Atmosphere and ocean carbonates

Fan, S., Gloor, M., Mahlman, J., Pacala, S., Sarmiento, ]., Takahashi, T., and Tans, P. (1998). A large terrestrial carbon sink in North America implied by atmospheric and oceanic carbon dioxide data and models. Science 282, 442-446. 

Human interaction with the global cycle is most evident in the movement of the element carbon. The burning of biomass, coal, oil, and natural gas to generate heat and electricity has released carbon to the atmosphere and oceans in the forms of CO2 and carbonate. Because of the relatively slow... 

The subsequent fate of the assimilated carbon depends on which biomass constituent the atom enters. Leaves, twigs, and the like enter litterfall, and decompose and recycle the carbon to the atmosphere within a few years, whereas carbon in stemwood has a turnover time counted in decades. In a steady-state ecosystem the net primary production is balanced by the total heterotrophic respiration plus other outputs. Non-respiratory outputs to be considered are fires and transport of organic material to the oceans. Fires mobilize about 5 Pg C/yr (Baes et ai, 1976 Crutzen and Andreae, 1990), most of which is converted to CO2. Since bacterial het-erotrophs are unable to oxidize elemental carbon, the production rate of pyroligneous graphite, a product of incomplete combustion (like forest fires), is an interesting quantity to assess. The inability of the biota to degrade elemental carbon puts carbon into a reservoir that is effectively isolated from the atmosphere and oceans. Seiler and Crutzen (1980) estimate the production rate of graphite to be 1 Pg C/yr. 

Revelle, R. and Suess, H. E. (1957). Carbon dioxide exchange between atmosphere and ocean, and the question of an increase of atmospheric CO2 during the past decades, Tellus 9,18-27. 

Response of the Atmosphere and Ocean to a Sudden Injection of Carbon Dioxide... 

Fig. 5-3. The response of carbon in atmosphere and ocean to a sudden increase of atmospheric carbon dioxide to a value of 5 PAL. Alkalinity is not plotted because it does not change in response to this perturbation.

Fig. 5-4. The response of carbon in atmosphere and ocean to a fossil fuel source of carbon dioxide that increases for a few hundred years and then decreases. The history of the source is plotted at the bottom of the figure (Broecker and Peng, 1982, p. 553).

The response of carbon isotopes in the atmosphere and ocean to fossil fuel burning is so familiar that the results of the calculation just carried out are not very interesting. It is, however, easy to adapt the program just discussed for application to a system for which the results are not immediately obvious. I will carry out an application of this kind in this section, just to have some fun with these equations and routines. 

Figure 1 presents the model. Precipitation rates are 9000 km3 between atmosphere and continental interior (Cl), 110000 km3 between atmosphere and continental margins (CM), and 458000 km3 between atmosphere and oceans. Mean DIC for global precipitation is 81.59 (xmol/l. Thus, the atmospheric C02 sink is 0.0044, 0.054, and 0.22 Pg C/a, respectively (Fig. 1). Annual global Cl RO and CM RO are 2000 and 44800 km3, respectively (Baumgartner Reichel 1975 Shiklomanov 1993). Using global mean soil pC02 of 6393 ppmv and global mean surface temperature of 15°C, the equilibrium values of DIC are 300 and 3640 amol/l for the non-carbonate and carbonate terranes, respectively. Thus, C02 sinks by Cl and CM RO are 0.013 and 0.28 Pg C/a, respectively.

Only a few evaporites have been found that are more than 800 miUion years old, indicating that most of the salt formed prior to this period has been recycled via uplift and weathering. No evaporites of Archean age have as yet been discovered. The oldest known chemical sediments were deposited 3.45 bybp in what is now western Australia. They appear to have precipitated as shallow-water carbonates. This suggests that sulfate concentrations during the Archean were much lower than present day, probably because of limited oxygenation of the atmosphere and ocean. 

The crust is the largest carbon reservoir in the crustal-ocean-atmosphere factory (8 x 10 Pg C including the sediments). Most of this carbon is in the form of inorganic minerals, predominantly limestone, with the rest being organic matter, predominantly contained in shale and secondarily in fossil fuel deposits (coal, oil, and natural gas). The oceanic reservoir (4 X lO" Pg C) and the terrestrial reservoir (2 to 3 x 10 Pg C) are both far smaller than the crustal reservoir. The smallest reservoir is found in the atmospheric, primarily as CO2 (preindustrial 6 x 10 Pg C, now 8 x 10 Pg C and rising). The flux estimates in Figure 25.1 have been constrained by an assumption that the preindustrial atmospheric and oceanic reservoirs were in steady state over intermediate time scales (millennia). 

Kondratyev K.Ya. and Isidorov V.A. (2001). Global carbon cycle. Atmosphere and Ocean Optics, 14(1), 1-10 [in Russian],... 

In recent years innumerable publications have dealt with the natural carbon cycle and its alteration by human activities. Some summary works of interest in this chapter are Atmospheric Carbon Dioxide and the Global Carbon Cycle (ed. Trabalka, 1985), The Carbon Cycle and Atmospheric CO2 Natural Variations, Archean to Present (eds. Sundquist and Broecker, 1985), Chemical Cycles in the Evolution of the Earth (eds. Gregor, Garrels, Mackenzie, and Maynard, 1988), History of the Earth s Atmosphere (Budyko, Ronov, and Yanshin, 1985), and The Chemical Evolution of the Atmosphere and Oceans (Holland, 1984). The interested reader is referred to these volumes for further discussion of material presented here. 

There are two major carbon cycles on Earth. The two cycles operate in parallel. One cycle is slow and abiotic. Its effects are observed on multimillion-year timescales and are dictated by tectonics and weathering (Berner, 1990). In this cycle, CO2 is released from the mantle to the atmosphere and oceans via vulcanism and seafloor spreading, and removed from the atmosphere and ocean primarily by reaction with silicates to form carbonates in the latter reservoir. Most of the carbonates are subsequently subducted into the mantle, where they are heated, and their carbon is released as CO2 to the atmosphere and ocean, to carry out the cycle again. The chemistry of this cycle is dependent on acid-base reactions, and would operate whether or not there was life on the planet (Kasting et al., 1988). This slow carbon cycle is a critical determinate of the concentration of CO2 in Earth s atmosphere and oceans on timescales of tens and hundreds of milhons of years (Kasting, 1993). 

Compounds of sulfur with carbon having the general formula are characterized through a series of linear poly carbon sulfides C S (n = 2-9), some of which can be detected in interstellar clouds. Carbon disulfide (CS2) occurs in the atmosphere and oceans of the Earth. Carbonyl sulfide (OCS) is also well known in nature and is one of many polycarbon oxide sulfides represented by the formula OC S where n < 6. 

We follow Tajika Matsui (1992) and apportion carbonate between five significant reservoirs the atmosphere and ocean, Rod carbonates lying upon (Rpei) or veined within (Rbas) oceanic basalt carbonates on continental platforms, R oiC, and CO2 in the mantle, Rman- The atmosphere and ocean are tightly coupled on geological time scales. We treat these together as a single reservoir with a current size of c. 3.3 x 10 moles. 

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