(F)
(C)
4
38
Ma
3
xim
um
36
De
2
ns
it
y
34
1
32
0
Freezin
g Point
1
30
2
28
3
26
4
24
5
10
20
30
0
40
Salinity (parts per thousand)
Figure 7. Relationship between the temperature of maximum density
and the freezing point of water with respect to salinity. (After Bowditch
1977.)
conditions of low turbulence, the crystals on the bot-
Snow on top of the ice cover acts as an even greater
tom side of the ice cover grow downward, becoming
insulator, further decreasing the growth rate (Fig. 8).
elongated and columnar shaped. This process is known
Despite snow's insulating effect, a thick snow cover
as congelation growth. The thickening ice cover be-
can sometimes speed the process of ice thickening.
comes a barrier to heat flow between the water and
When the snow weighs enough to depress the ice sur-
the colder air above it. As the ice thickens, the loss of
face below the water level, hydrostatic pressure causes
heat needed to maintain the ice growth process is
water to seep up through the ice and saturate the over-
slowed.
lying snow. Air temperatures that are sufficiently cold
(in.)
(cm)
100
35
80
hs = 0 cm
30
hs = 5 cm
25
60
hs = 10 cm
20
40
15
10
20
5
0
0
0
500
1000
1500
Freezing Degree-Days (C)
Figure 8. Relationship between the thickness of young sea ice, accumu-
lated freezing degree-days, and snow cover thickness, hs. (After
Untersteiner 1986.)
10
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