Geology Reference
In-Depth Information
Table 3.3
Typical physical and electrical properties of four ice types.
New Ice
Young Ice
First‐Year Ice
Multiyear Ice
Thickness (m)
< 0.1
0.1-0.3
> 0.3
> 2.0
Bulk salinity (‰ or ppt)
14
9
4
0.5
Density (kg/m
3
)
920
900
900
750-910
Dielectric constant (10 GHz)
5.65-
j
2.25
4.0-
j
.81
3.32-
j
0.23
2.77-
j
0.03
Therm. conductivity ( W/m · K)
2.14
2.14
2.09
1.88
Brine volume fraction
0.20
0.08
0.05
0.0
3.1. TemperaTure profiles in ice and snow
National Research Council (NRC) of Canada (see also
Section 5.2).
Under steady conditions in winter when the atmosphere is
considerably colder than the ocean, the temperature profile
usually features a linear increase with depth from the upper
cold surface to the lower ice‐water interface where the tem-
perature is typically −1.8 °C. The linear temperature gradi-
ents
G
i
and
G
s
in ice and snow, respectively, can be written as
As mentioned before, temperature profile of sea ice cover
is the driving parameter that influences the volume frac-
tions of sea ice constituents, namely pure ice, brine, and air
inclusions. Temperature also determines the brine salinity
and geometric characteristics of brine pockets. Since brine
should remain at thermal equilibrium, any temperature
change will adjust the salt composition inside brine pockets
according to the phase diagram shown in Figure 2.1.
Significant variations in the ice temperature profile cause
pronounced variations in salinity, brine volume fraction,
thermal conductivity, and the complex dielectric constant.
Temperature profiles of Arctic sea ice have been meas-
ured extensively during numerous field studies [e.g.,
Unterseiner,
1964;
Bilello,
1980;
Shokr and Barber,
1994].
All of these aforementioned measurements were per-
formed on an opportunity basis during short-duration
field campaigns conducted on fully grown ice during the
early spring season. The wisdom of the Inuit people of
the Arctic were not utilized in any of these field cam-
paigns. Historically, the first systematic measurements
on the evolution of snow and ice thickness, temperature
and salinity profiles throughout the entire ice growth sea-
sons of 1977-78 and 1978-79 were carried out in Eclipse
Sound as part of a ten-year program. An Inuit team of
Pond Inlet, Baffin Island provided their assistance from
the start of the freezing to the beginning of melt the sea-
son for all of these years, [See Section 1.3 in Chapter 1
and the papers,
Sinha and Nakaw,
1981;
Nakawo and
Sinha,
1981]. Recently,
Perovich and Elder
[2001] meas-
ured the temperature of the ice over the annual cycle from
October 1997 through October 1998 at several sites
selected to sample different ice types ranging from FY ice
to thick MY ice ridges. Long-term regular measurements
on the growth of sea ice along with the record of the
weather data were conducted at five Canadian High
Arctic weather stations: Alert, Eureka, Isachsen, Mould
Bay and Resolute Bay (Table 1.1), which have been
operated by Environment Canada (some have closed
down). The long‐term measurements program undertaken
during 1976-1986 in Eclipse Sound was supported by
Energy Mines and Resources, Canada (renamed later as
Natural Resources Canada—NRCan), through the Polar
Continental Shelf Project (PCSP) in association with the
G
TT
h
w
s i
/
(3.1)
i
i
G
TT
h
si
/
a
(3.2)
s
s
where
T
a
,
T
s
/
i
, and
T
w
are the air, snow‐ice interface, and sea-
water freezing temperatures, respectively;
h
i
is the ice thickness
and
h
s
the snow depth. If the ice thickness increases by Δ
h
i
in
a time period Δ
t
, then the quantity of heat released during
freezing is
L
si
ρ
si
Δ
h
i
, where
L
si
is the latent heat of fusion and
ρ
si
is the density of sea ice. This amount of heat must flow
through the ice and snow to the atmosphere, assuming that
there is no heat flow to the water underneath. Thus,
Lhk
TT
h
tk
TT
h
w
s i
/
si
/
a
(3.3)
t
i
i
i
si
s
i
s
where
k
si
and
k
s
are the average thermal conductivities of
sea ice and snow, respectively. After rearrangement, the
second equality in equation (3.3) gives
khTkhT
kh kh
T
si
sw sia
(3.4)
si
/
si
s
s
i
Substituting
T
s
/
i
from equation (3.4) in equations (3.1)
and (3.2),
TT
hkkh
G
w
a
(3.5)
i
si
/
i
s
s
TT
hkkh
(3.6)
G
w
a
s
/
s
s
si
i
Substituting
T
si
from equation (3.4) into equation (3.3)
produces the same equation for ice thickness presented in
the previous chapter [equation (2.12)].
