Terrestrial biosphere

Prentice, K. C. The Influence of the Terrestrial Biosphere on Seasonal Atmospheric Carbon Dioxide An Empirical Model Ph.D. Dissertation, Columbia University, New York, NY, 1986. 

The content of the material in a carbon reservoir is a measure of that reservoir s direct or indirect exchange rate with the atmosphere, although variations in solar also create variations in atmospheric content activity (Stuiver and Quay, 1980, 1981). Geologically important reservoirs (i.e., carbonate rocks and fossil carbon) contain no radiocarbon because the turnover times of these reservoirs are much longer than the isotope s half-life. The distribution of is used in studies of ocean circulation, soil sciences, and studies of the terrestrial biosphere. 

Carbon monoxide emissions from the terrestrial biosphere are small, but forest fires produce 0.02 Pg C/yr. Degradation of chlorophyll is dying plant material seems to be the largest CO-producing mechanism at 0.04-0.2 Pg C/yr (Freyer, 1979). 

Box, E. O. (1988). Estimating the seasonal carbon source-sink geography of a natural, steady-state terrestrial biosphere, /. Appl. Meteorol. 17,1109-1124. 

Fung, I. Y., Prentice, K. C., Matthews, E., Lerner, J. and Russell, G. (1983). Three-dimensional tracer model study of atmospheric CO2 Response to seasonal exchanges with the terrestrial biosphere, /. Geophys. Res. 88,1281-1294. 

Post, W. M., King, A. W. and Wullschleger, S. D. (1997). Historical variations in terrestrial biospheric carbon storage, Global Biogeochem. Cycles 11, 99-109. 

Assuming the current emissions and sinks remain about the same, estimate the global atmospheric CO2 mixing ratio in the year 2050. Now repeat this calculation, but this time assume that the terrestrial biosphere no longer continues to sequester some of this anthropogenic carbon. 

Hudson R. J. M. et al. (1994). Modeling the global carbon cycle Nitrogen fertilization of the terrestrial biosphere and the "missing" CO2 sink. Global Bio-geochem. Cycles 8, 307-333. 

Terrestrial biosphere tends toward a net carbon source as 15% -40% of ecosystems affected ----... 

There are different time scales associated with the various emissions and uptake processes. Two terms that are frequently used are turnover time and response or adjustment) time. The turnover time is defined as the ratio of the mass of the gas in the atmosphere to its total rate of removal from the atmosphere. The response or adjustment time, on the other hand, is the decay time for a compound emitted into the atmosphere as an instantaneous pulse. If the removal can be described as a first-order process, i.e., the rate of removal is proportional to the concentration and the constant of proportionality remains the same, the turnover and the response times are approximately equal. However, this is not the case if the parameter relating the removal rate and the concentration is not constant. They are also not equal if the gas exchanges between several different reservoirs, as is the case for C02. For example, the turnover time for C02 in the atmosphere is about 4 years because of the rapid uptake by the oceans and terrestrial biosphere, but the response time is about 100 years because of the time it takes for C02 in the ocean surface layer to be taken up into the deep ocean. A pulse of C02 emitted into the atmosphere is expected to decay more rapidly over the first decade or so and then more gradually over the next century. 

Including also uptake by the terrestrial biosphere. The mean residence time for exchange with the sea alone is expected to be larger than this value by about 25%. 

A number of other interesting possibilities for utilizing the excess 14C in the atmosphere as a tracer of natural processes come easily to mind. Not much is known about the rate of turnover of humus in the soil. Measurements of 14C in soil humus over the next several years, while the terrestrial biosphere continues to fix carbon with significant amounts of excess 14C, should help to determine the rate of turnover of carbon in the reservoir of humus. Some work along these lines is already in progress (41). 

The required reduction therefore amounts to only a tiny fraction of the theoretical sequestration potential of the world soils. Although evaluation and certification of emission credits for sequestration of C in the terrestrial biosphere is certainly difficult (Marland et al., 2001), it is worthwhile to consider C sequestration in developing possible mitigation plans. 

For example, in the carbon cycle consider the balance between terrestrial photosynthesis and respiration-decay. If the respiration and decay flux to the atmosphere were doubled (perhaps by a temperature increase) from about 5200 x 1012 to 10,400 x 1012 moles y-l, and photosynthesis remained constant, the CO2 content of the atmosphere would be doubled in about 12 years. If the reverse occurred, and photosynthesis were doubled, while respiration and decay remained constant, the CO2 content of the atmosphere would be halved in about the same time. An effective and rapid feedback mechanism is necessary to prevent such excursions, although they have occurred in the geologic past. On a short time scale (hundreds of years or less), the feedbacks involve the ocean and terrestrial biota. As was shown in Chapter 4, an increase in atmospheric CO2 leads to an increase in the uptake of CO2 in the ocean. Also, an initial increase in atmospheric CO2 could lead to fertilization of those terrestrial plants which are not nutrient limited, provided there is sufficient water, removal of CO2, and growth of the terrestrial biosphere. Thus, both of the aforementioned processes are feedback mechanisms that can operate in a positive or negative sense. An increased rate of photosynthesis would deplete atmospheric CO2, which would in turn decrease photosynthesis and increase the oceanic evasion rate of CO2, leading to a rise in atmospheric CO2 content. More will be said later about feedback mechanisms in the carbon system. 

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