Microbes in antarctic waters of the Drake Passage: Vertical patterns of substrate uptake, productivity and biomass in January 1980

Summary

Microbial distribution, substrate uptake, productivity and biomass were investigated in the water column of the Drake Pasage, Antarctica. Organic substrate uptake and productivity were determined by the utilization of [¹⁴C] and [³H] glucose and by the incorporation of [³H] adenine and [³H] thymidine into RNA and DNA. Microbial biomass was estimated by ATP concentrations and bacterial abundance by epifluorescence direct counts. Estimates of glucose uptake and productivity indicate that microbes were most active in surface waters and least active below 100 m. Although glucose uptake was generally less than 10 ng/l·h, microbes maintained a low available glucose pool. Glucose concentrations varied from undetectable to 7.5 μg/l with a turnover time of 5–20 days in the euphotic zone and greater than 365 days in Circumpolar Deep Waters. Microbes respired 12 to 32% of the assimilated [¹⁴C] glucose. Microbes responsible for the uptake of dissolved organic cabon in the euphotic zone were in the <3 μm size class, presumably bacteria whereas in the aphotic zone the uptake of organics, albeit low, was due to microbes >3 μm, most likely on particles. Microbial ATP-biomass decreased rapidly with increasing water depth and most (∼60–70%) of the ATP-biomass was due to microbes >3 μm. Although bacterial numbers were high (>10⁸ cells/l) at several stations, there were generally between 10⁷ and 10⁸ cells/l with increasing water depth. Bacterial biomass was estimated at <3% of the microbial biomass (7.3 gC/m²) in the euphotic zone. Conservative estimates of secondary productivity by microbes were between 0.5 and 3.0 mg C/m²·d (0.2–54 ng C/l·d).