Oceanic carbon cycle

Hooss, G., Voss, R., Hasselmann, K., Maier-Reimer, E., and Joos, F. (2001). A nonlinear impulse response model of the coupled carbon cycle-ocean-atmosphere climate system. Clim. Dyn. (in press). 

Carbon Cycle. Ocean Carbon System, Modeling of. Radiocarbon. Stabie Carbon isotope Variations in the Ocean. 

Like all matter, carbon can neither be created nor destroyed it can just be moved from one place to another. The carbon cycle depicts the various places where carbon can be found. Carbon occurs in the atmosphere, in the ocean, in plants and animals, and in fossil fuels. Carbon can be moved from the atmosphere into either producers (through the process of photosynthesis) or the ocean (through the process of diffusion). Some producers will become fossil fuels, and some will be eaten by either consumers or decomposers. The carbon is returned to the atmosphere when consumers respire, when fossil fuels are burned, and when plants are burned in a fire. The amount of carbon in the atmosphere can be changed by increasing or decreasing rates of photosynthesis, use of fossil fuels, and number of fires. 

Alternatives to fossil fuels, such as hydrogen, are explored in Box 6.2 and Section 14.3. Coal, which is mostly carbon, can be converted into fuels with a lower proportion of carbon. Its conversion into methane, CH4, for instance, would reduce C02 emissions per unit of energy. We can also work with nature by accelerating the uptake of carbon by the natural processes of the carbon cycle. For example, one proposed solution is to pump C02 exhaust deep into the ocean, where it would dissolve to form carbonic acid and bicarbonate ions. Carbon dioxide can also be removed from power plant exhaust gases by passing the exhaust through an aqueous slurry of calcium silicate to produce harmless solid products ... 

Figure 1. Changes in global climate due to increased atmospheric CO2 will alter carbon cycle processes in land, continent margins, and oceans, which will in turn effect the atmospheric C02concentration. Processes that may have effects large enough to Eilter future projections of atmospheric CO2 are listed under their geographic region.

The most common way in which the global carbon budget is calculated and analyzed is through simple diagrammatical or mathematical models. Diagrammatical models usually indicate sizes of reservoirs and fluxes (Figure 1). Most mathematical models use computers to simulate carbon flux between terrestrial ecosystems and the atmosphere, and between oceans and the atmosphere. Existing carbon cycle models are simple, in part, because few parameters can be estimated reliably. 

Another model, first introduced by Moore, et al. (2i), was used to examine the role of terrestrial vegetation and the global carbon cycle, but did not include an ocean component. This model depended on estimates of carbon pool size and rates of CO2 uptake and release. This model has been used to project the effect of forest clearing and land-use change on the global carbon cycle (22, 23, 24). 

Bjorkstrom, A. 1979. A model of CO2 interaction between atmosphere,oceans, and land biota. In The Global Carbon Cycle, Bolin, B. Degens, E. T. Kempe, S. Ketner, P., Eds. SCOPE 13 J Wiley Sons New York, NY, 1979 pp 403-457. 

Budgets and cycles can be considered on very different spatial scales. In this book we concentrate on global, hemispheric and regional scales. The choice of a suitable scale (i.e. the size of the reservoirs), is determined by the goals of the analysis as well as by the homogeneity of the spatial distribution. For example, in carbon cycle models it is reasonable to consider the atmosphere as one reservoir (the concentration of CO2 in the atmosphere is fairly uniform). On the other hand, oceanic carbon content and carbon exchange processes exhibit large spatial variations and it is reasonable to separate the... 

An important example of non-linearity in a biogeochemical cycle is the exchange of carbon dioxide between the ocean surface water and the atmosphere and between the atmosphere and the terrestrial system. To illustrate some effects of these non-linearities, let us consider the simplified model of the carbon cycle shown in Fig. 4-12. Ms represents the sum of all forms of dissolved carbon (CO2, H2CO3, HCOi" and... 

Rainwater and snowmelt water are primary factors determining the very nature of the terrestrial carbon cycle, with photosynthesis acting as the primary exchange mechanism from the atmosphere. Bicarbonate is the most prevalent ion in natural surface waters (rivers and lakes), which are extremely important in the carbon cycle, accoxmting for 90% of the carbon flux between the land surface and oceans (Holmen, Chapter 11). In addition, bicarbonate is a major component of soil water and a contributor to its natural acid-base balance. The carbonate equilibrium controls the pH of most natural waters, and high concentrations of bicarbonate provide a pH buffer in many systems. Other acid-base reactions (discussed in Chapter 16), particularly in the atmosphere, also influence pH (in both natural and polluted systems) but are generally less important than the carbonate system on a global basis. 

Baes, C. F., Bjdrkstrom, A. and MuIhoUand, P. J. (1985). Uptake of carbon dioxide by the oceans. In "Atmospheric Carbon Dioxide and the Global Carbon Cycle" (J. R. Trabalka, ed.). Report DOE/ ER-0239, US Department of Energy, Office of Energy Research, Washington, DC. 

Fig. 11-9 (a) The vertical distributions of alkalinity (Aik) and dissolved inorganic carbon (DIC) in the world oceans. Ocean regions shown are the North Atlantic (NA), South Atlantic (SA), Antarctic (AA), South Indian (SI), North Indian (NI), South Pacific (SP), and North Pacific (NP) oceans. (Modified with permission from T. Takahashi et ah, The alkalinity and total carbon dioxide concentration in the world oceans, in B. Bolin (1981). Carbon Cycle Modelling," pp. 276-277, John Wiley, Chichester.)... 

The freshwater cycle is an important link in the carbon cycle as an agent of erosion and as a necessary condition for terrestrial life. Although the amount of carbon stored in freshwater systems is insignificant as a carbon reservoir (De Vooys, 1979 Kempe, 1979a), about 90% of the material transported from land to oceans is carried by streams and rivers. 

Fig. 11-18 A four-box model of the global carbon cycle. Reservoir inventories are given in moles and fluxes in mol/yr. The turnover time of CO2 in each reservoir with respect to the outgoing flux is shown in brackets. (Reprinted with permission from L. Machta, The role of the oceans and biosphere in the carbon dioxide cycle, in D. Dryssen and D. Jagner (1972). "The Changing Chemistry of the Oceans," pp. 121-146, John Wiley.)...

There has been a tremendous development of various types of prognostic models of the carbon cycle during the past decades with increased refinement of both oceanic processes (see Siegenthaler and Sarmiento, 1993 Sarmiento et ah, 1992, 1998), terrestrial processes (Bonan,... 

Bacastow, R. B. and Bjdrkstrom, A. (1981). Comparison of ocean models for the carbon cycle. In "Carbon Cycle Modeling" (B. Bolin, ed.), pp. 29-79. Wiley, New York. 

Bjdrkstrom, A. (1979). A model of CO2 interaction between atmosphere, oceans, and land biota. In "The Global Carbon Cycle" (B. Bolin, E. T. Degens, S. Kempe, and P. Ketner, eds), pp. 403-457. Wiley, New York. 

Sarmiento, J. L., Hughes, T. M. C., Stouffer, R. J. and Manabe, S. (1998). Simulated response of the ocean carbon cycle to anthropogenic climate warming. Nature 393,245-249. 

Siegenthaler, U. and Joos, F. (1992). Use of a simple model for studying oceanic tracer distributions and the global carbon cycle, Tellus 44B, 186-207. 

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