Vertical distribution of faecal pellets during FLEX '76

During FLEX '76 (Fladen Ground Experiment), the vertical distribution of faecal pellets was studied at a time station on the Fladen Ground (North Sea). Generally, the faecal pellets showed a clearly-defined maximum above the main thermocline within a depth of 0–30 m. Only in a period of storms was the faeces-maximum lowered to the main thermocline, which occurred at 50–60 m depth. The maximum numbers of the copepodCalanus finmarchicus, the most important producer of faecal pellets, initially occupied the same level as the faeces maximum. However, from the middle of May, theC. finmarchicus population started a diel vertical migration, during which, as a rule, the copepods migrated away from the surface region into deeper waters. On this occasion, the faecal pellet maximum did not break up but remained in the uppermost layer of the water column. The high concentrations of faecal pellets found within the uppermost 30 m of the water column contradict the extremely high sinking rates of faeces reported by various authors. The quotients of the depth-integrated counts of faecal pellets andC. finmarchicus individuals were calculated. The main maximum of faeces per individual occurred in the period between 28 April and 6 May 1976. A second, smaller maximum was documented between 23–28 May 1976. These two maxima coincided with the development of phytoplankton blooms observed at this particular time station.JONSDAP '76 Contribution No. 68.