Marine primary production, global

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). 

The relative impact of zooplankton grazing on primary production decreases with increasing production levels the proportion of primary production that is consumed by zooplankton decreases exponentially as productivity levels increase (Calbet, 2001). This supports the observation that the ratio of export production to total production is higher in areas of high productivity. Globally, 12% of marine primary production, or 5.5 Pg C (0.5 Pmol C), is consumed by mesozoo-plankton each year (Calbet, 2001). 

Finally, we must somehow resolve the vexing problem of the chemical speciation of trace elements in seawater what is the chemical nature of the various metal chelators whose existence has been demonstrated by electrochemistry Is the chemistry of several metals in surface seawater really controlled by metallophores released by prokaryotes Or are dissolved metals chiefly present as parts of metalloproteins in the process of remineralization How do metal chelators affect the residence times of metals (in particular, scavenged elements such as iron and cobalt) and in turn how do those chelators influence the global carbon cycle via changes in marine primary productivity ... 

On a global basis, macroscopic, multicellular algae (seaweeds) make only a minor contribution to marine primary production 95% is accounted for by the phytoplankton. Phytoplankton are short-lived compared with terrestrial plants, especially trees, and do not need to produce supportive structural tissue, which is mostly photosynthetically inactive.Virtually the whole of the net primary production of phytoplankton is directed towards reproduction and growth, but much of this is grazed by herbivorous zooplankton. As a consequence of this efficient grazing, phytoplanktonic biomass is low and the ratio of animal to plant biomass in the oceans is greater than on land. 

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