Productivity in oceans

Bruland, K. W., Donat, J. R. and Hutchins, D. A. (1991). Interactive influence of bioactive trace metals on biological production in oceanic waters, Limnol. Oceanogr., 36, 1555-1577. 

Equation 17.26 is directly involved in DOM photomineralization, and Equation 17.25 yields Fe2+. Complexation of Fe(III) by organic ligands is in competition with the precipitation of ferric oxide colloids [79], and the formation of ferrous iron on photolysis of Fe(III)-carboxylate complexes is an important factor in defining the bioavailability of iron in aquatic systems. Iron bioavailabihty, minimal for the oxides and maximal for Fe2+, is considerably enhanced by the formation of Fe(III)-organic complexes and their subsequent photolysis. Iron bioavailabihty plays a key role in phytoplankton productivity in oceans [80-82], while that of freshwater is mainly controlled by nitrogen and phosphoms. 

WiUiams, R. G., and FoUows, M. J. (2003). Physical transport of nutrients and the maintenance of biological production. In Ocean Biogeochemistry The Role of the Ocean Carbon Cycle in Global Change (Fasham, M. J. R., ed.). Springer, Berlin, pp. 19—51. 

De Vooys (1979) is also of the opinion that the generally accepted estimates of primary productivity in the world ocean are too low, mainly as a result of shortcomings of the radiocarbon method. He proposes an overall correction of the existing values by an increase of 40% based on loss of radioactivity on storing plankton filters in a vacuum desiccator (20%), as is common practice in the standard method of Strickland and Parsons, (1972) and on account of loss of extracellular excretion products (20%). In his opinion the corrected estimate of Platt and Subba Rao (1975 44 X 10 t C yr" ) is the best approximation of primary production in oceans and seas. 

The demonstration that Cd might be utilized as a nutrient by phytoplankton - as implied by its nutrient-like profile in the ocean - came from culture studies in which the growth rate of Zn-limited phytoplankton species was markedly increased by addition of Cd to the medium (Figure 2) [21], The concentration of bioavailable free Zn in the surface waters of the open ocean is indeed quite low [14,22-25] and in the range fotuid to limit phytoplankton growth in cultures [24—26]. Some field studies have in fact found evidence of Zn-limitation of primary production in ocean water [27-29]. It is therefore plausible that phytoplanktmi may take up Cd to replace Zn for biological functions in the Zn-depleted conditions of the surface ocean. 

Comparison with other Studies. How do the results of our investigation compare with similar studies Our results corroborate the data provided in a similar study of the effect of UV-B on primary productivity in the southeastern Pacific Ocean (35). In the latter study, it was noted that enhanced UV-B radiation caused significant decreases in the productivity of surface and deep samples. Compared to ambient, primary productivity decreased with increasing doses of UV-B. In another study in which in situ experiments using natural Antarctic phytoplankton populations, it was noted that incident solar radiation significantly depressed photosynthetic rates in the upper 10-15 meters of the water column (36). It was also found that the spectral region between 305 and 350 nm was responsible for approximately 75 percent of the overall inhibitory effect. 

Recently, the ocean-basin distribution of marine biomass and productivity has been estimated by satellite remote sensing. Ocean color at different wavelengths is determined and used to estimate near-surface phytoplankton chlorophyll concentration. Production is then estimated from chlorophyll using either in situ calibration relationships or from empirical functional algorithms (e.g., Platt and Sathyendranth, 1988 Field et al., 1998). Such studies reveal a tremendous amount of temporal and spatial variability in ocean biological production. 

Fig. 10-14 Approximate geographical distibution of primary productivity in the oceans (g C/m per year).

Sediment trap studies in the open ocean show that the flux of organic carbon at any depth is directly proportional to the rate of primary productivity in the surface water and inversely proportional to the depth of the water column (Suess, 1980) ... 

Eppley, R. W. and Peterson, B. J. (1979). Particulate organic matter flux and planktonic new production in the deep ocean. Nature 282, 677-680. 

Falkowski, P. G., Greene, R. and Geider, R. (1992). Physiological limitations on phytoplankton productivity in the ocean. Oceanography 5, 84-91. 

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