Global primary production

Photosynthesis in the sea is carried out by microscopic unicellular algae — the phytoplankton — freely suspended in the water, and also by 

Global net primary production and standing crop (Woodwell et al., 1978) (t = 10 kg) 

Ecosystem type Area (10 km ) Total net primary production (10 tCyr- ) Total plant mass of carbon (10 tC) 

Riley (1944) obtained his estimates by measuring oxygen production of water samples. This method does not yield reliable results in oligotrophic waters (Section 3) and Riley s estimate is almost certainly much too high. 

Ryther (1969) divided the oceans into three arbitrary regions open ocean, coastal zone and upwelling areas, and considered mean production values of respectively 50, 100 and 300 g C yr . From this he calculated a total production of 20 X 10 t C yr .  

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Olson, R.J. and S.D. Prince (1996) Global primary production data initiative update.- Global Change Newsletter, The International Geosphere-Biosphere Programme A study of global change of the International Council of Scientific Unions 27, 13. 

Longhurst, A., Sathyendranath, S., Platt, T., and CaverhiU, C. (1995). An estimate of global primary production in the ocean from satelhte radiometer data.J. Plank. Res. 17, 1245—1271. 

Bender M., Labeyrie L. D., Raynaud D., and Lorius C. (1985) Isotopic composition of atmospheric O2 in ice Unked with deglaciation and global primary productivity. Nature 318(6044), 349-352. 

Jahnke (1996) extrapolated available benthic-flux measurements from landers and pore-water determinations into a global map of benthic oxygen flux for sediments deeper than 1,000 m. When compared with global primary production rates and sediment-trap particle fluxes, these data indicate that 1% of the primary production reaches deep-sea sediments and is oxidized there (Table 3). Also —45% of respiration in the ocean below 1,000 m occurs within sediments. 

Table 1 Global primary production and emissions of six heavy metals during the 1970s and the 1980s.

Dead material shed by plants is called litter. Reiners (1973) made an attempt to estimate total litter fall using four different procedures and derived values ranging from 37 to 64 Pg C/yr. The results are based largely on the estimates provided by Whittaker and Likens (1973) for the areal extent, primary productivity, and mean biomass of different ecosystems. Ajtay et al. (1979) repeated Reiner s calculations using their own data and obtained for the annual litter fall values between 37 and 49 PgC/yr. One of their detailed estimates is presented in Table 11-5. These results demonstrate that the global primary production of the biosphere of about 55 PgC/yr turns mainly into plant litter. Ajtay et al. further estimate a consumption by herbivores of about 6 Pg C/yr, including consumption by domestic livestock. This leaves only about 10% of net primary productivity to be incorporated annually into living biomass. 

This flux was greater in the distant past, due to higher heat flow (Turcotte 1980). Therefore, for the pre-oxygenic-photosynthetic biosphere, it is assumed that global primary productivity scaled with the square of heat flow, and thus was estimated to have been in the range (2 to 20) x 10 mol yr (Fig. 7). 

With the exception of autotrophic bacteria which contribute a negligible amount of organic matter to the global primary productivity, the interest in the position of non-auto trophic bacteria as secondary producers of organic matter over recent years warrants the treatment of this subject in a separate section. 

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