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

Abstract

ABSTRACT. 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.

Temperature and substrates as interactive limiting factors for marine heterotrophic bacteria

“…Mel'nikov & Pavlov (1978) found increased POC concentrations in Arctic sea ice but little increase in DOC. Pomeroy et al (1990) found high concentrations of DFAAs in melting spring fast ice at Resolute, Nunavut, and Thomas et al (1995) found high concentrations of DOC in multi-year ice in Fram Strait at 80 to 81°N. These studies emphasize the inherent heterogeneity of sea ice that must result from different local conditions.…”

“…Bacterial metabolic activity in polar waters in winter in the marginal ice zone is sometimes similar to that of summer (Rivkin et al 1989, Mordy et al 1995. In other instances very low rates are seen, although little seasonal temperature change occurred (Griffiths et al 1978, Pomeroy et al 1990, Karl 1993, Carlson et al 1998, Bird & Karl 1999. Rates of bacterial growth and respiration may, of course, be limited by the availability of organic substrates, by the availability of inorganic nutrients (Reay et al 1999, Kirchman 2000, or by interactions of both with temperature.…”

“…Fig 2 illustrates that bacteria in polar waters, at least those we have been able to culture, are always living at temperatures well below their optima for growth, which implies a higher concentration threshold for utilization of dissolved substrates. During polar winter, or under thick, snow-covered sea ice, substrate might become limiting, if the data of Pomeroy et al (1990) and Wiebe et al (1992) are generally applicable. The lack of any unusual accumulation of dissolved organic matter in polar seawater shows that marine heterotrophic bacteria do utilize labile DOC down to nanomolar concentrations at -1.8°C.…”

“…Pomeroy et al (1990) attempted to measure production of heterotrophic bacterioplankton in June, before spring melt had begun, at the Canadian Ice Island (then located at 79°37.3' N, 108°51.2' W), a drifting tabular iceberg in the Arctic Ocean north of Ellef Ringness Island. Because of its location in the Canadian Basin gyre, this region is covered by a mean ice thickness of 6 m (Maykut 1985).…”

Dynamics of dimethylsulfide production from dissolved dimethylsulfoniopropionate in the Labrador Sea

“…During incubations examining the effect of substrate on the generation time of facultatively psychrophilic and mesophilic bacteria, Wiebe et al (1992Wiebe et al ( , 1993 found that at lower temperatures, a higher substrate concentration was required to maintain the same growth rate. In the seasonally ice-covered waters of the Arctic Ocean and in Resolute Passage (High Canadian Arctic), Pomeroy et al (1990) observed active bacterial growth and substrate utilization only at substrate concentrations of dissolved amino acids with orders of magnitude above those measured in natural seawater. Similarly, the respiration of the microbial community during the spring bloom in Conception Bay, Newfoundland, at water temperatures below 3.5°C could only be stimulated by the addition of very high organic substrate concentrations (Pomeroy et al 1991) 202: 27-40, 2000 authors postulated that microbial metabolism and production in cold waters are limited by the ability of bacteria to transport and/or assimilate substrate at the usually low in situ concentrations.…”