark fjords in northern Norway in order to map and characterise pockmarks. The main data sources are regional side-scan sonar and deep-towed boomer lines and extensive bathymetric datasets of multibeam echo sounding. Small to medium-sized pockmark fields occur in several basins west of Nordkappbanken. The most extensive is in Ingøydjupet, where the largest pockmarks are nearly 100 m wide and up to 8 m deep. Small to medium-sized pockmarks are, however, more common (20-50 m wide, 2-5 m deep). The pockmark density is typically 150-200 per km². North of the Finnmark coast, from Magerøya/Nordkapp to the Russian border, pockmark distribution is nearly continuous. The density varies mainly between 300 and 600 per km², and most pockmarks are small (15-40 m wide, 1.5-4 m deep). Recent studies suggest that the pockmarks in the southwestern Barents Sea were formed from seabed expulsion of gas due to dissociation of gas hydrates during the last deglaciation. Locally, gas has been observed to leak from the Barents Sea floor, but not from pockmarks, suggesting recent inactivity. We further explore the possibility that the pockmarks were formed during a short-lived event and that their shapes have been preserved due to low sedimentation rates and turbulent ocean currents. Numerous small pockmarks also occur in four studied Finnmark fjords. They are most common in Varangerfjorden and Porsangerfjorden where non-gas generating Proterozoic rocks subcrop. The origin of these pockmarks is most likely related to groundwater seepage. [ABSTRACT FROM AUTHOR]

Abstract: Gas and gas hydrates have gained considerable attention in the last 20yr due to their possible impact on global climate change from methane escalations. Our study area, the SW Barents Sea, is unique in its evolution due to the effect of glaciations which removed thick layers of sediment from the seabed. Unloading due to erosion and deglaciation resulted in opening of pre-existing faults and creation of new ones, facilitating fluid migration and eventually escape into the water from the subsurface. Expressions of hydrocarbon gas accumulation and fluid flow such as gas hydrates and pockmarks are widely distributed in the Barents Sea. Several gas flares, some of them 200m high in echograms, occur along a segment of the Ringvassøy Loppa Fault Complex, indicating open fractures and active fluid flow. Observation of gas flares along regional fault complexes outside pockmark regions indicates that present gas escape occurs along faults only. The pockmark formation and gas flares belong to different episodes of fluid flow. The pockmarks are absent outside soft sediment depocentres indicating that their existence is related to the presence of recording medium. The thin sediment cover in pockmarks and their penetration down into glaciomarine sediments indicate that they formed after deposition of these sediments and that fluid escape was active to the very recent past. Methane hydrate stability zone (MHSZ) modelling shows that after the last glacial maximum 18000–20000 14Cyears ago, the MHSZ has thinned from 600m to zero in most parts of the SW Barents Sea. The fluid expulsion probably happened after retreat of the glaciers causing release of methane from dissociation of methane hydrates through fluid escape processes which lasted until recently. Bottom simulating reflectors (BSR) observed are probably due to structure II hydrates formed from gas containing higher order hydrocarbon components such as ethane, propane, etc. along with methane. The study area falls close to the new gigantic oil discoveries, Skrugard and Havis, and north of the Snøhvit hydrocarbon field. [Copyright &y& Elsevier]

The article focuses on the role of submarine underground discharge in the dissociation of marine methane hydrates in the Arctic Region. It says that the runoffs from the submarine underground discharge proceeds to Barents Sea and its heat are transferred through moisture convection, molecular thermal conductivity, and thermal radiation which causes heat transfer. It states that heat flow beneath the Arctic seas in the presence of water exchanges is a factor of thermal balance beneath the shelf zone. It adds that climate warming which causes increase atmospheric precipitation triggers heat flow density.