Accessibility of polar bear denning habitat in the Barents Sea

Polar bear in pack ice. Photo: Norwegian Polar Institute

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The Arctic is warming, and Arctic sea ice has shown a rapid decrease in sea ice extent, ice thickness, and ice age in the last decades. Polar bears rely on sea ice for hunting, resting, travelling and in some parts of the Arctic also reproduction. However, in the European Arctic, polar bears rely on snow drifts on land to den and get their young. Consequently, the timing of sea ice arrival around different land masses in the Barents Sea is important for the reproductive success of individuals spending most of the year on the sea ice. If pregnant females are unable to reach denning habitat by the end of the year (November/ December) they will most likely not be able to reproduce (Derocher et al. 2011).

This data product provides an overview over the arrival of sea ice around the island groups in the Barents Sea during autumn throughout the last four decades. This way inferences can be made about the suitability of potential maternity denning habitat for the Barents Sea polar bear population, i.e. what parts of Barents Sea islands was able to be reached by polar bears hunting on the sea ice in time to enter maternity dens for reproduction. Arrival timing of sea ice around islands in the Barents Sea are shown as decadal averages for the last 4 decades, i.e. 1980’s, 1990’s, 2000’s and 2010’s. It is colour coded in green, yellow and red according to polar bear ecology corresponding to early enough to reach denning habitat (before 1st December), just in time (after 1st December and before new year), and too late to reach denning habitat (after new year).

Decadal average arrival timing of sea ice around the islands in the Barents Sea (a to d). Arrival timing is colour coded in green, yellow and red according to polar bear ecology corresponding to early enough to reach denning habitat (before 1st December), just in time (after 1st December and before new year), and too late to reach denning habitat (after new year), respectively. Black areas are not considered to be polar bear habitat as they are too far inland and mainly consist of glacier caps. Decadal average arrival timing of sea ice around the islands in the Barents Sea (a to d). Arrival timing is colour coded in green, yellow and red according to polar bear ecology corresponding to early enough to reach denning habitat (before 1st December), just in time (after 1st December and before new year), and too late to reach denning habitat (after new year), respectively. Black areas are not considered to be polar bear habitat as they are too far inland and mainly consist of glacier caps.

 In addition to decadal changes in sea ice arrival, annual changes in arrival timing throughout the four decades (1979 - 2018) are visualized as animation below.

During the 1980’s and 90’s many important denning areas in eastern Svalbard, Franz Josef Land and eastern Novaya Zemlya were accessible for bears spending their summer on the sea ice in time to enter maternity dens. However, in recent decades less and less denning areas were accessible particularly in Svalbard and southern Novaya Zemlya due to a lack of sea ice around these islands.

This data product follows the methodology by Derocher et al. (2011) and defines sea ice arrival around land masses as the first instance after each summer when 60 % sea ice cover was present within a 50 km buffer. Sea ice concentration was estimated using passive microwave SSM/I (Special Sensor Microwave Imager) remote sensing data with a 25 x 25 km resolution from NASA’s Earth Observing System Distributed Active Archive Center (National Snow and Ice Data Center, University of Colorado, Boulder).

 

REFERENCES

Derocher, A.E., Andersen, M., Wiig, O., Aars, J., Hansen, E. & Biuw, M. 2011 Sea ice and polar bear den ecology at Hopen Island, Svalbard. Marine Ecology Progress Series 441, 273-279.