CO2 flux

Figure 4 Mean annual net CO2 flux over the global oceans (in 10 " grams of C per year per 5" square)"...

Research is needed to quantify and assess data sets on pools and fluxes of subfossil carbon for North America, Scandinavia, and the Soviet Union where large amounts of such material exists and is vulnerable to accelerated decomposition with expected C02-induced climate change 66-69). Billings et al. 70, 71) performed fleld experiments that mimicked the changes expected to occur in the tundra as a result of climatic change. The direction of CO2 flux was reversed from a net storage of 150 g C02 m -season to a net release of 300-400 g C02 m" season . Annual liberation of as little as 1% per year of either the 300 Pg C stored in the top meter of soils above the 60° latitude band or... 

In this tectonic situation, intense bimodal volcanism and associated seawater circulation occur, resulting to the formation of Kuroko deposits on the seafloor and formation of vein-type mineralization under subaerial condition and intense hydrothermal and volcanic CO2 fluxes to ocean and atmosphere. Such fluxes affect the long-term environmental changes (see Chapter 4). 

Previous studies demonstrated that the CO2 fluxes by hydrothermal solution and volcanic gas from midoceanic ridges play an important role in the global CO2 cycle and affect the CO2 concentration in the atmosphere (e.g., Javoy, 1988). However, submarine volcanism and hydrothermal activity occur not only at midoceanic ridges but also at island arc and back-arc basins as already noted. 

In order to estimate hydrothermal CO2 flux, fluxes of hydrothermal solution into the ocean have to be estimated. 

Using 2.5 X lO g/m.y. as oceanic production rate and 5-20 as seawater/rock ratio and assuming that 30% of oceanic crust interacts with circulating seawater, and the crustal production rate is (0.8-1.1) x 10 kg/m.y., then the rate of seawater cycling through back-arc basin is estimated to be (4-22) x lO kg/m.y. Using this value and the CO2 concentration of hydrothermal solution ((0.05-0.3) mol/kg -H20) (Table 3.2), hydrothermal CO2 flux into the ocean is estimated to be (0.2-6) x lO kg/m.y. 

The CO2 flux by hydrothermal solution from midoceanic ridges can be estimated based on the similar procedure mentioned above. The crustal production rate at midoceanic ridges (discharge zone) is 5 x 10 g/m.y. by Kaiho and Saito (1994) and 4.5 x 10 g/m.y. by Holland et al. (1996). Seawater/rock ratios for midoceanic ridge hydrothermal systems previously estimated vary widely Humphris and Thompson (1978), 2-17 (by weight) Wolery and Sleep (1976), 3.5 (by weight) Holland (1978), 10 (by weight). 

The above argument indicates that hydrothermal CO2 flux from back-arc basins is similar to or greater than that from midoceanic ridges, and thus the hydrothermal flux from back-arc basins as well as hydrothermal flux from midoceanic ridges have to be taken into account when we calculate global geochemical CO2 flux. 

At the convergent plate boundaries, CO2 degasses not only from back-arc basins by hydrothermal solutions but also from terrestrial subduction zones by volcanic gases and hydrothermal solutions. However, the studies on CO2 degassing from terrestrial subduction zones are not many. Seward and Kerrich (1996) have shown that hydrothermal CO2 flux from terrestrial geothermal system (such as Taupo volcanic zone in New Zealand) exceeds lO mol/year which is comparable to that of midoceanic ridges (Table 3.4). 

Sano and Williams (1996) calculated present-day volcanic carbon flux from subduction zones to be 3.1 x 10 mol/year based on He and C isotopes and C02/ He ratios of volcanic gases and fumaroles in circum-Pacific volcanic regions. Williams et al. (1992) and Brantley and Koepenich (1995) reported that the global CO2 flux by subaerial volcanoes is (0.5-2.0) x lO mol/m.y. and (2-3) x 10 mol/m.y. (maximum value), respectively. Le Guern (1982) has compiled several measurements from terrestrial individual volcanoes to derive a CO2 flux of ca. 2 x 10 mol/m.y. Le Cloarec and Marty (1991) and Marty and Jambon (1987) estimated a volcanic gas carbon flux of 3.3 X 10 mol/m.y. based on C/S ratio of volcanic gas and sulfur flux. Gerlach (1991) estimated about 1.8 x 10 mol/m.y. based on an extrapolation of measured flux. Thus, from previous estimates it is considered that the volcanic gas carbon flux from subduction zones is similar to or lower than that of hydrothermal solution from back-arc basins. 

Influence of Hydrothermal CO2 Flux on Tertiary Climate Change... 

Tertiary climate change in relation to CO2 flux by volcanic, hydrothermal and metamorphic activities... 

Budyko et al. (1987) pointed out that Eocene and Miocene volcanisms and related CO2 fluxes have been large. 

Recently, Ishikawa (1996), and Kashiwagi et al. (2000) calculated CO2 change in atmosphere during the last 30 Ma and the last 60 Ma respectively, mainly based on the method developed by Berner et al. (BLAG model) (1983), Bemer (GEOCARB model) (1994), and Tajika (1998) taking into account hydrothermal CO2 flux from back arc basins and island arcs which were not considered in previous studies. 

In this section, Ishikawa (1996), and Kashiwagi et al. (2000) studies are described. Then, their calculated results are given, emphasizing the influence of hydrothermal and volcanic gas CO2 flux from back arc basins and island arc on CO2 concentration of atmosphere and climate change and are compared with the changes in CO2 and temperature obtained by analytical and paleontological data (S 0 of foraminiferal shell, Ce anomaly, 5 C, etc.). 

Fig. 4.10. Atmo.spheric CO2 variation estimated by modified BLAG model including CO2 flux related to mantle plume activity (Ishikawa, 1996). t c02 = 202/ 002 - prescut-day PcOi)-...

Fluxes of volatile elements (CO2, S, As) and other elements (Hg, Mn, Ba) due to hydrothermal activities at back-arc basins were calculated. Probably the hydrothermal flux of minor elements concentrated in Kuroko deposits (Sb, Tl, etc.) is large compared with those from midoceanic ridges. CO2 flux from back-arc basins is estimated to be large compared with that from midoceanic ridges. 

Chen QQ, Sun YM, Shen CD, Peng SL, Yi WX, Li ZA, Jiang MT (2002b) Organic matter turnover rates and CO2 flux from organic matter decomposition of mountain soil profiles in the subtropical area, south China. Catena 49 217-229... 

Liger-Belair, G., Villaume, S., Cilindre, C., and Jeandet, P. (2009b). Kinetics of CO2 fluxes outgassing from champagne glasses in tasting conditions The role of temperature. /. Agric. Food Chem. 57,1997-2003. 

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