Archaea in particle-rich waters of the Beaufort Shelf and Franklin Bay, Canadian Arctic: Clues to an allochthonous origin?

We used 4ʹ,6-diamidino-2-phenylindole (DAPI) staining and fluorescent in situ hybridization to examine total bacterioplankton and archaeal distributions in surface waters and in deeper nepheloid layers and particle-poor waters across the Beaufort Shelf of the Canadian Arctic, including the Mackenzie River and Kugmallit Bay, as well as more distant Franklin Bay. Although the regional distribution of bacterioplankton was best explained by salinity (rs = -0.89, n = 28, p < 0.001) and indicators of primary production (chlorophyll a [Chl a], total organic carbon, and the ratio of Chl a to particulate organic carbon [Chl a: POC]), that of Archaea instead reflected measures of particulate matter, specifically microscopically determined particle concentration (rs = 0.85, n = 30, p < 0.001), suspended particulate matter, POC, particulate organic nitrogen (PON), and the beam attenuation coefficient. Moreover, when compared with similarly deep particle-poor waters, nepheloid layers were significantly enriched in Archaea (median concentration of 6.00 x 10^4 mL^-1 [15.5% of bacterioplankton] vs. 1.79 x 4 mL^-1 [3.6%]; p < 0.05), but not total bacterioplankton. The relationship between Archaea and particles, the dominance of the Mackenzie River as the regional particle source, the detection of highest archaeal concentrations (11.5-14.4 x 4 mL^-1) in the river, and the highly significant correlation (rs = 0.97, n = 12, p < 0.001) between Archaea in particle-rich waters and PON (the river providing the upper end member) suggest that many of these Archaea derive from the river.