BACTERIAL STANDING STOCK, ACTIVITY, AND CARBON PRODUCTION DURING FORMATION AND GROWTH OF SEA-ICE IN THE WEDDELL SEA, ANTARCTICA

Bacterial response to formation and growth of sea ice was investigated during autumn in the northeastern Weddell Sea. Changes in standing st ock, activity, and carbon production of bacteria were determined in su ccessive stages of ice development. During initial ice formation, conc entrations of bacterial cells, in the order of 1 x 10(8) to 3 x 10(8) liter(-1), were not enhanced within the ice matrix. This suggests that physical enrichment of bacteria by ice crystals is not effective. Due to low concentrations of phytoplankton in the water column during fre ezing, incorporation of bacteria into newly formed ice via attachment to algal cells or aggregates was not recorded in this study. As soon a s the ice had formed, the general metabolic activity of bacterial popu lations was strongly suppressed. Furthermore, the ratio of [H-3]leucin e incorporation into proteins to [H-3]thymidine incorporation into DNA changed during ice growth. In thick pack ice, bacterial activity reco vered and growth rates up to 0.6 day(-1) indicated actively dividing p opulations. However, biomass-specific utilization of organic compounds remained tower than in open water. Bacterial concentrations of up to 2.8 x 10(9) cells liter(-1) along with considerably enlarged cell volu mes accumulated within thick pack ice, suggesting reduced mortality ra tes of bacteria within the small brine pores. In the course of ice dev elopment, bacterial carbon production increased from about 0.01 to 0.4 mu g of C liter(-1) h(-1). In thick ice, bacterial secondary producti on exceeded primary production of microalgae.