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Ocean Carbon Changes
As was previously pointed out, the ocean is both a major source and sink
of carbon for the atmosphere. Inorganic carbon in the form of dissolved carbon
dioxide and carbonates accounts for about 37,000 gigatons. Dissolved organic
carbon contributes an additional 1,000 gigatons. Particulate carbon such as
from live organisms or dead plants and animals or fragments add about 30
units. We should remember that there are large uncertainties in these estimates
because of the wide variations over the planetary oceans.
Oceans regulate carbon in 3 different ways: by physical processes, chemical processes, and biological processes. Physical processes include the movement of carbon by ocean circulation from one location to another. Meteorologists and oceanographers call this process advection. Differences in temperature and salt content (salinity), in addition to the driving force of the wind and rotation of the earth, lead to bulk transport of carbon within and between major ocean basins. Another physical process is the diffusive mixing of water from one vertical level to another. Carbon dioxide dissolved in surface water is in equilibrium with CO2 in the atmosphere because of efficient mixing in the ocean surface water.
Chemical processes transform carbon among different molecular forms. Biological processes include the production and decomposition of organic matter, which are confined to the upper layer of the ocean where photosynthesis can operate. If this biological material remains near the surface, it will continue to cycle with the atmosphere. Some carbon, such as in the form of phytoplankton that thrive in the surface water of the ocean, are eaten by small fish and eventually larger fish or animals that ultimately die, leaving skeletons or carbonate shells that sink to the ocean floor. This process, sometimes referred to as "biological pumping", takes carbon from the rapidly changing part of the cycle near the ocean's surface to the deep ocean where it may be stored for thousands of years. The deep ocean is richer in dissolved inorganic carbon, and the surface water has a predominance of organic carbon.
The increase of ultraviolet radiation, which we will discuss in connection with ozone depletion, also has implications for ocean biology. Many of the simple organisms in the ocean surface are very vulnerable to ultraviolet radiation, and increases in ultraviolet radiation due to ozone depletion could significantly affect simple organisms at the bottom of the food chain that thrive in the ocean surface water. This presents a linkage between the ozone depletion problem and the build-up of atmospheric CO2: decreased ozone could contribute to increased ultraviolet light, which decreases ocean plant life, which decreases CO2 consumption by the ocean, which allows for increased rates of CO2 build-up in the atmosphere.