270
High concentrations of suspended particulate carbonate along continental margins (Lisitzin,
1972; see above) might well correspond to coccolithophore blooms, as observed by Holligan
et al. (1983) along the continental shelf edge in the Celtic Sea. According to Holligan (1987),
blooms of coccolithophores occur under conditions of intermediate turbulence, maintained by
physical instabilities such as tidal mixing and upwelling. An example of the significance of
coccolithophore blooms for the vertical transport of carbonate is provided by Honjo (1982)
who observed, during a bloom of the coccolithophore Umbellicosphaera sibogae, a mass flux
of particles of 876 mg m- 2 d- 1 with carbonate accounting for 62 % of the total flux at 3560 m.
The production and export of coccolithophores in oceans, as well as their significance for the
global biogeochemical cycles, are discussed in detail by Holligan and Balch (this volume).
An important aspect of foraminiferal production is that several planktonic species (belonging
to the genera Globigerinoides and Orbulina) consistently possess symbiotic dinoflagellates
(zooxanthellae), and a species of the genus Hastigerina harbours commensal dinoflagellates
(refs. in Be et al., 1982). Experimental study of photosynthesis in the planktonic
foraminiferan Globigerinoides sacculifer (J¢rgensen et al., 1985) has shown that the uptake
of dissolved nitrogen and phosphorus by the organism is diffusion-limited, so that the capture
of prey is necessary to supply nutrients to the dinoflagellate symbiont; however, symbiotic
photosynthesis can cover the energy requirements of the foraminifers and allow efficient
recycling of the nutrients. In addition, Be et al. (1982) have shown that the symbionts enhance
calcification of their host's skeleton, as in the case of corals (see above). In the tropical
oligotrophic ocean, however, foraminifers are found in very low numbers, so that their
contribution to the total carbon production is small (e.g. 0.1-0.2%; J¢rgensen et al., 1985);
given their calcareous tests and their high sinking velocities, the contribution of foraminifers
to the export and sequestration of carbon may nevertheless be proportionally higher. The
significance of the phenomenon in other environments remains to be quantified.
While apparently no data are available on the partition of carbon between organic matter and
carbonate in coccolithophores or foraminiferans, some information on the matter can be found
in the literature for thecosomatous pteropods. The values given by Gorsky et al. (1988)
convert to a C/N ratio of 6.5 for the organic matter of Cavolinia inflexa, i.e. almost exactly
the Redfield ratio, while Curl (1962) ascribes 2.74% of the dryweight in Limacina sp. to
High concentrations of suspended particulate carbonate along continental margins (Lisitzin,
1972; see above) might well correspond to coccolithophore blooms, as observed by Holligan
et al. (1983) along the continental shelf edge in the Celtic Sea. According to Holligan (1987),
blooms of coccolithophores occur under conditions of intermediate turbulence, maintained by
physical instabilities such as tidal mixing and upwelling. An example of the significance of
coccolithophore blooms for the vertical transport of carbonate is provided by Honjo (1982)
who observed, during a bloom of the coccolithophore Umbellicosphaera sibogae, a mass flux
of particles of 876 mg m- 2 d- 1 with carbonate accounting for 62 % of the total flux at 3560 m.
The production and export of coccolithophores in oceans, as well as their significance for the
global biogeochemical cycles, are discussed in detail by Holligan and Balch (this volume).
An important aspect of foraminiferal production is that several planktonic species (belonging
to the genera Globigerinoides and Orbulina) consistently possess symbiotic dinoflagellates
(zooxanthellae), and a species of the genus Hastigerina harbours commensal dinoflagellates
(refs. in Be et al., 1982). Experimental study of photosynthesis in the planktonic
foraminiferan Globigerinoides sacculifer (J¢rgensen et al., 1985) has shown that the uptake
of dissolved nitrogen and phosphorus by the organism is diffusion-limited, so that the capture
of prey is necessary to supply nutrients to the dinoflagellate symbiont; however, symbiotic
photosynthesis can cover the energy requirements of the foraminifers and allow efficient
recycling of the nutrients. In addition, Be et al. (1982) have shown that the symbionts enhance
calcification of their host's skeleton, as in the case of corals (see above). In the tropical
oligotrophic ocean, however, foraminifers are found in very low numbers, so that their
contribution to the total carbon production is small (e.g. 0.1-0.2%; J¢rgensen et al., 1985);
given their calcareous tests and their high sinking velocities, the contribution of foraminifers
to the export and sequestration of carbon may nevertheless be proportionally higher. The
significance of the phenomenon in other environments remains to be quantified.
While apparently no data are available on the partition of carbon between organic matter and
carbonate in coccolithophores or foraminiferans, some information on the matter can be found
in the literature for thecosomatous pteropods. The values given by Gorsky et al. (1988)
convert to a C/N ratio of 6.5 for the organic matter of Cavolinia inflexa, i.e. almost exactly
the Redfield ratio, while Curl (1962) ascribes 2.74% of the dryweight in Limacina sp. to