| Summary: | Dissertation (Ph.D.) University of Alaska Fairbanks, 2014. Marine production across the Bering-Chukchi continental shelf is influenced by seasonal sea ice dynamics and climatic conditions. Of particular importance is variability in the magnitude and timing of annual phytoplankton production in the water column and in sea ice, and effects of such variability on food web composition and productivity. Of primary concern is the long-term effect of the projected loss of Arctic sea ice on ecosystem productivity and stability, and the fate of upper trophic level species. I examined a portion of the Bering-Chukchi Sea food web by analyzing the fatty acid composition and stable carbon isotope ratios of individual fatty acids in particulate organic matter from sea ice and the water column. These techniques were used to make inferences about diets of three species of zooplankton (Themisto libellula, Calanus marshallae/glacialis, Thysanoessa raschii) sampled during a recent climatically cold, relatively heavy sea ice period in the Bering Sea. I also analyzed fatty acids of four species of ice-associated seals--ringed (Pusa/Phoca hispida), bearded (Erignathus barbatus), spotted (Phoca largha), and ribbon seals (Histriophoca fasciata)--sampled during the same relatively cold period (2007-2010) as well as a preceding warm (2002-2005), relatively low sea ice period in the Bering Sea. Particulate organic matter from sea ice and the water column had different fatty acid characteristics, most likely stemming from differences in algal composition. My results also showed that in the Bering Sea cold period, the amphipod T. libellula was predominately carnivorous, and the copepod C. marshallae/glacialis and euphausiid T. raschii were primarily herbivorous, but displayed some degree of omnivory. Across all years (2002-2010), fatty acid composition of ice seals showed clear evidence of resource partitioning among them, and little niche separation between spotted and ribbon seals, which is consistent with previous studies. The fatty ...
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