• A Multiple Stable Isotope Study Of Steller Sea Lions And Bowhead Whales: Signals Of A Changing Northern Environment

      Dehart, Pieter Andrew Philip; Wooller, Matthew J. (2006)
      The North Pacific and Arctic marine realm is currently experiencing dramatic environmental changes as a result of global climate change. Stable isotope analysis of western arctic bowhead whales (WABW, Balaena mysticetus ) and Steller sea lions (SSL, Eumetopias jubatus) were conducted to examine the influence of these changes on life history characteristics (migration and foraging) of these marine mammals. WABW baleen plates were analyzed for their stable oxygen and hydrogen isotope composition (delta 18O and deltaD) and were compared to the delta18O and deltaD in water and zooplankton prey along their seasonal migratory route. The delta18O and deltaD varied along the baleen (8 to 18�; -180 to -80�, respectively) and corresponded to stable isotopic differences in zooplankton from the winter (Bering Sea) and summer (eastern Beaufort Sea) habitats of WABW. Baleen delta18O and deltaD confirmed the seasonal annual migration of WABW and were subsequently compared to historical sea ice concentrations (SIC). This illustrated that WABW migration patterns appeared to have altered concomitant with changes in SIC. Years with a higher SIC (colder climate regimes) correlated with the largest difference in deltaD between winter and summer in WABW baleen during the period from 1972 to 1988. For a similar time period (1955 to 2000), the feeding ecology of SSL was also examined by analyzing the stable carbon and nitrogen isotope compositions (delta13C and delta 15N, respectively) of archived SSL bone and tooth collagen. Both delta 15N and delta13C varied greatly with location and sample year (14.6 to 20.5�; - 16.7 to -11.8�, respectively), with a significant change in delta13C observed around the 1976 regime shift. Bottom-up processes may have limited growth of SSL populations throughout this region over time, with animals focusing their foraging on offshore regions to mitigate this environmental change. Stable isotope analyses of historical samples of WABW (baleen) and SSL (bone and tooth collagen) both illustrated that recent environmental changes influenced the ecology (migration and feeding) of these marine mammals in the recent past.
    • Adaptations Of The Bacterial Flywheel For Optimal Mineral Cycling In Oligotrophic Surface Waters

      Gustafson, Elizabeth S.; Button, Don K. (2008)
      Nutrient cycling in a subarctic oligotrophic lake was explored using current kinetic theory for organisms adapted to low nutrient environments with emphasis on bacterial contributions to system function. Techniques were refined which minimize sample disturbance and contamination for the purpose of accurately measuring bacterioplankton activity. Seasonal variations in DNA content, cell mass, species composition, specific affinity for amino acids and cell yield were observed. Quasi-steady state formulae describe bacteria as a flywheel in nutrient cycling; energy is conserved within a relatively constant biomass by varying bacterial activity with nutrient availability. The bacterial flywheel paradigm provides a bacteriocentric view of mineral cycling, linking kinetics to specific cytoarchitectural properties while maintaining links to substrate and grazing pressures. As an extention of the microbial loop paradigm, the flywheel becomes essential at high latitudes. In winter, low solar input interrupts the microbial loop so that the dissolved organic carbon (DOC) pool is cycled through bacteria only. This activity allows bacterioplankton to persist through winter and respond rapidly to springtime warming and nutrients. Microbial adaptations to seasonal variations in nutrient availability and temperatures were examined within the bacterial flywheel framework. Organisms are well-adapted to a narrow (17°C) in situ temperature range. Activation energies for small warming were low at the temperature extremes (20.6 kJ mol -1 at 0.5°C; -32 kJ mol-1 at 17°C) and high in spring (110 kJ mol-1 at 1.2°C). Nutrition varies by season, supplied in large part by amino acids in spring and summer. Winter growth rates are at least 0.013 day-1 whereas partial growth rate on amino acids for that season is only 2.8 x 10-5 day -1. It is proposed that winter organisms rely on diffusion transport and/or shift toward concurrent use of a large suite of substrate types for growth and maintenance.
    • Decomposition and adsorption of peptides in Alaskan coastal marine sediments

      Luo, Honghong (1994)
      In organic-rich coastal sediments, hydrolyzable amino acids make up a substantial fraction of the sedimentary content of organic nitrogen. How this organic nitrogen resists decomposition and is preserved in sediments is poorly understood. In order to investigate the factors controlling mineralization and preservation of hydrolyzable amino acids, decomposition and adsorption of peptides were studied in suboxic and anoxic pore water and sediments from Resurrection Bay (RB) and Skan Bay (SB), Alaska. Five tritium-labeled peptides, basic di-lysine, acidic di-glutamic acid, and neutral di-alanine, tri-alanine and hexa-alanine, were used as tracers. In filtered pore water, the hydrolysis rates were usually low. The exception was that the initial enzymatic hydrolysis of di-alanine and di-glutamic acid was rapid in SB pore water. The hydrolysis rates of both peptides increased with concentration. In sediments, hydrolysis was found to be the rate-limiting step of peptide decomposition. Alanyl and glutamyl peptides were hydrolyzed faster than lysyl peptide, and the hydrolysis rates among alanyl peptides decreased with increasing molecular weight. Peptide hydrolysis was affected more by molecular structure than by oxic or anoxic conditions. Adsorption of lysyl peptide to sediments was greater than that of other peptides. Basicity enhanced peptide adsorption more than increased molecular weight. Sedimentary organic matter was mainly responsible for peptide adsorption. The different patterns of peptide adsorption in RB and SB sediments were related to the greater total organic carbon concentration in SB sediment. Some of the peptide adsorption was irreversible. Adsorbed peptides were more resistant to biological decomposition than dissolved peptides. Adsorption may be an important step in the process of peptide preservation in sediments, and thus the preservation of sediment organic matter during early diagenesis.
    • Natural abundance of nitrogen(15) in a subarctic lake and biogeochemical implications to nitrogen cycling

      Gu, Binhe (1993)
      Stable isotope ratios of nitrogen ($\delta\sp{15}$N) were employed to track the origin and fate of nitrogen in a subarctic lake, Alaska. The annual planktonic nitrogen cycle was dominated by N$\sb2$ fixation in spring and NH$\sb4\sp+$ assimilation in summer. In winter, microbial nitrification was the major sink for NH$\sb4\sp+$ and denitrification was accounted for most of the loss of NO$\sb3\sp-.$ The small isotope fractionation in nitrification is proposed as a result of substrate (NH$\sb4\sp+)$ limitation. The temporal and spatial homogeneity of the $\delta\sp{15}$N of dissolved organic nitrogen may be related to its large pool size and refractory nature. A stable isotope mass balance suggests that the winter phytoplankton was only composed of 10 to 20% of the suspended organic matter in water column due to low primary productivity during the ice cover period. A close correlation between $\delta\sp{15}$N of phytoplankton and $\delta\sp{15}$N of dissolved pools indicates that NH$\sb4\sp+$ was the predominant nitrogen source for non-N$\sb2$-fixing algae. The similarity of $\delta\sp{15}$N between a spring blue-green bloom and N$\sb2$ suggests an atmospheric origin for nitrogen. A mixing model estimated that the blue-green algal bloom derived approximately 70% of its nitrogen from molecular nitrogen. This fixed nitrogen was further transferred to higher trophic levels via the food chain and to other primary producers following mineralization. The $\delta\sp{15}$N of aquatic macrophytes indicates that non-rooted species obtained their nitrogen from the water column while rooted species obtained their nitrogen largely from the sediment. Evidence from dual isotope tracers ($\delta\sp{15}$N and $\delta\sp{13}$C) suggests that the zooplankton were supported by phytoplankton throughout the growing season despite an apparent abundance of detritus in the water column. Benthic fauna relied on either phytoplankton detritus or other organic matter in the sediment. The $\delta\sp{15}$N data exhibit only two to three trophic levels in both planktonic and the benthic communities in Smith Lake.
    • Organic matter accumulation and preservation in Alaskan continental margin sediments

      Ding, Xiaoling; Henrichs, Susan M. (1998)
      Continental margin sediments provide a historical record of the sources and fate of organic matter (OM) originating both from the continents and from primary productivity in the overlying water column. However, since this record can be altered by microbial decomposition within the sediment, the history cannot be interpreted without understanding how decomposition can affect OM composition. Also, the margins accumulate much of the OM buried in ocean sediments; hence, knowledge of processes influencing preservation of OM in these sediments is essential to understanding the global carbon cycle. OM preservation was examined using two approaches. First, I studied sediments in the northeastern Gulf of Alaska to determine sources of OM and temporal changes in carbon accumulation. A large amount of OM, 45--70 x 104 tons/yr, accumulated in this region, about 50% from terrestrial sources. Most of the sediment cores showed little evidence of change in TOC, TN, or C and N stable isotope compositions due to decomposition within the sediment. Second, I investigated the processes that control OM preservation, focusing on the role of the OM adsorption to mineral surfaces. Because proteins are major constituents of sedimentary OM, I examined factors controlling their adsorption, decomposition, and preservation. Three hydrophilic proteins were strongly adsorbed by two clay minerals, an iron oxide, sub-oxic sediments from Resurrection Bay (RB), Alaska, and anoxic sediments from Skan Bay (SB), Alaska. The partition coefficients were large enough to lead to their preservation provided that the proteins did not decompose while adsorbed. Generally, adsorption of proteins to solid phases decreased decomposition rates, suggesting that adsorption is important in protecting these compounds from microbial attack. Greater protein decomposition rates were found in SB than in RB sediments, indicating that anoxia did not inhibit protein biodegradation. Naturally-occurring adsorbed proteins were extracted from SB and RB sediments using a detergent solution. Most of these adsorbed proteins were small (<12 kDa), indicating that only the proteins adsorbed within the micropores of particle surfaces are preserved long-term.
    • The Geochemistry Of Manganese, Iron And Phosphorus In An Arctic Lake

      Cornwell, Jeffrey Clayton (1983)
      Sediment redox processes were investigated in an oligotrophic, arctic lake containing metal oxide crusts in oxidizing surficial sediments (up to 22% Mn and 26% Fe). Toolik Lake, Alaska, a 12,000 year old kettle lake, has the lowest Pb-210 derived sedimentation rates reported for any lake (27 g m('-2) yr('-1)). Three independent methods for estimation of Mn, Fe and P retention within the lake (stream budgets, sediment traps and sediment burial rates) provide similar rates. Of the amounts entering the lake, 28% of P, 50% of Mn and 55% of Fe are retained. Common water column removal mechanisms for these elements and organic C are suggested by sediment trap data. A steady state diagenetic model with terms for diffusion, reduction and oxidation shows that Mn and Fe crusts migrate within surficial sediments. Metal oxide burial rates are equivalent to oxide dissolution rates (reduction), rates of upward diffusion of soluble divalent metals and metal precipitation rates (oxidation). High inputs of labile Mn and Fe from streams, plus low sedimentation and organic matter oxidation rates are important for crust formation. Approximately 12% of Mn and 2% of acid reducible Fe retained by the lake since its formation exist as diagenetic oxides; the rest is buried within reducing sediment. Sediment inorganic P migrates with Fe to form P enriched sediment zones with pore water PO(,4) concentrations beneath these zones regulated by vivianite (Fe(,3)(PO(,4))(,2) 8H(,2)O) formation. The migration of Mn and Fe within sediments results in the enrichment of Ba, Co, Ca, Ni, Ra-226 and carbonate in metal oxide enriched sediments. Barium is enriched in Mn crusts because of diagenetic migration.