Archaeal distribution and abundance in water masses of the Arctic Ocean, Pacific sector

Marine planktonic Archaea have been recently recognized as an ecologically important component of marine prokaryotic biomass in the world's oceans. Their abundance and metabolism are closely connected with marine geochemical cycling. We evaluated the distribution of planktonic Archaea in the Pacific sector of the Arctic Ocean using fluorescence in situ hybridization (FISH) with catalyzed reporter deposition (CARD-FISH) and performed statistical analyses using data for archaeal abundance and geochemical variables. The relative abundance of Thaumarchaeota generally increased with depth, and euryarchaeal abundance was the lowest of all planktonic prokaryotes. Multiple regression analysis showed that the thaumarchaeal relative abundance was negatively correlated with ammonium and dissolved oxygen concentrations and chlorophyll fluorescence. Canonical correspondence analysis showed that archaeal distributions differed with oceanographic water masses; in particular, Thaumarchaeota were abundant from the halocline layer to deep water, where salinity was higher and most nutrients were depleted. However, at several stations on the East Siberian Sea side of the study area and along the Northwind Ridge, Thaumarchaeota and Bacteria were proportionally very abundant at the bottom in association with higher nutrient conditions. The abundance of Euryarchaeota was high (>1.0 10 5 cells ml -1 ) at one of our stations in the Chukchi Sea and was positively correlated with temperature and ammonium concentration, suggesting that there could be 'hot spots' with increased euryarchaeal abundance in the Arctic Ocean.