EFFECTS OF ENVIRONMENTAL VARIATION ON SINKING RATES OF MARINE PHYTOPLANKTON

The effects of environmental variables, particularly irradiance, on the sinking rates of phytoplankton were investigated using cultures of Chaetoceros gracilis Schuett and C. flexuosum Mangin in laboratory experiments; these data were compared with results from assemblages in the open ocean and marginal ice zone of the Greenland Sea. In culture experiments both the irradiance under which the diatom was grown and culture growth rate were positively correlated with sinking rates. Sinking rates in the Greenland Sea were smallest when determined from chlorophyll and biogenic silica and greatest when determined from particulate carbon and nitrogen. Field measurements indicated that variations in sinking may be associated with changes in irradiance and nitrate concentrations.