The microbial food web in Arctic seawater concentration of dissolved free amino acids and bacterial abundance and activity in the Arctic Ocean and in Resolute Passage

In June 1988 the naturally occurring concentration of each of 15 amino acids was less than 20 nM at all depths at a station in the Canadian sector of the Arctic Ocean and a t a station in Resolute Passage. In Arctic Ocean water, under the permanent ice pack, bacterial uptake of amino acids and tritiated thymidine was near to below detection, although there were 104 to 10' heterotrophic bacteria ml-l. In Resolute Passage, uptake of amino acids and thymidine at all depths was low, even at depths where there were visible accumulations of algae which had melted out of the fast ice. Numbers of bacteria were lo5 ml '. In water collected in a small, recently opened lead in land-fast ice, containing substantial clumps of ice algae, amino acid concentrations were micromolar and bacterial uptake rates were high. The spring food web of the high Arctic thus appears to b e supported mostly by ice algae, and ice algae were sparse under the permanent pack ice at our Arctic Ocean statlon. Under seasonal ice in Resolute Passage, however, there was copious fallout of ice algae from melting of the bottom of the Ice. but the response of the bacteria was limited to lead water having h g h concentrations of dissolved free amino acids. These observations support previously reported evidence for disparity between algal production and microbial production in polar waters.