Now showing items 21-39 of 39

    • Numerical modeling study of the circulation in the Gulf of Alaska

      Bang, Inkweon (1991)
      A series of numerical experiments are performed to simulate the Gulf of Alaska circulation and to examine the dynamical ocean response to the annual mean and seasonal forcing using a primitive equation model (Semtner 1974). The model domain encompasses the North Pacific north of 45$\sp\circ$ N and east of 180$\sp\circ$ and is surrounded by artificial walls in the south and west. Biharmonic diffusion is used in the interior to excite mesoscale eddies. A sponge layer with high Laplacian diffusion is incorporated near the western boundary. Horizontal resolution of 30$\sp\prime$ x 20$\sp\prime$ and 20 vertical levels are used to resolve the mesoscale topography and eddies. Wind stress computed from sea level atmospheric pressure and temperature and salinity data of Levitus (1982) are used. A diagnostic model produces a circulation in the Gulf of Alaska which agrees with observed patterns. In a three-layer flat-bottom baroclinic model, baroclinic Rossby waves propagate at 0.8 cm/sec and it takes a decade for spin-up to be completed. Baroclinic models forced by the annual mean wind and thermohaline forcings show the generation of eddies by baroclinic instability. The eddies in the flat-bottom model have a period of 75 days and are interpreted as barotropic Rossby waves. In the model with topography, the period of dominant eddies is 3-4 years and they are interpreted as baroclinic Rossby waves. Anticyclonic eddies near Sitka show similar characteristics as the Sitka eddy. They propagate westward and cause meanders in the Alaska Stream near Kodiak Island. The abnormal shift of the Alaska gyre in 1981 is probably due to the presence of one of these anticyclonic eddies. A flat-bottom model with seasonal forcing shows a large seasonal variability. When bottom topography is present, however, seasonal response is greatly reduced due to the dissipation of barotropic response by bottom topography. The seasonal baroclinic model shows a similar seasonal variability to the seasonal barotropic model indicating that the seasonal response is mainly barotropic. Eddies are also excited in the seasonal case and are almost identical to those of the annual mean case.
    • Phenanthrene Adsorption And Desorption By Melanoidins And Marine Sediment Humic Acids

      Terschak, John Andrew; Henrichs, Susan M. (2002)
      Sediments are major reservoirs of persistent petroleum contamination in marine environments. Petroleum hydrocarbons associate with the sediment organic matter, of which humic acids are an important constituent. This study examined the role that humic acid and its structure plays in the kinetics and mechanisms of polycyclic aromatic hydrocarbon (PAH) interactions with sediments. Natural humic acids, with a wide range of properties, were isolated from Alaska coastal marine sediments. Melanoidins were synthesized and used as humic acid analogs. The humic acids were characterized by elemental and isotopic analyses, Fourier transform infrared spectroscopy, and cross-polarized magic angle spinning 13C nuclear magnetic resonance spectroscopy. The humic acids were coated onto a standard montmorillonite clay, and the adsorption and desorption of phenanthrene was measured using a radiotracer. Adsorption required about one week to reach steady state, indicative of slow diffusion of PAH within the humic acid. The composition of the humic acids had a greater effect on phenanthrene adsorption than their concentrations on the clay. Organic carbon normalized adsorption partition coefficients were closely correlated with the sum of amide and carboxylic carbons, a measure of the polarity of the humic acids, but were independent of initial phenanthrene concentration, indicating that the binding sites were unlimited and uniform in strength. This explains the fact that initial adsorbed concentration of phenanthrene had no effect on subsequent phenanthrene adsorption. Desorption of phenanthrene was not related to any of the humic acid structural characteristics measured. The initial desorption rate was linearly related to the initial adsorbed concentration, as expected for a diffusive process, and was negatively correlated with the carbon content of the humic acid coated clay. Under most conditions, desorption was complete after one to seven days; there was little evidence for irreversible adsorption. Because of the substantial variability of adsorption and desorption behavior with organic matter characteristics, interactions of aromatic hydrocarbons with marine sediments cannot be predicted based on total organic matter concentration alone. Information on aspects of organic matter composition is needed in order to make accurate predictions.
    • Millennial To Annual Scale Paleoclimatic Change In Central Alaska During The Late Quaternary Interpreted From Lake Sediments And Tree Rings

      Barber, Valerie Ann; Finney, Bruce; Juday, Glenn (2002)
      The theme of this dissertation is the importance of effective moisture (precipitation minus evaporation) in subarctic ecosystems. Interior Alaska has a relatively dry climate with annual precipitation ranging from 25--45 cm. Records from interior Alaska lake sediment cores show low lake levels following the Last Glacial Maximum, with significant increases at 12,000 and 9,000 14C years BP. Using lake-level reconstructions and models based on modern hydrologic and meteorologic data, we infer precipitation of 35--75% less than modern at 12,000 yr. BP, 25--45% less than modern at 9,000 yr. BP, and 10--20% less than modern at 6,000 yr. BP. Trees were scarce on the interior Alaskan landscape during the late Pleistocene with birch species appearing about 12,000 BP and spruce species approximately 3500 years later. The correspondence between lake-level and vegetation changes suggests that moisture may have been one of the limiting factors in the establishment of these tree species. Alaska climate records show a climatic regime shift in the mid-1970s. Less effective moisture is available over the past 30 years because summer temperatures in interior Alaska have been increasing without a concurrent increase in precipitation. Radial growth of white spruce at 20 low elevation stands in interior Alaska declined corresponding with this climatic change. The observation that moisture limits spruce growth in Alaska today is consistent with our inference of moisture limitation in the early Holocene. A 200-year reconstruction was developed based on two tree ring proxies, 13C discrimination and maximum latewood density, which together show excellent agreement with the recorded Fairbanks average May through August temperatures. The first half of the 20th century is characterized by the coolest summers of the 200 year period of reconstruction, while the latter part of the 20th century, particularly from 1974 onward, is characterized by some of the warmest summers of the 200 year period. Mid-19 th summer temperatures reconstruct to be as warm as the latter part of the 20th century, which is inconsistent with reconstructions of other regions. It seems likely, based on current information, that these inconsistencies may be real and may reflect regional synoptic conditions unique to interior Alaska. Distinctive decadal scale regimes were identified throughout the record.
    • Circulation and dynamics on the Northeastern Chukchi Sea Shelf

      Fang, Ying-Chih; Weingartner, Thomas J.; Winsor, Peter; Kowalik, Zygmunt; McDonnell, Andrew; Williams, William J. (2017-12)
      The circulation on the northeastern Chukchi Sea shelf is controlled by the poleward pressure gradient between the Pacific and Arctic Oceans. Local winds modulate the upper ocean and can rapidly alter the flow field. Present understanding of the circulation is largely based on subsurface measurements, but the response of near-surface currents to the slowly-varying secular pressure gradient and rapidly-varying local winds has not been addressed. I analyzed surface current data, extending more ~150 km offshore in the northeastern Chukchi Sea, collected from shore-based high-frequency radar systems (HFR) during the open water season. I find three wind-induced circulation regimes. Two of these are related to strong northeasterly winds when wind speeds approach or exceed 6 m s⁻¹ and the third results from infrequent northwesterly winds at >~6 m s⁻¹ . I find two dynamically different regions separated along ~71.5°N associated with hydrographic changes. North of 71.5°N the water column is strongly stratified due to cold and dilute ice meltwaters, whereas the water column to the south is much less stratified. These differences are reflected in the current response to the winds. I also adapted and refined an HFR data processing technique and developed an economical way to assess HFR-derived data quality, which is beneficial when using HFR data collected from networks having suboptimal coverage. I investigated the poorly understood circulation around Hanna Shoal. North of the Shoal there is a zonal gradient in the thermohaline and flow fields. The eastern side of the Shoal is strongly stratified year-round and vertically sheared unlike the western side, where the flow is steadily northeastward over the water column. Dense bottom waters flow clockwise around Hanna Shoal, but zonal convergence is implied in the upper water column north of the Shoal. The circulation is influenced by the distribution of late summer sea ice and by clockwise-propagating topographic waves.
    • Trace metals in Arctic fast ice

      Domena, Vincent; Aguilar-Islas, Ana; Rember, Robert; McDonnell, Andrew (2017-12)
      Trace metals in the marine environment are found in trace amounts, but are important tracers of oceanographic processes, and bioactive trace metals can impact ocean biogeochemistry through their nutrient or toxic influence of microbial populations. Sea ice is an intrinsic feature of the Arctic Ocean that likely plays a key role in the cycling of trace metals, given that this substrate can concentrate, alter, and transport these elements. Warming conditions in the Arctic have decreased sea ice cover over the past decades and the loss of sea ice threatens to drastically change the Arctic ecosystem, but the implications are not entirely understood. The scarcity of studies on Arctic sea ice entrained trace metals is due in part to the lack of commercially available sampling equipment capable of collecting sea ice without introducing contamination, and in part to the logistic and economic difficulties in accessing remote Arctic sea ice sites. Natural heterogeneity related to large sediment loads incorporated in uneven patches across Arctic fast ice poses a challenge when designing observational studies of trace metals in sea ice. The scope of this thesis is on the study of trace metals in Alaskan Beaufort Sea fast ice environment. The study includes snow, sea ice and seawater under the ice. Analysis of dissolved (Mn, Fe, Cu and Zn) and particulate (Al, Mn, Fe, Cu and Zn) phases was carried out from 50 ice cores collected with a trace metal clean ice corer developed at the University of Alaska Fairbanks. The results of this study indicated that the ice corer developed at UAF was able to collect uncontaminated samples. Highly variable and elevated concentrations of particulate (> 0.2 μm) trace elements were observed due to the notable variability in the amount of sediment incorporated within ice cores, but surprisingly dissolved (< 0.2 μm) metal concentrations were relatively low and consistent. The observed low dissolved metal concentrations, along with low bulk salinity and low percent leachable particulate trace metal fractions, suggest that desalination removed reactive metals from the ice matrix prior to sampling. Spatial variability of dissolved and particulate trace metals was statistically analyzed and indicated generally negligible variability on the meter scale, but significant variability on the kilometer scale, for both size classes. These results emphasize that future studies of trace metals in sea ice should include temporal and spatial considerations.
    • Controls on zooplankton assemblages in the northeastern Chukchi Sea

      Questel, Jennifer; Hopcroft, Russell R.; Bucklin, Ann C.; Mathis, Jeremy T.; Weingartner, Thomas J.; Coyle, Kenneth O. (2016-08)
      The Chukchi Sea is a broad and shallow marginal sea of the western Arctic Ocean that lies between the Bering Sea and the deeper Amerasian basin. It plays a pivotal role as the only gateway for transporting heat, carbon, nutrients, and plankton from the North Pacific into the Arctic Ocean. I examined the seasonal and inter-annual variability of the zooplankton communities in the northeastern region of the Chukchi Sea as part of a high-resolution multidisciplinary ecosystem study. Specifically, I examined how the physical onset of each open water season influenced the composition, abundance, and biomass of zooplankton assemblages from the 2008 to 2010 field seasons. Copepods in the genus Pseudocalanus are key members of the Chukchi community, and may be undergoing species-level biogeographic shift in response to climate change. I determined the degree of gene flow and population connectivity in the Chukchi Sea through comparative phylogeographic analysis of the Pseudocalanus species complex to the northern Gulf of Alaska and Beaufort Sea. I then investigated the extent to which biogeochemical factors influence these zooplankton assemblages by relating a portion of the seasonal production to concurrent changes in herbivorous mesozooplankton biomass during 2010 and 2011. This work demonstrates just how complex and variable marine ecosystems of the western Arctic are, where multidisciplinary and analytical approaches will become essential in detecting change, especially with the rate of present-day climate perturbations.
    • The exchange of water between Prince William Sound and the Gulf of Alaska

      Schmidt, George Michael, Iii (1977-05)
      Prince William Sound is a complex fjord-type estuarine system bordering the northern Gulf of Alaska. This study is an analysis of exchange between Prince William Sound and the Gulf of Alaska. Warm, high salinity deep water appears outside the Sound during summer and early autumn. Exchange between this ocean water and fjord water is a combination of deep and intermediate advective intrusions plus deep diffusive mixing. Intermediate exchange appears to be an annual phenomenon occurring throughout the summer. During this season, medium scale parcels of ocean water centered on temperature and NO maxima appear in the intermediate depth fjord water. Deep advective exchange also occurs as a regular annual event through the late summer and early autumn. Deep diffusive exchange probably occurs throughout the year, being more evident during the winter in the absence of advective intrusions.
    • Analysis of a ten-day wave record obtained near Middleton Island in the Gulf of Alaska

      Roberts, Jo (1976-05)
      A bottom mounted surface wave gauge was operated in 70 m of water near Middleton Island in the Gulf of Alaska for 10 days in October and November 1973. Standard fast-Fourier transform techniques have been applied to the data, and a second-order lowpass Butterworth filter has been designed to examine low-frequency components in the record. During the time the wave gauge was in operation, two earthquakes were reported with epicenters near the middle of the Aleutian Islands. The first had a surface wave magnitude of 6.4 on the Richter scale; the second, which occurred about 9 hours later, had a surface wave magnitude of 6.3. Spectra for data taken after the occurrence of these earthquakes have shown that generation of ocean waves by these quakes is questionable. Hourly spectra from the first part of the record reveal a peak around 0.065 Hz which moves toward higher frequencies for about 18 hours. The frequency of the peak then remains constant for about 24 hours, after which it again increases. The changes are well correlated with a large storm which remained stationary in the North Pacific, then moved rapidly into the Gulf of Alaska and subsided. Wave group velocities are used to estimate possible distances of the wave source from the gauge. The actual distances of the storm from the gauge show a close correlation with wave-derived distances. Comparison with changes in wave spectra for a storm in the North Atlantic in March 1968 indicates the same time rate of change in the spectral peak as was found in the North Pacific for time periods when the storms are subsiding.
    • Bioassay and distribution of thiamine in the sea

      Natarajan, Kottayam Viswanathan (1965-05)
    • Major nutrient distribution in relation to the physical structure of the Gulf of Alaska shelf

      Childers, Amy Ruehs (2001-08)
      The northern Gulf of Alaska is a biologically productive downwelling shelf. Nutrient sources supporting such productivity have not been adequately studied. Thirteen primary stations were occupied twelve times throughout 1998 and 1999 in an attempt to clarify nutrient distributions and sources. The shelf waters were warmer, fresher, lower in nitrate, and higher in phytoplankton biomass in the spring of 1998 compared to 1999. Nitrate, silicate, and phosphate were positively correlated with salinity indicating an offshore nutrient source. The largest rates of new production, estimated from nitrate drawdown in the upper layer between March and July/August, were 2.6 mmole nitrate m⁻² day⁻¹ in 1998 and 1.9 mmole nitrate m⁻² day⁻¹ in 1999. There was evidence of a summer onshore flux of dense, nutrient-rich bottom water when the downwelling regime relaxed or reversed. This seasonal flux was 20% less than the estimated nitrate flux through nearby Hinchinbrook Canyon.
    • Time and space scales of some oceanic and atmospheric parameters in the Gulf of Alaska

      Beegle, Cynthia Juyne (1986-05)
      Time series of monthly means up to 65 years long were examined to determine the time and spatial scales of variablity in the Gulf of Alaska. Sea level, sea level pressure (SLP), air temperature, fresh water discharge, sea surface temperature (SST) and the Southern Oscillation Index (SOI) are the variables chosen to gain insight into local and global responses in the gulf. This study reports four major results. 1) Sea level anomalies (variations from the annual cycle) are driven by wind and fresh water; temperature effects in sea level are not seen. 2) SST anomalies cannot be predicted from sea level data, but SLP in southeastern Alaska and air temperature in Seward may be useful indicators on a two to three month time scale. 3) On the whole, anomalies in coastal and interior Alaska weather occur together, with SLP 180° out of phase with air temperature and precipitation. Using empirical orthogonal functions, the Southeast and Southcoast district can be separated. 4) A statistically significant SOI signal is seen is both SLP (p>0.995, Seward) and sea level (p>0.995) records.
    • The sedimentary environment of an arctic lagoon

      Tucker, Robert William (1973-05)
      The sediments of Simpson Lagoon are sandy muds and sandy silts. Skewness and kurtosis appear to be functions of the mixing of sand and silt populations by seasonal energy fluctuations. Westward sediment transport is predominant as indicated by sand mode analysis and regional clay mineral variations. General statistical parameter variations are north-south apparently relating to the topography of the lagoon floor. No definitive characteristic of an arctic lagoon has been found and neither seasonal ice cover nor ice rafting are discernable in sedimentologic parameters.
    • Gold in sea water

      Wood, Elwyn Devere (1971-05)
    • A study of near-surface currents in Endicott Arm

      Gleason, Robert R. (1972-05)
      Currents in Endicott Arm were measured by parachute drogues and ice drift photogrammetry. The parachute drogues showed mean outflow speeds between 2 and 20 cm/sec. The mean outflow extended at reduce speeds to below ten meters and may have extended to Bill depth at twenty meters. From equations of drag and inertia, a differential equation was formed to describe tidal ice drift speeds. The equation was solved on an Analog computer and the solution shown as plotted. Coupling curves were used to measure the net tidal speed. Ice drift mean out flow speeds based upon these computations agreed with parachute drogue mean outflow speeds.
    • Seasonal and spatial variations in the water mass characteristics of Muir Inlet, Glacier Bay, Alaska

      Quinlan, Alician Veronica (1970-05)
      Muir Inlet, a Southeast Alaska fjord with tidal glaciers, is investigated. Its water masses show definite seasonal and spatial responses in temperature, salinity, and dissolved oxygen distributions and in circulation patterns. Its basin water is continually renewed. Two seasonal parameter structures are found. The winter - spring structure is characterized by the homogeneity of the water masses, with up to 84% of the fjord water having a temperature between 3.0 - 3.5°C and up to 55%, a salinity of 31.3 - 31.4%. The summer - fall fjord water masses are heterogeneous, with temperatures ranging from 0.5 - 7.5°C., salinities from 13.0 - 32.0% and dissolved oxygen levels ranging from 1.8 - 0.5 milliliters per liter. The heterogeneous state develops gradually from April through November. The homogeneous state is regained abruptly in late fall. The salinity of water below the pycnocline continually increases from late fall through early summer. The salinity of the surface water decreases from mid-spring through early fall. Several spatial parameter patterns are observed. Both salinities and temperatures decrease progressively from the Pacific Ocean to the head of the fjord. The tidal glaciers serve both as heat sinks and as freshwater sources, producing negative temperature and salinity gradients upfjord. The data are consistent with a three-layer flow system: outflowing brackish surface layer, intermediate zone of net upward transport, and a higher salinity deep layer with an upfjord transport. Advective inflows and thermohaline convection may occur from late fall through early summer.
    • On the physical oceanography of Bristol Bay 1969-1970

      Myers, Richard L. (1976-08)
      The examination of hydrographic data obtained in Bristol Bay 1969-1970 allowed oceanographic conditions in this region to be described for shorter time periods (several weeks) than previous studies (several months). This data revealed that during early spring Bristol Bay was homogeneous both vertically and horizontally in temperature and vertically in salinity. During late spring, a steep thermocline developed in the offshore regions and was present throughout summer, while the salinity structure remained vertically homogeneous. Salinity and bottom temperature contours tended to follow isobaths and indicated a cyclonic circulation in the bay. Summer surface temperature distributions are characterized by regions of cold water. These regions are believed to be maintained by upwelling of cold bottom water due to a subsurface convergence in the bottom Ekman layer. Data from 1970 showed that low temperature and high salinity water was much more extensive in that year than in 1969. This is attributed to deeper water from outer Bristol Bay surfacing in central Bristol Bay.
    • Carbon and nitrogen uptake dynamics during 1997 and 1998 anomalous conditions in the Bering Sea

      Rho, TaeKeun (2000-12)
      During 1997 and 1998, unusual physical conditions caused dramatic changes in the regional oceanic environment and function of the southeastern Bering Sea ecosystem. The changes in ecosystem function were examined using ¹³C and ¹⁵N tracer techniques. In 1997, unusually clear and calm conditions allowed an ice-related early bloom over the middle shelf of the southeastern Bering Sea and resulted in nitrate uptake below the pycnocline. In 1998, the duration of phytoplankton growth was extended by warm temperatures and frequent storms that resulted in slow growth of phytoplankton and prevented rapid utilization of nitrate over the shelf. In coccolithophorid bloom regions, ammonium concentrations were high (>3 uM), while nitrate concentrations had a larger range (O.1-10.8 uM). Nitrate utilization rates, which estimate 'new' production, were similar for both years and were somewhate greater (ca. 30%) than those observed during the 70's and 80's PROBES studies. The fate of primary production may have differed in 1997 and 1998.
    • On interannual variability and climate change in the north Pacific

      Salmon, David Kurt (1992-05)
      Long term changes in the atmospheric and oceanic environment of the North Pacific were investigated for the period 1946-1991. A climatology of North Pacific wind stress curl was developed because of the relevance of changes in wind stress curl to both oceanic and atmospheric variability. The dominant scales of spatial and temporal wind stress curl variability were determined and examined within the context of observed changes in North Pacific air temperature, sea surface temperature (SST), sea ice cover, oceanic mass transport and the occurrence of blocking anticyclones. Relationships between these variables and indices of tropical Pacific variability were also determined on interannual time scales. During 1976-1988, phase relationships were very strong between long term mean anomalies of wind stress curl, SST, air temperature, sea ice cover, The Pacific North American index, the Southern Oscillation Index (SOI), and tropical Pacific SST. Long term mean anomalies of these parameters did not change sign during 1976-88. These strong phase relationships did not occur amongst these variables during any other period of the record. The 1976-1988 period is characterized by intensified storminess, the decreased occurrence of blocking anticyclones, and decreased sea ice cover in the subarctic North Pacific. Intensified atmospheric circulation also occurred in the western Pacific subtropical anticyclone. Anomalously low SST occurred across the central and western North Pacific during this period while anomalously high SST was present in the eastern North Pacific adjacent to North America. Changes in the sign of the long term mean anomalies of wind stress curl, central North Pacific SST and the SOI suggest that this climate regime ended or relaxed after 1988. After 1975, long term changes in anomalies of the Southern Oscillation Index, tropical Atlantic wind stress, Sahel rainfall, and Greenland Sea ice cover have characteristics similar to those observed in the North Pacific. It is suggested that the climate anomalies observed in the North Pacific during 1976-1988 occurred as part of a hemispheric or global scale climate regime.
    • Adaptations of the surfgrass phyllospadix to hard marine substrates: tests of anatomical differentiation and carbon isotope fractionation hypotheses

      Cooper, Lee W.; Chapin, F. Stuart; McRoy, C. Peter; Cooney, Robert T.; Kipphut, George W. (1987-05)
      The study examined adaptation in the seagrass genus Phyllospadix to rocky substrates, habitats not generally exploited by seagrasses. One hypothesis tested whether the genus exhibits anatomical features distinguishing it from other seagrasses. A corollary predicted that individual Phyllospadix species show additional specialization, based on observations that three species are distinctly zoned where they occur together. A second hypothesis tested a model of carbon assimilation that predicts that submerged aquatic plants growing on hard substrates, such as Phyllospadix species and most marine algae, experience less transport resistances to inorganic carbon uptake than rooted and rhizoidal plants. As a consequence, it was predicted that Phyllospadix species would show enzymatic discrimination against carbon-13 similar to marine algae and dissimilar to other seagrasses. Carbon isotopic variability in Phyllospadix serrulatus and Phyllospadix torreyi was compared with that of the algae Egregia menziesii and Halosaccion amerlcanum growing at the same location. Carbon isotopic variability in eelgrass. Zostera marina, was also examined to provide a basis of comparison to sediment rooted seagrasses. Comparison with Z. marina was useful in defining anatomical features in Phyllospadix that are adaptations to rocky littoral environments. These features include greater hypodermal fiber and roothair development, thickened rhizomes, and smaller lacunae. Comparison among Phyllospadix spp. for microhabitat adaptations was less fruitful. Phyllospadix spp. show carbon isotopic discriminatory patterns distinct from Z. marina and marine algae. Although marine algae and Phyllospadix spp. overlapped isotopically, only the seagrasses became isotopically lighter with increasing intertidal height, probably through atmospheric carbon dioxide incorporation. Carbon isotope ratios in submerged seagrasses did not appear to be affected by water motion, as predicted by boundary layer considerations. An observed correlation between leaf thickness and leaf isotopic ratios also indicated complications to simple models of carbon assimilation in submerged aquatic plants.