BACTERIAL PRODUCTION IN THE BOTTOM SURFACE OF SEA ICE IN THE CANADIAN SUB-ARCTIC

Standing stocks of bacteria in the bottom of first-year sea ice at Frobisher Bay, NWT increased 5-fold between March and May (1985 and 1986) and constituted up to 5% of particulate organic carbon (POC). About 1/3 of the bacterial assemblage incorporated radioactive thymidine. The mean volume of cells was 6 times larger than that in the underlying water, and the assemblage was dominated by rod-shaped cells rather than the coccus-shaped cells prevalent in the water column. Bacterial carbon production by 3H-thymidine incorporation amounted to 0.04 mg carbon m-2.h-1, or a doubling time of about 22 h, in the bottom ice surface and 0.01 mg carbon m-3.h-1 in the underlying water. The concentration of dissolved organic carbon (DOC) was generally much higher in the bottom ice surface than in the underlying water, and was closely related to rate of cell production. A model of bacterial dependancy on DOC derived from primary production suggests that bacteria are important in the localized production of POC in the bottom of arctic sea ice, and contribute to an early source of nutrition for higher trophic levels before summer production in open water. -Authors