Geoscience Reference
In-Depth Information
MultiyearIce
Fresh Water Layer
False Bottom
Seawater~ Slightly above freezing
T
up
=0ºC
h
T
w
=
-
1.7 ºC
T
0
S
0
w
'
T
'
,
,
0
w
'
S
'
0
u
*0
,
,
Fig. 6.8
Schematic of a thin layer of fresh ice that forms between meltwater trapped in underice
concavities andcolder seawater
where the latent heat of ice formation balances the downward heat flux. The lower
boundarywillalsomoveverticallyinresponsetothecombinationof
q
and
w
T
0
.
Thetotalrateofchangeofthicknessforthefalsebottomlayeristhen
h
h
up
−
(
ρ
w
/
ρ
ice
)
=
w
0
=
−
(
ρ
w
/
ρ
ice
)(
q
/
Q
fresh
+
w
0
)
(6.12)
Thebottomheatandmassbalancecan againbereducedtoa quadraticequationfor
salinityat theinterface
mS
0
2
(
1
+
γ
1
)
+(
T
w
+
T
L
−
(
1
+
γ
1
)
mS
ice
)
S
0
−
T
w
S
ice
−
T
L
S
w
=
0
(6.13)
K
ice
ρ
w
c
p
α
h
u
where
0
h
.
Bottomiceelevationrelativetoastartingpointon9July1975(yearday190)in-
dicatesfalsebottomsatfourofHanson'sicethicknesssites(Fig.6.9).Theyformed
at different times, and there is some indication of multiple layer formation during
a relatively calm period from day 205 to 210. But beginningwith a period of more
rapid ice drift from day 210 to 220, thickness decreased more or less uniformly at
all four sites. Following the modeling approach of Notz et al. (2003), the evolu-
tion of a false bottom starting from an initial thickness of 2.5cm was simulated by
solving the combinedequations (6.11),(6.12), and (6.13),with
u
∗
0
estimated from
Rossbysimilarity(4.19)appliedtotheicedriftspeedandwithseawatertemperature
andsalinityinterpolatedfromdailyCTDobservations.Wefurtherspecifiedthatthe
γ
1
=
∗
