Geoscience Reference
In-Depth Information
The exchange processes taking place on the atmosphere-ocean border have been
experimentally studied by Kiseleva (1990), Zaitsev (1988), and others. In their
works it has been shown that at high wind speeds the rate of gas exchange sharply
increases. This is connected with the mechanism of the foam formation on wave
crests as well as an intensive catching of air bubbles and their penetration beneath
the water surface. The dependence of the amount of spray Q on the height over the
water surface is well approximated by a linear function. For instance, for the wind
speed V = 11.1 m/s this approximation is (Kiseleva 1990):
Q
0
exp
14
f
:
5z
þ
0
:
684
g
without wave breaking,
Q ¼
Q
0
exp
7
f
:
48z
þ
0
:
842
g
with wave breaking,
where Q
0
cm
2
s
1
½
is the dimensional multiplier.
Experimental estimates of the net gas transport due to the droplet mechanism
have shown that the CO
2
fl
flux between water and air can vary from 1.44 mg CO
2
/
m
2
/h in the absence of wave breaking to 26.6 mg CO
2
/m
2
/h. The rate of the gas
exchange on the atmosphere-ocean border is markedly affected by the foam for-
mation on the ocean surface. In this case, the rate of the gas exchange can increase
up to 28 %. All this suggests the conclusion that a detailed modeling of the
mechanisms of the atmosphere-water CO
2
transport is needed. The satellite World
Ocean monitoring allows one to identify the zones of foam formation and, hence,
along with the modeling of the processes of foam formation, to perform direct
measurements of the areas of the foam-covered basins.
The mechanism of the air bubbles behaviour in the upper layer of the ocean has
been poorly studied. The available theoretical results are based, as a rule, on a
number of suppositions, which in many cases can drastically distort the ideas about
real processes of the gas exchange between the atmosphere and the ocean. Among
these suppositions the following have been used most often:
air bubbles in the upper layer of the ocean practically instantly acquire the
temperature of the environment, since the molecular coef
cient of heat con-
ductivity exceeds that of gases by 2
3 orders of magnitude;
-
air bubbles in water do not affect its dynamics; and
air bubbles do not merge in water.
The size of air bubbles in water varies constantly because of their gradual
solution. The gas
fl
flux through the bubbles is described by the relationship:
Q ¼ 4
p
RD
j
D
p
j
S
Nu
;
where
is the difference of the partial pressures of gas in the water and in the
atmosphere, R is the bubble
∣D
p
∣
'
is radius,
8
<
5Pe
2
ln 2Pe
1
þ
0
:
5Pe
þ
0
:
ð
Þ
for R
20
l
m
;
p
2
p
Pe
1
=
3
l
R
200
l
;
Nu ¼
=
3
for
20
m
\
m
:
45Pe
1
=
3
Re
1
=
3
0
:
for
200
l
m
\
R
400
l
m
;
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