Pockmarks in the southwestern Barents Sea and Finnmark fjords

Abstract

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 Ingydjupet, 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 km 2 . North of the Finnmark coast, from Magerya/Nordkapp to the Russian border, pockmark distribution is nearly continuous. The density varies mainly between 300 and 600 per km 2 , 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.