Arctic Yearbook 2012
Østreng
259
Ice-free does not necessarily mean problem-free, or for that matter preclude icebreaker assistance.
The inter-annual variability in sea ice conditions of the Canadian Archipelago will continue to be
extreme. According to the Canadian Ice Service,
It is quite likely that the latter half of this century will still experience occasional
summers with ice conditions as severe as those witnessed in the 1980s. Multi-year ice,
particular in low concentrations, will present the major hazard to shipping…. Since the
oldest and thickest ice in the Arctic Ocean is that which is driven against the western
flank of the Canadian Archipelago, this will likely be the last multi-year ice to remain. As
long as there is a source of multi-year ice in the Arctic Ocean, it will continue to drift
through the Canadian Archipelago (Falkingham, 2004).
M’Clure Strait between Melville and Banks Island is one of the straits that have a fairly long history
of being blocked with multi-year ice drifting in from the Central Arctic Ocean. In addition comes
shallow waters and draft restrictions, narrow straits acting like choke points and the combination of
the two, making navigation a regular and punctual activity hard to achieve. The AMSA study
concludes that even during the most recent periods of reduced ice, the location of the ice, its
thickness from year to year and the variability of ice-free areas makes it nearly impossible to schedule
transits with any degree of certainty of reaching the desired port on schedule.
In addition come the
obstructions stemming from seabed pingoes (AMSA, 2009: 19).
In 1969, the ice-strengthened American super tanker
Manhattan
transited the Canadian archipelago
from the East Coast of the USA to Prudhoe Bay in Alaska. The next year it returned the same way
back. During the first voyage,
Manhattan
was accompanied by the Canadian icebreaker
Macdonald
which at one point registered an unexpected “shoal” in the vicinity of the sailing route. The shoal
turned out to be a seabed pingo, which is old ice shaped like a cone extending like a “knife” from the
seabed upwards towards the surface of the ocean. At the base, the biggest can measure more than
300 m, and may raise more than 60 m above seabed. The assumption is that seabed pingoes, which
are often covered and strengthened with frozen clay and mud, are relics from the time when the
seabed was above sea level. More than 100 pingoes were registered scattered around on the
continental shelf of the Beaufort Sea and within the shallow channels of the Canadian Archipelago
(Information Canada, 1972).
Seabed pingoes undoubtedly represent a danger to ships with deep draughts.
Manhattan
had a
draught of 56 feet whereas the peak of pingoes are often no more than 40 feet beneath the surface of
the ocean. The semi-official journal,
Canada Today,
claimed in 1974 that: