baa as ek
as C'4/C or Si3?/S ratios. As shown by
Lal et al. (8) transthermocline mixing
rates (that is, deep water residence
times) calculated from such ratios are
independentof the effects of downward
particulate transport.
A series of 13 measurements made
on surface ocean water (depth 1 m)
between Hawaii and Japan (Table 2)
clearly demonstrate that a significant
amount of radon escapes to the atmosphere. As shown in Fig. 2, the radon
concentration in surface water aver-
ages 0.54 of that in water from 100 to
300 m. Three measurements from 25 m
average 0.68 in the equilibrium value
and one measurement from 75 m, 0.77.
The
depth
at
which
the
anomaly
reaches one-half its surface value is
thus about 75 m. The seas were calm
during the entire period of these
measurements; the wind force averaged
1 to 2 and did not exceed 4; and the
seasonal thermocline averaged 25 m.
As previously shown (/), the fraction of equilibrium, /,, between radon
and its parent radium at any depth, x,
below the sea surface is given by
fi, =
Cr
Ceaull
1
Dy + ZVxDs|
_, nit
|»
Dy exp (
)+ZvVADeE
os
Table 3. Concentration of Ra“-Rn™ in near-bottom water from the South Atlantic Ocean
(Conrad-11). All samples of water were 19 liters. Numerals in parentheses are assumed values.
Radon contrations are given in radium equivalents.
Sample
Distance
above
R1-A
RI-B
R1-C
R1i-D
R3-A
10
17
24
31
5
R3-C
R3-D
No.
ne
the coefficient of molecular diffusion;
eddy mixing; and ,, the decay constant
for radon. If x1,/2 is defined as the depth
ps
T
t
Pa
‘
‘
\
4
‘
:
= BF
ty
=
‘
a
}
6.
‘
‘‘
+
'
5h
i°
4
1
4
el
ji
!
12
1
16
:
2
Fig. 1. The vertical distribution of Ra?26
in the oceans. @, Northwest Pacific Ocean;
+, east equatorial Pacific; and A, north2 DEFCEMRER 1967
it
(T)
(7)
9
47°02’S
43°41°W
2162
1
. 26
1050
47°02’S
47°02’S
R4-A
R4-B
18
R4-C
R4-D
52°41 W
47°02’S
at which the radon anomaly becomes
half of that at the surface,
where f, = [(fo + 1)/2]
xy
De = ( 0.693
that is,
43°41°W
43° 40W
43°41°W
182+
(7)
(7)
1
(7)
17.0+ 0.8
662 5
(7)
(7)
Since # averages 25 m (compared to
X1/2/0.693 = 108 m), R becomes 14
mole m-? year-!, a value consistent with
the distribution of natural C1‘. This
question cannot be resolved until de-
*
cm?/sec.
The rate of exchange, R, of CO. gas
tailed vertical profiles of the radon deficiency have been obtained.
The last column in Table 1 proves
our previous prediction that easily
measured excesses of radon exist in
R = [Du(CO2)\/Z = DuPco,Cs')/Z
excesses ranging from 5 to 12 x 10-4
gram equivalent of Ra** per liter were
If x12 is 7.50 X 10? cm and X is 2.1
x 10-6 second, D, turns out to be 120
will be given by
1+
Du
ZViADzE
.
we have
R = Pco.Cs’ VADe (1 — fo)/fo
Finally, writing Dy in terms of x12
near-bottom waters. In these samples
found 25 m abovethe sea floor [with the
use of the 200-liter sampler developed
by Gerard et al. (9)]. In order to ob-
tain bottom profiles, four 30-liter Niskin
samplers (Von Dorn type) were placed
at 7-m intervals on the camera wire
and triggered from the surface by messenger. The results (see Table 3) show
that, as expected, the excess decreases
away from the bottom.
R= [(PcogCs’x3d)/ 0.693] x kes —_ fo)/ fol
The CO: exchange rate can be calculated in another way. Instead of assuming an exponential drop-off with
Ra 226 (107 g/liter)
west Atlantic Ocean.
200+ 1
16.5+0.8
cay in the sea (4).
t
' rs
1
a
L
8
§2°41'W
52°41°W
39°04’S
result is about four times larger than
the average demanded to replenish the
radiocarbon undergoing radioactive de-
?
1
4
39°04’S
39°04’S
TT
TT
T
Surface sampies (depth 1 meter)
year). If x12 is 75 m and fo is 0.54,
R turns out to be 60 mole m~? year -’.
Although similar in magnitude, this
\
*
“4
=
19
26
20.9>
TA + 06.5
Wx OS
73a 45
6.6 5
(7)
is 30 mole m—*? atm—! and A is 66
+e
‘
‘
21
401+ 2
220+ 1
14.107
8.0— 5
20.7+ 1
solubility of CO, in seawater at 25°C
~~. “h,
\
32°37 W
32°37'W
32°37W
32°37'W
52°41W
The partial pressure in the atmosphere
over the ocean and in mid-latitude seawater is about 3.2 X 10-* atm. The
4
4+
lie
22°47'S
22°47'S
22°AT7'S
22°4T'S
39°04’S
12
fo=(
Dy, the apparent coefficient of vertical
nee
g/liter)
|
must pass by molecular diffusion; Dz,
anu
g/liter)
Since for x = 0
where Z is the thickness of a hypothetical boundary layer through which gases
Position
Longitude
R3-B
Latitude
No. of samples
ee
7
'
as wai tte ete ek be
=
2
or
\
:
2
Oe = 120 =F
8
X)7 75 m)
-
= 200
4
\ EZ
ead
\
em?
\
\
a
\
\
\
depth, let us assume that the deficient
zone lies above the seasonal thermocline and is roughly uniform over this
interval. Taking the depth to the seasonal thermocline to be ft, we have
R= Poo CsA — fo)/ fol
/
200
rs
1
,
z
oa
3
4
Rn22 ag equiv. Ra7@® {107M g /Iiter}
Fig. 2. The vertical distribution of Rn?22
in surface waters of the northwest Pacific.
1309