Geoscience Reference
In-Depth Information
Figure 7.5.
Mean annual sea ice drift in the Arctic, based on data from the IABP,
the North Pole program and other sources with overlay of sea level pressure from
NCEP/NCAR (ice drift field courtesy of I. Rigor, Polar Science Center, University of
Washington, Seattle, WA, sea level pressure field by the authors).
The mean annual drift of the pack ice consists of two primary features: the
Beaufort Gyre, the clockwise (anticyclonic) motion of ice in the Canada Basin; and
the Transpolar Drift Stream (TPDS), characterizing the motion of ice away from
the Siberian coast, across the pole, and through the Fram Strait. This mean pattern
reflects roughly equal contributions by winds and surface currents. Hence, the mean
ice drift pattern roughly resembles the distribution of mean sea level pressure. The
overlay of annual sea level pressure in
Figure 7.3
is for 1979-1999, the period on
which most of the drift data are based.
With a mean drift speed of 1-3 cm s
−1
, typically, five to ten years are required
for ice to make one circuit around the Beaufort Gyre (Thorndike,
1986
). Ice
can circulate around the gyre for many years. It can take up to three years for
a parcel of ice to move along the TPDS (Thorndike,
1986
). Ice velocities in the
