Microbial uptake of dissolved organic nitrogen along the coastal Alaskan Arctic

Productivity in the coastal Arctic is expected to increase as temperatures continue to rise and as the number of open water days grow. With this increased productivity, the coastal shelves of the Arctic Ocean may act as a sink for atmospheric carbon. However, this storage is dependent on a sufficient nitrogen supply. One potential source for this supply is dissolved organic nitrogen (DON), which includes compounds such as urea and amino acids. To investigate the spatial extent and the rate at which the Arctic microbial community utilizes organic substrates, size-fractionated (>3µm and <3 µm) uptake rates were determined in both the Chukchi and Beaufort Seas during late summer. Uptake incubations were conducted with isotopically-labeled inorganic and organic nitrogen sources including, ammonium, nitrate, urea, creatine, and mixed algal amino acids. We found that while ammonium was the predominately utilized substrate, uptake rates of urea were often greater than nitrate, and that amino acid uptake was wide-spread. Collecting these organic substrate uptake rates across the Alaskan Arctic is a critical step in establishing the importance of DON nutrient sources in the changing Arctic shelves.