(^) Similar patterns also occur in the phytoplankton distributions after the main spring
bloom, as seen in a June satellite image of waters south of Iceland (Fig. 2.4), a picture
derived from reflections from the calcite plates of coccolithophores. The importance
of the mesoscale eddy field to oceanic phytoplankton is evident from this picture.
Coastal chlorophyll concentrations estimated from satellite data collected over the
western north Atlantic (cover of this book) show that phytoplankton stocks there also
vary in swirling, active patterns.
Species Successions in the Spring Bloom
(^) No floristic analysis based on microscopy was included in the JGOFS North Atlantic
bloom study. However, Barlow et al. (1993) did examine this question indirectly in
the JGOFS project, applying a chromatographic analysis to identify the main algal
groups at different times from differences in their accessory chloroplast pigments. At
a so-called Langrangian station following a drifter with a drogue at 20 m from 49°N,
19°W along a southeasterly track, the relative pigment composition changed (Fig.
2.20), from predominantly fucoxanthin to predominantly 19′-butanoyloxyfucoxanthin,
implying a shift in phytoplankton from mainly diatoms to a preponderance of
prymnesiophytes. This happened in less than 10 days, after the peak of chlorophyll-a
but while it remained relatively high (>1.5 mg m−3). Thus, spring blooms are not
driven by just the production needed to raise stock levels once. The phytoplankton are
turning over rapidly and an initially dominant species can be replaced by another.