Long-term observations (2014–2020) of level ice draft, keel depth and ridge frequency in the Barents Sea

Abstract

Results from consistent long-term observations of sea ice draft by upward looking sonars at five sites in the Barents Sea during the period 2014–2020 are presented. The recordings were initiated by the Barents Sea Metocean and Ice Network (BaSMIN) with the objective to provide data for design of offshore structures in Norwegian oil and gas license areas. Sea ice imported from the Arctic Ocean, ocean heat of Atlantic origin as well as dynamic deformation contribute to spatial and temporal variability in drafts. The average draft of locally grown level ice at the end of winter is approximately 0.6 m. Reflecting a decreasing trend in ocean temperatures at the observation site, the timeseries of locally grown level ice draft exhibits an increasing trend during the observation period of approximately 5 cm per year. During events of sea ice drifting in from the north, the level ice draft reaches up to 1.5–1.8 m. Keels deeper than 2.5 m have an average keel depth of 3.8 m. The 99th percentile keel depth is 9.4 m, while the deepest keels protrude down to nearly 20 m. The average ridge frequency is 3.6 ridges/km, with a corresponding 99th percentile of 25 ridges/km. Sea ice on Spitsbergenbanken has deeper keels and larger frequency of ridges than sea ice on Storbanken at the northern end of the Hopen Trench. We hypothesize that more vigorous currents with convergence and shear on the shallower Spitsbergenbanken contribute to this geographical difference.