The distribution and activity of bacterioplankton, and the turnover of dissolved organic matter (DOM) were examined in McMurdo Sound, Antarctica. On the eastern side of the Sound, bacteria averaged 6.5 x 108 1-1 , and turnover rates of dissolved adenosine triphosphate, Dglucose and l-leucine averaged 16, 116 and 124 h, respectively. These molecules as well as thymidine were taken up maximally from 0 ~ to 5 ~ and near-maximally from -1.5 ~ to 0 ~ indicating bacterial adaptation to rapid turnover of dissolved organic matter at the ambient temperature. On the west side of the Sound, bacteria averaged only 0.65 x 108 1-1 , and turnover times for adenosine triphosphate, D-glucose and 1leucine averaged 59, 20454, and 3070 h, respectively. Total microbial adenosine triphosphate (an indicator of total microbial bi0mass) and chlorophyll a were also much lower at the western than at the eastern side stations. Moreover, no primary production could be detected at one western side station (New Harbor). Thus, in McMurdo Sound, the western side is highly oligotrophic, but the eastern side has an abundant active bacterioplankton, comparable to that of temperate coastal waters.
ter was supposed to downwell with dense water at the Antarctic convergence, be advected to low latitudes by deep oceanic circulation, eventually be upwelled to warm surface waters where its utilization by bacteria would contribute to the productivity of the tropical waters. Contrary to this hypothesis Gillespie et al. (1976) found high microbial heterotrophic potential for the assimilation of several organic substrates from Antarctic seawater at low temperatures. Moreover, the likely dominance of bacterial flora by psychrophlles argues against the preservation of organic matter in Antarctic waters. Thus, Wiebe and Hendricks (1974) found that 77% of the bacterial isolates from south of the Antarctic convergence would not grow above 25 ~
To elucidate the role of Antarctic bacterioplankton in the food-web and in the cycling of organic matter, we have studied the distribution and activity of baterioplankton around McMurdo Sound and under the Ross Ice Shelf during three austral summers (1976-77-78).
Mc Murdo Sound is a specially interesting study area because of the dramatic difference between the macrobenthic productivity of the eastern (very high) and western (very low) sides of the sound (Dayton and Oliver, 1977). Dayton and Oliver have also suggested that similar differences exist in the productivity of the overlying water column.