• Six Thousand Years Of Change In The Northeast Pacific: An Interdisciplinary View Of Maritime Ecosystems

      Misarti, Nicole; Finney, Bruce (2007)
      The goal of this thesis is to develop long-term records of North Pacific ecosystems and explore relationships between change in marine ecosystems and prehistoric Aleut culture through soil chemistry, isotope analyses of lake cores, and isotope analyses of bone from archaeological middens. Chemical analysis of soils yielded differences in soils of various archaeological features as well as middens of varying composition. Sites that had no middens were chemically distinguishable from sites that did have middens helping to define resource consumption in the local region. An important result of this study is that no single ecosystem (nearshore benthic, coastal pelagic or deep-ocean pelagic) experienced the same changes in delta13C and delta 15N over the past 4,500 years. This suggests that changes in climate affected different ecosystems in unique ways. Only one change spans all species studied, the decrease in modern delta13C in comparison to delta13C of prehistoric specimens. According to these comparisons, the modern Gulf of Alaska may not be in the highly productive state that it was for the past 4,500 years, with the possible exception of the Medieval Warm Period. Lake core sediment analysis suggests an increase in salmon stocks in the Gulf of Alaska beginning ∼6,000 years ago, with a decrease during the Medieval Warm Period. In fact, salmon stocks in the Gulf of Alaska appear to be healthiest during periods of atmospheric cooler and wetter climate over the past 4,500 years. In comparing my paleoecological records to the archaeological record of the area it appears that humans were affected by changes in their environment but, even in relatively small numbers, humans also influenced local ecosystems for the past 6,000 years. By building on our understanding of long-term climate change and long-term fluctuations in ecosystems and trophic dynamics of species in the North Pacific, and through considering humans in the ecological context, we can better understand present conditions in marine ecosystems.
    • The carbon cycle in an anoxic marine sediment: Concentrations, rates, isotope ratios, and diagenetic models

      Alperin, Marc Jon; Reeburgh, W. S. (1988)
      The carbon cycle in the anoxic sediments of Skan Bay, Alaska, was investigated in order to better understand the processes that control biogeochemical transformations in an organic-rich sediment environment. Depth distributions of concentration and $\delta\sp{13}$C were determined for five major carbon reservoirs: methane (CH$\sb4$), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate inorganic carbon (PIC), and particulate organic carbon (POC). In addition, methane oxidation and sulfate reduction rates were measured under quasi-in situ conditions using radio-tracer techniques. Diagenetic models were applied to concentration, reaction rate, and isotope ratio depth distributions and the results were integrated into a comprehensive, depth-dependent model of the Skan Bay carbon cycle that considered advective, diffusive, and biological and chemical reactive fluxes for the five major carbon reservoirs. The Skan Bay carbon cycle is fuelled by POC, which is deposited at the sediment surface at a rate of 2290 $\pm$ 480 umol $\cdot$ cm$\sp{-2}$ $\cdot$ yr$\sp{-1}$. Isotope mass-balance calculations indicate that about 60% of this material is derived from kelp while the remainder originates as phytoplankton. About 60% of the organic matter is consumed in the upper 40 cm of the sediment column. The $\delta\sp{13}$C-POC and $\delta\sp{13}$C-DOC depth distributions suggest that the material derived from kelp is more labile, accounting for greater than 60% of the total POC consumption. The products of anaerobic metabolism of POC accumulate in the DOC reservoir creating a large DOC concentration gradient at the sediment-water interface. Flux and stable carbon isotope mass-balance calculations suggest that a sizable portion (30 to 80%) of the DOC produced by degradation of POC diffuses from the sediment prior to oxidation to dissolved inorganic carbon. Methane production appears to occur primarily at depths greater than 40 cm. The CH$\sb4$ diffuses upward and is almost quantitatively oxidized to DIC in a narrow subsurface zone. Methane oxidation accounts for only 20% of the DIC production, but exerts a profound influence on the $\delta\sp{13}$C-DIC profile, contributing to the distinct mid-depth minimum. Pore waters are supersaturated with respect to calcite at depths greater than 10 cm, but isotope mass-balance considerations indicate that carbonate mineral formation is not occurring in these sediments.