SPATIAL-DISTRIBUTION OF PARTICLE COMPOSITION AND MICROBIAL ACTIVITY IN BENTHIC BOUNDARY-LAYER (BBL) OF THE NORTHEAST WATER POLYNYA

Heterotrophic activity and related measures of pelagic microorganisms were studied in the Northeast Water Polynya, (NEWP 77-82 degrees N, 10 -15 degrees W) in 1993 during a FS Polarstern cruise. A bottom water s ampler (BWS), which enabled collection of distinct 12 1 water samples at variable heights above the seabed, was used to study the distributi on of various biological parameters with high vertical resolution in t he benthic boundary layer (BBL). Samples were taken in the water colum n from varying depths in the intermediate water column (IWC) down to 5 m above bottom using a CTD as well as at 40, 20, 12 and 7 cm above th e sea bed using the bottom water sampler. Total suspended matter, part iculate organic carbon and nitrogen (POC, PON), chlorophyll a equivale nts (chi. a equiv,), bacterial abundance and size distribution and mic robial activity were determined in each of the samples. Most of the de ep samples (IWC and BBL, maximum water depth 479 m) came from warmer A tlantic influenced water that fills a circular trough system on the no rth east Greenland shelf. In general the activity of the microbial com munity, cell-specific activity and concentrations of POC and chi. a eq uiv, were significantly higher in the BBL compared to the IWC. Microbi al activity appeared to be independent of the quantity of available PO C, indicating the nutritional importance of dissolved organic matter f or microorganisms. The spatial distribution of particle composition an d microbial activity in the BBL was strongly determined by the anticyc lonic current pattern and the spatial pattern of primary production in the polynya. Close coupling of biological processes in the surface wa ters and particle composition and microbial activity in the BBL were f ound below areas of fluctuating ice cover and above 260 m water depth in the northeastern Westwind Trough. Highest microbial activity occurr ed in the heavily ice covered Belgica Trough, although only remnants o f freshly produced organic matter were present. In the open polynya ne ar-bottom particle properties were mainly determined by lateral advect ion. The benthic boundary layer is shown to represent a distinct envir onment, with small scale vertical distribution of particle properties and stimulated microbial activity, indicating that rapid modification of organic matter occurs in the BBL before its final incorporation int o the sediment.