Thesis (Ph. D.)--Massachusetts Institute of Thechnology and Woods Hole Oceanographic Intitution, 1980. / Vita. Grant no: OCE-7826318, OCE-7825724, OCE-7727004, EY-76-S-02-3566. Photocopy of typescript. Bibliography: p. 262-273.

<p> The aqueous chemistry, precipitation, and crystallization of metal-carbonates comprises a vast field of research that underlies the urgency of CO₂ sequestration, ocean-acidification, and biomineralization. The results of recent experimental and computational studies suggest that amorphous calcium and magnesium carbonates are precipitated from supersaturated aqueous conditions by non-classical aggregation of ion pairs, dimers, dynamically-ordered-liquid-likeoxypolymers (DOLLOPS), and prenucleation clusters (PNCs). We present the first high field (20 T) ⁴³Ca and ²⁵Mg NMR studies of amorphous calcium-magnesium carbonates (ACC, ACMC, AMC) materials. Direct integration of computational techniques with experimental NMR provides a novel step forward toward multi-scale integration of computational and experimental techniques. Supporting information is derived from X-ray diffraction (XRD), thermogravimetric/differential thermal analysis (TGA-DTA), and scanning electron microscopy&mdash;energy dispersive spectroscopy (SEM-EDS) and provides important comparison to the bulk structures and composition. </p><p> High field NMR of amorphous carbonates demonstrates that amorphous carbonates contain various types of local disorder, but does not corroborate the theory of polyamorphism nor nano scale phase separations postulated by other workers. Carbon (¹³C) NMR of ¹³Cenriched materials indicates a degree of Ca-Mg solid solution in ACMCs, as ACMC ¹³C resonances cannot be adequately reconstructed from the pure ACC and AMC ¹³C resonances. However, with increasing Mg-content (and therefore H₂O content) ¹³C NMR resonances are strongly influenced by water-carbonate hydrogen bonding, shifting to lower resonance frequency and broadening. The ¹³C-NMR are well-fit with single Gaussian distributions, suggesting that two-phase models of ACMCs are not required to explain our ¹³C NMR observations. Protoncarbon cross polarization indicates that there is a H population proximal to carbonate groups for all amorphous phases. ⁴³Ca NMR yields line shapes that span the resonance frequency range of all known crystalline calcium carbonate polymorphs and is well fit with a single Gaussian distributions. ⁴³Ca NMR does not support a theory of polyamorphisms, but rather suggests an unstructured, continuous distribution of local environments that is unlike any specific crystalline phase. The mean ⁴³Ca chemical shifts vary 0.77 ppm from compositions x = 0 to 0.5 [x = Mg/(Mg + Ca)], demonstrating that Mg²⁺ has very little influence on the molecular-scale ⁴³Ca environment in ACMCs. Through integration of quantum mechanical calculations, classical MD, and NMR we ascertain a maximum mean Ca-O bond distance in our ACCs/ACMCs of 2.45 &plusmn; 1 &Aring; that is independent of composition. Unlike the indistinguishable local calcium environments, ²⁵Mg NMR of amorphous material gives evidence for several distinct overlapping quadrupolar line shapes. These sites do not generate NMR resonances that are perfect matches for known crystalline polymorphs of magnesian carbonates and extend toward lower resonance frequencies far beyond the range of known equilibrium analogs. By comparison to the range of reference phases, the low frequency singularities of ACMC-AMC resonances are consistent with some population of Mg-O bond distances greater than 2.10 &Aring; and/or some fraction of sites with high coordination numbers (up to 8). The local Mg environment of a protodolomite crystallization [x = Mg/(Mg + Ca) = 0.6] exhibits ²⁵Mg NMR parameters most similar to the asymmetric Mg²⁺ coordination environment of lansfordite [Mg(CO₃)2(H₂O)₄]^2&ndash; or huntite. Although H-C cross polarization indicates no H-bonding with carbonate the XRD gives not longrange indications of huntite. The large effective radius of strongly hydrated Mg in the protodolomite likely provides a driving force for cation ordering in dolomite.</p><p>

Continuous event-based rainfall samples were collected at three sites throughout the Pensacola airshed from 2005 - 2011. Samples were analyzed for total mercury (Hg), a suite of trace metals (TMs), and major ions in order to understand how thunderstorms affected their wet deposition and concentrations in rainfall, estimate the contributions from regional coal combustion and other anthropogenic sources to Hg and TMs in rainfall along the Gulf Coast, and investigate the possible influence that a local 950 megawatt coal-fired power plant had on rainfall chemistry in the Pensacola airshed. Mercury was measured with a Tekran 2600 using a method that was a variation of the standard method used by the US Environmental Protection Agency (EPA) to measure total Hg in water which allowed for the analysis of TMs from the same bottle without having to worry about contamination from reagents during sample preparation. Trace metals were measured used an Agilent 7500cs quadrupole inductively coupled plasma mass spectrometer (ICP-MS) while utilizing an octopole reaction cell (ORC) which allowed for the detection of key coal-combustion tracers like arsenic (As) and selenium (Se). Our findings show that summertime rainfall Hg concentrations are higher compared to other months despite higher rainfall amounts. In contrast, other measured pollutant TMs and ions did not show a consistent seasonal pattern. By incorporating Automated Surface Observing System data from nearby Pensacola International Airport and WSR-88D radar data from Eglin Air Force Base, we were able to classify the storm type (thunderstorms or non-thunderstorms) and analyze altitudes of hydrometeor formation for individual rain events. This showed that mid-altitude and high-altitude composite reflectivity radar values were higher for both thunderstorm and non-thunderstorm ”warm season” (May - Sept) rain events compared to ”cool season” (Oct - Apr) events including cool season thunderstorms. Thus, warm season events can scavenge more soluble reactive gaseous Hg from the free troposphere. Two separate multiple linear regression analyses were conducted on log-transformed data using interaction and non-interaction terms to understand the relationship between precipitation depth, season, and storm-type on sample concentrations. The regressions without interaction terms showed that the washout coefficients for more volatile TMs like Hg and Se were less pronounced compared to other pollution-type elements and that their concentrations were therefore less diluted for a given increase in precipitation depth, but otherwise displayed similar coefficients for season and storm-type. The regression model with interaction terms revealed a more interesting dynamic where thunderstorms caused enhanced Hg concentrations in rainfall regardless of season or precipitation depth while showing a more volume-dependent relationship with TM concentrations as concentrations increased with increasing rainfall amounts relative to non-thunderstorm events. This suggests a vacuum cleaner effect such that for increasing storm strength, non-Hg aerosol TMs in the boundary layer are further entrained into a storm cell. With this understanding, a positive matrix factorization (PMF) analysis was conducted using the EPA PMF 5.0 software to estimate the contribution of different sources to Hg deposition. Our results suggest that approximately 84% (72 - 89%; 95% CI) of Hg in rainfall along the northern Gulf of Mexico is due to long-range transport from distant sources while a negligible amount (0 - 21%; 95% CI) comes from regional coal combustion. However, we found that anthropogenic sources like regional coal combustion and ore smelting were significant contributors to rainfall concentrations of other pollution-type TMs like copper, zinc, As, Se, and non-sea salt SO42-. Using modeled wind profiles via the HYSPLIT trajectory model, we assessed whether plumes from a local coal-fired power plant (”Plant Crist”) could be detected in the rainfall chemistry of rain events occurring downwind of the plant. We limit this analysis to cool season rain events between June 2007 (when the model began) and December 2011 (when the study ended) because modeled wind profiles showed better agreement with observations during this time period compared to the warm season. We also limit this analysis to cool season events since the spatial distribution of rainfall throughout the area is more even during this time which makes sample comparisons between sites easier since Hg/TM concentrations are affected by precipitation depth. Furthermore, we focus on Hg and other pollution-type TMs and major ions such as As, Se, and non-sea salt SO42- in this analysis as they serve as tracers of coal combustion. For our ”unpaired-site” analysis, we analyzed, for each individual site, the rainfall chemistry in a given sample as a function of the proportion of rain events associated with that sample that occurred downwind of Plant Crist. Using this method, we were not able to find evidence that the plant had a significant influence on Hg/TM concentrations or Hg/TM:Al enrichment ratios in rainfall. Similarly, for our ”paired-site” analysis, we consider the differences in rainfall chemistry between two sites - an upwind and downwind site pair - that were impacted by the same rain event where the downwind site was exposed to plumes from Plant Crist while the upwind site was not. As with the unpaired-site analysis, we did not find significant differences in the rainfall chemistry between upwind-downwind site pairs with regards to sample concentrations or enrichment ratios. A multiple linear regression analysis was then conducted using interaction terms to understand the relationship between the operation of a wet flue-gas desulfurization system (which began operation at the plant during the middle of the study), the relative exposure a rainfall sample had to the plumes coming from the plant, and the log-transformed precipitation depth on log-transformed sample concentrations. Besides for As, the first regression analysis did not find coefficient values of any statistical significance for any of the variables that would indicate that the scrubber affected the rainfall chemistry at the two urban sites nearest to the plant. The calculations for As gave mixed results as the coefficients for the non-interaction terms suggested that the scrubber and the plumes emanating from Plant Crist affected the concentration of As in rainfall while the interaction terms suggested that they did not. We perform another multiple linear regression analysis, but remove the complicating effects of precipitation depth on Hg/TM concentrations and instead analyze the effects that the scrubber and the plumes coming from the plant might have had on Hg/TM:Al ratios. Again, these results were inconclusive as the regression coefficients suggested that the scrubber helped reduce Hg and TM emissions from the plant while also suggesting that samples with more exposure to the plant’s plumes had lower enrichment ratios. We propose that we were unable to detect a chemical signal from Plant Crist in our rain samples due to a few possible reasons including quick scavenging of TMs from the plume at the onset of a rain event before reaching our sites, the reliance on radar data to determine start and stop times for rain events at the sites as opposed to on-site measurements, and relatively low spatiotemporal resolution for the wind trajectory model. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2018. / July 16, 2018. / Coal combustion, Mercury, Source-apportionment, Thunderstorms, Trace metals, Trajectory analyis / Includes bibliographical references. / William M. Landing, Professor Directing Dissertation; Thomas E. Miller, University Representative; Christopher D. Holmes, Committee Member; Henry E. Fuelberg, Committee Member; Vincent J. M. Salters, Committee Member.

Uranium and thorium isotopes are powerful and sensitive tracers of a wide range of oceanographic and environmental processes. This thesis makes use of these isotopes in deep sea sediments to reconstruct dust fluxes and deep ocean respired carbon storage over the last 350 kyr in the central equatorial Pacific. The paleoenvironmental information obtained through the application of these isotopes as proxies reveals important information about the Earth’s ocean and atmosphere, and their connectivity on millennial and glacial-interglacial timescales. In Chapter 1 of this thesis I introduce the proxies and principals employed in our paleoenvironmental reconstructions. Subsequently, the first section of this thesis explores the use of 230Thxs,0-derived 232Th fluxes as a proxy for aeolian dust deposition at three sites beneath the shifting Pacific Intertropical Convergence Zone (ITCZ). The new records presented here improve upon existing records of tropical Pacific dust fluxes by increasing the temporal resolution ~5 fold and adding almost an order of magnitude more data. Specifically, we reconstruct dust fluxes in two cores from 0-150 ka and from one core from 0-350 ka In addition to substantially improving constraints on tropical dust fluxes this work also utilizes the spatial transect of cores to infer past positions of the ITCZ on glacial-interglacial and millennial timescales. This proxy approach to reconstruct ITCZ position has only been applied and published once previously, in a relatively low-resolution study. Chapter 2, entitled “Large deglacial shifts of the Pacific Intertropical Convergence Zone,” presents evidence that the Pacific ITCZ experienced large shifts in latitudinal position, on millennial timescales during the penultimate deglaciation. The data resolve abrupt shifts in atmospheric circulation associated with deglaciation, in this case Termination II, at the boundary between the full glacial marine isotope stage (MIS) 6 and the peak interglacial MIS 5. These shifts are significant in that they appear to have occurred at the same time as changes in the North Atlantic driven by Heinrich Stadial 11 and may have played an important role in pushing the climate system over the threshold for deglaciation. Indeed, this study is the first to show evidence of a millennial-scale ITCZ response at the time of the Heinrich Event 11 catastrophic iceberg discharge event. Additionally, the data point to the existence of a previously unidentified millennial peak in northern hemisphere dust abundance during the penultimate deglaciation. In Chapter 3, “Climate-related response of dust flux to the central equatorial Pacific over the past 150 kyr,” records of dust flux are used to provide strong evidence for an association between high latitude stadial events and tropical dust fluxes during the last 150 kyr. These high-resolution observations permit the drawing of conclusions about the meridional location of the Pacific ITCZ during six Greenland stadials. As with the shift of the ITCZ during Heinrich Stadial 11, these events were associated with perturbations of the interhemispheric thermal gradient and coincident movement of the ITCZ presents an important constraint on the sensitivity of the tropical atmosphere to high latitude perturbations. The conclusions stemming from the interpretation of geochemical and paleoceanographic data presented in Chapters 2 and 3 are of broad relevance to a variety of geoscience disciplines that seek an understanding of the climate system. For example, these results confirm predictions made by modeling studies about the response of the ITCZ to high latitude climate forcing and provide an important new set of boundary conditions for modeling studies aimed at reconstructing changes in insolation forcing and tropical hydroclimate. The results show that paleo-reconstructions can constrain the magnitude of even abrupt ITCZ movement, demonstrating the potential to relate ITCZ changes to the magnitude of thermal forcing and to investigate thermal and hydrological components of other climate change events, past and future. Additionally, these results help improve understanding of the relationship between atmospheric dust abundance and climate, with implications for planetary albedo and micronutrient fertilization of the oceans. The second portion of this thesis focuses on using authigenic uranium (aU) to reconstruct deep water chemistry with implications for paleocirculation. Chapter 4, “Repeated storage of respired carbon in the equatorial Pacific Ocean over the last three glacial cycles,” presents evidence that the Pacific was a significant reservoir for respired carbon during glacial periods over at least the last 350 kyr. This reconstruction is based on the precipitation of the redox sensitive metal uranium as a proxy for deep water oxygen concentrations. Because any change in oceanic storage of respiratory carbon must be accompanied by corresponding changes in dissolved oxygen concentrations, data reflecting bottom water oxygenation are of value in addressing questions of glacial carbon sequestration. The record reveals periods of deep ocean aU deposition during each of the last three glacial maxima. Export productivity data indicate these intervals are not associated with local productivity increases, indicating episodic precipitation of aU occurs in response to basin-wide decreases in deep water oxygen concentrations. Not only does the aU record show the history of dissolved oxygen concentrations in the central equatorial Pacific, it also provides an opportunity for the reconciliation of records previously interpreted as incompatible with one another and with the storage of respired carbon. Synthesis of existing data suggests the existence of a ’floating’ pool of respired carbon between 2 and 3.5 km depth in the equatorial Pacific. This hypothesis permits the interpretation of existing proxy data reflecting abyssal LGM circulation and carbon storage without invoking a glacial watermass geometry significantly different from present. The new data and conclusions presented in Chapter 4 represent a significant advance in our understanding of where carbon was stored in the ocean during successive glacial periods. The perspective provided by the new aU time series is spatiotemporally unique and constitutes compelling evidence that hypotheses of marine carbon storage developed to explain the last glacial period are equally applicable to previous Pleistocene glacial periods. The three studies presented in this thesis provide strong support for the utility of U and Th series isotopes in paleoenvironmental reconstructions. Not only does this work demonstrate the range of paleoclimatic proxy data that can be obtained from isotopes of U and Th, it also illustrates the value of interpretations derived from their analysis. The records presented here represent a substantial contribution to our knowledge of marine hydroclimate and ocean circulation over the last 350 kyr and motivate additional high resolution paleoclimate work using isotopes of U and Th.

No description available.

<p> The export of particulate carbon from the surface ocean into deeper water and to the seabed is a critical component of the carbon cycle. The concentrations and compositions of particulate pigments collected at different depths and sinking at different settling velocities can be used as a proxy for biologically mediated processes important to the early degradation of OM. By knowing what processes the compositional and quantitative changes in the particulate pigments represent, the POM cycle of the BaRFlux area can be better understood. It is important to understand the POM cycle because deposition of OM to the seabed is the only way that OM is sequestered. The removal of POM from the marine POM cycle is especially important to understand in subtropical gyre areas like the BaRFlux site because: 1. subtropical gyres are areas of downwelling, and therefore POM transport to the deep ocean and may increase as global warming continues. 2.the flux of CO₂ to the ocean is increasing from rising levels of atmospheric CO₂, and CO₂ removed by the biological pump will lessen processes like ocean acidification.</p><p> This thesis examines the early degradation of chloropigments in the sediment and water column in the Bermuda Rise area of the Sargasso Sea. Water column particulate samples were collected with in-situ pumps, Niskin bottles, and Indented Rotating Sphere (IRS) sediment traps, and sediment was collected by box cores during 2011-2013 to record seasonal patterns in quantity and quality of particulate pigments as a function of water column depth and particle size. Chl-a, Chl-b, and pheopigments were separated and quantified using reverse-phase High Performance Liquid Chromatography (HPLC).</p><p> The comparison of data from in-situ pumps and Niskin bottles indicates that collection method significantly affects particulate pigment data concentrations. Niskin bottle data showed total pigment concentrations 10 times greater than in-situ pump pigment concentrations at shallow depths. At depths below the euphotic zone, Niskin bottle and in-situ pump concentrations both appear similar because the particulate pigment concentrations were below the detection limit. For the BaRFlux study area, the differences in Niskin bottle and pump data are most likely from: 1. the biased particle distribution due to sampling a small volume of seawater with Niskin bottles in an area of dilute particle concentration; 2. the greater retention efficiency of picophytoplankton on Niskin GF/F filters than 1-<i>&micro;</i>m in-situ pump microquartz filters.</p><p> The compositional changes seen in small suspended particulate pigments over depth is consist with small suspended particles being consumed by shallow water zooplankton and then increasingly altered by microbial activity with increasing depth. The composition of small and large particulate pigments were compared to determine if aggregation-disaggregation was an important process. Larger suspended particulate pigments were nearly 100% Chl-a over depth and distinct from smaller suspended particulate pigments other than samples from May or June, during which particle exchange may be more important. The comparison of particulate pigment data to CTD beam transmissivity profiles suggests that the nepheloid layer consists of small suspended particulate matter rather than large particles.</p><p> Sediment trap samples were compositionally enriched in pheopigments relative to smaller bottle and pump samples, indicative of enrichment with more rapidly sinking larger zooplankton fecal pellets. The mole% of chlorophyll-a labile pigment increased with increasing settling velocity, suggesting aggregation may increase the settling velocity of particles enough to escape zooplankton feeding. The particulate pigment composition of seafloor sediment collected in August was compositionally distinct from that of suspended and sinking particulate pigments and was nearly 100% pheophorbide-a, indicating POM degradation by feeding macrobenthos.</p>

Thesis (Ph. D.)--University of Washington. / Bibliography: l. 156-177.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (p. [156]-164).

Thesis--Northwestern University. / Vita. Includes bibliographical references (p. 212-225).

Thesis (Ph. D.)--University of California, Santa Cruz, 1996. / Typescript. Includes bibliographical references (leaves 149-150).