Geoscience Reference
In-Depth Information
Table A1.
(continued)
Node
Name
Node Title
Node Description
States
expansive compared to earlier years. This rough ice may also provide refuge for seals,
and it also is surely difficult for polar bear COYs to negotiate as they attempt to move
out onto the ice after den emergence in spring.
More optimal ice is somewhat heavier and not as rough, with pressure ridges com-
posed of larger ice blocks. however, it can go the other way. Very heavy stable ice in
the Beaufort Sea in the past may have been limiting polar bears. This is also probably
currently true in portions of the AE and in the northern part of the PBCE. So, in those
areas, I expect that ice quality will at first improve with global warming and then
decline.
Because my only sense of this ice quality is in the polar basin, I am leaving all priors
uniform for the other ice regions.
C
Foraging
habitat
Absence
Change
This node expresses the length, in months, of ice absence from the continental shelf
regions currently preferred by polar bears. It corresponds to the value “proportional
ice-free months” from D. Douglas' calculations based on GCMs. This is the number
of months during which the continental shelf was ice free where ice free is defined as
fewer than 50% of the pixels over the shelf having less than 50% ice cover.
We express this as a change from now. So the figures in this node represent the dif-
ference in months between the forecasted number of ice-free months for four future
time periods and the number of ice-free months for the present which is defined as the
GCM model outputs for the period 2000-2009.
The bears in some regions already experience protracted ice-free periods. In other re-
gions they do not. The impact of the length of the ice-free period is dependent mainly
upon the productivity of the environment, and has a different impact in the Beaufort
Sea, for example, than it does in the currently seasonal ice environments which are, for
the most part, very productive.
For example, a difference in the amount of time ice was absent of GT 3 months means
a mean absence of 7 or 8 months in the PBDE, and 8, 9 or 10 months in the seasonal
ice zone, but only 3+ months in portions of the AE or the PBCE where ice is now
present year-round.
-1 to 0
0 to 1
1 to 3
>=3
B
Foraging
habitat
Quantity
Change
This node expresses the proportional change in the area of polar bear habitat over time.
Polar bear habitat is expressed as the number of square km months of optimal RSF
habitat in the two polar basin geographic units, and as square km months of ice over
continental shelf in the other regions. Because the other regions are almost entirely
shallow water areas, the habitat in those areas boils down to essentially the ice extent
months over each region.
We further express this as the percent change in quantity of these ice habitats, from the
baseline now which is defined as the period 1996-2006.
Interpreting the percent difference must take into account that a given percent change
in the archipelago or the PB convergent region is a very different thing than it might
be in the other two units. The absolute change in the archipelago, for example, may
be very small, but because it is measured from essentially 0, it may look like a great% .
These measurements are derived from the satellite record for the observational period
and from the GCM outputs of sea ice for future periods.
0 to 20
-20 to 0
-40 to -20
< -40
N
Shelf Distance
Change (km)
This node expresses the distance that the ice retreats from traditional autumn/winter
foraging areas which are over the continental shelves and other shallow water areas
within the polar basin. It is calculated by extracting the largest contiguous chunk of
ice whose pixels have >50% concentration and determining the mean of the measured
distances between all cells in the subpopulation unit and the nearest point within that
chunk of ice. It is expressed as the difference between this mean distance calculated
for the period 1996-2006 and the same mean distance calculated for the other time
periods of interest. These distances are derived from the satellite record for the obser-
vational period and from the GCM outputs of sea ice for future periods.
-200 to 0
0 to 200
200 to 800
>= 800
Search WWH ::
Custom Search