Microbial Processes Relating to Carbon Cycling in Southeastern Bering Sea Sediments

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Abstract
Several microbial variables were measured in southeastern Bering Sea sediments which should theoretically be related to C cycling. The variables studied included glutamate and glucose uptake and respiration rates, CO2 and methane production rates and the activities of the following hydrolases: cellulase, amylase, laminarinase, protease and xylanase. N fixation (acetylene reduction) and denitrification rates and phosphatase and arylsulfatase activities were also determined. The 2 regions studied were offshore sediments in the Saint George Basin (SGB) and inshore bay sediments in Port Moller (PM) [Alaska, USA]. Mean rates of all variables studied were higher in PM sediments when compared to SGB. The rates of methane production, CO2 production and N fixation were comparable to those reported in temperate marine sediments indicating that these rates were not depressed because of low temperature. In sediments of both areas, phosphatase and arylsulfatase activities were highly correlated. In PM, the activity of these 2 enzymes was highly correlated with protease activity, glutamate uptake rates and CO2 evolution rates. These correlations suggest that in PM sediments, all of these variables were interrelated and probably reflected relative levels of microbial heterotrophic activity. In the same sediments, the linear correlation between glutamate uptake rates and protease activity was very high (r = 0.993). The high correlation suggests that protease activity reflects amino acid availability to the microbial population as the result of protein hydrolysis. The glutamate uptake rates reflect the adjustment of the microbial population to levels of amino acids available in the sediments. There was a region within SGB where microbial processes were elevated during both sample periods (Jan. and May). This area was located on an oceanographic frontal system. The high microbial activity observed there may be related to the influence of the frontal system on primary productivity and sedimentation processes.
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