BACTERIOPLANKTON IN THE MARGINAL ICE-ZONE OF THE WEDDELL SEA - BIOMASS, PRODUCTION AND METABOLIC-ACTIVITIES DURING AUSTRAL AUTUMN

Observations of microbial distributions and metabolic activities were made during early austral autumn, 1986, in the marginal ice zone of the Weddell Sea east of the Antarctic peninsula. Bacterioplankton had distributions and activities similar to those of phytoplankton within the marginal ice zone. Bacterial production averaged 19 ± 10 mg C m-2 d-1 in regions partially covered with ice, and in open waters mean rates were 119 ± 69 mg C m-2 d-1. Pronounced productivity maxima were present seaward of the ice edge. Although biomass and productivity maxima for algae and bacteria were largely superimposed spatially, there was no obvious relationship between these biological features and the density field. Rates of primary production in early autumn, adjacent to a nearly stationary ice edge, were much lower than rates observed in spring when the ice edge was retreating. However, bacterial production rates were comparable during both seasons. During autumn secondary production by bacterioplankton in the upper 100 m often equaled or exceeded primary productivity; integrated bacterial production in open water areas averaged 76% of primary production. Mean bacterial growth rates in ice-covered and open water regions were 0.33 and 0.58 d-1, respectively, or from 5 to 11 times those of phytoplankton. Rates and ratios of macromolecular synthesis by bacterioplankton were comparable with previous temperature and polar studies. Several lines of evidence indicate that this ice edge bloom was dominated by heterotrophic processes. © 1990.