1,721,004 research outputs found
Current Primary Production Rates Of The Western Arctic Ocean Estimated By Stable Carbon And Nitrogen Isotope Tracers
Full text linkDissertation (Ph.D.) University of Alaska Fairbanks, 2005Currently, 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
Paleoceanographic shifts in the Gulf of Alaska over the past 2000 years: A Multi-proxy perspective
Full text linkThesis (M.S.) University of Alaska Fairbanks, 2008The Gulf of Alaska (GOA) is a dynamic region influenced by climate
variability on time scales ranging from days to millennia. Recent regime shifts suggest interdecadal GOA primary productivity patterns, yet it is unclear whether such fluctuations extend beyond the instrumental record. This thesis examined the nature of prevalent climatic and oceanographic patterns before the twentieth century using several marine sediment core proxies for paleoproductivity and paleoceanography. Sediment cores were from two locations: Bay of Pillars, Kuiu Island, in southeast Alaska (56.63 ̊N, 134.35 ̊W), and a central midshelf location (GAK4) along the Global Ecosystem Dynamics (GLOBEC) Seward Line (59.25 ̊N, 148.82 ̊ W). Proxy data from these cores include: percentages of organic carbon, nitrogen and biogenic opal; organic carbon-to-nitrogen ratios; stable isotope ratios from sediment organic matter (δ13C and δ15N) and foraminifera tests (δ13C and δ18O); and foraminifera faunal analysis. Bay of Pillars proxy data suggest that the onset of the Little Ice Age (LIA) ca. 1200 AD coincides with pulses of decreased salinity and increased productivity. GAK4 proxy data indicate increased productivity and decreased terrestrial input over the past century; as well as fresher surface water was during the latter portion of the LIA (1716 – 1894) and positive Pacific Decadal Oscillation phases
(Table 4a) Biomass of Emiliania huxleyi and its role in total biomass of phytoplankton at the section along 70 m isobath on 26-27 August 2001
No full text(Table 4a) Biomass of Emiliania huxleyi and its role in total biomass of phytoplankton at the section along 70 m isobath on 26-27 August 200
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Nutrient distributions and dynamics in Lavaca, San Antonio and Nueces/Corpus Christi bays in relation to freshwater inflow
Full text linkFor Bays and Estuaries Program, Environmental Systems Section, Texas Water Development BoardDecember 1989Part I: The Nitrogen Processes Study (NIPS) was undertaken under contract from the Texas Water Development Board in order to better understand the relationship of freshwater inflow into South Texas estuaries and the biological productivity that occurs in them. It is important to study the characteristics of the inflow especially the nitrogen components because nitrogen is generally regarded as the "essential" nutrient whose abundance controls the amount of biological production of an ecosystem (Ryther and Dunston, 1972; Thayer, 1974; Boynton et al., 1982).Part II: This volume contains all hydrographic, nutrient and chlorophyll data collected at discrete sampling depths during 1986-1987 in San Antonio Bay and 1987-1988 in Nueces/Corpus Christi Bay. Water samples were normally collected just under the surface by hand and approximately 4 inches above the bottom by a horizontal water sampling bottle. Since the Seabird CTD instrument records a continuous profile, not all of the data are reported here. The surface and bottom values were extracted from the data and merged with the water sample data. The complete profiles of CTD data are contained in the reports of A. Amos. Additional details of sampling and analysis methods are given in Volume I of this report.Part III: This volume contains time series data plots obtained on experimental stations during intensive process oriented samplings. Suitable shipboard space was not available during the initial phase of NIPS-I in San Antonio Bay so the temporal resolution was relatively poor. Later samplings at station locations A and C improved to hourly samples for as long as 24 hours, however sites B and D were still sampled by small boat so darkness an d inclement weather prevented some collections. Better ship availability reduced these problems during NIPS-II in Nueces/Corpus Christi Bays. Additional details of sampling and analysis methods are given in Volume 1 of this report and tabular listings are contained in Part III.pt. 1. Results and discussion -- pt. 2. Hydrography, nutrient and chlorophyll data tables -- pt. 3. Data plots.Marine Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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Research report : enhanced hydrographic survey for CPL discharge in Nueces Bay
Full text linkThe objectives of the enhanced hydrographic survey in Nueces were: A. to monitor the vertical and horizontal distributions of temperature and salinity, nutrients and plant pigments in the nearby area of the CPL cooling water discharge channel in Nueces Bay. B. to compare the distributions of the above parameters to those throughout other portions of Nueces Bay during freshwater release and non-release periodsFor Central Power and Light Company ... Corpus Christi, Texas ...November 1993Marine Scienc
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
A numerical model of seasonal primary production within the Chukchi/Beaufort Seas
No full textA coupled three-dimensional circulation and ecological model provided numerical analysis of daily carbon/nitrogen cycling by the planktonic and benthic components of western Arctic shelf/basin ecosystems during 2002, when extensive field data were obtained by American and Canadian ice-breakers. Seasonal model budgets of April–May, July–August, and September–October 2002 allowed both interpolation and extrapolation of these validation data, suggesting that the most productive shelf regime of the Chukchi/Beaufort Seas was that of summer. Yet, during this period of July–August, a combination of light-limitation and nutrient-limitation limited shelf-wide mean simulated net photosynthesis to only 709mg Cm2 day 1 for shelf waters of o220m depth. This modeled seasonal carbon fixation then accounted for 45% of the annual shelf primary production of 97.4g Cm 2 yr 1. Identification of the relative importance of natural control factors of light and nutrients by the coupled model provided insight into possible consequences of future global climatic changes at these high latitudes.The model’s seasonal penetration of relatively saline, nutrient-rich Anadyr Water of Pacific origin into the eastern Chukchi Sea replicated the time series of observed salinity fields. A similar fidelity of the simulated nitrate, silicate and dissolved inorganic carbon fields with the observed ones yielded an assessment of nutrient uptake and photosynthesis during a natural fertilization experiment. The simulated chlorophyll, dissolved organic carbon (DOC), and NH4 stocks also mimicked these shipboard observations. We found that the spring 2002 stocks of new nutrients were stripped by the end of summer, with little fall nutrient resupply by physical and biotic factors, when incident light waned. However, because of extensive ice cover and nutrient-poor upper waters within the Canadian Basin, the slope regions remained oligotrophic throughout the year, yielding a simulated annual net photosynthesis of 50g Cm 2 yr 1. We conclude that future ice cover retreat, without eutrophication, may have little impact on increased carbon sequestration within these high-latitude ecosystems
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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