Role of planktonic bacteria in productivity and cycling of organic matter in the Eastern Pacific Ocean

Abstract

Total number, biomass, production, and respiration of bacterioplankton were measured in oligotrophic, mesotrophic and eutrophic waters of the Eastern Pacific. Total number of bacteria in the upper mixed layer and in the upper thermocline boundary layers varied from 30–60.103 ml-1 in oligotrophic waters to 100–400.103 ml-1 in mesotrophic waters of fronts and divergences, and to 1–2,5.106 ml-1 in eutrophic waters of coastal upwellings. Wet biomass varied from 5–10 mg l-1 in oligotrophic waters, to 50–200 mg l-1 in mesotrophic waters, and to 1–2 g m-3 in eutrophic waters. Below the layer of maximum temperature gradient i.e. below 35–50 m, bacterioplankton density decreased 5–10 times. P/B coefficients per day were highest in the oligotrophic surface water (∼ 1), and lowest in the eutrophic ones (0.2–0.4). In mesotrophic waters they were intermediate (0.4–1.0). the stock of labile organic matter (LOM) accessible to microbial action varied from 0.3 to 1.6 mg Cl-1. Its highest value occurred in the upwelling area. The stock of LOM does not noticeably decrease from the euphotic zone to a depth of 2 000 m. Its turnover time varied from 5 to 45 days in surface waters, and 30–50 years in deep oceanic waters. The role of bacterioplankton in productivity and in cycling of organic matter in surface — and deep oceanic waters is discussed.