The mechanisms controlling the timing and intensity of spring blooms in inshore,
temperate waters, across the North Atlantic and elsewhere, are an unending source of
fascination to oceanographers. Models of seasonal cycles of phytoplankton stock, as
considered in Chapter 4, are a sub-industry in our profession. Measurements from
boats and ships, moorings, autonomous floats, and satellites are all enlisted to
improve our insights, and we are far from finished. Phytoplankton stock size depends
upon the past history of productivity and also upon the history of cell mortality.
“Death” (or at least loss to the surface layer stock) comes from grazing, mixing out of
the euphotic zone, sinking, or disease. The latter was largely ignored until recently;
marine waters contain viruses that are capable of lysing phytoplankton cells (Chapter
5).
(^) Seasonal cycles vary markedly among subregions, but there is a classic cycle that is
observed in coastal Atlantic waters, such as the North Sea or off Cape Cod, and all
across the high-temperate Atlantic. Characteristically, textbooks show this cycle in a
schematic way (Fig. 11.7). That is symptomatic of a problem of the discipline.
Because getting out to sea on a regular or sustained basis is difficult, we still have no
single time-series quantifying the progression of a spring bloom with good (daily, or
near-daily) resolution of required variables, although some data series from moorings,
and lately ARGO floats, supply part of what is required. Measurements needed are
phytoplankton stock and species composition, irradiance, water-column density
structure, nutrients, and grazer community data, all from well before the stock
increase until it has subsided again. Evaluation of exactly which species make up the
phytoplankton stock during the progress of the bloom would be particularly useful,