314
grazing, it is not possible to calculate total coccolith production. For illustrative purposes an
estimate of total calcite productivity can be inferred from typical observed maximum densities
of cells (3.10 9 m· 3 ) and coccoliths (lOll m· 3 ) if it is assumed that each cell has 20 coccoliths
(Fig. IB), that the thickness of the population layer is 20m and that an equal number of
coccoliths to the maximum standing crop are lost by grazing and sinking during the
development of the bloom. The calculated value is 64.10 11 coccoliths m· 2 which is equivalent
to 13.0g CaC0 3 or 1.55g calcite-carbon m· 2 , based on a volume for each E. huxleyi coccolith
of 3/4 /-tm 3 (Westbroek et al., 1983).
Such fluxes are compatible both with sediment trap data (Honjo, 1976; Cadee, 1985; Kempe
and Jennerjahn, 1988; Hay et al., 1990) and with information on the rate of accumulation of
coccoliths in bottom sediments (see below) for coccolithophore-rich waters. However, more
important is that the timescale of 3-4 weeks for bloom development inferred from ecological
and remote sensing information gives an indication of the rates at which surface water optical
properties and biogeochemical fluxes are likely to change as such blooms develop.
Holocene rates of accumulation of calcareous sediments in the NE Atlantic range from
> 20 cm ky·l on sediment ridges to < 3 cm ky'! south of 45
0
N towards the SUbtropical gyre.
The inorganic (calcite) and organic carbon contents are typically 7% (Fig. 10) and 0.3%
(Romankevich, 1984) respectively, and mainly associated with the fine « 63 /-tm diameter)
material. For an intermediate deposition rate of 7 cm ky'!, and assuming a sediment density
of 0.76 g cc'! and 80% of the calcite to be in the form of coccoliths (unpublished data), the
accumulation rates of coccolith inorganic carbon and of total organic carbon are 2.98 and
0.16 g m· 2 y.l (a ratio of 19: 1). The value for inorganic carbon is about twice that estimated
above for an E. huxleyi bloom, but the coccoliths of other species (Fig. 1) are also abundant
in the sediments. The significance of the inorganic to organic carbon ratio for coccolith-rich
sediments lies in understanding the degree to which the two might be associated. Carbonate
surfaces adsorb organic material (Suess, 1973; also see Degens and Ittekot, 1986), a process
that enhances the final preservation of organic carbon in marine sediments (Gordon and
Millero, 1985). Using the estimate of Suess that 1m 2 of carbonate surface holds 1.2 mg
organic carbon, and a surface area value for each E. huxleyi coccolith of 15/-tm 2 (Westbroek
et al., 1983), a predicted inorganic to organic carbon ratio of about 13: 1 is calculated for such
coccoliths. Since this is lower than observed ratio for coccolith-rich sediments, most if not all
the organic carbon in such sediments may be adsorbed onto the coccoliths. Some is derived
directly from coccolithophores. including acidic polysaccharides that form the matrix of the
coccoliths of E. huxleyi (Westbroek et al., 1989) and long chained ketones in sediments that
grazing, it is not possible to calculate total coccolith production. For illustrative purposes an
estimate of total calcite productivity can be inferred from typical observed maximum densities
of cells (3.10 9 m· 3 ) and coccoliths (lOll m· 3 ) if it is assumed that each cell has 20 coccoliths
(Fig. IB), that the thickness of the population layer is 20m and that an equal number of
coccoliths to the maximum standing crop are lost by grazing and sinking during the
development of the bloom. The calculated value is 64.10 11 coccoliths m· 2 which is equivalent
to 13.0g CaC0 3 or 1.55g calcite-carbon m· 2 , based on a volume for each E. huxleyi coccolith
of 3/4 /-tm 3 (Westbroek et al., 1983).
Such fluxes are compatible both with sediment trap data (Honjo, 1976; Cadee, 1985; Kempe
and Jennerjahn, 1988; Hay et al., 1990) and with information on the rate of accumulation of
coccoliths in bottom sediments (see below) for coccolithophore-rich waters. However, more
important is that the timescale of 3-4 weeks for bloom development inferred from ecological
and remote sensing information gives an indication of the rates at which surface water optical
properties and biogeochemical fluxes are likely to change as such blooms develop.
Holocene rates of accumulation of calcareous sediments in the NE Atlantic range from
> 20 cm ky·l on sediment ridges to < 3 cm ky'! south of 45
0
N towards the SUbtropical gyre.
The inorganic (calcite) and organic carbon contents are typically 7% (Fig. 10) and 0.3%
(Romankevich, 1984) respectively, and mainly associated with the fine « 63 /-tm diameter)
material. For an intermediate deposition rate of 7 cm ky'!, and assuming a sediment density
of 0.76 g cc'! and 80% of the calcite to be in the form of coccoliths (unpublished data), the
accumulation rates of coccolith inorganic carbon and of total organic carbon are 2.98 and
0.16 g m· 2 y.l (a ratio of 19: 1). The value for inorganic carbon is about twice that estimated
above for an E. huxleyi bloom, but the coccoliths of other species (Fig. 1) are also abundant
in the sediments. The significance of the inorganic to organic carbon ratio for coccolith-rich
sediments lies in understanding the degree to which the two might be associated. Carbonate
surfaces adsorb organic material (Suess, 1973; also see Degens and Ittekot, 1986), a process
that enhances the final preservation of organic carbon in marine sediments (Gordon and
Millero, 1985). Using the estimate of Suess that 1m 2 of carbonate surface holds 1.2 mg
organic carbon, and a surface area value for each E. huxleyi coccolith of 15/-tm 2 (Westbroek
et al., 1983), a predicted inorganic to organic carbon ratio of about 13: 1 is calculated for such
coccoliths. Since this is lower than observed ratio for coccolith-rich sediments, most if not all
the organic carbon in such sediments may be adsorbed onto the coccoliths. Some is derived
directly from coccolithophores. including acidic polysaccharides that form the matrix of the
coccoliths of E. huxleyi (Westbroek et al., 1989) and long chained ketones in sediments that