Marine primary production, global estimates

In terms of organic carbon generation, the coccolithophorids are a minor player, representing only 6 to 8% of global marine primary production. But their detrital remains contribute disproportionately to the burial of carbon in marine sediments. This is due to near complete loss of POC via remineralization as the detrital hard and soft parts settle to the seafloor. As estimated from Broecker s Box model in Chapter 9, only about 1% of the POM that sinks out of the surfece water is buried in marine sediments. In comparison, about 20% of the biogenic PIC survives to become buried in the sediments. 

There are no global estimates of the production and biomass of aquatic phanerogams, but rough estimates of estuarine primary production (in which submerged phanerogams mainly share) do exist 1 X 10 t C yr" (Woodwell et al., 1978), which is 4% of the total global marine primary production. 

The amount of primary production carried out in the oceans each year has been estimated from ocean color satellite data and shipboard incubations to be 140 g C m for a total of 50-60 Pg C (4-5 Pmol C) hxed in the surface ocean each year (Shuskina, 1985 Martin et al, 1987 Field et al, 1998). This represents roughly half of the global annual 105 Pg C hxed each year (Field etal., 1998), despite the fact that marine phytoplankton comprise less than 1 % of the total photosynthehc biomass on Earth. Extrapolahon from Redheld ratios suggests the incorporation 0.6-0.8 Pmol N, 40-50 Tmol P into biogenic particles each year in associahon with marine primary production. From the proportion of primary production carried out by diatoms and the average Si C raho of diatoms, silica production rates may be calculated to be 200-280 Tmol Si yr (Nelson et al, 1995 Treguer et al, 1995). 

Turning to Table I it is obvious that by far the largest share (75% according to Woodwell et al. 1978) in the global marine net primary production comes from the open oceans and hence from the phytoplankton in that system. It is at the same time remarkable that this production is out of proportion in relation to the phytoplankton biomass 26% of the total aquatic marine plant mass could be estimated in the open ocean. It should be realised that the distribution of phytoplankton in the sea is rarely uniform and frequently extremely patchy. Horizontally, patches are usually elliptical and vary in size from a few metres to hundreds of kilometres across. Long narrow bands or streaks, a few metres in width, are common and may form a pattern superimposed on that of the patches. Under conditions of strong mixing, vertical distribution of phytoplankton may be uniform, but if the water column becomes stabilised, non-motile forms denser than water will... 

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]. 

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