CO2 degassing

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). 

Hanor J.S. (1978) Precipitation of beachrock cements Mixing of marine and meteoric waters vs. CO2 degassing. J. Sediment. Petrol. 48,489-501. 

In addition to alkalinity inputs from rivers, estuaries can also receive inputs from bordering wetlands. For example, Cai et al. (1999) have shown that respiration rates in rivers/estuaries of Georgia (USA) cannot account for O2 consumption and CO2 degassing. It has since been shown that the missing DIC source is from marshes in the Satilla estuary (USA) (Cai et al., 2000). Other studies have also shown that intertidal marshes are important sources of DIC in estuaries (Raymond et al., 1997, 2000 Neubauer and Anderson, 2003). It has been further suggested that CO2 fixation of marsh grasses and the subsequent export of DIC and organic C to the coastal ocean can be described as... 

Kerrick D. M. and Caldeira K. (1998) Metamorphic CO2 degassing from orogenic belts. Chem. Geol. 145, 213-232. 

Kerrick D. M. (2001) Present and past nonanthropogenic CO2 degassing from the solid earth. Rev. Geophys. 39, 565-585. 

B. Ivanov, F. Langenhorst, A. Deutseh, and U. Homemann, How strong was impact-induced CO2 degassing in the K/T event Numerieal modelling of laboratory experiments, in Catastrophic Events Mass Extinctions Impacts and Beyond, (eds. C. Koeberl and K.G. MacLeod), Geol. Soc. Amer. Spec. Paper, (2001) in press. 

Some surface waters (deep, stratifled, and poorly mixed, with little sunlight penetration, heavily polluted) are physically isolated from the atmosphere. In such waters, the apparent CO2 pressure, which is defined by Pqq = IH2C03]//lcOj will usually exceed the atmospheric value. This disequilibrium partly reflects the fact that the rate of CO2 degassing from water is slower than its rate of gaseous uptake from the atmosphere (cf. Schmiermund 1991 Morel and Hering 1993 Cole et al. 1994). 

The positive correlation (r = + 0.85) between 5 C and 5 0 values (Fig. 22) of the eogenetic Lunde carbonates may be related to relatively rapid near-surface precipitation caused by evaporation and CO2 degassing (e.g. Salomons et al., 1978 Schlesinger, 1985 Salomons Mook, 1986 Spotl Wright, 1992), which increases the enrichment of C and 0 isotopes. However, it is believed that at depths of a decimetre the evaporation rate is substantially reduced, and there is thus very little opportunity for significant 0 enrichment in soil water before the next rainfall causes sufficient infiltration to obliterate this effect (Hellwig, 1973). 

Dolomite cement components were all sourced from outside the sand body, most probably from local or basinal mudrocks. Stable isotope data indicate a mixed organogenic-marine carbonate source, and precipitation at relatively low temperatures (s70°C, if pore fluids were sourced from clay mineral dehydration reactions during deep burial of Carboniferous mudrocks in the Rathlin basin 55°C if they were locally sourced). Thermobaric mass transfer was enhanced by tectonic pulsing and dolomite precipitation was driven by CO2 degassing. 

Additionally one has to include in the budget still permanent CO2 degassing (unknown value) from the crust (accepting the deep carbon hypothesis). There is also no doubt that degassed CH4 is partly a product of deep rock chemistry (cf Eq. 2.4-2.7). 

Experience shows that the layer of sprung acids forms in 15 min to a few hours and almost always in the upper part of a test tube. This is due to the difference in real specific gravities or to assisted flotation promoted by the amount of H S and CO2 degassing into the atmosphere, something that would not happen in a pressurized vessel. 

Water Management in Micro DMFCs, Rgure 1 Schematic of a passive micro-scale CO2 degassing system in a DMFC... 

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