Carbon reservoirs phytoplankton

The dynamics of marine organic carbon can be described as a set of three nested cycles in which the biological pump is the cycle with flux and reservoir of intermediate magnitude (Figure 3). The cycle with the shortest timescale, which operates within the surface ocean, is composed of net primary production by phytoplankton... 

Most of the allochthonous, or foreign, sources represent carbon with lower concentrations ( older radiocarbon ages) than the fraction of TOC originating from phytoplanktonic production. The only exception is the rapid transport and sedimentation of recently synthesized terrestrial plant material, which is in equilibrium with the " C concentration of atmospheric CO2. Other sources of nonmarine carbon typically are of intermediate (lO lO" years) or infinite A C (beyond the detection limit of 50-60 000 years) radiocarbon age, depending on the amount of time spent in other reservoirs such as soils, fluvial deposits, or carbon-rich rocks. 

The ocean is one of the largest reservoirs of organic (biogenic) carbon on the earth s surface [1]. Globally, the composition of this reservoir is regulated by feedback mechanisms that maintain the planetary environment within the relatively narrow range necessary for life [2,3]. Phytoplankton productivity is the ultimate source of organic carbon in the ocean [4] the best estimate of this primary production is 45-50 Gt C year [5] - about half of the combined total for terrestrial and marine productivity [1]. 

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 ocean, which is by far the largest active reservoir of carbon, covering 71 percent of the globe, is the main sink in the global carbon cycle and hence the ultimate repository for fossil fuel CO2. Phytoplankton is the major organism that fixes CO2, either in particulate or dissolved forms via the pho-tosynthetic process. This constitutes the basis of the marine food chains and... 

The present model is based on mass balances for three main components representing phytoplankton (A), nutrients (E), and organic phosphorus (C), which can describe phosphorus cycle within a water body as follows. Phytoplankton biomass is produced by the photosynthesis reaction, consuming nutrients (in lakes and reservoirs, the limiting nutrient is phosphorus) and dissolved carbon dioxide, with solar radiation and adequate temperature. Upon death, phytoplankton biomass increases the pool of organic phosphorus, which is in turn converted to phosphate by mineralization bacteria. The model has several kinetic parameters that have to be estimated based on collected data from the specific reservoir under study. 

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