Particle-associated microbial community dynamics in the Southern Beaufort Sea

Our project examines the role that microbes play in attenuating particle flux on Arctic Shelves. We are coupling geochemical and microbiological analyses in a joint effort, with Kirk Cochran's lab at Stony Brook University in New York, to examine particle flux, the diversity and extracellular enzymatic (hydrolytic) activities of microbes associated with particles of different size classes, and corresponding chemical composition and likely source (marine or terrestrial) of the POM. Our specific objectives are threefold: 1) to assess microbial community structure on sinking (>60 µm) and suspended particles (1-60 µm) in reference to the free-living community (0.2-1 µm), using a microbial DNA fingerprinting technique called Terminal Restriction Fragment Length Polymorphism (T-RFLP); 2) to measure extracellular protease, glucosidase and chitinase actvities associated with these particle classes, via incubations with fluorescently tagged substrate analogs; and 3) to quantify associated particulate amino acids, lipids and carbohydrates. Samples were collected via in situ pumps (deployed by Cochran's team) and CTD rosette casts with subsequent in-line size fractionation in the ship's cold room. We will assess how the various factors measured change with depth in the water column, horizontally as particles move off-shelf in nepheloid layers, and with particle source (marine versus terrestrial, as indicated by stable C isotope values measured by Cochran's team).