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

We used 49,6-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 5 20.89, n 5 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 5 0.85, n 5 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 3 104 mL21 [15.5% of bacterioplankton] vs. 1.79 3 104 mL21 [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 3 104 mL21) in the river, and the highly significant correlation (rs 5 0.97, n 5 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. Archaea have now been recognized as ubiquitous and sometimes abundant members of the marine bacterioplank1 Corresponding author ([email protected]). 2 Present address: Department of Bioengineering, Rice University, Houston, Texas 77005. 3 Present address: Department of Biology, University of Washington, Seattle, Washington 98195.