Diatom carbon demand

Carbon and Phosphorus Burial Efficiencies. The estimate of diatom carbon demand (12-15 g/m2 per year) is consistent with the flux of carbon to the sediment surface. With sediment-trap fluxes corrected for resuspension, we measured a total annual deposition flux of 12.5 g of C/m2. In comparison, Eadie et al. (24) obtained 23 g of C/m2 for a 100-m station, based on three midsummer metalimnion deployments. Of our total, 83% of the carbon was associated with diatoms, and the primary diatom carbon flux was 10.3 g of C/m2. Thus, about 15-30% of the diatom carbon was regenerated in the water column during sedimentation. Approximately 10% of the diatom flux reached the sediment surface encapsulated in copepod fecal pellets the remaining 90% was unpackaged. 

In contrast to zinc, the crucial role of Fe in the bioenergetics of carbon (C) and N metabolism is well recognized (e.g., Morel et al., 1991 Sunda, 1989). Substantial amounts of Fe are required in both photosynthetic and respiratory electron transport chains (e.g., Raven, 1988), the synthesis of chlorophyll (Chereskin and Castelfranco, 1982), and the assimilation ofNOj. Theoretical calculations based on Fe utilization efficiencies and cellular metabolic Fe demands, predict that phytoplankton growing on NOJ require 60% more Fe than those growing on NH (Raven, 1988, 1990), and greater cellular Fe requirements for NO growth have indeed been demonstrated for laboratory cultures of diatoms (Maldonado and Price, 1996). The extra Fe is needed to reduce NO to NH4 before it can be incorporated into amino acids. This process requires the assimilatory enzymes nitrate reductase (requires one... 

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