Marine bacteria serve as a significant source of biologically available nitrogen to the global ocean. Many of these nitrogen fixers reside in tropical, subtropical and temperate waters, but measurements in the Arctic Ocean suggest that a substantial community of nitrogen fixers can also be found in the high-latitude waters of the Beaufort Sea.
Marjolaine Blais of Laval University, Canada, and colleagues assessed rates of biological nitrogen fixation — that is, the conversion of atmospheric nitrogen into a biologically usable form — at various locations in the Canadian Arctic. Rates of nitrogen fixation were greatest at the mouth of the Mackenzie River, a region highly influenced by freshwater runoff. Nitrogen fixation declined in waters less influenced by the Mackenzie River. According to a phylogenetic analysis, heterotrophic bacteria — and not the cyanobacteria that are typically implicated at lower latitudes — were probably responsible for nitrogen fixation in these river-influenced waters.
The researchers suggest that the Mackenzie River serves as a source of nitrogen-fixing heterotrophic bacteria to the Beaufort Sea.