Supplementary data files

We measured N₂ fixation along the Western Antarctic Peninsula (WAP) and at Palmer Station over two austral summer months. N₂ fixation rates measured by ¹⁵N₂ assays were below conservative detection limits, despite being detected when using less stringent detection thresholds, suggesting a potential for N₂ fixation. This was confirmed by our continuous acetylene reduction method (FARACAS). <i>nifH </i>gene amplicon sequencing revealed that Gammaproteobacteria were the dominant class of identified diazotrophs in the WAP’s coastal waters. However, Epsilonproteobacteria contributed disproportionally to <i>nifH</i> expression, particularly when putative N₂ fixation rates were at the highest. Combining diazotroph communities with environmental observations, we hypothesize that vertical water mixing resuspended sediments into the water column and contributed to the limited N₂ fixation in Antarctic waters.