Measured stable-carbon and/or nitrogen isotope ratios in 43 species from primary producers through polar bears Ursus maritimus in the Barrow Strait-Lancaster Sound marine food web during July-August, 1988-1990. d13C ranged from -21.6 ± 0.3‰ for particulate organic matter (POM) to -15.0 ± 0.7‰ for the predatory amphipod Stegocephalus inflatus. d15N was least enriched for POM (5.4±0.8‰), most enriched for polar bears (21.2±0.6‰), and showed a step-wise enrichment with trophic level of +3.8‰. This enrichment value was used to construct a simple isotopic food-web consisting primarily of five trophic levels. d13C showed no discernible pattern of enrichment after the first two trophic levels, an effect that could not be attributed to differential lipid concentrations in food-web components. Although Arctic cod Boreogadus saida is an important link between primary producers and higher trophic-level vertebrates during late summer, the isotopic model generally predicts closer links between lower trophic-level invertebrates and several species of seabirds and marine mammals than previously established.
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