7.4. Atmosphere-Ocean Interaction Model
131
Solving equation (2) at each time step ena bles us to determine the flux of
CO 2 from the atmosphere into the ocea n (and in the reverse direction if the
sign is negative). The conce ntration of CO 2 in a given volume of atmosphere (ppm/v) can easily be calculated from the total molar amount of CO 2
,
The corres po nding calculations are carried out in the CO 2 module shown in
Figure 7.1. In that module, the particulate C associated with sinking N is
calculated using the average CIN ratio of marine plankton of 6.6 mol mol"
(Redfield et al. 1963). Diffusion of CO 2 into and out of the surface ocean
from and to the atmosphere is set by the conce ntration gradient of CO 2 betwee n the atmosphere and the ocean. Calculations of surface p CO 2 and pH
are shown in Figure 7.2. Note that in the real wo rld a o is also a function of
temp erature and the ionic strength of seawater.
7.4.2. Nutrient Regulation
of Phytoplankton Carbon Fixation
The growth and sinking of marine phytoplankton represen ts an important
conduit through which atmosphe ric CO 2 can enter, and be sequestered in,
the deep ocean. The growth of marine phytoplankton requ ires the presence of many nutrients. Recent laboratory and field studies have shown N
and Fe to be particularly important (Coale et al. 1996b; Price et al. 1994).
Nitrogen in the form of ammo nium is an essential compo nent of amino
acids, the building blocks of proteins. Nitrogen limitation therefore results
in a host of problems at biochemical and biophysical levels, causing reduced CO 2 fixation and ultimately reduced growth. In the oxyge nated modem ocean, the thermodynamically stable form of N is nitrate (N0 3
- ) . Before
nitrate can be incorporated into amino acids, for example, it must be reduced to NH 3
- . This incorporation is accomplished with the two ironcontaining enzymes , nitrite and nitrate redu ctase.
Iron is an essential part of the ph otosynthetic apparatus. Iron limitation
leads to a decrease in the efficiency of light energy conversation to reducing agents (Greene et al. 1991; Greene et al. 1992). In areas of the ocean
with high N0 3
- concentrations but low chlorophyll and low productivity,
an addition of iron stimulates uptake of N0 3
- by marine phytoplankton ,
pC02 Surface
AlphaO
pH
FIGURE 7 .2
131
Solving equation (2) at each time step ena bles us to determine the flux of
CO 2 from the atmosphere into the ocea n (and in the reverse direction if the
sign is negative). The conce ntration of CO 2 in a given volume of atmosphere (ppm/v) can easily be calculated from the total molar amount of CO 2
,
The corres po nding calculations are carried out in the CO 2 module shown in
Figure 7.1. In that module, the particulate C associated with sinking N is
calculated using the average CIN ratio of marine plankton of 6.6 mol mol"
(Redfield et al. 1963). Diffusion of CO 2 into and out of the surface ocean
from and to the atmosphere is set by the conce ntration gradient of CO 2 betwee n the atmosphere and the ocean. Calculations of surface p CO 2 and pH
are shown in Figure 7.2. Note that in the real wo rld a o is also a function of
temp erature and the ionic strength of seawater.
7.4.2. Nutrient Regulation
of Phytoplankton Carbon Fixation
The growth and sinking of marine phytoplankton represen ts an important
conduit through which atmosphe ric CO 2 can enter, and be sequestered in,
the deep ocean. The growth of marine phytoplankton requ ires the presence of many nutrients. Recent laboratory and field studies have shown N
and Fe to be particularly important (Coale et al. 1996b; Price et al. 1994).
Nitrogen in the form of ammo nium is an essential compo nent of amino
acids, the building blocks of proteins. Nitrogen limitation therefore results
in a host of problems at biochemical and biophysical levels, causing reduced CO 2 fixation and ultimately reduced growth. In the oxyge nated modem ocean, the thermodynamically stable form of N is nitrate (N0 3
- ) . Before
nitrate can be incorporated into amino acids, for example, it must be reduced to NH 3
- . This incorporation is accomplished with the two ironcontaining enzymes , nitrite and nitrate redu ctase.
Iron is an essential part of the ph otosynthetic apparatus. Iron limitation
leads to a decrease in the efficiency of light energy conversation to reducing agents (Greene et al. 1991; Greene et al. 1992). In areas of the ocean
with high N0 3
- concentrations but low chlorophyll and low productivity,
an addition of iron stimulates uptake of N0 3
- by marine phytoplankton ,
pC02 Surface
AlphaO
pH
FIGURE 7 .2