Geoscience Reference
In-Depth Information
Table A1.
(continued)
Node
Name
Node Title
Node Description
States
likely to converge on the archipelago rather than form disjunct chunks of ice (although
some GCMs do predict the latter, this is contrary to the historical record and the paleo-
record).
yes = other suitable areas are contiguous
No = other suitable regions are not contiguous
R2
Relative
Ringed Seal
Availability
This node expresses changes in prey availability that are likely to occur as sea ice
cover declines and its character changes.
This node specifically includes only the possibility that ringed seals, the mainstay
of polar bears over most of their range, might change in abundance and availability.
This is specific to the amount of remaining ice. That is, as sea ice declines in cover-
age (which is the only way it seems possible for it to go) will the remaining habitat be
more productive?
Availability here refers to the combined effects of abundance and accessibility, recog-
nizing that seals may occupy areas that make them less available to polar bears even
if the seals are still relatively abundant. Examples of this are the recent observations
of failed bear attempts to dig through solid ice (a result of the thinner ice that deforms
and rafts more easily) that predominates now, and the fact that seals may simply stay
in open water all summer and not be available to bears even if the seal numbers are
stable.
My judgment is that only in the northern part of the ice convergent zone of the polar
basin and in portions of the archipelago are conditions likely to improve for ringed seal
availability. And, there, such improvements are likely to be transient perhaps through
mid century.
increase = greater abundance or availability of ringed seals compared to now
decrease = less abundance or availability
increase
same_as_now
decrease
R3
Alternate Prey
Availability
This node expresses changes in prey availability that are likely to occur as sea ice
cover declines and its character changes. This is largely expert opinion because there
is little to go on to suggest prey base change possibilities in the future. With very dif-
ferent ice and other ecological differences that may accompany global warming things
could occur which are totally unforeseen. Today's experience, however, suggests
that little in the way of significant alternate prey is likely to emerge to allow bears to
replace traditional prey that may be greatly reduced in the future.
Where alternate prey could become important is in the seasonal ice regions and the
archipelago. Now, harp (
Phoca groenlandicus
) and hooded (
Cystophora cristata
) seals
have become important to polar bears as they have moved farther north than histori-
cally. As the ice retreats into the archipelago it is reasonable to expect that these
animals may penetrate deeper into the archipelago and provide at least a transient
improvement in alternate prey. It is unclear, however, that such changes could persist
as bears prey on these seals which are forced onto smaller and smaller areas of ice. So,
I project only transient improvements followed by decline.
This node specifically addresses the possibility that alternate prey, either marine or ter-
restrial, might change in a way that would allow polar bears to take advantage of it.
increase = greater availability of alternate prey
decrease = less opportunity for access to prey items other than ringed seals
increase
same_as_now
decrease
S1
Foraging
habitat
Character
This node expresses a subjective assessment of the quality of sea ice for foraging by
polar bears. Recent observations of the changes in sea ice character in the southern
Beaufort Sea suggest that the later freeze-up, warmer winters, and earlier ice retreat in
summer have resulted in thinner ice that more easily deforms and more frequently rafts
over itself. These changes have reduced the quality of ice as a denning substrate, and
may have reduced its quality as a foraging substrate since the extensive ice deforma-
tion can result in ice covered refugia for ringed seals which are less likely for polar
bears to get into. Also, it can result in very rough sharp pressure ridges that are hugely
more_optimal
same_as_now
less_optimal
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