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School of Earth and Atmospheric Sciences

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Now showing 1 - 10 of 781
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    Analysis of landsat data and testing of hypothesis for Charleston earthquake
    (Georgia Institute of Technology, 1987) Long, Leland Timothy ; Georgia Institute of Technology. Office of Sponsored Programs ; Georgia Institute of Technology. School of Geophysical Sciences ; Georgia Institute of Technology. Office of Sponsored Programs
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    Understanding the mechanisms of dissolved oxygen trends and variability in the ocean
    (Georgia Institute of Technology, 2016-04-08) Takano, Yohei ; Ito, Takamitsu ; Di Lorenzo, Emanuele ; Bracco, Annalisa ; Deutsch, Curtis ; Montoya, Joseph ; Earth and Atmospheric Sciences
    A widely observed tracer in the field of oceanography is dissolved oxygen (O2). A tracer crucial to ocean biogeochemical cycles, O2 plays an active role in chemical processes, marine life, and ecosystems. Recent advances in observation and numerical simulation have introduced opportunities for furthering our understanding of the variability and long-term changes in oceanic O2. This work examines the underlying mechanisms driving O2 variability and long-term changes. It focuses on two distinct time-scales: intra-seasonal variability (i.e., a time scale of less than a month) and centennial changes in O2. The first half of this work analyzes state-of-the-art observations from a profiling float in an investigation of the mechanisms driving the intra-seasonal variability of oceanic O2. Observations from the float show enhanced intra-seasonal variability (i.e., a time scale of about two weeks) that could be driven by isopycnal heaving resulting from internal waves or tidal processes. Observed signals could result from aliased signals from internal waves or tides and should be taken into account in analyses of the growing observational dataset. The methods proposed in this study may be useful for future analyses of high-frequency tracer variability associated with mesoscale and sub-mesoscale processes. Using outputs from state-of-the-art earth system models and a suite of sensitivity experiments based on a general circulation and biogeochemistry ocean model, the second half of this work focuses on investigating mechanisms regulating centennial changes in O2. It explores the aspect of anthropogenic climate change (e.g., changes in the sea surface temperature and wind stress fields) that significantly impacts oceanic O2, focusing specifically on tropical oxygen minimum zones. Results suggest that ocean heating induces a water mass shift, leads to decrease apparent oxygen utilization (AOU) in the tropical thermocline. The AOU decrease compensates the effect of decrease in oxygen saturation due to the ocean warming. Our sensitivity experiments show that both physically (i.e., age) and biologically (i.e., the oxygen utilization rate) driven AOU will contribute almost equally to controlling changes in oceanic O2 in the next century. However, additional sensitivity experiments indicate that physically and biologically driven AOU balance has regional characteristics. We need to address the unanswered question of how varying large-scale oceanic circulations regulate this balance and answer fundamental questions that lead to a more comprehensive understanding of the mechanisms that control the variability and the future evolution of oceanic O2.
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    Controls of sorbed aluminum of quartz reactivity : an integrated experimental investigation of dissolution rates and surface reaction processes
    (Georgia Institute of Technology, 1999) Dove, Patricia M. ; Georgia Institute of Technology. School of Earth and Atmospheric Sciences ; Georgia Institute of Technology. Office of Sponsored Programs ; Georgia Institute of Technology. Office of Sponsored Programs
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    The variability and seasonal cycle of the Southern Ocean carbon flux
    (Georgia Institute of Technology, 2013-07-03) Hsu, Wei-Ching ; Ito, Takamitsu ; Di Lorenzo, Emanuele ; Jones, Daniel ; Earth and Atmospheric Sciences
    Both physical circulation and biogeochemical characteristics are unique in the Southern Ocean (SO) region, and are fundamentally different from those of the northern hemisphere. Moreover, according to previous research, the oceanic response to the trend of the Southern Annual Mode (SAM) has profound impacts on the future oceanic uptake of carbon dioxide in the SO. In other words, the climate and circulation of the SO are strongly coupled to the overlying atmospheric variability. However, while we have understanding on the SO physical circulation and have the ability to predict the future changes of the SO climate and physical processes, the link between the SO physical processes, the air-sea carbon flux, and correlated climate variability remains unknown. Even though scientists have been studying the spatial and temporal variability of the SO carbon flux and the associated biogeochemical processes, the spatial patterns and the magnitudes of the air-sea carbon flux do not agree between models and observations. Therefore, in this study, we utilized a modified version of a general circulation model (GCM) to performed realistic simulations of the SO carbon on seasonal to interannual timescales, and focused on the crucial physical and biogeochemical processes that control the carbon flux. The spatial pattern and the seasonal cycle of the air-sea carbon dioxide flux is calculated, and is broadly consistent with the climatological observations. The variability of air-sea carbon flux is mainly controlled by the gas exchange rate and the partial pressure of carbon dioxide, which is in turn controlled by the compensating changes in temperature and dissolved inorganic carbon. We investigated the seasonal variability of dissolved inorganic carbon based on different regional processes. Furthermore, we also investigated the dynamical adjustment of the surface carbon flux in response to the different gas exchange parameterizations, and conclude that parameterization has little impact on spatially integrated carbon flux. Our simulation well captured the SO carbon cycle variability on seasonal to interannual timescales, and we will improve our model by employ a better scheme of nutrient cycle, and consider more nutrients as well as ecological processes in our future study.
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    Analysis of arctic haze scattering data obtained during AGASP
    (Georgia Institute of Technology, 1985) Patterson, Edward Matthew ; Georgia Institute of Technology. Office of Sponsored Programs ; Georgia Institute of Technology. School of Geophysical Sciences ; Georgia Institute of Technology. Office of Sponsored Programs
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    Recognition and evaluation of seismicity anomalies in California
    (Georgia Institute of Technology, 1986) Habermann, Ray Edward ; Georgia Institute of Technology. Office of Sponsored Programs ; Georgia Institute of Technology. School of Geophysical Sciences ; Georgia Institute of Technology. Office of Sponsored Programs
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    Anhydrite precipitation and evolution of permeability in ocean ridge crest hydrothemal systems
    (Georgia Institute of Technology, 2001-05) Yao, Yufeng ; Lowell, Robert P. ; Earth and atmospheric sciences
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    Understanding ocean iron dynamics and impacts on marine ecosystems
    (Georgia Institute of Technology, 2019-11-12) Pham, Anh Le-Duy ; Ito, Takamitsu ; Glass, Jennifer ; Taillefert, Martial ; Montoya, Joseph ; Weber, Thomas ; Earth and Atmospheric Sciences
    Fe is one of the most important nutrients for phytoplankton growth in the ocean, making it a crucial element in the regulation of the ocean carbon balance and biogeochemical cycles. Atmospheric deposition of dissolved Fe (dFe) to the ocean has increased over the last decades partly due to human activities, which can significantly alter marine ecosystems. Thus, a comprehensive understanding of how the ocean Fe cycling operates and how it will respond to human perturbations is urgently needed. In this work, I first significantly improve the Fe parameterization in a global ocean biogeochemistry model, constrained by new high-quality ocean Fe datasets. Then, I identify key mechanisms that control the ocean Fe cycle in various ocean basins and examine the responses of marine phytoplankton to an increasing Fe deposition through a suite of model simulations. These simulations are performed in an ocean biogeochemistry and an ecosystem models, which incorporate the newly improved Fe scheme. The refinement of model Fe parameterization and its evaluation are undertaken in chapters two to four. In these chapters, I show that my newly developed Fe scheme displays a remarkable improvement in reproducing observations over the old scheme. Through a suite of model simulations, I reveal the crucial role of the concurrent release of dFe and ligands from sinking organic particles in forming and maintaining the subsurface dFe maxima observed in many ocean transects. Moreover, the inclusion of spatially varying ligand classes with different binding strengths in the model is important to explain the strong vertical dFe gradient observed in the upper ocean. I also identify the relative roles of different external dFe sources in different ocean basins. While atmospheric deposition is an important source of dFe in the Atlantic and Indian Oceans, sedimentary and hydrothermal dFe inputs are more important in the Pacific Ocean. The relative contributions of external sources and ocean interior processes on regulating the upper ocean dFe pattern are explored in chapter five. This task is done by analyzing the dFe budget and the dFe distribution field simulated in different ocean Fe models, using an unsupervised classification technique. The results show that the upper ocean dFe patterns are largely controlled by interior ocean processes and that without an appropriate representation of these processes, Fe models cannot reproduce observations, even with a correct magnitude of the external fluxes. In chapter six, I explore the impact of an increasing dFe atmospheric deposition on the Indian Ocean phytoplankton and carbon balance by using an ocean ecosystem model, which incorporates the newly improved Fe scheme. I found that while diatom growth and export organic carbon flux are enhanced south of 40 degree S, they decrease in some regions in the northern Indian Ocean, compensated by increases in coccolithophores growth and carbonate carbon export. These changes lead to a decrease in the carbon dioxide uptake over the Indian Ocean.
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    Wave disturbances associated with the Red River Valley severe weather outbreak of 10-11 April by Rossella Ferretti
    (Georgia Institute of Technology, 1986-12) Ferretti, Rossella ; Einaudi, Franco ; Geophysics
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    An implementation of the competitive Gaussian model for metal-humic binding in a general speciation model
    (Georgia Institute of Technology, 1997-12) Allison, Jerry Dewell ; Perdue, E. Michael ; Earth and atmospheric sciences