Dissolved organic carbon oceanic reservoirs

The dissolved organic carbon (DOC) reservoir in sea water represents a very significant component of the oceanic carbon cycle but reliable quantitative determination of this parameter has proved to be difficult. For over a decade since the publication of Sugimura and Suzuki s Marine Chemistry paper there has been considerable debate about the most appropriate technique(s) for the determination of DOC in seawater. Techniques can be effectively divided into three categories ... 

The quantity of dissolved organic carbon in the oceans has been estimated to be about 1018 g and constitutes one of the major reservoirs of organic carbon. Although large in total mass, the concentration of organic carbon in seawater is low (typically 0.5 -1.5 mg C per litre). 

Fig. 1. Dissolved organic carbon (DOC) and the other major reservoirs of living and nonliving organic carbon in the world s ocean. DOC, zooplankton and bacterial biomass are from Cauwet [137] and Siegenthaler and Sarmiento [138] phytoplankton biomass is from Table 1 macrobiota biomass is from Stewart [139]...

The difference between the total dissolved carbon in the surface and in deep-sea reservoirs depends on productivity. And the difference between the alkalinity in these reservoirs depends on productivity and also corat, the calcium-carbonate-to-organic-carbon ratio. The carbon dioxide partial pressure depends on the difference between total carbon and alkalinity in the surface reservoir, and all these depend on the total amount of carbon and alkalinity at the start of the calculation in the three reservoirs combined. By adjusting the values of these various parameters and repeating the calculation, I arrive at the following values for a steady-state system that is close to the present-day ocean with a preindustrial level of atmospheric carbon dioxide ... 

The error results in the following way. The amount of organic carbon dissolved in the oceans is 0.14 gm/cm2, about equal to the amount of carbon in atmospheric carbon dioxide of 0.13 g C/cm2. Since the organic carbon is 2.7 percent depleted in carbon-13, the atmospheric reservoir is correspondingly enriched by 2.7 percent. 

---