Spatial and seasonal variations in primary production of sea ice microalgae and phytoplankton in Frobisher Bay, Arctic Canada

Spatial and seasonal variations in primary production by sea ice microalgae and phytoplankton in Frobisher Bay were studied from 1976 to 1986. Sea ice microalgae grew from late winter to spring. Maximal production of 2.0 mg C m-3 h-' (12 mg C m-' h-') was reached in late spring when a microalgal bloom occurred in the bottom 5 cm of the ice. At the same time, photosynthetic production rates of phytoplankton in the water under the ice began to increase but were generally several times lower than those within the ice. The greatest rate of carbon production in the water column was 4 mg C m-3 h-' (55 mg C m-'h-'), reached during the summer. The phytoplankton bloom took place in the upper 10 m where the pycnocline existed. Production decreased after the summer through the fall and winter. The most important factors governing primary production of the microalgae in the upper part of the sea ice were the combined effects of light and temperature. Light alone was the most important factor for the bottom ice microalgae and the phytoplankton in the water column under the ice and in the lower parts of the euphotic zone during open water seasons. Nutrients were never limiting during this study. Evidence is given for the important role of such auxiliary factors as salinity changes, tides, airwater heat exchanges and winds in generating vertical mixing, either alone or in combination with light, ir. regulating !he !imc and iiiagiiitiide of Ll~e 'uioom.