Carbon remineralisation

The rate of organic carbon remineralisation by microbial oxidation has been empirically shown by Middleburg (1989) to follow a first order decay curve. This relationship accounts for carbon diagenesis over about eight orders of magnitude in the carbon influx, covering very diverse environments. 

Sulphate reduction in marine sediments is often the dominant form of carbon remineralisation, and contributes most of the alkalinity observed in the sediment pore-water. When concentrations of sulphate fall below 35 to 40 pM, carbon dioxide reduction by methanogens may begin, whereas sulphate levels below about 30 pM are required before the onset of acetate-type reduction reactions that dominate methanogenesis (Kuivila et al., 1989). Carbon dioxide reduction is usually only evident in the sulphate reduction zone, where bicarbonate is produced, but it can contribute about 65% of the methane flux at its peak (Crill Martens, 1986). 

At steady state, the carbon leaving the system as carbon dioxide and methane fluxes into the overlying water or air, will be equivalent to the amount of carbon remineralised in the column below, integrated over its depth. Dissolved organic carbon (DOC) exchange from pore-water to sea water is thought to have a minor effect on the mass balance (Martens ... 

Witte, U. and Pfannkuche, O. (2000) High rates of benthic carbon remineralisation in the abyssal Arabian Sea. Deep-Sea Research II, 47, 2785-2804. 

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