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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

Sinking particle dynamics in the Gaoping Submarine Canyon

Kuo, Chia-Ta 13 December 2011 (has links)
The purpose of this research is to understand the sinking particle dynamics in the Gaoping Submarine Canyon (GPSC), the change of their geochemical character, and their causal relationship with dynamic parameters. Also this research inquires into the significance of sedimentary environment, transport process, and the influence of non-tidal actions (turbidity current) in the sedimentary environment. The field experiments including LADCP moorings, T6KP(1/10/-3/20), and T7KP (7/7-9/11) sediment traps moorings were deployed in the GPSC to collect the time-series data of sinking particle and related dynamic parameters. Parameters of discrete sediment analysis were used to build continuous time-series data by interpolation, and time series analysis applied to understand the change of physical and geochemical character and their correlation with dynamic parameters. The results showed that sinking particles of different grain-size classes confront different forces in the canyon and their grain-size distribution structures are influenced accordingly. Vertical component of the flow has more influences on coarse particles, while the along canyon flow component has more influences on fine particles. The influence of semidiurnal tide on sinking particle is not clearly resoloved, but spring tide and neap tide affect them significantly. GPSC is normally a stable deposition environment dominated by tidal currents. Particle-reactive materials vary upon with clay concentration, coarse paericles vary upon with the flow field, and the change of benthic nepheloid layer thickness during spring and neap tide cycle affects the vertical distribution of particle size-groups near the bottom of canyon. The particle in the upper (rim) and lower (near the bottom) canyon belong to different transport and dynamic regimes. The upper part was affected by upwelling and shelf processes, while the lower part was affected by tidal currents. In case of episodic event, if surge-like turbidity flows pass near the canyon floor, in the waxing phase, the sinking particle would be affected by the strong momentum of resuspension and mixing which leads to a dramatic change of geochemical character of these particles. In turbidity current event, coarse sand and silt are the major particle sizes with low clay content, suspended sediment concentration about 4.41 g / l. The fluctuation of time series analysis by HHT found a frequency between 2.1~9.8 clcle per day. In the waning phase, dynamics and geochemical character of sinking particle will gradually return to those variations in tidal dominance. In winter, most sinking particles in GPSC are the source material (particles of biological origin) coming from the off-sea with the upcanyon flow during spring tide period. In summer, most sinking particles in GPSC are the terrigenous material (higher organic matter) output from the Gaoping River during typhoons, and flowing to the South China Sea along the canyon with turbidity flow.
242

The Last 180 ka Benthic Foraminiferal Mg/Ca Record and the Implication on Intermediate Water Hydrology Variations of the Western Equatorial Pacific ( MD052922C )

Feng, Chun-Chin 29 August 2012 (has links)
The Antarctic Intermediate Water (AAIW) plays an important role on controlling globally climatic change. Numbers of researchers attempted to discuss whether AAIW across the equator or notduring glacial- interglacial transitions. In this study, we analyzed Mg/Ca and £UREE/Ca on benthic foraminiferal species, Cibicidoides wuellerstorfi, from core MD052922C, which retrieved from western equatorial Pacific region, for revealing the long-term variations of Paleohydrology in intermediate water depths of tropical Pacific. Our evaluated results reveal that the Mg/Ca ratios ranging from 1.27 to 2.04 mmol/mol, and ranging between 2.2 and 3.2¢J when calculating into paleotemoeratures.Highest Mg/Ca can be observed in MIS 6. This finding implies that the present AAIW mean temperature is colder than glacials, and the present AAIW is well-ventilated than that in glacials.Higher £UREEs/Ca values are usually well correlated with old and poor ventilated water masses. In our record, higher £UREEs/Ca values are observed at MIS 5 impling that the intermediate depth water mass of the western tropical Pacific is poor ventilated when comparing to glacials.
243

Response of Benthic Microalgal Community Composition at East Beach, Galveston Bay, Texas to Changes in Salinity and Nutrients

Lee, Alyce R. 2009 May 1900 (has links)
Benthic microalgal community composition on an ephemerally submerged sandflat at East Beach, Galveston Island, Texas was studied to determine the spatial and temporal variability of total biomass and community composition and its responses to experimental manipulations of two environmental factors (salinity and nutrients). Four field studies were conducted between August 2004 and February 2005. The community consisted of two major algal groups, diatoms, and cyanobacteria with two less abundant groups, green algae, and phototrophic bacteria. Spatial variability showed that patch sizes of 12 - 25 m were detected over larger scales with smaller scale (cm) patches of approximately 28 - 201 cm^-2 contained within the larger patches. The second study examined the spatio-temporal variability of BMA over a 21-month period in a 1,000 m^2 area. Sampling location and date explained a significant amount of the variability in the abundances of algal groups, which were positively correlated with the water content of the sediments and negatively correlated with temperature (sediment and water). All of the algal groups showed a seasonal pattern with higher abundances measured in the winter months and lower abundances found during the summer. BMA biomass (100 mg Chl a m^-2 or greater) maxima occurred at temperatures less than 22 degrees C and sediment water content greater than 15% (g water g sediment^-1). BMA response to different salinities and nutrient (N+P) amended sediments was assessed in four bioassays conducted over a 6-month period (Aug. 2004, Oct. 2004, Dec. 2004, and Feb. 2005). In the salinity study, the treatments that were either 100% or partially diluted with deionized water had the lowest BMA biomass over all. Chlorophyll a and fucoxanthin were significantly affected by salinity with higher abundances found in salinities that averaged 15 with a preference for salinities greater than 22. Chlorophyll b was affected by salinity with higher abundances measured in the treatments with lowest salinity (DL and DI); and was affected by the time of year. This would suggest that this algal group prefers an environment with salinity less than 2 but can easily adapt to environments with higher salinities. BMA abundances were not significantly affected by the nutrient amended sediment, but were significantly affected by stations with higher water content, and during the cooler months (Dec. 2004 and Feb. 2005).
244

Taxonomy And Distribution Of The Benthic Foraminifera In The Gulf Of Iskenderun, Eastern Mediterranean

Oflaz, Sabire Asli 01 August 2006 (has links) (PDF)
The present study aims to investigate the foraminiferal assemblages of the recent samples in terms of abundance and diversity, to determine the bathymetrical and the geographical distributions of the foraminiferal assemblages. This study further intends to put forward the responses of foraminifers to environmental factors (e.g. bathymetry, salinity, substrate, pollution, water currents, etc.) on the distribution of foraminifers. In this manner, foraminiferal fauna has been taxonomically identified and quantitatively analyzed in the 34 grab samples distributed at depths from 18 m. to 190 m. collected from the Gulf of iskenderun. Counting 300 individuals from each sample, the relative abundances of 151 benthic foraminiferal species belonging to suborders of Rotaliina, Miliolina, Textulariina, Spirillinina and Lagenina have been determined. The relative abundances of samples are dominated by Ammonia tepida / Adelosina cliarensis, Nonion sp.A, Textularia bocki, Reussella spinulosa, Cribroelphidium poeyanum, Adelosina pulchella, Buccella granulata, Elphidium advenum and Nonion depressulum that are also common in the western Mediterranean. Furthermore, the Lessepsian migrants / Peneroplis pertusus, Septoloculina angulata, Septloculina rotunda, Septoloculina tortuosa, Vertebralina striata and Amphistegina lobifera are abundant in only southeastern part of the gulf. Because of complex distribution scheme of benthic foraminifers, some statistical analysis (Cluster Analysis, DCA and CCA) have been applied to relative abundance (percentage) of the most abundant, ecologically important taxa in order to visualize assemblages and their representative species. Two main clusters, mainly controlled by CaCO3 and substrate, have been obtained. It is recognized that the distribution of benthic foraminiferal assemblages are not strongly depend on depth as it expected.
245

Sedimentary Cyclicity And Micropaleontological Investigations In The Upper Triassic Shallow Marine Carbonate Successions (central And Western Taurides, Turkey)

Coskun Tunaboylu, Burcu 01 February 2008 (has links) (PDF)
Shallowing-upward meter-scale cycles (parasequences) consisting of megalodont-bearing limestones or clay levels at the bottom and fenestral limestones, breccias, stromatolites or vadose pisoids at the top constitute the basic working units of the Upper Triassic successions in the Central and Western Taurides. These cycles are mainly represented by subtidal through supratidal carbonate facies and known as Lofer cycles in the literature. The presence of breccias, mud cracks, dissolution vugs and vadose pisoids indicates subaerially exposed conditions at the top of the cycles. Shallowing-upward meter-scale cycles are interpreted as 4th and 5th order cycles in this study. Megalodont-bearing limestones of the subtidal zone are characterized by wackestones/packstones with abundant involutinids. However, involutinids are poorly represented in the intertidal-supratidal zone. To determine the relationship between cyclicity and foraminifers, the vertical variation of benthic foraminifer abundance has been analysed in the cycles. This analysis leads us to conclude that the foraminiferal abundance decreases from subtidal through supratidal zone. Furthermore, cluster analysis was performed in order to delineate the relation between the biofacies and foraminiferal associations. Micropaleontological analysis of the uppermost Triassic carbonates reveals the presence of restricted platform foraminiferal associations in the studied successions. Foraminiferal associations discovered in the samples belong to the Upper Norian (Sevatian)-Rhaetian Triasina hantkeni assemblage zone. Detailed examination of peritidal carbonates in the Central and Western Taurides against the studies, which claimed that the Dachstein-type platform carbonates are characterized by the transgressive models, should be explained by regressive models.
246

Foraminiferal Paleontology, Biostratigraphy And Sequence Stratigraphy Of The Permian-triassic Boundary Beds Of The Bolkar Dagi Unit (central Taurides, Turkey)

Esatoglu, Aysel Hande 01 June 2011 (has links) (PDF)
The aim of this study is to designate paleontologic, biostratigraphic and sequence stratigraphic characteristics of the Permian-Triassic Boundary beds of the Bolkar Dagi Unit in the Hadim region (Central Taurides). For this purpose a 48,06m thick stratigraphic section, composed of limestone, siltstone and sandstone, was measured and 116 samples were analyzed through the Permian Ta
247

Abhängigkeit der Besiedlung benthischer Invertebraten von Hydromorphologie und Saprobie in silikatischen Mittelgebirgsbächen

Völker, Jeanette 19 January 2009 (has links) (PDF)
Das Verständnis über die Ausprägung der Lebensgemeinschaften von benthischen Invertebraten in aquatischen Ökosystemen in Abhängigkeit von abiotischen Faktoren ist von grundlegender wissenschaftlicher Bedeutung und eine Voraussetzung für die Bewertung, den Schutz und die Wiederherstellung der ökologischen Integrität in Fließgewässern. Für die Erarbeitung von Abhängigkeiten zwischen der benthischen Lebensgemeinschaft, der Hydromorphologie und der Saprobie standen insgesamt 409 Datensätze in Form von Taxalisten des Makrozoobenthos zur Verfügung. Diese wurden mit Strukturgütedaten verschnitten und anhand uni- und multivariater statistischer Methoden analysiert. Folgende Ergebnisse konnten dabei erzielt werden: (a) es können sieben Einzelparameter der Gewässerstruktur identifiziert werden, die einen signifikanten Einfluss auf die benthische Biozönose ausüben, (b) die Fließgewässertypen 5 und 5.1 unterscheiden sich auf Basis des vorliegenden Datensatzes weder in der taxonomischen noch in der funktionalen Zusammensetzung der Makrozoobenthoszönose und (c) bei einer erhöhten saprobiellen Belastung überlagert der Einfluss der organischen Belastung die strukturellen Gegebenheiten. Für die Entwicklung und Anpassung effizienter Strukturgüteverfahren und die daraus resultierenden Monitoring- und Maßnahmenprogramme für ein integriertes Fließgewässermanagement ist die Auswahl ökologisch relevanter Parameter von immenser Bedeutung. / The understanding about the development of benthic invertebrate communities as a function of abiotic influencing factors in aquatic ecosystems is of essential scientific relevance for the assessment of the ecological status of rivers and streams. For the development of interdependencies between benthic invertebrates, hydromorphology and saprobity, 409 species lists of the macroinvertebrates were provided. They were aggregated with morphological features and analysed with different uni- and multivariate statistical methods. On the basis of the used analyses, the following results were achieved: (a) seven ecological relevant morphological features with significant influence to benthic invertebrate community could be identified, (b) on the basis of the present database, the structural and functional composition of the benthic invertebrates can not be differ river type specific (type 5 and 5.1) and (c) if the saprobic pressure decrease, the organic pressure superpose the hydromorphology. The values of the biological attributes are low in spite of near natural morphological conditions. For an ecological efficiency stream habitat assessment, the identified relevant morphological parameters have to consider. The “morphological characteristic curves” are well describing the results of a local monitoring. This application-oriented instrument can be used for (a) the operationalisation of environmental objectives, (b) the development and adaption of monitoring strategies and (c) the derivation and prioritisation of ecological and economic efficiency measurements for an integrated river management.
248

Woody debris and macroinvertebrate community structure of low-order streams in Colville National Forest, Washington

Rogers, Megan Bryn, January 2003 (has links) (PDF)
Thesis (M.S.)--Washington State University, 2003. / Title from PDF title page (viewed on May 22, 2005). Includes bibliographical references (p. 52-56).
249

Foraminiferal assemblages as bioindicators of potentially toxic elements in Biscayne Bay, Florida

Carnahan, Elizabeth A 01 June 2005 (has links)
Heavy-metal pollution is an issue of concern in estuaries such as Biscayne Bay that are heavily influenced by agricultural, urban, and harbor activities. The goals of this study were to provide a state of the bay assessment that can be used to interpret changes that have occurred over the past 60 years in Biscayne Bay, to provide a baseline to compare changes in the ecosystems during and after execution of the Comprehensive Everglades Restorations Plan (CERP), and to determine if benthic foraminiferal assemblages in Biscayne Bay reflect heavy-metal contamination in sediments. Surficial samples were collected at 147 sites throughout the bay. Analyses included geochemical assessment of the mud fraction for 32 chemical parameters, grain-size analysis, and assessment of foraminiferal assemblages at the genus level. Geochemical analyses revealed elevated concentrations of a suite of heavy metals in the sediments of the northern bay, between Miami and Key Biscayne, and the periphery of the southern bay from Black Creek Canal south to Turkey Point. Cluster analysis, multi-dimensional scaling, and multivariate-correlation analyses revealed three distinct foraminiferal assemblages. One assemblage, characteristic of the northern bay, was defined by stress-tolerant taxa including Ammonia, Cribroelphidium, Nonion, and Haynesina, which were present in low abundances. Distribution of this assemblage correlated with the most elevated concentrations of heavy metals. The assemblage that defined the southwestern margin of the bay was dominated by Ammonia and Quinqueloculina. This assemblage is characterized by the lowest diversities and highest abundances, and is likely influenced by both reduced salinity and elevated organic-carbon concentrations.
250

Dynamics of Stony Coral Assemblages on Patch Reefs of the Upper Florida Reef Tract, Including Biscayne National Park

Wallace, Amy 01 January 2011 (has links)
The patch reefs located in Biscayne National Park (BNP) are some of the most northern reefs of the Florida reef system. The focus of my study is seven patch reefs that were first surveyed annually between 1977 and 1981, revealing 8% - 28% cover by scleractinian corals. An assessment of BNP patch reefs completed in 2000 reported that coral cover had decreased to approximately 0.4% - 10%. The once dominant species in the Florida reef tract, Acropora palmata and A. cervicornis, have rapidly declined over time and were not found in any transects during the 2000 survey. This study is a re-assessment of the BNP patch reefs surveyed in 1977-1981. In addition, one patch reef from BNP and three in upper keys region of the Florida Keys National Marine Sanctuary (FKNMS) have been included (a total of 11 patch reefs, all with historical data available). This study found 2% - 13% coral cover at these 11 reefs using a photographic survey (Point Count) and 4% - 21% coral cover using Atlantic and Gulf Rapid Reef Assessment (AGRRA) survey methods. These results are relatively similar to results reported for the same patch reefs in the 1990s and in 2002, indicating that the major changes occurred earlier with the extreme decline in Acropora spp. Montastraea annularis complex cover has also declined substantially at the BNP sites from 5.4% in 1977-81 to 1.3% in 2009. Although the number of species recoded on the seven resurveyed BNP patch reefs was only 23, compared with 28 recorded in the 1977-81 study, all species are still present in the region surveyed, indicating no actual loss of over all species richness.

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