283
The Carbonate System
difficult to use Equation 7.122 to calculate global fluxes of CO 2 . When ΔpCO 2 is positive, the
oceans are a source of CO 2 ; when it is negative, the oceans are a sink for CO 2 . To take up the
missing CO 2 , the value of ΔpCO 2 worldwide would have to be about 8 ppm.
As discussed for other gases, the value of k (the exit coefficient) is a function of the wind
speed and is difficult to determine. If rapid exchange takes place, one would expect the
pCO 2 in the atmosphere to be equal to the values in the surface waters. If the exchange is
sluggish, the pCO 2 in surface waters will be higher in upwelling areas and lower in colder
waters than the values in the atmosphere.
Measurements of pCO 2 in the Atlantic surface waters are shown in Figure 7.13.
The higher values of pCO 2 near the equator are the result of equatorial upwelling. The
lower values of pCO 2 in the polar regions make these waters a sink for CO 2 As discussed
by Broecker and Peng (1982), the levels of TCO 2 and pCO 2 in surface waters are related to
the exchange of CO 2 across the air–sea interface. Sluggish exchange causes pCO 2 to be
greater than the values in the atmosphere near the equator and lower in polar waters. A
north- south section of pCO 2 in the surface waters in the Pacific shown in Figure 7.14 provides values similar to the values in the Atlantic Ocean.
A number of workers have attempted to separate the causes of the changes in the pCO 2
of surface waters from physical (temperature and salinity) and biological (chlorophyll) factors. An example of such a separation is shown in Figure 7.15 using the Atlantic data. The
relative importance based on the magnitude of the changes is in the order temperature,
chlorophyll, and salinity. This way of examining the importance of physical and biological
process slopes neglects the importance of nutrients and the formation of phytoplankton
blooms that can pull down the surface values of pCO 2 .
Wind Speed (m s
–1 )
0
4
8
12
16
20
Transfer Velocity, Sc = 600 (cm h
–1
)
0
20
40
60
80
100
Ocean
14 C
Figure 7.12
The transfer velocity of CO 2 at 20°C as a function of wind speed. The straight lines are based on the relationships of Liss and Merlivat (1986): k = 0.17U 10 for U 10 ≤ 3.6 m s –1 , k = 2.85U 10 – 9.65 for 3.6 m s –1 < U 10 ≤ 13 m s –1 and
k = 5.9U 10 – 49.3 for U 10 > 13 m s –1 (where U 10 is the wind speed 10 m s –1 above the surface). The Schmidt number
Sc = ν/ D where ν is the kinematic viscosity (η/ ρ) and D is the diffusion coefficient.
The Carbonate System
difficult to use Equation 7.122 to calculate global fluxes of CO 2 . When ΔpCO 2 is positive, the
oceans are a source of CO 2 ; when it is negative, the oceans are a sink for CO 2 . To take up the
missing CO 2 , the value of ΔpCO 2 worldwide would have to be about 8 ppm.
As discussed for other gases, the value of k (the exit coefficient) is a function of the wind
speed and is difficult to determine. If rapid exchange takes place, one would expect the
pCO 2 in the atmosphere to be equal to the values in the surface waters. If the exchange is
sluggish, the pCO 2 in surface waters will be higher in upwelling areas and lower in colder
waters than the values in the atmosphere.
Measurements of pCO 2 in the Atlantic surface waters are shown in Figure 7.13.
The higher values of pCO 2 near the equator are the result of equatorial upwelling. The
lower values of pCO 2 in the polar regions make these waters a sink for CO 2 As discussed
by Broecker and Peng (1982), the levels of TCO 2 and pCO 2 in surface waters are related to
the exchange of CO 2 across the air–sea interface. Sluggish exchange causes pCO 2 to be
greater than the values in the atmosphere near the equator and lower in polar waters. A
north- south section of pCO 2 in the surface waters in the Pacific shown in Figure 7.14 provides values similar to the values in the Atlantic Ocean.
A number of workers have attempted to separate the causes of the changes in the pCO 2
of surface waters from physical (temperature and salinity) and biological (chlorophyll) factors. An example of such a separation is shown in Figure 7.15 using the Atlantic data. The
relative importance based on the magnitude of the changes is in the order temperature,
chlorophyll, and salinity. This way of examining the importance of physical and biological
process slopes neglects the importance of nutrients and the formation of phytoplankton
blooms that can pull down the surface values of pCO 2 .
Wind Speed (m s
–1 )
0
4
8
12
16
20
Transfer Velocity, Sc = 600 (cm h
–1
)
0
20
40
60
80
100
Ocean
14 C
Figure 7.12
The transfer velocity of CO 2 at 20°C as a function of wind speed. The straight lines are based on the relationships of Liss and Merlivat (1986): k = 0.17U 10 for U 10 ≤ 3.6 m s –1 , k = 2.85U 10 – 9.65 for 3.6 m s –1 < U 10 ≤ 13 m s –1 and
k = 5.9U 10 – 49.3 for U 10 > 13 m s –1 (where U 10 is the wind speed 10 m s –1 above the surface). The Schmidt number
Sc = ν/ D where ν is the kinematic viscosity (η/ ρ) and D is the diffusion coefficient.