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Uncertainties in Projections of Tropical Precipitation and Atmospheric Circulation and Their Remote Impacts

(Georgia Institute of Technology, 2023-12-10) Lu, Kezhou

My doctoral work focuses on understanding anthropogenic responses of precipitation and atmospheric circulation by employing both statistical methods and climate models of varying levels of complexity. My research has two main goals: (1) to understand the forced response of tropical air-sea interactions across different time scales and their subtropical impact, and (2) to investigate the reasons underlying the uncertainties in climate models when simulating tropical and extra-tropical climate. My dissertation research comprises four individual projects. For my first project, I have explored the mechanism of how the Walker circulation (WC) responds to CO2 forcing across different time scales. The WC, a significant tropical atmospheric circulation spanning both horizontally and vertically, plays a crucial role in the tropical climate and is closely related to phenomena such as the Madden–Julian Oscillation and El Nino-Southern Oscillation. The prevailing consensus suggests that the long-term weakening of the WC is primarily driven by the sea surface temperature (SST) warming caused by increased greenhouse gases, while the fast response of the WC appears largely independent of changes in SST. However, my findings indicate that the air-sea interactions play a substantial role. By analyzing data output from Coupled Model Intercomparison Project Phase 5 (CMIP5) under abrupt4xCO2 scenarios, models with a stronger air-sea coupling in the equatorial Pacific are discovered to simulate an initial strengthening of the WC following the external forcing, which contrasts with the long-term response. Conversely, models characterized by weaker air-sea coupling simulate a monotonically weakening of the WC. My results suggest that the inter-model discrepancy in the WC changes is associated with then uncertainty in the fast component. My second project focuses on understanding the summer North Pacific subtropical high (NPSH). As part of the planetary wave system, the NPSH integrates both tropical and extra-tropical impacts on the monsoons and typhoons over East Asia and hydroclimate over California. Given its considerable socioeconomic significance, reliable future projections of the NPSH are crucial for preparing adaptation plans. However, state-of-the-art climate models exhibit diverging responses of the NPSH to anthropogenic CO2 forcing. This project has revealed that model variability in the future projection of the summer NPSH originates from both inter-model SST-driven and non-inter-model SST-driven uncertainties in the tropical precipitation. Specifically, I investigate the connection between the tropical precipitation and the NPSH by modifying the diabatic heating in both a baroclinic stationary wave model and a comprehensive climate model, i.e. the Community Atmospheric Model version 5 (CAM5). Drawing upon the knowledge acquired from the previous two chapters, my third project has explored how the tropical air-sea interaction and the summer NPSH are influenced by anthropogenic forcing, as well as their interplay. I have discovered that the inter-model spread in projecting the fast changes of the WC directly contributes to the inter-model spread in tropical SST responses. By analyzing CMIP5 and CMIP6 data under abrupt4xCO2 scenario, models with a stronger tropical equatorial Pacific air-sea coupling simulate a strengthening of the WC and a La Nina-like central Pacific cooling. And this La Nina-like SST anomaly induces anomalous tropical precipitation and further modulates the NPSH via the Matsuno-Gill wave response. During the collaboration with my advisor on the fourth project, we have found considerable inter-basin variations in the future projection of the tropical Hydrological sensitivity (HS) regardless of how SST warms. I have further demonstrated the remote impact of the inter-basin discrepancy in HS on land precipitation and surface temperature by understanding the corresponding tropical-extra-tropical teleconnections. Specifically, I have analyzed the atmospheric circulation response induced by tropical precipitation with and without inter-basin discrepancy in HS by conducting diabatic heating adjustment experiments in CAM5.
Observations of peroxyacyl nitrates in polluted and remote troposphere

(Georgia Institute of Technology, 2023-08-01) Lee, Young Ro

Emissions of volatile organic compounds (VOCs) and their photooxidation with nitrogen oxides (NOx) play a significant role in atmospheric chemistry and have substantial effects on air quality. Understanding these processes in the ambient environments is a challenge, in part, due to uncertainties in emission sources and the complex chemical evolution of emissions. This dissertation leverages a comprehensive suite of ground-based and airborne observations to investigate the impacts of VOCs-NOx photochemistry on atmospheric trace gas compositions, both in heavily polluted and pristine environments. In particular, this work focuses on observations of peroxyacyl nitrates (PANs) to provide a detailed diagnosis of photochemistry in the regions discussed throughout the dissertation. East Asian countries such as South Korea and China have experienced severe air pollution problems. In this work, extensive observations of primary and secondary pollutants were conducted in two locations: a remote ground site in the Yellow River Delta, China, during the Ozone Photochemistry and Export from China Experiment (OPECE) in 2018, and a petrochemical producing region in South Korea during the Korea-United States Air quality (KORUS-AQ) campaign in 2016. Our findings during the field observations indicated that both regions are characterized by heterogeneous VOC composition with substantial emissions of alkenes and aromatics. Photooxidation of these VOCs led to efficient ozone production in a radical-limited environment. In addition, elevated levels of peroxyacetic nitric anhydride (PAN), as well as rarely measured homologs such as peroxybenzoic nitric anhydride (PBzN) and peroxyacrylic nitric anhydride (APAN), illustrated the unique atmospheric chemistry in East Asian environments. This dissertation presents global-scale airborne observations of PAN from the NASA DC-8 research aircraft during the ATmospheric Tomography (ATom) campaign. The focus of this investigation was on PAN observations in remote tropospheric regions such as over the Pacific and Atlantic Oceans. We found that PAN over remote oceans is significantly influenced by relatively simple sources including anthropogenic and biomass burning emissions. Notably, biomass burning has a dominant and persistent impact on the global distribution of PAN. Based on a diagnostic evaluation using observations, this work suggests that accurate model treatment of biomass burning can improve prediction of PAN in the remote troposphere. Lastly, the characterization of a low-activity 210Po ion source with an initial activity of 1.5 mCi was performed for use with iodide-chemical ionization mass spectrometry (I--CIMS). We demonstrated that the low activity source is a viable substitute of higher activity radioactive source, offering advantages in terms of reduced regulatory burden during storage and shipping. The performance of the low activity source is illustrated using airborne measurements of PANs during the ATom campaign.
Surface Gravity Waves in Global Climate Models: Development, Evaluation and Optimization

(Georgia Institute of Technology, 2023-07-25) Ikuyajolu, Olawale James

Surface gravity waves play a critical role in several processes at the air-sea interface, including mixing, coastal inundation, and surface fluxes. Yet wind–wave processes are usually excluded from Earth system models partly due to a lack of physical understanding and the high computational costs of spectral wave models. Most wave modeling studies utilize uncoupled short-term simulations and focus on the upper ocean. The impacts of wind-wave processes on coupled climate variability have yet to be thoroughly evaluated. This all underscores the need to advance surface gravity wave modeling frameworks within general circulation models (GCMs). Herein, the first half of this thesis partly addresses the high computational cost of running spectral wave models on a global grid. I identify the wave action source terms as the most computationally intensive part of the spectral wave model WAVEWATCH III (WW3), and then accelerate them on Graphics Processing Units (GPUs) using OpenACC. An average speedup of 1.4x was achieved, resulting in a reduction of 35-40% in runtime and resource usage. In the second half of this thesis, I incorporated a wave-state dependent bulk formula by fully coupling WW3 to the Energy Exascale Earth System Model (E3SM). Current state of the science GCM bulk parameterizations estimate the sea-state roughness as a function of surface wind speed, ignoring wave effects. The newly implemented parameterization includes two primary wave effects: first, a wave-state dependent surface roughness computed by WW3; second, the alteration of momentum flux from the atmosphere to the ocean due to wave growth and dissipation. I conducted numerical experiments with this new parameterization to investigate the sensitivity of the mean climate and Madden-Julian Oscillation (MJO) to different bulk flux parameterizations and the role of waves in air-sea coupling. My results highlight that discrepancies between bulk algorithms have nonnegligible impacts on mean climate such as ocean heat content, sea-ice concentration and a 2℃ difference in sea surface temperature in the North Atlantic. Also, the proper treatment of air-sea coupling via the inclusion of wave-induced effects improves the simulation of MJO. Most importantly, the analysis emphasizes the importance of considering the role of waves in redistributing momentum flux between the atmosphere and the ocean, especially in coastal and high-latitude regions. This work is key to enhancing the capability of future GCMs to simulate coastal changes and extreme events.
A Deep Look into Continental Tectonic Processes Using High-resolution Earthquake Catalogs

(Georgia Institute of Technology, 2023-04-28) Gois Ferreira Gaspar Neves, Miguel Joao

According to the theory of plate tectonics, the Earth’s crust is formed by rigid blocks (tectonic plates) that move relative to each other along linear faults that bound the blocks. The model further assumes that deformation occurs mainly at plate boundaries. In the past decades the definition of plate boundaries has evolved, and it is now recognized that plate boundaries can also be broad areas of deformation, and slowly deforming regions in plate interiors can also generate significant and destructive earthquakes. But even at linear plate boundaries seismologists still struggle to understand the seismic cycle, and improvements in seismic monitoring also revealed different stress sources capable of interacting with faults and earthquakes, such as tidal stresses and stress variations generated by anthropogenic activities. The work presented here focuses on how we can systemically and efficiently compile high-resolution earthquake catalogs and use them to better understand earthquake sequences, the kinematics of faults, and stress interactions in different continental regions. Earthquake catalogs are one of the most important tools in seismology, but these catalogs are often incomplete at lower magnitudes, limiting the information available for understanding the sequence and faulting processes. To improve earthquake catalogs, the past decades have seen the development of different techniques to automatically analyze seismic data, such as matched filter and deep learning earthquake detectors. I first present a study where I use matched filter detection and cross-correlation derived differential travel times to study the 2004 M6 Parkfield, California, earthquake sequence along the San Andreas Fault. I improve the earthquake catalog by about 3 times the number of events listed in the Northern California Seismic Network catalog and use the new catalog to study the period prior to the 2004 mainshock and interactions with tidal stresses. No clear precursory signals to the 2004 mainshock are identified, but an increase in the seismic activity is observed in the creeping section of the San Andreas Fault (about 30 km northwest of the mainshock epicenter) in the weeks prior to the mainshock. This activity increase is also accompanied by a decrease in the b-value parameter in the Gutenberg-Richter relationship in the creeping section. These results suggest stress is increasingly released seismically in the creeping section, accompanied by a decreasing aseismic creeping rate before the mainshock occurrence. However, seismicity rates remain stable in the Parkfield section where the 2004 mainshock ruptured. The analysis of tidal stress variations in the Parkfield segment during the 2004 sequence also reveals that microearthquakes at Parkfield are modulated by tidal stresses, but with different impacts before and after the mainshock. I then describe a project using a deep learning earthquake detector in Iberia, a mostly slowly deforming region in Southwest Europe. I analyze 7 years of seismic data from 552 stations in Iberia to improve the quality of the regional earthquake catalog and gain new insights into the seismicity behavior in the region. I fine-tune a deep-learning earthquake detector and phase picker to analyze the Iberian datasets, using a small dataset of 28,622 waveforms from the region. Using the new phase picker, I compile an earthquake catalog with 56,354 events. Additional analysis to identify anthropogenic signals in the catalog reveals that most clusters in slowly deforming Iberia are connected to areas of anthropogenic signals, which suggests that induced activity is widespread in the region. Using the new catalog, I was also able to identify new lineaments in Iberia, likely illuminating new fault structures in that region. Lastly, combining matched filter detection and a deep learning detector, I study the August 9, 2020, Mw5.1 Sparta, North Carolina, earthquake sequence. This earthquake ruptured the uppermost crust near the town of Sparta and is likely the first reported surface-rupturing event in the Eastern United States. The new catalog reveals that the mainshock nucleated near an intersection point of two fault strands, a blind strike-slip fault where the rupture was possibly initiated, and a reverse fault associated with the identified surface rupture, possibly part of a flower structure like diffuse fault zone. The high-resolution catalogs developed in these studies still present some limitations, but they highlight how high-resolution earthquake catalogs can reveal fault structures and kinematics, stress interactions and seismicity patterns. These findings give insights into the seismic cycle and can have important implications on seismic hazard estimation, particularly in slowly deforming settings. Additionally, the earthquake catalogs presented here hold further opportunities for future studies. For example, they can be used to extend focal mechanism catalogs, and further constrain the kinematics of the structures in the studied regions. The magnitude calibration procedures used in some of the catalog compilation procedures can hold important information to resolve the inconsistencies between different magnitude metrics and potentially improve hazard assessments. The improved catalogs can also be compared with current physics-based models and possibly better constrain the limitations of these models or even improve them.
Advanced methods for real-time identification and determination of seismic events

(Georgia Institute of Technology, 2022-12-20) Barama, Louisa

Natural disasters pose an indistinguishable threat to populations all around the world, affecting ~200 hundred million every year, with earthquakes being the most deadly. Global seismic monitoring allows for robust real-time analysis to provide useful information about an event to assist in earthquake emergency response. Additionally it is an essential tool for monitoring anthropogenic seismic sources like nuclear weapons tests, the use of which can have disastrous effects on human life, ecological environments and public health, ramifications that can last for generations. The focus of this thesis is on characterizing and identifying unique seismic events in near-real-time using the waveforms of initial seismic phase arrivals from teleseismic stations, their derivative products like radiated earthquake energy and rupture duration, and machine learning (ML). This thesis is a compilation of several works addressing novel methods for seismic event identification of: global tsunamigenic earthquakes, uncharacteristically high-energy tsunami earthquakes, deep earthquakes, and underground nuclear explosions (UNE). First, I present the current Real-Time Earthquake Energy and Rupture Duration Determinations (RTerg) products and methodology applied to a case study of fast-rupturing tsunami earthquakes in the Solomon Islands, testing the robustness of the RTerg derivative waveform products and Tsunami Earthquake (TsE) discriminant threshold used for real-time analysis. Second, I show how peaks in RTerg energy flux curves from teleseismic stations and their differences in broadband and high frequency bandwidths can be associated with depth phase arrivals (P, pP, sP) to identify deep earthquakes, highlighting the potential for real-time depth determinations using first derivative waveform products without additional processing of waveforms. Next, I introduce nuclear explosion monitoring from a global network of stations, starting with the compilation of the first openly available and comprehensive UNE seismic waveform and event catalog termed GTUNE (Georgia Tech Underground Nuclear Explosions). GTUNE seismic records are sourced from declassified nuclear tests, previously published datasets and openly available waveforms and were assembled into a user‐friendly format compatible with most python‐based ML packages. The next contribution to this thesis is the development of a global UNE classifier using labeled P-wave seismograms from GTUNE. I trained a Convolutional Neural Network (CNN) to identify three classes: earthquake P-wave, nuclear P-wave, and noise. I found that the model can accurately characterize most events, finding over 90% of the signals in the validation set, even with limited training data. Lastly, I combine the thesis works described thus far and applied similar ML methodology to classify/predict deep earthquakes, using both a CNN and a Deep Neural Net (DNN), trained on both physical features of the energy flux time series (prominence and peak density) as well as the original waveforms. Results show better single station predictions using the original waveforms. By contrast, for full network determinations, the energy flux products perform the best, despite the smaller training dataset. We anticipate that ML models like our UNE and deep earthquake classifiers can have broad application for other “small data” seismic signals including volcanic and non-volcanic tremor, anomalous earthquakes, tsunami earthquakes, ice-quakes or landslide-quakes.
Production of Light-independent Reactive Oxygen Species during Microbially-mediated Fe(II)/Fe(III) redox cycling and its Application in the Degradation of Organic Contaminants

(Georgia Institute of Technology, 2022-12-08) Xie, Nan

Reactive oxygen species (ROS), such as superoxide (O2•−), hydrogen peroxide (H2O2), and the hydroxyl radical (•OH), represent transient reactants that are redox active and ubiquitous in aquatic systems. In the presence of Fe(II), H2O2 represents a potential source of •OH via the Fenton reaction, which is commonly used in remediation for organic contaminant degradation. The degradation of various organic contaminants during aerobic oxidation of Fe(II) species without addition of exogenous peroxide has also been demonstrated, suggesting that oxidation of natural organic matter and organic contaminants may occur naturally at redox interfaces. In redox-dynamic environments, facultative anaerobic microorganisms such as Shewanella species may alternate between respiration of O2 and Fe(III) oxides as terminal electron acceptor and potentially produce ROS during redox oscillations. Although these processes have been proposed, and the formation of ROS has been increasingly documented in natural environments, a mechanistic investigation of the processes regulating the generation of ROS during redox oscillations with Fe(III) oxides is lacking. The overall objective of this research was to investigate the mechanism of light-independent ROS production during microbially-mediated Fe(III)/Fe(II) redox cycling with iron oxides and its potential application for field remediation of organic contaminants. The role of nutrients, organic ligands, and redox conditions on ROS generation in the presence of Fe(III) oxides was investigated in both batch and flow-through reactors to gain insights into the complex mechanism of ROS production and consumption and its effect on organic carbon degradation, using 1,4-dioxane as a recalcitrant model organic contaminant. Overall, this dissertation contributes to our understanding of the light-independent production and role of ROS in natural environments by: 1) providing new insights into the importance of nutrients in the production of ROS during Fe redox cycling; 2) highlighting the importance of ligands in promoting both Fe redox cycles and •OH production in subsurface environments; 3) demonstrating that the production of ROS is sustainable at redox interfaces without high frequency redox oscillations; and 4) providing a new process that could be exploited in in situ bioremediation strategies aimed at using •OH for contaminant remediation.
The impacts of climate variability and change on the physical and social-ecological dynamics of the Kuroshio and North Pacific Transition Zone

(Georgia Institute of Technology, 2022-12-08) Navarra, Giangiacomo Giacomo

There is growing recognition that climate change is impacting the ocean's western boundary current system. In the Pacific, the Kuroshio and its offshore Kuroshio-Oyashio Extension (KOE) play a central role in the North Pacific climate and impact the social-ecological dynamics of countries that rely on marine ecosystem services (e.g. fisheries). In the thesis, we have used a combination of observations and modeling approaches to understand how past and projected changes in the physical environment of KOE impact social-ecological dynamics linked to the fish industry of Japan and the North Pacific more widely. The thesis is articulated in 3 Chapters. In Chapter 1 we have introduced the problem and the main motivation that lead us to perform this study. In Chapter 2, we analyze the climate variability and change of the KOE over the historical and future projection period 1920-2100. We perform this task using Coupled Model Intercomparison Project 5 (CMIP5) models and a large ensemble from the Community Earth System Model (CESM-LE) output runs. The reason for considering also the CESM-LE runs is that they give the possibility to explore how the variance of the KOE in one model (e.g. a fixed set of dynamics) responds to anthropogenic forcing when compared to the range of natural variability of the CESM-LE model. In this way, we can perform a scenario which goes beyond the time of the observational data. In Chapter 3, we have used an Empirical Dynamical Model approach to characterize the joint statistics of the physical and social-ecological environmental system (SEES) that is relevant to climate and fisheries. To define the states of the SEES we use three international fish databases, (1) the Large Marine Ecosystem (LME, 9,000 fish stocks), (2) the NOAA fishery database referred to as Restricted Access Management (RAM, 300 fish stock) and the (3) the Food and Agriculture Organization (FAO, 1400 fish stocks). Among the approaches used to explore the relationship between KOE’s climate and the SEES response, we have developed a Linear Inverse Model (LIM) approach that has been very successful to simulate and predict the KOE physical climate and its relation to large-scale Pacific dynamics such as El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and others.
Understanding microseismicity behavior and their response to earth processes by improving earthquake catalogs

(Georgia Institute of Technology, 2022-08-01) Zhai, Qiushi

Natural earthquakes occur on faults ranging from 0 to 700 km beneath Earth's surface in different tectonic settings, such as along major subduction zones in Japan and the arc-continent collisional environment in Taiwan. Recent studies suggest that earthquake activities can be affected by various Earth processes, including extreme weather events on the Earth’s surface, large earthquakes, water/snow/glacier loading and unloading, erosion and sedimentation, etc. The Gutenberg–Richter magnitude-frequency statistics suggest that the number of earthquakes decays as a power law with the increase of earthquake magnitude, which means most earthquakes are of small magnitudes, i.e., microseismicity. Studying the behavior of microseismicity and their response to the Earth’s surface process can help us to better understand fault structures at depth as well as the physics of earthquake nucleation, and to mitigate seismic as well as other natural hazards. However, the understanding of microseismicity may be limited by the incompleteness of standard earthquake catalogs, especially during the noisy period following extreme weather events and large earthquakes. During my Ph.D. study, I have developed/applied machine-learning and template-matching tools to improve earthquake catalogs by detecting microearthquakes and calculating their focal mechanisms. Based on the improved high-resolution catalogs, I then perform a detailed analysis of the microseismicity behavior and their response to Earth processes. Specifically, I build a deep-learning Network for Polarity Classification (NPC) to automatically determine P-wave first-motion polarity. The outputs of NPC can directly be used to build focal mechanism catalogs for several times more microearthquakes than those listed in the standard catalogs. Next, I use template-matching and deep-learning methods to build a more complete earthquake catalog in Taiwan before and after the 2009 typhoon Morakot, which brought the highest rainfall in southern Taiwan in the past 60 years and triggered numerous landslides. I then use the new catalog to investigate the impact of this wet typhoon on microseismicity. I observe no other significant seismicity changes that can be attributed to surface changes induced by typhoon Morakot, but a clear reduction in seismicity rate near the typhoon’s low-pressure eye center in northeastern Taiwan during the typhoon passed by. I also relocate earthquakes in this new catalog and use it to study the spatiotemporal variations of mainshock-aftershock sequences and the subsurface faults structure in Taiwan. Last, I perform a systematic detection of intermediate-depth earthquakes (IDEQs) in the Japan subduction zone using the template-matching technique. I obtain a more complete IDEQ catalog before and after the 2011 magnitude (M) 9 Tohoku-Oki earthquake (TOEQ) and ten M5+ IDEQ mainshocks in Japan. The newly built template-matching catalog does not show any significant increase in IDEQs in the two months prior to TOEQ. But following the TOEQ, I find a significant increase in the rate of IDEQs in both upper and lower planes of the double seismic zone beneath 70 km depth. These results suggest that like seismic activity at shallow depth, IDEQs in the double seismic zone also respond to stress perturbations generated by the 2011 M9 TOEQ, highlighting a sustained seismic hazard associated with these intraslab events in the next decades.
Antarctic ice shelves as ocean world analogs

(Georgia Institute of Technology, 2022-08-01) Lawrence, Justin

The search for life beyond Earth is a primary goal of NASA, and in our solar system ocean worlds such as Jupiter’s moon Europa are among the most promising targets. Europa has a global outer shell of ice which is likely to be tens of km thick – but also a lower mass meaning pressures and temperatures in the upper ocean below the shell may be similar to Earth’s polar oceans. Models for the habitability of Europa’s hydrosphere suggest that exchange between the ice shell and ocean, controlled by melting and freezing processes, is important for Europa’s overall habitability. Ahead of the Europa Clipper mission which is anticipated to reach the Jovian system by ~2030, we turn to Antarctica’s ice-covered oceans to build our understanding of how sub-ice ecosystems operate while simultaneously applying these lessons to other oceans worlds in our solar system. Around the edge of the Antarctic continent, floating extensions of the ice sheet called ice shelves cover 1.5 million square kilometers of the coastal ocean, an area the size of Mongolia, in ice hundreds to thousands of meters thick. Ross Ice Shelf represents a third of this area alone but the thick ice poses a significant barrier to exploration and since the late 1970s only four projects (two of which are included here) have accessed the ocean below. Sub- ice shelf ocean and ecosystem dynamics are understudied – by analogy this would be like trying to sort out the weather in a region the size of France based on launching one weather balloon a decade. Here, we used a novel remotely-operated underwater vehicle designed for sub-ice oceanography, ROV Icefin, to study the environments and ecosystems beneath Earth’s ice shelves. Over several field seasons below Ross and McMurdo Ice Shelves, we have contributed a new understanding of interactions between ice shelves, ocean, and seafloor processes. By pairing oceanographic observations with a complementary survey of bacteria and archaeal diversity under the shelf, we provide additional evidence for the importance of ice-ocean interactions to sub-ice nutrient availability and ecosystem structure.
Thallium isotope investigation of paleo ocean redox and carbon dioxide removal via enhanced rock weathering

(Georgia Institute of Technology, 2022-07-30) Li, Zijian

The oxygenation of Earth’s surface fundamentally reshaped global biogeochemical cycles, and surface oxygen levels have played a critical role in the origin and diversification of metazoans. Stable thallium (Tl) isotope systematics are mechanistically linked to the burial of manganese (Mn) oxides, making the system an effective redox proxy to track free oxygen (O2) levels in the ocean. The Mesoarchean and mid-Proterozoic are two critical periods of time in geologic history for the evolution of microbial and complex life. In the first half of this thesis, I analyze Tl isotopic compositions of mid-Proterozoic black shales and Mesoarchean siliciclastic sediments and perform stochastic modeling of marine Tl isotope mass balance to extract paleo-redox conditions that have been poorly constrained. The e205Tl composition of the upper Velkerri Formation is indistinguishable from the crustal value, which implies the global burial of Mn oxides was limited at 1.36 Ga and contemporaneous deep ocean was pervasively anoxic. The strong positive e205Tl values of the 2.95 Ga Sinqeni Formation are not likely to represent global seawater records, but rather preserve a primary signal of localized Mn oxide burial in Mesoarchean marine sediments. Because free O2 is required to stabilize Mn oxides against reductive dissolution during settling, our results provide strong evidence for the early emergence of oxygenic photosynthesis at least 3 billion years ago. There is increasing consensus that immediate and deep reductions in greenhouse gas (GHG) emissions are necessary in the coming decades to limit global warming to the 1.5C target (the Paris Agreement). Carbon dioxide removal (CDR) from Earth’s atmosphere is likely to play a significant role in achieving the climate mitigation goals. The second half of this thesis focuses on enhanced rock weathering (ERW), a negative-emission CDR strategy that spreads milled calcium- and magnesium-rich silicates (or alkaline materials) on croplands or in the ocean to artificially speed up the weathering process and associated atmospheric CO2 removal. A hierarchy of models is adopted to evaluate the CDR potential and environmental impacts of ocean-based ERW using natural and synthetic mineral feedstocks. Compared to olivine and basalt, application of alkaline metal oxides (CaO and MgO) leads to higher CDR efficiency with reduced environmental impacts, but deployment at scale faces challenges of substrate limitation and process CO2 emissions. I then perform an analysis of the energetic and economic demands of rock grinding, the most energy-demanding and cost-intensive step in the ERW life cycle, and conduct state-level assessment of carbon footprints, costs, and energy requirements associated with grinding for the U.S. The results of geospatial analysis highlight the regional differences in deploying grinding and indicate that the operation of grinding in the U.S. is generally cost-effective and energy-efficient based on the nation’s average electricity mix.