Geoscience Reference
In-Depth Information
90°
60°
30°W
0°
30°E
60°
90°
120°
150°
180°
150°
120°
90°
90°
S
S
60°
60°
U
30°N
30°N
0°
0°
30°S
30°S
ty
60°
60°
S
S
90°
60°
30°W
0°
30°E
60°
90°
120°
150°
180°
150°
120°
Other
return
flows
Zones of
high-density
subsidence
Zones of
oceanic
upwelling
Deep-
density
currents
Permanent
Seasonal
Less deep
return flow
Coastal
upwelling
S
U
Figure 7.32
The deep ocean thermohaline circulation system leading to Broecker's concept of the
oceanic conveyor belt.
Source: Kerr (1988). Reprinted with permission from Science 239, Fig. 259. Copyright © 1988 American Association for the
Advancement of Science.
results in atmospheric CO
2
being dissolved in
the oceans, Some of this CO
2
is subsequently
converted into particulate carbon, mainly through
the agency of plankton, and ultimately sinks to
form carbon-rich deposits in the deep ocean as
part of a cycle lasting hundreds of years. Thus two
of the major effects of ocean surface warming
would be to increase its CO
2
equilibrium partial
pressure and to decrease the abundance of
plankton. Both of these effects would tend to
decrease the oceanic uptake of CO
2
. This would
increase its atmospheric concentration, thereby
producing a positive feedback (i.e., enhancing)
effect on global warming. However, as will
be seen in Chapter 13, the operation of the
atmosphere-ocean system is complex. Thus, for
example, global warming may so increase oceanic
convective mixing that the resulting imports of
3 The oceans and atmospheric
regulation
The atmosphere and the surface ocean waters are
closely connected both in temperature and in CO
2
concentrations. The atmosphere contains less
than 1.7 percent of the CO
2
held by the oceans,
and the amount absorbed by the ocean surface
rapidly regulates the concentration in the atmos-
phere. The absorption of CO
2
by the oceans is
greatest where the water is rich in organic matter,
or where it is cold. Thus the oceans can regulate
atmospheric CO
2
, changing the greenhouse
effect and contributing to climate change. The
most important aspect of the carbon cycle linking
atmosphere and ocean is the difference between
the partial pressure of CO
2
in the lower atmos-
phere and that in the upper oceanic layer. This
