each 1000 feet increase in depth (500 pounds in 
hydrostatic pressure) the current decreases about 
3 per cent. Beyond 5000 pounds the rate decreases. 
At 15000 pounds only 30 per cent of the initial 
electrode response is left. 
The decreasing electrode current represents 
a decrease in the permeability of the plastic 
film to the diffusion of 0,. The shape of the 
curve indicates that diffuSion through the plastic 
is more of a pore-type phenomenon than one of the 
gas being in solid solution. The first part of 
the curve is the same for teflon and polyethylene 
so there seems little chance of decreasing this 
undesirable pressure dependence by using a dif- 
ferent plastic. The only approach at this time 
seems to be to compute it out of the raw signal. 
Fortunately much of the most interesting 0, vari- 
ations are close to the surface where the 
pressure dependence can either be neglected or 
assumed linear. 
D. In situ recording 
The electrode has been tested twice for 
recording vertical profiles in the ocean. The 
first measurements were done by Dr. Richardson 
with his ingenious free-falling instruments. The 
electrode current was recorded in the instrument 
along with temperature. Depth was determined by 
time and the rate of fall. The current was then 
corrected for temperature and pressure to obtain 
Oy concentration. The location off Bermuda is 
one where frequent chemical determinations of 0 
are made. The two curves in Figure 3 show essen- 
tial agreement. The electrode showed interesting 
detail below the 0, minimum. These would ordinar- 
ily not be seen from the usual spot measurements 
made from Nansen bottle samples. 
I later lowered an electrode along with a 
pressure transducer on the end of a 3-mile length 
of well-logging cable. No amplification was 
needed. This allowed direct x-y recording of 0 
vs depth during the lowering. The curve in 
Figure 4 shows a well mixed surface layer with a 
sharp drop in 05 at 125 meters. This drop did not 
come at a thermocline. The temperature actually 
increased .7° C. In such a case O,, more clearly 
than temperature or salinity, shows two water 
types. A regular hydrographic station was made at 
this time. The Nansen bottles were placed at the 
standard depths and the chemical determinations 
from these are included on the plot. One can 
easily see the difficulty of accurately determin- 
ing the shape of the curve from such spot values. 
If the electrode does not replace the chemical 
method it can at least be used to determine the 
best depths at which to place the Nansen bottles, 
2 
I have also lowered the electrode from row- 
boats for continuous 0, profiles in lakes. 
Initially an uncorrectéd electrode was used and 
temperature was simultaneously recorded. The 
advent of solid state choppers has allowed me to 
record the corrected 0, value directly, using 
thermistor temperature correction, with light 
battery-operated apparatus. 
II CO2 MEASUREMENT 
The measurement of CO, requires a different 
approach from that used for 05. It occurs in only 
1/600 the concentration in air (.03 as compared 
with 21 per cent). But its chemical and physical 
properties result in its being nearly 10 times as 
concentrated in sea water (45 ml/l vs 5 ml/1 0,). 
We can summarize this chemistry by ‘the following 
equations: 
AIR CO» 
— - = 
CO, ar H,0 _ H,CO, rate HCO, ae co, 
SEA WATER Tl 
COMPLEXES 
Any change in the amount of CO, in this system 
will, through these reversible equilibria, alter 
the values of pCO, and pH. I have been able to 
use the former as a convenient and sensitive index 
of such changes 
The measurement of CO, is accomplished by equi- 
librating sea water with a gas phase and then 
measuring the CO, concentration in the gas. The 
partial pressure in the gas is then equal to that 
in the water, if equilibration is gentle and 
complete. It is an attractive approach since CO 
in gas mixtures can be determined to better than 
1 part per million by means of a modern infrared 
analyzer. 
We can expect surface sea water to be more or 
less equilibrated with the atmosphere above the 
surface. Since air contains 300 ppm COy, the 
values of pCO, in the water will center about this 
value. With the infrared analyzer technique out- 
lined it is possible to determine pCO, in this 
range to 1 per cent (+ 3 ppm). 
The chemistry of CO, outlined in the above 
equations results in pco being non-linearly 
related to the total amount of the gas in sea 
water. This makes it necessary to calibrate the 
apparatus by introducing known changes in total 
CO, and measuring the resulting partial pressure. 
Figure 5 shows the result of such a procedure. It 
can be seen that there are very large changes in 
the partial pressure for the variations in total 
CO. we know to exist in the deep ocean waters. 
When such water is anaerobic, or nearly so, its 
pcO, may be 10 times that of equilibrated surface 
water. I have tested this in Eel Pond, a small bay 
here in Woods Hole. It has a sill at its entrance 
which prevents free exchange of the bottom water. 
Sewage from the surrounding houses creates a large 
biological O, demand (co, production). The bottom 
336 
