• Sea Ice Strength

      Peyton, Harold R. (1967)
    • Tracing Amino Acid Metabolism Of Harbor Seals (Phoca Vitulina) Using Stable Isotope Techniques

      Zhao, Liying; Schell, Donald M. (2002)
      Compound specific isotope techniques were used to trace amino acid metabolism in captive harbor seals (Phoca vitulina) through a two-year controlled feeding trial with either Pacific herring (Clupea pallasi ) or walleye pollock (Theragra chalcogramma). Techniques were developed for measuring carbon and nitrogen isotope ratios of individual amino acids. Carbon and nitrogen trophic enrichments in serum of captive harbor seals varied with the two fish diets, which might have resulted from the changes in metabolic pathway due to the differing dietary protein intake between herring and pollock. Data on serum free amino acid compositions also showed, from a different perspective, that changes in seal metabolism occurred in response to these different feeding regimes. Carbon and nitrogen isotopic composition of individual amino acids varied much more within an organism than across trophic levels, reflecting the distinct amino acid biosynthetic pathways. The similar patterns in relative amino acid carbon isotopic composition at different trophic levels indicated a conservative transfer of delta13C from primary producers to top predators. Nitrogen trophic enrichments in different amino acids were not uniform, depending upon the extent to which a given amino acid was transaminated or deaminated, with several essential amino acids showing lesser variations than most non-essential and branched-chain amino acids. The differences in amino acid isotope ratios among phocids from the North Pacific or Atlantic and their counterparts from the Antarctic reflected the geographic variations in isotopic composition of phytoplankton. The striking similarities in relative amino acid isotopic composition among phocids from the three distinct geographic locations indicated that phytoplankton worldwide had similar biosynthetic pathways during initial amino acid biosynthesis. This has important implications for using individual amino acid isotope ratios in studies of modern and prehistoric marine organisms. Amino acid metabolic pathways governed the varying patterns of 15N enrichments following 15N-labeled amino acid tracer infusions. Tracer experiments further confirmed that phenylalanine, threonine, lysine and probably histidine may be useful as relatively conservative natural biomarkers. This study provided new insight into mechanisms of isotopic trophic dynamics in food web studies and improved our understanding of seal protein metabolism.
    • Use of synthetic aperture radar in estimation of wave climate for coastal engineering design

      Blackstone, Jill Ellen (1995)
      Development of Alaska's maritime resources requires design of efficient, reliable, safe facilities by coastal engineers who have a thorough knowledge of site specific wave climate: wave height, length, period, direction, and storm duration. Unfortunately, lack of wave information and validated hindcast models along the Alaskan coast often results in costly overdesigned facilities or underdesigned coastal structures which have a high risk of performance failure. To expand the nearshore wave climate availability, use of spaceborne synthetic aperture radar (SAR) data to estimate wave parameters was evaluated. SAR data were examined in raw and filtered forms, and the extracted wave climate compared to field measured data at three sites. Based on this comparison, the applications and limitations of SAR estimated parameters were established and incorporation of the information into current design practice was addressed. SAR based spectra were dominated by low frequency spectral peaks, likely due to random noise associated with SAR images, as these peaks were not present in the field measured spectra. Due to discrepancies between SAR and measured spectra, wave height, and storm duration could not be determined. Although error ranged from 12.5% to over 100% for SAR estimated wave lengths, the fact that wave lengths, although inaccurate, could be determined from SAR is promising. SAR based wave direction compared favorably to theoretical propagation directions which affirms the potential of wave parameter extraction from SAR data. However, directional field data were not available for comparison. Due to the current errors associated with SAR based wave estimations, SAR estimated wave climate cannot be incorporated into coastal design practice at this time. Research results suggest SAR data still hold great potential for estimating wave parameters. Examination of SAR based wave climate in an extensively monitored, open ocean setting would be beneficial, and the influence of environmental factors on SAR imaging of waves warrants additional investigation. Furthermore, development of a tandem SAR platform with temporal resolution on the order of seconds would be useful for wave period estimation and interferometric wave height determination. After this background research has been accomplished, another evaluation of SAR based nearshore wave climate would be worthwhile.