311
Satellite images show that the highest concentrations of coccoliths in oceanic situations are
often along temperature gradients within eddy structures (Fig. 6). Such distributions may
indicate local enhancement of coccolithophore growth and calcification due to the upward
mixing of nutrients, or the surface outcropping of sub-surface coccolith-rich layers. On the
continental shelf, however, regions of strong reflectance due to coccoliths tend to be
associated with relatively warm surface water (Ackleson et al., 1988) and it is possible to
estimate from sequences of satellite images the enhancement of local heating rates attributable
to coccolith light scatter. For the 1988 and 1989 E. huxleyi blooms in the Gulf of Maine, the
coccoliths were associated with a rate of surface warming 0.05 to 0.08 °C d- ' greater than that
for nearby regions outside the bloom (S.G. Ackleson pers.comm.). Experiments with cultures
of naked and calcifying strains of E. huxleyi also show that the presence of coccoliths leads
to significantly greater heating of the growth medium under equivalent conditions of
illumination and external temperature (van Leeuwe, 1990).
UOR sections through a coccolithophore population illustrate how variations in reflectance
(550nm) are accompanied by shifts in the depths of penetration for the 10 and 1 % light levels
at this wavelength (Fig. 7). Although quantitative comparisons of the light fields have yet to
be carried out, it appears that the loss of light energy to the atmosphere due to near-surface
backscattering is accompanied by an increase in overall light absorption within the coccolith
layer. Sub-surface chlorophyll maxima are generally absent or only weakly developed within
N. Atlantic coccolithophore blooms possibly due to light limitation of phytoplankton growth
at the level of the seasonal thermocline. (Discrete chlorophyll determinations indicate that subsurface maxima in chlorophyll fluorescence as seen in Fig. 7 are due largely to daytime solar
inhibition of fluorescence near the surface.)
INORGANIC AND ORGANIC CARBON FLUXES
Laboratory studies with batch cultures of a calcifying strain of E. huxleyi isolated from the
Gulf of Maine in 1988 have shown that carbon incorporation into calcite exceeds that into
organic carbon during at least part of the growth cycle (Fig. 8). Field measurements have
given similar results (unpubl. data), although the measured rates of calcification relative to
photosynthesis are often low due in part to the presence of non-calcifying types of
phytoplankton and in part to the highly localised distribution in space and time of actively
calcifying cells (by the time blooms are detected as high reflectance features on satellite
images coccolith formation has largely stopped). In the experiment illustrated in Fig. 8 the
total production of new cells to coccoliths was in the proportion 1: 53, assuming that each cell
Satellite images show that the highest concentrations of coccoliths in oceanic situations are
often along temperature gradients within eddy structures (Fig. 6). Such distributions may
indicate local enhancement of coccolithophore growth and calcification due to the upward
mixing of nutrients, or the surface outcropping of sub-surface coccolith-rich layers. On the
continental shelf, however, regions of strong reflectance due to coccoliths tend to be
associated with relatively warm surface water (Ackleson et al., 1988) and it is possible to
estimate from sequences of satellite images the enhancement of local heating rates attributable
to coccolith light scatter. For the 1988 and 1989 E. huxleyi blooms in the Gulf of Maine, the
coccoliths were associated with a rate of surface warming 0.05 to 0.08 °C d- ' greater than that
for nearby regions outside the bloom (S.G. Ackleson pers.comm.). Experiments with cultures
of naked and calcifying strains of E. huxleyi also show that the presence of coccoliths leads
to significantly greater heating of the growth medium under equivalent conditions of
illumination and external temperature (van Leeuwe, 1990).
UOR sections through a coccolithophore population illustrate how variations in reflectance
(550nm) are accompanied by shifts in the depths of penetration for the 10 and 1 % light levels
at this wavelength (Fig. 7). Although quantitative comparisons of the light fields have yet to
be carried out, it appears that the loss of light energy to the atmosphere due to near-surface
backscattering is accompanied by an increase in overall light absorption within the coccolith
layer. Sub-surface chlorophyll maxima are generally absent or only weakly developed within
N. Atlantic coccolithophore blooms possibly due to light limitation of phytoplankton growth
at the level of the seasonal thermocline. (Discrete chlorophyll determinations indicate that subsurface maxima in chlorophyll fluorescence as seen in Fig. 7 are due largely to daytime solar
inhibition of fluorescence near the surface.)
INORGANIC AND ORGANIC CARBON FLUXES
Laboratory studies with batch cultures of a calcifying strain of E. huxleyi isolated from the
Gulf of Maine in 1988 have shown that carbon incorporation into calcite exceeds that into
organic carbon during at least part of the growth cycle (Fig. 8). Field measurements have
given similar results (unpubl. data), although the measured rates of calcification relative to
photosynthesis are often low due in part to the presence of non-calcifying types of
phytoplankton and in part to the highly localised distribution in space and time of actively
calcifying cells (by the time blooms are detected as high reflectance features on satellite
images coccolith formation has largely stopped). In the experiment illustrated in Fig. 8 the
total production of new cells to coccoliths was in the proportion 1: 53, assuming that each cell