Evidence for circumpolar distribution of planktonic Archaea in the Southern Ocean

Surveys using rRNA-targeted probes specific for the 3 domains of life (Euca rya, Archaea, and Bacteria) indicated the presence, and at times high abund ance, of archaeal rRNA in a variety of water masses surrounding Antarctica. Hybridization signals of archaeal rRNA contributed significantly to that o f total picoplankton rRNA both north and south of the Polar Front in Drake Passage. Late winter surface water populations collected around the South S hetland Islands also yielded relatively high archaeal rRNA hybridization si gnals, approaching 10% or greater of the total rRNA. Summer samples collect ed in the western region of the Antarctic Peninsula and at McMurdo Sound in the Ross Sea region of Antarctica yielded lower amounts of archaeal rRNA i n the surface waters, and higher levels of archaeal rRNA at depth (150 to 5 00 m). The hybridization data were compared to biological, chemical, and hy drographic information when possible. In surface waters, archaeal rRNA and chlorophyll a varied inversely. The data presented here further supports th e hypothesis that planktonic archaea are a common, widespread and likely ec ologically important component of Antarctic picoplankton assemblages. The p resence of these archaea in circumpolar deep water suggests a conduit for t heir circumpolar transport around Antarctica via the Antarctic Circumpolar Current, as well as their export to the deep sea, or to intermediate waters of the South Atlantic via mixing at the polar front.