174
H. Siegel et al.
9.5.2 Coccolithophore Blooms
The occurrence and bloom of coccolithophores in front of Namibia were intensively
investigated by Siegel et al. (2007). Coccolithophores are the most productive calcifying organism on earth and play an important role in the marine carbon cycle
effecting the carbon and carbonate content. A summary about the research on the
coccolithophore and particularly on the species Emiliania huxleyi is presented in
the monograph edited by (Thierstein and Young 2004). After the nutrient input into
the euphotic zone by upwelling the phytoplankton development starts with diatoms
and dinoflagellates. These algae are characterized by conspicuous absorption in the
visible spectral range and can be studied by satellite derived chlorophyll-a concentrations. Under certain conditions the succession may develop to coccolithophores
which discolour the surface water milky turquoise due to their scattering properties.
The enhanced scattering allows to apply quasi true colour images to follow the spatial and temporal development. Coccolithophore blooms are known from different
regions of the world ocean (Weeks et al. 2004b; Tyrrell et al. 2008; Holligan et al.
2010; Painter et al. 2010; Garcia et al. 2011). Milky turquoise discolouration were
found off the coast of the Republic of South Africa which were identified as coccolithophore blooms (see also Mitchell-Innes and Winter 1987). These blooms have
been mainly associated with sub-polar regions as in the global maps by Brown and
Yoder (1994) based on SeaWiFS data have shown.
The optimal growth conditions are high incident solar radiation, stable shallow
top-layer, silicate depletion, specific nutrient conditions, and reduced grazing by zooplankton (Rost and Riebesell 2004; Tyrrell and Merico 2004). Nanninga and Tyrrell
(1996) and Garcia et al. (2011) determined a mixed layer depth of less than 30 m,
that the coccolithophores remain under high solar radiation (Iglesias-Rodriguez et al.
2002). Emiliania huxleyi is a fast growing phytoplankton which develops in eutrophic
environments, when the fastest growing diatoms are excluded by silicate depletion
(Humborg et al. 1997). Emiliania huxleyi can grow if phosphate is exhausted because
it is able to synthesize enzyme alkaline phosphatase and may use dissolved organic
phosphorus (Riegman et al. 2000). Start conditions are high N:P ratios but during
the bloom the ratio is highly variable (Fanning 1992; Townsend et al. 1994; Tyrrell
and Taylor 1996).
A milky turquoise offshore plume was identified as a coccolithophore bloom for
the first time in the region off Namibia in March/April 2003. The plume was followed
by satellite imagery for about 10 days (Siegel et al. 2007). An example of the time
series is presented in Fig. 9.4 (left panel) and the SeaWiFS derived calcite flag (right
panel). Near real-time satellite data access enabled the research crew to perform
interdisciplinary investigation in the patch. Different methods such as HPLC pigment
analysis, Energy Dispersive X-Ray analysis, Scanning Electronic Microscopy, and
measurements of inherent and apparent optical properties were used to validate the
coccolithophore bloom of Emiliania huxleyi.
The water was characterized by high reflectances, the occurrence of the marker
pigment 19’-Hexanoyloxyfucoxanthin and a double maximum of the spectral
H. Siegel et al.
9.5.2 Coccolithophore Blooms
The occurrence and bloom of coccolithophores in front of Namibia were intensively
investigated by Siegel et al. (2007). Coccolithophores are the most productive calcifying organism on earth and play an important role in the marine carbon cycle
effecting the carbon and carbonate content. A summary about the research on the
coccolithophore and particularly on the species Emiliania huxleyi is presented in
the monograph edited by (Thierstein and Young 2004). After the nutrient input into
the euphotic zone by upwelling the phytoplankton development starts with diatoms
and dinoflagellates. These algae are characterized by conspicuous absorption in the
visible spectral range and can be studied by satellite derived chlorophyll-a concentrations. Under certain conditions the succession may develop to coccolithophores
which discolour the surface water milky turquoise due to their scattering properties.
The enhanced scattering allows to apply quasi true colour images to follow the spatial and temporal development. Coccolithophore blooms are known from different
regions of the world ocean (Weeks et al. 2004b; Tyrrell et al. 2008; Holligan et al.
2010; Painter et al. 2010; Garcia et al. 2011). Milky turquoise discolouration were
found off the coast of the Republic of South Africa which were identified as coccolithophore blooms (see also Mitchell-Innes and Winter 1987). These blooms have
been mainly associated with sub-polar regions as in the global maps by Brown and
Yoder (1994) based on SeaWiFS data have shown.
The optimal growth conditions are high incident solar radiation, stable shallow
top-layer, silicate depletion, specific nutrient conditions, and reduced grazing by zooplankton (Rost and Riebesell 2004; Tyrrell and Merico 2004). Nanninga and Tyrrell
(1996) and Garcia et al. (2011) determined a mixed layer depth of less than 30 m,
that the coccolithophores remain under high solar radiation (Iglesias-Rodriguez et al.
2002). Emiliania huxleyi is a fast growing phytoplankton which develops in eutrophic
environments, when the fastest growing diatoms are excluded by silicate depletion
(Humborg et al. 1997). Emiliania huxleyi can grow if phosphate is exhausted because
it is able to synthesize enzyme alkaline phosphatase and may use dissolved organic
phosphorus (Riegman et al. 2000). Start conditions are high N:P ratios but during
the bloom the ratio is highly variable (Fanning 1992; Townsend et al. 1994; Tyrrell
and Taylor 1996).
A milky turquoise offshore plume was identified as a coccolithophore bloom for
the first time in the region off Namibia in March/April 2003. The plume was followed
by satellite imagery for about 10 days (Siegel et al. 2007). An example of the time
series is presented in Fig. 9.4 (left panel) and the SeaWiFS derived calcite flag (right
panel). Near real-time satellite data access enabled the research crew to perform
interdisciplinary investigation in the patch. Different methods such as HPLC pigment
analysis, Energy Dispersive X-Ray analysis, Scanning Electronic Microscopy, and
measurements of inherent and apparent optical properties were used to validate the
coccolithophore bloom of Emiliania huxleyi.
The water was characterized by high reflectances, the occurrence of the marker
pigment 19’-Hexanoyloxyfucoxanthin and a double maximum of the spectral