• Current Primary Production Rates Of The Western Arctic Ocean Estimated By Stable Carbon And Nitrogen Isotope Tracers

      Lee, Sang Heon; Whitledge, Terry E. (2005)
      Currently, the environments in the Arctic are rapidly changing. These changes of climate and ice conditions may alter the quantity, quality, and timing of production of ice algae and phytoplankton in the Arctic Ocean. The objectives in this study were to detect any change in the carbon production between current and previous studies and lay the groundwork for the future monitoring of ecosystem response to climate change in the different regions of the western Arctic Ocean. As an Arctic ocean mostly covered by multi or first-year ice, the deep Canada Basin had generally low photosynthetic rates and the maximum rates were found between 50 and 60 m in the basin. Based on the percentage of ice cover, the annual production ranged from 3 to 7.5 g C m-2 Z in the basin. Nutrients appear to be a main limiting factor at surface, whereas the phytoplankton activity might be limited by the low light in the Chl a-max layer. At the surface below the ice, photosynthetic activity might be controlled by both low light and nutrients. Studies of ice algae and phytoplankton at the first-year sea ice of Barrow in Alaska showed that bottom sea ice algae and phytoplankton are limited mainly by light. Therefore, the current downward trend of sea ice thickness and extent in Arctic Oceans might cause an increase in primary production or/and change in timing of the production. In addition, the composition in macromolecules of primary producers might be changed under the current ice conditions and thus nutritional status of higher trophic levels might be altered. As shallow shelf regions, Bering Strait/Chukchi Sea showed that the range of nitrate in the central Chukchi Sea was rather higher whereas the biomass of phytoplankton was lower in this study than in previous studies. Consistently, the mean carbon and nitrogen productivities from this study were almost half of values from previous studies. In conclusion, it appears that lower phytoplankton biomass in Bering Strait and the Chukchi Sea resulted in the lower carbon and nitrogen uptake rates and consequently more unused nitrate in the regions.
    • Use of Beaufort Sea as feeding habitat by bowhead whales (Balaena mysticetus) as indicated by stable isotope ratios

      Lee, Sang Heon; Schell, Donald; Finney, Bruce; Weingartner, Thomas (2000-12)
      The feeding habitats of the Western Arctic bowhead whales (Balaena mysticetus) during summer are generally known, but the precise amounts of food consumed from the eastern Beaufort Sea (EBS) are not known. [Alpha]13C and [alpha]15N ratios in whale tissues were used to estimate the amounts of food required from EBS. The feeding strategies of adults and subadults were also compared. For all whales, the [alpha]13C values in muscle sampled in fall were not significantly different from those in the muscle sampled in spring, indicating most food of adults and subadults comes from the Bering/Chukchi seas. The ¹³C data from baleen showed, however, that EBS may be a significant feeding area for subadults. [alpha]15N values are significantly different between fall and spring muscle in subadults, suggesting a shift to different prey and/or nutritional stress during winter followed by feeding in EBS in summer.