Sea-ice indicators of polar bear habitat
Nineteen subpopulations of polar bears (<i>Ursus maritimus</i>) are found throughout the circumpolar Arctic, and in all regions they depend on sea ice as a platform for traveling, hunting, and breeding. Therefore polar bear phenology – the cycle of biological events – is linked to the...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-09-01
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| Series: | The Cryosphere |
| Online Access: | https://www.the-cryosphere.net/10/2027/2016/tc-10-2027-2016.pdf |
| Summary: | Nineteen subpopulations of polar bears (<i>Ursus maritimus</i>)
are found throughout the circumpolar Arctic, and in all regions they depend
on sea ice as a platform for traveling, hunting, and breeding. Therefore
polar bear phenology – the cycle of biological events – is linked to the
timing of sea-ice retreat in spring and advance in fall. We analyzed the
dates of sea-ice retreat and advance in all 19 polar bear subpopulation
regions from 1979 to 2014, using daily sea-ice concentration data from
satellite passive microwave instruments. We define the dates of sea-ice
retreat and advance in a region as the dates when the area of sea ice drops
below a certain threshold (retreat) on its way to the summer minimum or
rises above the threshold (advance) on its way to the winter maximum. The
threshold is chosen to be halfway between the historical (1979–2014) mean
September and mean March sea-ice areas. In all 19 regions there is a trend
toward earlier sea-ice retreat and later sea-ice advance. Trends generally
range from −3 to −9 days decade<sup>−1</sup> in spring and from +3 to +9 days decade<sup>−1</sup> in fall, with larger trends in the Barents Sea and
central Arctic Basin. The trends are not sensitive to the threshold. We also
calculated the number of days per year that the sea-ice area exceeded the
threshold (termed ice-covered days) and the average sea-ice concentration
from 1 June through 31 October. The number of ice-covered days is declining
in all regions at the rate of −7 to −19 days decade<sup>−1</sup>, with larger
trends in the Barents Sea and central Arctic Basin. The June–October sea-ice
concentration is declining in all regions at rates ranging from −1 to −9 percent decade<sup>−1</sup>. These sea-ice metrics (or indicators of habitat
change) were designed to be useful for management agencies and for
comparative purposes among subpopulations. We recommend that the National
Climate Assessment include the timing of sea-ice retreat and advance in
future reports. |
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| ISSN: | 1994-0416 1994-0424 |