foreign ships seeking passage at any time through
Table 6. Probability (%) of occurrence of conditions
that require icebreaker assistance through various
certain island straits (Vil'kitskogo, Shokal'skogo,
NSR massifs (from Buzuev 1991).
Dmitriya Lapteva, and Sannikova).
The summer season occurs roughly from June
Amguema-class
Noril'sk-class
to September when the ice cover melts significantly,
Ice massif
Jun
Aug Oct
Jun
Aug Oct
diminishing in both extent and strength. Figure 17
shows the seasonal changes in the normal ice cover.
Novaya Zemlya
95
0
0
95
0
0
Severnaya Zemlya
100
75
25
100
60
5
It can be seen that the greatest seasonal fluctua-
Taymyr
95
65
40
95
55
15
tion occurs at the east and west ends of the route.
Novosibirskiy
95
60
20
90
45
10
This is due to the influence of ocean currents mov-
Ayon
95
35
15
95
30
5
ing northward from the warmer Atlantic Ocean in
Wrangel
95
10
25
95
5
5
the west and the Bering Sea in the east, which
accelerate ice decay in the spring and retard
freezeup in the fall. Of greater interest to shipping
size. For example, the Novaya Zemlya massif
is the mean July-to-September location of the ice
nearly melts out completely, while the Taymyr,
edge with 7/10ths or greater concentration.* These
Ayon, and Wrangel massifs are more resistant and
isolines are shown in Figure 18. This map does not
experience less ablation.
take into account the location of the ice massifs, as
Table 6 shows the probability for ice conditions
the September and, to a large extent, the August
that necessitate icebreaker assistance through NSR
isolines are well north of the massifs shown in
massifs for ULA-class ships (the highest ice classi-
Figure 16.
fication for cargo ships under the Russian regis-
Between the freezing and melting seasons is a
try). The data include observations from 1970
brief interphase of ice pack movement from wind
through 1991. Although the individual probabili-
and ocean currents. This interphase is character-
ties are quite low for October, there is a high prob-
ability that all cargo vessels will need icebreaker
assistance somewhere along the way, even in Oc-
* Ice concentration is usually expressed in tenths or
tober. In fact, Section 7.4 of the ANSR regulations
octas describing the amount of sea surface covered by
(1991) stipulates that escort is mandatory for all
ice as a fraction of the total area being considered.
Sea Ice Extent
GREENLAND
Alaska
Bering
S
A
Minimum Ice Limit (mild summer)
ea
Average Summer Ice Extent
C hS k c h i
u
Mverage Winter Ice Extent
ea
aximum Ice Limit (severe winter)
Provideniya
ORT
S Mys
hmidta
OL
Pevek
ARCTIC
OCEAN
a d yr
NORWAY
0
60
SWEDEN
12
Ea
90
In
e
Riv
Laptev
S
FINLAND
ea
Barents
S
Murmansk
Magadan
ea
iver
Kara Sea
Tiksi
St. Petersburg
Nordvik
r
O ea of
S
Dikson
Arkhangel'sk
khotsk
Khatanga
er
ek
Dudinka
River
Salekhard
Noril'sk
500
0
E
Yakutsk
CL
Yamburg
Igarka
IR
C
Nautical Miles
R
IC
ARCT
0
1000
R
U
S
S
I
A
Kilometers
JAPAN
Figure 17. Seasonal extent of the sea-ice edge (from Barnett 1991; USNODC 1986a,b).
24
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