247
Dissolved Gases Other than CO 2
information is needed for other inert gases. By using Ar as a reference gas, one can make a
reasonable correction for the deviations caused by nonideal equilibria. The concentration
of oxygen consumed since the waters left the surface is given by
[O 2 ] surf – [O 2 ] meas [O 2 ]* × [Ar] meas /{[Ar]* – [O 2 ] meas }
(6.48)
where [i]* is the predicted value at the given temperature and salinity and [i] meas is the
measured value.
In the absence of Ar measurements, the apparent oxygen utilization (AOU) is determined from
AOU [O 2 ]* – [O 2 ] meas
(6.49)
The AOU is used to recognize that the [O 2 ]* may depart from ideal values because of air
injection and so on. As shown previously, surface waters are about 3% supersaturated.
At upwelling areas, the surface O 2 concentrations can be 20% less than saturation. This is
shown in Figure 6.13 for Pacific waters. The surface AOU values are 15 μmol kg −1 near the
equator because of upwelling. This can be compared to values around –7 μmol kg −1 for
other surface waters.
The distribution of O 2 and AOU at a depth of 4000 m is shown in Figure 6.14. The sinking bottom waters in the North Atlantic have high concentrations of O 2 (~300 μmol kg –1 )
and low AOU (~50 μmol kg –1 ). The older waters in the North Pacific have very low O 2 (~50
μmol kg –1 ) and high AOU (~200 μmol kg –1 ). The values of AOU and pCFC ages in the Pacific
Ocean waters from the surface to 1000 m are shown in Figure 6.15. The equatorial upwelling waters have high values of AOU and are very old. The waters in the gyres in the north
have AOU of about 150 μmol kg –1 and an age of 10 yr. This gives a loss of about 15 μmol
kg –1 yr –1 . The ages of the upwelling or deeper waters cannot be accurately determined by
the pCFC method since they have been around for about 50 yr. By examining the AOU at
Latitude
[O
2 ]
MEAS – [O
2 ]
CALC (µmol kg
–1
)
–15
–10
–5
0
5
10
Surface Waters
5°S
0
5°N
Figure 6.13
The differences in the measured and calculated dissolved oxygen concentrations in surface waters.
Dissolved Gases Other than CO 2
information is needed for other inert gases. By using Ar as a reference gas, one can make a
reasonable correction for the deviations caused by nonideal equilibria. The concentration
of oxygen consumed since the waters left the surface is given by
[O 2 ] surf – [O 2 ] meas [O 2 ]* × [Ar] meas /{[Ar]* – [O 2 ] meas }
(6.48)
where [i]* is the predicted value at the given temperature and salinity and [i] meas is the
measured value.
In the absence of Ar measurements, the apparent oxygen utilization (AOU) is determined from
AOU [O 2 ]* – [O 2 ] meas
(6.49)
The AOU is used to recognize that the [O 2 ]* may depart from ideal values because of air
injection and so on. As shown previously, surface waters are about 3% supersaturated.
At upwelling areas, the surface O 2 concentrations can be 20% less than saturation. This is
shown in Figure 6.13 for Pacific waters. The surface AOU values are 15 μmol kg −1 near the
equator because of upwelling. This can be compared to values around –7 μmol kg −1 for
other surface waters.
The distribution of O 2 and AOU at a depth of 4000 m is shown in Figure 6.14. The sinking bottom waters in the North Atlantic have high concentrations of O 2 (~300 μmol kg –1 )
and low AOU (~50 μmol kg –1 ). The older waters in the North Pacific have very low O 2 (~50
μmol kg –1 ) and high AOU (~200 μmol kg –1 ). The values of AOU and pCFC ages in the Pacific
Ocean waters from the surface to 1000 m are shown in Figure 6.15. The equatorial upwelling waters have high values of AOU and are very old. The waters in the gyres in the north
have AOU of about 150 μmol kg –1 and an age of 10 yr. This gives a loss of about 15 μmol
kg –1 yr –1 . The ages of the upwelling or deeper waters cannot be accurately determined by
the pCFC method since they have been around for about 50 yr. By examining the AOU at
Latitude
[O
2 ]
MEAS – [O
2 ]
CALC (µmol kg
–1
)
–15
–10
–5
0
5
10
Surface Waters
5°S
0
5°N
Figure 6.13
The differences in the measured and calculated dissolved oxygen concentrations in surface waters.