Geology Reference
In-Depth Information
(a)
(b)
0
0
Station 2, 13 June
Station 3, 13 June
−0.5
−0.5
Station 5, 14 June
Station 6A, 14 June
−1
−1
Station 7, 14 June
−1.5
5
−1.5
7
3
6A
−2
−2
Station 2
−2.5
4 ppt
Marker
−2.5
−3
0
2
4
Salinity, ppt
6
8
0
5
10
15
20
25
30
Salinity, ppt (expanded scale)
Figure 5.10
Vertical salinity profile in ice at five sites across Mould Bay on 13 June 1982 (a) using normal plots
and (b) using an expanded scale for salinity in which the broken lines indicate salinity of 4‰.
June, 1982. The snow cover became increasingly damp,
first developing a thin crust on the top and then the thick-
ness reduced to about 60-100 mm by 21 June. The simul-
taneous formation of nodules in crustal snow and near
the ice surface essentially roughened the surface layer of
the ice cover, which had a strong effect on the backscatter
measured by the active microwave instruments. A detailed
description of the characteristics of snow and ice (thick-
ness, temperature, salinity, and surface roughness) in
Mould Bay during the short period of consolidation
and melting in June is given in
Digby
[1982] and
Holt and
Digby
[1985].
During the 11 days from 20 to 30 June, the weather
station data showed that the minimum air temperature
was slightly below the freezing point, but the daily
mean temperature increased slowly from 1.6° to 8.5°C.
Consequently, rapid melting of snow and surface layers
of ice occurred. About 85%-95% of the ice surface in the
bay was covered with a layer of meltwater. All the snow
deposits, excepting the ridges of snow, eventually melted
and formed melt ponds and drainage channels on top of
the ice surface. The water depth varied from 50 mm on
flat surface areas to 200 mm or more in deep melt ponds.
The areas near the shore melted rapidly, making it impos-
sible to use any surface vehicles to go on the ice, as shown
in Figure 5.11 for sampling of ice blocks using a helicop-
ter. Figure 5.12a is a photograph of the bay during the
late melting period. The meltwater, however, drained
quickly within a few days and the ice surface was almost
bare by 3 July, the day the AES Electra flew over the bay
for the SLAR image of Figure 5.12b.
As pointed out in Figure 5.8, a large crack in the ice
sheet developed some time during the week between the
measurement days of 21 May and 29 May 1982. This
Figure 5.11
Extraction of ice blocks with a chain saw and an
ice tong at station 3 in Mould Bay on 30 June 1982 (photo by
N. K. Sinha, unpublished).
The vertical salinity distributions in ice across the bay
for data collected on 13 June are plotted in Figure 5.10.
The plots indicate that during the first 2 weeks of June
1982 the ice cover maintained a condition close to its win-
ter state, except for the materials near the top surface
depending on location. Melting processes in the snow
cover affected the ice salinity at the top. In a few days, the
vertical salinity distribution at all sampling stations, i.e.,
the entire ice sheet, changed to the shape of a Z. Melting
and rapid morphological changes in the snow started to
occur during the middle of June. Toward the end of this
month ponding on the surface started to develop, and
eventually the entire ice surface was flooded as illustrated
in Figure 5.11.
The average air temperature during 13-17 June was
slightly above 0°C and slightly below 0°C during 18-21
