278
In general, the length and complexity of the food webs involved in the export of biogenic
carbon increase towards the right of Fig. 2. Rapid sedimentation of intact cells or other
biogenic particles (e.g. some faecal pellets) into deep waters would favour the sequestration
of carbon, since the amount of organic material respired during the downwards transit (and
potentially rapidly returned to the atmosphere) is largely determined by sinking velocity. The
export pathways thus often strongly influence the amount of carbon sequestered by the ocean.
TYPOLOGY OF PELAGIC MARINE ECOSYSTEMS
Several authors (e.g. Miller and SUPER Group, 1988; Parsons and Lalli, 1988; Peinert et al.,
1989; Legendre, 1990) have recently pointed out that two contrasting types of ecosystems may
be found in temperate and subpolar waters, despite relatively similar annual and/or maximal
levels of carbon fixation by the phytoplankton in both cases, i.e. some ecosystems present a
well-established spring phytoplankton bloom while others show little increase in the average
seasonal chlorophyll a. For the subarctic Atlantic and Pacific Oceans, as an example, Parsons
and Lalli (1988) explain the observed difference in standing stocks by the fact that, in the
North Pacific, both microzooplankton and large-sized copepods react almost immediately to
any increase in primary production while, in the North Atlantic, there is a lag between
phytoplankton production and grazing by zooplankton. As a consequence, standing stocks of
phytoplankton in the North Pacific are dominated by small cells, while both large and small
cells are found in the North Atlantic during the summer, even though the production of large
and small cells might be similar in the two systems. Such contrasting ecosystems have also
been described in the Bering Sea (see Legendre, 1990), while Peinert et al. (1989) report the
existence, in the region of the Norwegian Current, of an ecosystem rather similar to the one
described by Parsons and Lalli (1988) in the Pacific.
There are pelagic marine ecosystems that exhibit phytoplankton production and standing stock
characteristics quite different from those described in the previous paragraph. For example,
in upwelling and other systems with intense blooms, large phytoplankton cells may dominate
both the primary production and the biomass (e.g. upwelling and ice-edge blooms). At the
other end of the spectrum, in oligotrophic tropical waters, picoplankton « 2 /-tm) dominate
both the production (50-60%) and biomass (> 50% and sometimes> 90%) of primary
In general, the length and complexity of the food webs involved in the export of biogenic
carbon increase towards the right of Fig. 2. Rapid sedimentation of intact cells or other
biogenic particles (e.g. some faecal pellets) into deep waters would favour the sequestration
of carbon, since the amount of organic material respired during the downwards transit (and
potentially rapidly returned to the atmosphere) is largely determined by sinking velocity. The
export pathways thus often strongly influence the amount of carbon sequestered by the ocean.
TYPOLOGY OF PELAGIC MARINE ECOSYSTEMS
Several authors (e.g. Miller and SUPER Group, 1988; Parsons and Lalli, 1988; Peinert et al.,
1989; Legendre, 1990) have recently pointed out that two contrasting types of ecosystems may
be found in temperate and subpolar waters, despite relatively similar annual and/or maximal
levels of carbon fixation by the phytoplankton in both cases, i.e. some ecosystems present a
well-established spring phytoplankton bloom while others show little increase in the average
seasonal chlorophyll a. For the subarctic Atlantic and Pacific Oceans, as an example, Parsons
and Lalli (1988) explain the observed difference in standing stocks by the fact that, in the
North Pacific, both microzooplankton and large-sized copepods react almost immediately to
any increase in primary production while, in the North Atlantic, there is a lag between
phytoplankton production and grazing by zooplankton. As a consequence, standing stocks of
phytoplankton in the North Pacific are dominated by small cells, while both large and small
cells are found in the North Atlantic during the summer, even though the production of large
and small cells might be similar in the two systems. Such contrasting ecosystems have also
been described in the Bering Sea (see Legendre, 1990), while Peinert et al. (1989) report the
existence, in the region of the Norwegian Current, of an ecosystem rather similar to the one
described by Parsons and Lalli (1988) in the Pacific.
There are pelagic marine ecosystems that exhibit phytoplankton production and standing stock
characteristics quite different from those described in the previous paragraph. For example,
in upwelling and other systems with intense blooms, large phytoplankton cells may dominate
both the primary production and the biomass (e.g. upwelling and ice-edge blooms). At the
other end of the spectrum, in oligotrophic tropical waters, picoplankton « 2 /-tm) dominate
both the production (50-60%) and biomass (> 50% and sometimes> 90%) of primary