The Carbon Cycle - Introduction to Carbon Capture and Sequestration - page 117

buoyant surface waters of the high latitudes of the Southern Ocean the
biological activity is less optimal and hence most of the nutrients are
returned into the deep ocean unused. Because of this difference the
biological pump is much more effi cient for the Atlantic Ocean, which can
sequester more CO 2 compared to the Southern Ocean. Thus, an impor-
tant consequence of the difference in fl ow patterns is that in the North
Atlantic the amount of carbon that is sequestered is much larger.
Recent theories have connected this excess to the glacial and inter-
glacial periods. The details of this mechanism are outside the scope of
this text, but we cannot resist giving a short version of this elegant theory.
The hypothesis is that part of the excess CO 2 generated by the biological
pump is stored in the deep part of the Southern Ocean that is not well
mixed [3.8]. Because of this, there is a net fl ux of CO 2 from the atmos-
phere into this deep ocean reservoir. This drop in atmospheric CO 2
causes a temperature drop and a growth in polar ice. The reservoir of
deep CO 2 is, however, fi nite and eventually the excess CO 2 will be
released, causing a reversal of the glacial period. Many of these theories
are speculations, but this build up of CO 2 in the Southern Ocean is pre-
dicted to occur on a time scale of 10 5 years, which is one of the peaks in
Figure 3.1.3 for which we have no other explanation.
Section 4
The inorganic carbon cycle
In Figure 3.1.3 the largest peak represents fl uctuations of 10,000 times
the current CO 2 level with a period of about 10 9 years, which is about the
age of the earth. We see that the effect of this “perturbation” has not yet
fully decayed. This peak is associated with the inorganic carbon cycle,
which is the most important mechanism to regulate the temperature of
the earth. The fact that we need to regulate the temperature is closely
related to the faint young sun paradox, described below.