Geoscience Reference
In-Depth Information
Fig. 6.7
Ice bottom elevation relative to the upper surface from ablation measurements made by
A.Hanson during the 1975 AIDJEX project inthewestern Arctic(Adapted from Notzet al. 2003.
Withpermission American Geophysical Union) (see also colorplate on p. 206)
bottoms,inbothlaboratoryandnaturalsettings,includinga simulationoftheAID-
JEXobservations.Thestudyshowedthatdoublediffusionisacriticalprocessinthe
formationoffalsebottoms,whichinturnmayplayanimportantroleinmaintenance
ofperennialsea ice.
In anidealizedviewofthe false bottomlayerafterit hasattainedaninitial finite
thickness(Fig.6.8),we assumehorizontalhomogeneity,andthatthelayerofwater
betweentheexistingmultiyeariceandthenewlyformedfalsebottomisfresh,with
temperature equal to 0
◦
C. We also assume that the thin ice layer is fresh with a
linear temperature gradient. The false bottom thus borders on two different water
types, and because it sustains a significant positive temperaturegradient, there will
bedownwardheattransfer.Withthese assumptions
K
ice
(
T
up
−
T
0
)
K
ice
mS
0
ρ
w
c
p
h
q
=
−
=
−
(6.11)
ρ
w
c
p
h
where
h
is the thickness of the false bottom layer. The upper surface will migrate
upwardintothefreshwaterlayeratrate
ρ
w
q
ρ
ice
Q
fresh
h
up
=
−
