1994 Arctic Ocean Section
and the type was recorded qualitatively. Typical global
Ice properties in four navigation zones
snow densities were 0.42 Mg/m3 for large-grained, wet
during AOS-94. The maximum ice
strength is an index of maximum hull
snow and 0.25 Mg/m3 for fine, new snow.
loads, and the mean ice strength is an
For evaluating the ship's performance, and also for
index of ship performance.
interpreting the ice forces on the hull of the ship, the
Ice
Floe
Max
Mean
ice and snow mechanical properties data were separated
cover
size strength strength
into four navigation zones. Up to latitude 80N, there
(N)
(10ths)
(km) (kPa)
(kPa)
was considerable surface melt and brine drainage. The
7080
8 to 9+
0.5
470
250
8088
9+ to 10
3.0
250
250
ice was porous and contained many flaws, allowing
8890
10
1.0
500
500
relatively easy ship passage. However, mean ice tem-
8581
8 to 9+
0.5
600
300
peratures indicate that layers of intact, relatively cold
ice were present in some floes, with a risk of significant hull loads.
North of 80, where air temperatures were lower, mean ice temperatures
were slightly higher than in the first zone. This apparent paradox is due to
melt surfaces advancing more rapidly than conduction isotherms and is recog-
nized in icebergs (Diemand 1984). The ice was close to its melting point and
presented low strengths throughout the thickness.
The heavy ice at the highest latitudes, 88N and beyond, was composed of
extensively damaged, worked and reconsolidated ice features. For this fairly
homogeneous ice, a higher ice strength applies to both ship performance and
load risk.
The transit was rapid and the sampling sparse from 90N south to 85N.
Hence, it is not certain where to place the boundary between zone 3 and zone
4. However, south of 85N the ice was clearly thinner, less complex and of
lower concentration. The drained, low-salinity ice had begun to refreeze. The
completely frozen freshwater melt pond at Station 37 was an illustration.
Because of extensive flaws due to melting, the mean ice strength was low, but
the presence of solid, low-salinity ice pushed up load risk levels.
REFERENCES
Diemand, D. (1984) Iceberg temperatures in the North Atlantic--Theoreti-
cal and measured. Cold Regions Science and Technology, 9(2): 171178.
Williams, F.M. (1994) The Canada/U.S. 1994 Arctic Ocean Section--Ice mech-
anical properties measurements. Institute for Marine Dynamics: TR-1994-29.
Williams, F.M., and B.L. Parsons (1994) Size effect in the flexural strength of
ice. 13th International Conference on Offshore Mechanics and Arctic Engi-
neering, Houston, Vol. IV, p. 1522.
88
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