Geology Reference
In-Depth Information
are sampled when the ambient air temperatures are close
to the freezing point or higher. There is an abundance of
the Ɔ‐shaped vertical salinity profiles in the open ice litera-
ture, primarily due to the fact that most sea ice researchers
traditionally go to the field (Arctic or Antarctic) when day-
light is available and the ambient air temperatures are desir-
able for human activities. Undeniably, this generalized
comment does not apply to the famous and much quoted
plot of the pioneering scientific adventurer
Malmgren
[1927] who spent the entire period of his study in the field.
He plotted the measurements on the variation in sea ice
salinity profiles for five different thicknesses across
the central Arctic basin. The data was collected during
the voyage of the drift of the Norwegian ship
Maud
,
and the samples were collected from five different geo-
graphical locations of the ship. Consequently, his data did
not represent decay of sea ice at a given geographical loca-
tion. Although measurement problems mentioned earlier
equally apply to his data, Malmgren established probably
for the first time, for the people of the south (outside the
Innuit communities of the north), the most important
fact that the average sea ice salinity decreases with time.
Keeping aside the points of argument, the Ɔ‐shaped ver-
tical salinity profiles probably can be considered as a “trade
mark” of decaying ice because such profiles are generated
from data collected from ice cores sampled from the ocean
when the ice covers are (a) close to melting or (b) snowmelt
percolating through the ice sheet and/or at (c) isothermal
conditions and (d) decreasing in thickness by melting
from the top as well as from the bottom. The warm and
decay period in sea ice also provides comfortable air tem-
peratures for fieldwork and sample collections. Most
investigators spend only a short period of a week or so in
the field and forget the environmental conditions in the
field after their return to their home bases. There is a gen-
eral tendency to forget or ignore (or fail to discuss and
point out) the reality that it is impossible to remove iso-
thermal ice cores without major losses of brine contents
of the entire core. The water simply drains out of the ice
when pulling the cores out of the ice. Actually, the changes
in the color of the cores from dark gray or white are easily
noticeable. Thereafter, further brine drainage occurs dur-
ing storage and transportation. In a way, plotting such
salinity profiles, without warning, is not scientifically ethi-
cal. There is a danger too. The novice or the uninitiated
researchers, who never went to the field or had the field
experience, may assume the results as reliable in situ prop-
erties and may start theorizing the phenomenon.
Severe vertical drainage of brine occurs as the ice
cores are sampled. Further drainage occurs when the
cores are packed and transported to laboratories. This
also applies to the Mould Bay observations of July 1982,
even though the cores were stored in deep freezers
(shown in the photograph of Figure 5.2 and kept at
about −22°C) after taking them to the field laboratory
“as soon as possible” after sampling them. Storing the
cores in the deep freezer, of course, prevented the ice
from further drainage. The thickness of the ice cover
had diminished to about 1.4 m at station 3 by the middle
of July 1982, primarily by surface ablation (judging from
wooden posts frozen in the ice) and probably to a lesser
extent by bottom melt. The decay in the ice cover can be
judged from the desalination processes that occurred
during the rapid melting period as shown in Figure 5.13,
(a)
(b)
3.0
0
13 June, 2.20
2.5
−0.5
Freeboard,
13 June, 1982
13 July, 1.27 m
2.0
−1
1. 5
−1.5
1. 0
7 July, 1.56 m
13 June, 2.20 m
−2
Ice thickness reduced to 0.5 m by the end of summer
3 July, 1. 83 m
0.5
June, 1982
July, 1982
21 June, 2.17m
−2.5
0.0
0
1
2
3
4
5
6
7
0
10
20
30
40
50
Salinity, ppt
Number of days
Figure 5.13
Vertical salinity profile (a) exhibiting both desalination and reduction in ice thickness and
(b) thickness‐time history from 13 June to 13 July, 1982 at station 3. (Caution: salinity data for isothermal ice from
3 to 13 July 1982 are subjected to unavoidable brine loss during core sampling.)
