285
The Carbonate System
does not change significantly in these waters. The TCO 2 increases by 0.68 and 1.26 μmol
kg –1 yr –1 and the δ 13 C decreases by 0.024 and 027 ppm yr –1 , respectively, at the Bermuda and
Hawaii time series stations.
The growth of phytoplankton blooms also affects the levels of pCO 2 in surface waters.
The pull- down of surface pCO 2 by phytoplankton and delivery of the CO 2 to deep waters
after decomposition is the so- called biological pump (Figure 7.2). Studies have shown that
the pull- down of CO 2 by plankton occurs in the North Atlantic during the spring blooms.
For this biological pump to take CO 2 permanently from the atmosphere, the organic carbon
must sink below the thermocline and be oxidized back to CO 2 that will be stored for hundreds of years in deep waters.
The depth profiles of pCO 2 for the Atlantic and Pacific are shown in Figure 7.18. These
values were calculated from TA and TCO 2 , so they are not as accurate as direct measurements. The general trends, however, are real and as expected. The surface values are similar to atmospheric values. The values increase to a maximum (500 μatm in the North
Chlorophyll (µg L
–1 )
0
1
2
3
4
260
280
300
320
340
Temperature (°C)
14
16
18
20
22
24
26
280
300
320
340
360
380
Salinity
34.8
35.0
35.2
35.4
35.6
35.8
36.0
320
340
360
380
pCO
2 (µatm)
pCO
2 (µatm)
pCO
2 (µatm)
Figure 7.15
The relationship between the partial pressure of carbon dioxide in Atlantic surface waters to the concentrations
of chlorophyll, the temperature, and the salinity. (Adapted from B. Schneider).