Geography Reference
In-Depth Information
The fluctuation effect is dominated by the northern hemisphere
forests. Since there is more land mass in the northern hemisphere
and forests are concentrated here then there is much more carbon
uptake in the northern hemisphere summer and therefore global
atmospheric carbon dioxide concentrations decrease during each
northern hemisphere summer and rise each winter.
As discussed earlier in this chapter, the oceans also absorb
carbon dioxide from the atmosphere via photosynthesis by micro-
scopic plants such as algae. This photosynthetic activity occurs
mainly in the upper 50 metres of the ocean but varies widely
across the oceans depending on temperature and the amount of
nutrients available in the water to support life. While most of the
carbon is returned to the atmosphere as part of the cycle of life
some of it falls to the deep ocean floor within the detritus of dead
plant and animal material. Part of this carbon can dissolve into the
seawater whereas some of the carbon can remain stored for thou-
sands or even millions of years on the ocean floor. However, deep
ocean currents can stir up the sediment and bring some of the
carbon back to the surface to later be released back to the atmo-
sphere. The oceans currently store around 60 times more carbon
than is in the atmosphere and 20 times more than in the eco-
systems and soils on land.
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Figure 2.4
Major components of the carbon cycle.
