Seasonal and inter-annual variability of bacterioplankton biomass at station Kerfix, off Kerguelen Islands, Antarctica

Between January 1992 and March 1995, the research project Kerfix undertook the first regular non-coastal multiyear acquisition of parameters related to the carbon cycle in the Southern Ocean at a time series station located at 50°40’S-68°25’E, 110 km southwest of the Kerguelen Islands. I present here a general overview of the bacteriological data collected during this survey. Bacterioplankton biomass at Kerfix station was always significantly lower than in the direct vicinity of the Kerguelen Islands. Bacterial abundance decreased from surface to deepest layers (from 10⁶ cells ml^–1 in surface layer to 5.0 × 10⁴ cells ml^–1 at 1500 m). In contrast, mean cell volume (0.1 μm³) and proportion of free-living bacteria (80%) were relatively constant through the entire water column. The results suggest that a relatively low seasonal and inter-annual variability affect the total bacterial abundance, the mean cell volume and the percentage of free-living cells. The bacterial biomass is at least equivalent to that of phytoplankton in the surface layers. If integrated over the whole water column it reaches values higher than 1 g C m^–2 , which are higher than the corresponding values of phototrophic biomass.