Past Climate Variability and Change in the Arctic and at High Latitudes

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The U.S. Climate Science Program
whale, and bowhead (Greenland right) whale.
Of these, the bowhead has left the most abundant,
hence most useful, fossil record, followed
by the walrus and the narwhal. Radiocarbon
dating of these remains has yielded a large set
of results, largely available through Harington
(2003) and Kaufman et al. (2004).
Former sea-ice conditions can be reconstructed
from bowhead whale remains because seasonal
migrations of the whale are dictated by the
oscillations of the sea-ice pack. The species
is thought to have had a strong preference
for ice-edge environments since the Pliocene
(2.6–5.3 million years ago (Ma)), perhaps because
that environment allows it to escape from
its only natural predator, the killer whale. The
Pacific population of bowheads spends winter
and early spring along the ice edge in the berinG
SeA and advances northward in the summer
ice into the Canadian Beaufort Sea region along
the western edge of the cAnAdiAn Arctic ArchipelAGo.
The Atlantic population spends winter
and early spring in the northern lAbrAdor SeA
between southwest GreenlAnd and northern
Labrador and advances northward in summer
into the eastern channels of the cAnAdiAn Arctic
ArchipelAGo. In normal summers, the Pacific
and Atlantic bowheads are prevented from meeting
by a large, persistent, plug of sea ice that
Chapter 6
occupies the central region of the cAnAdiAn
Arctic ArchipelAGo; i.e., the central part of the
Northwest Passage (Figure 6.4). Both populations
retreat southward upon autumn freeze-up.
However, the ice-edge environment is hazardous,
especially during freeze-up, and individuals or
pods may become entrapped (as has been observed
today). Detailed measurements of fossil
bowhead skulls (a proxy of age) now found in
raised marine deposits allow a reconstruction
of their lengths (Dyke et al., 1996; Savelle et al.,
2000). The distribution of lengths compares very
closely with the length distribution of the modern
Beaufort Sea bowhead population (Figure 6.5),
indicating that the cause of death of many bowheads
in the past was a catastrophic process that
affected all ages indiscriminately. This process
can be best interpreted as ice entrapment.
6.3.6 Ice Cores
Among paleoenvironmental archives, ice cores
from glaciers and ice sheets have a particular
strength as a direct recorder of atmospheric
composition, especially in the polar regions, at
a fine time resolution. The main issue is whether
ice cores contain any information about the
past extent of sea ice. Such information may be
Figure 6.4. Arctic sea ice conditions in September 1996. These conditions were typical for late 20th century summer sea ice in
the Canadian arCtiC arChipelago. [Data from the National Snow and Ice Data Center using NASA Goddard Space Flight Center
Scientific Visualization Studio Blue Marble.]