P. Vanderwal et al., PRODUCTION AND DOWNWARD FLUX OF ORGANIC-MATTER AND CALCITE IN A NORTH-SEA BLOOM OF THE COCCOLITHOPHORE EMILIANIA-HUXLEYI, Marine ecology. Progress series, 126(1-3), 1995, pp. 247-265
In July 1993, an extensive study was made of a large bloom of the cocc
olithophorid Emiliania huxleyi in the North Sea halfway between the Sh
etland Islands and Norway. Here we report on the hydrography, producti
on and sedimentation of particulate organic carbon (POC) and calcite c
arbon (calcite-C) at 4 stations occupied for 24 h, 2 inside the bloom
and 2 just outside. The coccolithophorid bloom was confined to North S
ea waters, where a stable shallow mixed layer had been formed. Bloom d
evelopment had entered the decaying phase, judged by the relatively lo
w living cell number (maximally 1200 cells cm(-3)), the high number of
loose coccoliths (up to 350 000 coccoliths cm(-3)), and the fact that
sedimentation of calcite-C exceeded production. In the top 15 m at th
e bloom stations, the mean daily production of coccoliths was 17 per c
ell. At the 2 stations outside the bloom, the dominant coccolithophore
was a holococcolithophorid (up to 1400 cells cm(-3)), with insignific
ant amounts of calcite produced per cell. At these stations, nutrients
were present in non-limiting concentrations and production of POC was
twice as high as at the bloom stations. In the bloom, mixed layer nit
rate levels were below 0.2 mu M. Faecal pellets collected in the sedim
ent traps contained large numbers of coccoliths of E. huxleyi. Althoug
h the numbers of grazers at the 2 stations outside the bloom were not
lower than those in the bloom, the volume of faecal matter sedimenting
at 50 m was about 70 times lower. It is hypothesized that faecal pell
ets outside the bloom were so Light in weight that they did not sink v
ery far before degradation, whereas the pellets produced in the E. hux
leyi bloom in general were exported rapidly due to their heavy load of
calcite. This implies that recycling of materials in the mixed layer
of this bloom is relatively low due to high downward flux rate. The ra
tio at which POC and calcite-C were sedimenting amounted to 1.3 on ave
rage for the 2 bloom stations at 50 m water depth.