Phytoplankton and bacterial productivity in the Tugur Bay (Sea of Okhotsk) in July-August 1990

A study of quantitative characteristics: phytoplankton photosynthesis (Ph), bacterial assimilation of CO2 (BA), total abundance of bacteria (TAB) and organic matter destruction (D) was carried out in waters the Tugur Bay (tidal level fluctuations up to 7 m) in July-August 1990. Calculations were made of integral indices in some parts: Ph -10-630, BA - 8-29, D - 280-1015 and of total primary production (TPP) - 18-652 mg C/(m2 day). According to obtained data and TAB the ecosystem of the Tugur Bay can be regarded as oligotrophic-mesotrophic one. Dependence on spatial and temporal inhomogeneity of primary productional processes on tide-ebb cycles was found. The role of bacterial relations in the ecosystem of the bay was shown. Portion of ?A in TPP varied from 4 to 44% reaching the maximum in desalinated water during the tide-ebb.

(Table 4) Distribution of bacterial populations in sediments of ODP Hole 128-798B

Sediment whole-round cores from a dedicated hole (798B) were obtained for detailed microbiological analysis, down to 518 m below the seafloor (mbsf). These sediments have characteristic bacterial profiles in the top 6 mbsf, with high but rapidly decreasing bacterial populations (total and dividing bacteria, and concentrations of different types of viable heterotrophic bacteria) and potential bacterial activities. Rates of thymidine incorporation into bacterial DNA and anaerobic sulfate reduction are high in the surface sediments and decrease rapidly down to 3 mbsf. Methanogenesis from CO2/H2 peaks below the maximum in sulfate reduction and although it decreases markedly down the core, is present at low rates at all but one depth. Consistent with these activities is the removal of pore-water sulfate, methane gas production, and accumulation of reduced sulfide species. Rates of decrease in bacterial populations slow down below 6 mbsf, and there are some distinct increases in bacterial populations and activities that continue over considerable depth intervals. These include a large and significant increase in total heterotrophic bacteria below 375 mbsf, which corresponds to an increase in the total bacterial population, bacterial viability, a small increase in potential rates of sulfate reduction, and the presence of thermogenic methane and other gases. Bacterial distributions seem to be controlled by the availability of terminal electron acceptors (e.g., sulfate), the bioavailability of organic carbon (which may be related to the dark/light bands within the sediment), and biological and geothermal methane production. Significant bacterial populations are present even in the deepest samples (518 mbsf) and hence it seems likely that bacteria may continue to be present and active much deeper than the sediments studied here. These results confirm and extend our previous results of bacterial activity within deep sediments of the Peru Margin from Leg 112, and to our knowledge this is the first comprehensive report of the presence of active bacterial populations from the sediment surface to in excess of 500 mbsf and sediments > 4 m.y. old.