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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
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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.
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Showing 71 to 76 of 76 (0.133 seconds)Spelling suggestions: "subject:"isotope geochemistry"" "subject:"lsotope geochemistry""
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CO2 Ventilation, Hydrological Cycle over Southern Ocean and Clumped Isotope Thermometry in Biogenic CarbonatesPrasanna, K January 2016 (has links) (PDF)
The thesis presents observations on the CO2 concentration and carbon isotopes in air CO2 (δ13C) to constrain the inter-annual variability of carbon inventory over the Southern Ocean between the years 2011-2013. Based on the observation, the region of CO2 venting was identified over the Southern Ocean. Further, isotopic characterization allowed inferring about the possible sources of CO2 degassing and contribution from the dissolved inorganic carbon (DIC) that exsolved to generate CO2. It is concluded that the origin CO2 is mainly from the degassing of CO2 available from the dissociation of DIC or organic degradation.
Live Foraminiferal samples of Globigerina bulloides from towing were captured, separated and analysed for δ18O and δ13C from various locations across the Southern Ocean between 10°N−60°S. A large similarities in the estimated values (deduced from simultaneous composition of ocean water 18O, δ13C in DIC and temperature i.e. SST under equilibrium condition) and measured δ18O and δ13C values were observed until 40°S from the equator, and hence it was concluded that the calcification depth of G. bulloides is confined to a depth of ~75-200m till 40°S latitude. However, further south (>40oS) disequilibrium from the estimates was detected. A number of possible reasons were cited for the observed disequilibrium such as (1) Deeper depth habitat (2) Partial dissolution (3) Non-equilibrium
calcification (4) Oceanic Suess Effect and (5) Genetic Variability. A box model of isotopic mass balance was presented in this study to explain the pattern of enrichment in the 13C values of sea water DIC with latitude (up to about 43°S). The model shows that a steady state of the carbon isotope ratio of water is achieved in a relatively short time of ~5000 days. Rainwater isotope
in the open marine condition across the latitudinal transects over Southern Ocean marking zone of precipitation and evaporation is another element of this thesis. A variation with excess lighter isotopes in rainwater was observed in high latitude rain in this study. Observed isotopic depletion is attributed to rainout process over the ocean. The average rainout fraction over the Southern Ocean in the region of zone of precipitation is ~44%, while it drops to ~25% in the zone of evaporation. Second part of the thesis presents a novel method of isotope thermometry which is called “clumped isotope (13C18O16O16O-2 in the calcite structure) thermometry”. A revision in the thermometry equation relating 47 vs T in synthetic carbonates precipitates and otoliths was proposed. The revised calibration was used on fish otoliths from the modern and past environment to estimate the temperatures. Together with the clumped isotope, conventional stable isotopes in the shell carbonates were measured to effectively reconstruct the seasonal fresh water fraction at seasonal time scales.
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THE IMPACT OF MELTING GLACIERS ON MOUNTAIN GROUNDWATER SYSTEMS: A MULTI-YEAR STUDY INCORPORATING ISOTOPIC TRACERS AND MICROBIOLOGY IN MOUNT HOOD NATIONAL FOREST, OREGON, AND GLACIER NATIONAL PARK, MONTANA, AND TIME SERIES ANALYSES IN THE SWISS ALPSJordyn B Miller (11852195) 17 December 2021 (has links)
<p>Alpine glaciers around the world are in retreat and are unlikely to reverse course. This dissertation focuses on improving our understanding of the impact of glacial melt on mountainous alpine groundwater systems. Studies on glacial melt-groundwater interactions have become more prevalent, particularly in the past 5 years, because we are recognizing that the contribution of glacial melt to the hydrologic cycle is not limited to melt-season surficial streamflow. The importance of glacial melt to mountain groundwater systems has the potential to not only influence spring and streamflow generation, but also the longevity of alpine specific, and frequently endangered species, dependent on this source of recharge. This recharge may be vital for human water needs such as potable water, agriculture, and hydrothermal power.</p>The impact that a transition from glacial melt to snow- or rain-dominated streamflow and recharge will have on alpine ecosystems in a continually warming climate is far reaching. This dissertation: 1) tests whether glacial melt is an important source of recharge for mountain springs and their microbial communities, 2) investigates the spatial impact of glacial-melt recharge on residence times and flowpaths that support alpine springs, and 3) explores the impact of post-peak water on alpine baseflow using a statistical, timeseries approach. My results show that the groundwater systems in glaciated mountainous, alpine regions are particularly vulnerable to climate change. Springs in Mount Hood National Forest and Glacier National Park were sampled over a 4-year period, and in addition, publicly available long-term streamflow datasets were are also utilized. The chapters composing this work build upon each other, and compare and contrast the factors most important in glacial melt recharging the mountain-block. Information that is vital to the management of alpine water resources by landowners, watershed groups, scientists, and others interested in mountain groundwater systems in glaciated alpine regions is presented in the following pages.
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Hafnium Isotope Geochemistry of the Gabbroic Crust Sampled Along the Mid-Atlantic Ridge: Constraints on the Nature of the Upper MantleThomas, Christine L. 26 September 2013 (has links)
No description available.
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LIFE IN THE RAIN SHADOW: UNDERSTANDING SOURCES OF RECHARGE, GROUNDWATER FLOW, AND THEIR EFFECTS ON GROUNDWATER DEPENDENT ECOSYSTEMS IN THE PANAMINT RANGE, DEATH VALLEY, CALIFORNIA, USACarolyn L. Gleason (5930639) 16 January 2019 (has links)
<div>
<p>Despite
its location in the rain shadow of the southern Sierra Nevada, the Panamint
Range within Death Valley National Park, CA hosts a complex aquifer system that
supports numerous springs. These springs, in turn, support unique
groundwater-dependent ecological communities. Spring emergences range in
elevation from 2434 m above sea level (within the mountain block) to 77 m below
sea level (in the adjacent basins). Waters were collected from representative
Panamint Range springs and analyzed for environmental isotopes and geochemical
tracers to address the following questions: 1) What is the primary source of
recharge for the springs? How much
recharge occurs on the Panamint Range? 2) What groundwater flowpaths and
geologic units support springflow generation? and 3) What are the residence
times of the springs? The stable isotopic composition (δ<sup>18</sup>O and δ<sup>2</sup>H) of spring
water and precipitation indicate that localized high-elevation snowmelt is the
dominant source of recharge to these perennial springs, though recharge from
rainfall is not wholly insignificant. Geochemical evolution was evaluated using
principle component analysis to compare the concentrations of all major spring
cations and anions in a multidimensional space and group them according to
dominant geochemical signatures. These resulting geochemical groups are controlled
primarily by topography. The Noonday Dolomite and other carbonate units in the
range are identified as the water-bearing units in the mountain block based on
the <sup>87</sup>Sr/<sup>86</sup>Sr of spring
waters and rock samples. These units also offer higher hydraulic conductivities
than other formations and are chemically similar. Radiocarbon- and <sup>3</sup>H derived residence
times of these spring waters range from modern to approximately 1840 years,
with the shortest residence times at higher altitudes and Hanaupah Canyon and
increasing residence times with decreasing altitude. This residence time-altitude
relationship is likewise likely topography-driven though there are significant
disparities in mountain block storage between the various canyons of the range
resulting in variable residence times between drainages. Lower Warm Springs A
and B, however, are the exceptions to this trend as they emerge at lower
altitudes (750m above sea level) and are likely driven by the transport of
groundwater to the surface along faults which increases both the temperature
and groundwater residence times of waters from these springs. Benthic
macroinvertebrates and benthic and planktonic microbes were also sampled for
each spring studied. BMI and microbial community structure in the Panamint Range
is likewise topography-controlled with more tolerant communities at lower
elevations (within more chemically evolved waters) and less tolerant species in
the unevolved waters at higher elevations.</p></div>
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Evaluation of the mechanisms of trace elements transport (Pb, Rare Earth Elements,... ) and the elemental and isotopic fractionation (Ca and Sr) at the interface water-soil-plant / Évaluation des mécanismes de transport des éléments traces (Pb, REE, ...) et du fractionnement des rapports élémentaires et isotopiques (Ca et Sr) à l'interface eau, sol, planteGangloff, Sophie 28 January 2016 (has links)
Ce travail est axé sur l’étude d’un profil de sol et des solutions de sol prélevés sur une parcelle expérimentale couvertes d’épicéas. Tous ces échantillons proviennent du Bassin Versant du Strengbach (Observatoire HydroGéochimique de l’Environnement – OHGE), ont été échantillonnés à différentes profondeurs (5, 10, 30 et 60 cm) et durant la période comprise entre 2009 et 2013.Les caractérisations des extraits des sols par spectroscopie Infra-Rouge ont permis de mettre en évidence les modifications des groupements fonctionnels organiques avec la profondeur et que ces modifications ont une forte incidence sur le comportement des cations (majeurs et traces) dans le sol. Des expérimentations d’ultra-filtration ont permis d’identifier les flux colloïdaux et dissous du carbone organique ainsi que ceux des éléments majeurs et traces présents dans les solutions de sol. L’utilisation conjointe des traceurs isotopiques (87Sr/86Sr et δ44/40Ca) et chimiques (Terres Rares) ont mis en évidence des processus ayant lieu aux interfaces eau-sol-plante, comme le prélèvement racinaire ou l’altération des sols. / This work is focused on the study of a profile of soil and soil solutions collected on an experimental plot covered with spruce. All these samples come from the watershed of the Strengbach (environment - OHGE Hydrogeochimique Observatory), were sampled at different depths (5, 10, 30 and 60 cm) and during the period between 2009 and 2013. Characterizations of soil extracts by infrared spectroscopy allowed to highlight changes in the organic functional groups with depth and that these changes have a significant impact on the behaviour of the cations (major and trace) in the soil. Ultrafiltration experiments helped to identify flows of colloidal and dissolved organic carbon as well as those of the major and trace-element present in soil solutions. The joint use of isotope tracers (87Sr / 86Sr and δ44 / 40 Ca) and chemical (Rare Earth Elements) have highlighted processes taking place at the water-soil-plant interface, as the uptake by root or soil alteration.
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Postglazialer Anstieg des Meeresspiegels, Paläoklima und Hydrographie, aufgezeichnet in Sedimenten der Bermuda inshore waters / Postglacial rise of sea level, palaeoclimate and hydrography, recorded in sediments of the Bermuda inshore watersVollbrecht, Rüdiger Dr. 13 January 1997 (has links)
No description available.
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