<div>Since the debut of graphene, many 2D materials have emerged as promising candidates for silicon alternatives to extend Moore’s Law, such as MoS₂ and phosphorene. However, some common shortcomings such as low mobility, instability and lack of massive production methods limit the exploration and applications of these materials. Here, we introduce a novel member to the 2D category – high-mobility air-stable 2D tellurium film (tellurene).</div><div><br></div><div>Tellurium (Te) is a narrow bandgap semiconductor with unique one-dimensional chiral structure. Recently, a hydrothermal synthesizing method was developed to produce large-area tellurene nanofilms with thickness ranging from tens of nanometers down to few layers. In this thesis, a thorough investigation of Te properties in 2D quantum region was first carried out by various material characterization techniques including TEM and Raman spectroscopy. Potential applications of Te-based electronics, optoelectronic and thermoelectric devices were explored, and high-performance Te FETs were achieved with record-high drive current over 1 A/mm via device scaling and contact engineering. Magneto-transport, including weak anti-localization and Shubnikov-de-Haas oscillations was studied at cryogenic temperature. Quantum Hall effect was observed for the first time in both 2D electron and hole gases with mobility of 6,000 and 3,000 cm²/Vs, and non-trivial Berry phase in Te 2D electron system was detected as the first experimental evidence of massive Weyl fermions. This work not only demonstrates the great potential of tellurene films for electronics and quantum device applications, but also expands the spectrum of topological matters into a new material species - Weyl semiconductors.</div>

Climate change is predicted to impact organismal nutritional ecology. Increased temperatures can directly accelerate physiological rate processes, which in turn, impact nutritional requirements. Climate change can also impact organisms indirectly by altering the quality and quantity of nutritional resources, creating the potential for nutritional mismatch between what nutrients are available in the environment and what organisms require. Investigation of organismal stoichiometry, particularly the balance of carbon, nitrogen, and phosphorus content of organisms, can help illuminate the extent to which changes in climate may impact organism nutritional ecology. Ants represent an excellent system to examine stoichiometry because they occur across a broad range of environmental conditions and perform important ecosystem services, such as seed dispersal, which may impact ecosystem functioning. In this thesis, I examined how climate variables influence ant stoichiometry across a broad latitudinal gradient in natural populations of three closely-related ant species in the genus Aphaenogaster. In a common garden study, I tested the extent to which such stoichiometric variation was due to plastic or evolved variation. I found significant species-specific differences in how ant stoichiometry responded to climate gradients. The northern species, A. picea contained more C, and less N and P at higher latitudes and elevation, consistent with increased winter lipid storage. In contrast, the more southern species, A. rudis, showed the opposite pattern, which may reflect N and P limitation at southern extremes. Aphaenogaster fulva, whose range is intermediate in latitude and partially overlaps with both congeners, contained more C in environments with more seasonal precipitation. Thus, these species appear to use different nutrient storage strategies in response to the variation in abiotic and trophic conditions across their range. When reared under the same feeding regime and thermal conditions, site-level differences in nitrogen storage between a northern and a southern ant population were retained over time and across years, suggesting that adaptive divergence in elemental composition is at least partially responsible for clinal patterns in the field. To connect latitudinal patterns to temporal changes projected under climate change, I evaluated how increases in temperature impact ant stoichiometry and associated functional traits at the individual and colony level using an experimental field mesocosm experiment at two sites, Harvard Forest (HF) and Duke Forest (DF). I examined how experimental increases in temperature impacted ant body size, colony demography, and nutritional status of two Aphaenogaster ant species. I found that Aphaenogaster ants at the northern site, HF, responded positively to direct increases in temperature, with increases in colony biomass, colony size, total reproductive output, and shifts toward increased nitrogen content with increases in temperature. In contrast, Aphaenogaster ants at the southern site, DF, were generally unaffected by temperature except for a decrease in maximum colony size with increases in temperature. Together, my findings provide evidence that both climate variables and evolutionary history impacts ant stoichiometry, which in turn, may impact ant colony fitness. Examination of the biochemical basis of stoichiometric trait variation is needed to ascertain the role stoichiometry may play in how ant species adapt to changing environmental conditions.

The research presented in this doctoral dissertation aimed to improve knowledge on methods to evaluate exposures to carbon-containing nanomaterials and to develop optimized respiratory filters properties to protect workers from these exposures while minimizing discomfort due to breathing resistance. In the initial study, a novel laboratory-based system generated aerosols of four carbon-containing powders (carbon black, a small-diameter (< 8 nm) multi-walled carbon nanotube (MWCNT), a large-diameter (50-80 nm) MWCNT, and a nickel-coated MWCNT) to evaluate the effectiveness of NIOSH Method 5040 for measuring masses as low as 1 μg. A targeted mass of a powder ranging from 1 to 30 μg was deposited on filters for gravimetric and elemental carbon (EC) analysis. The gravimetric mass was compared to the EC mass, and a regression model developed for each powder type. Additionally, the limit of detection (LOD) of the NIOSH Method 5040 for each powder type was determined. The regression models had significant slopes relative to zero for all powder types with all but carbon black demonstrating a statistical difference between the two methods. The LOD of NIOSH Method 5040 ranged from 4.5 for small-diameter MWCNTs to 31.8 μg for nickel-coated MWCNTs. Assuming a sample flow rate of 4.2 L/min and an 8-hour sample duration, the concentration-based LOD for NIOSH Method 5040 ranged from 2.2 μg/m3 for small-diameter MWCNTs to 15.8 μg/m3 for nickel-coated MWCNTs. These results indicate the analysis of EC is affected by the structure and elemental content of the CNTs. Additionally, based on the LOD determined for each powder type, the method may not be sufficient to assess exposures at and below the recommended exposure limit accurately without sampling durations longer than 8 hours. A second study used a laboratory-based system to evaluate an aethalometer response to carbon-containing nanomaterials including carbon black and MWCNTs. Concentrations ranging from 1 to 20 μg/m3 were generated to evaluate the device at concentrations expected in occupational settings. The concentration of the aerosol was measured by an aethalometer alongside a sample collected for EC analysis using NIOSH Method 5040. Additionally, NIOSH Method 7300 was used to determine the concentration of nickel during trials with a nickel-coated MWCNT to determine if the method along with the aethalometer can be used to assess metal-coated MWCNTs. A regression model was developed for each powder type, and the slopes for each were significant relative to zero. The LOD of the aethalometer ranged from 0.56 μg/m3 for nickel-coated MWCNTs to 7.2 μg/m3 for small-diameter MWCNTs. These results indicate the response of the aethalometer may be affected by particle structure and elemental content. NIOSH Method 5040 performed better than the aethalometer for all powder types except the nickel-coated MWCNT. Additionally, based on the LOD determined for each powder, an aethalometer may not be able to assess low-level exposures. In the third study, a mathematical model was used to predict the particle penetration and pressure drop of respirator filters with varying filter thickness, fiber diameter, solidity, and electrostatic charge. Particle penetration was determined experimentally for two different commercially available respirator filters against a sodium chloride aerosol using a scanning mobility particle sizer (SMPS). Optimized filter designs were developed using the model to minimize the pressure drop by adjusting the filter depth, fiber diameter, and solidity of the filter. The model and experimental data were used to maintain a 5% maximum penetration against nanoparticle exposures while minimizing breathing resistance. Model results indicated electrostatic charging played a significant role in improving collection efficiency of respirator filters while not increasing the breathing resistance of the filter. Filter thickness and solidity also played a key role in minimizing breathing resistance. Pressure drop decreased with decreasing solidity, however, the filter depth increased to maintain the collection efficiency of the filter. This increase in filter depth introduced a decision point of determining the practical implications of increased filter thickness on the end user. Filter depth increases dramatically as the solidity decreases below 0.20. The breathing resistance that corresponds to this design is heavily dependent on the face velocity and electrostatic charge of the filter. The electrostatic charge should be maximized during filter production as this was the dominant collection method for nanoparticle aerosols.

O Planalto de Poços de Caldas, localizado a sudoeste de Minas Gerais, é exemplo da maior intrusão alcalina ocorrida no Brasil, formada por processos de vulcanismo e intemperismo, ocorridos há cerca de 60-80 milhões de anos. Estes processos foram responsáveis pela formação de mineralizações de zircônio e molibdênio e diversas anomalias radioativas. Mais recentemente, a presença na região de várias fontes antrópicas, dentre elas o beneficiamento de urânio da Indústrias Nucleares Brasileiras Caldas, contribuíram para a inserção de vários elementos nos corpos d\'água da bacia do Ribeirão das Antas. O objetivo principal deste estudo foi fazer uso de perfis sedimentares e taxas de sedimentação para reconstituir historicamente a inserção de radionuclídeos e possíveis contaminantes na represa Bortolan e Poço Fundo ao longo dos anos. Nesses perfis foram determinados os teores dos radionuclídeos naturais U, 226Ra e 210Pb e dos elementos Mn, Mo, Ni, Zn e P por meio das técnicas de espectrometria gama, espectrometria de emissão atômica por plasma acoplado indutivamente (ICP- AES) e espectrofotometria. A taxa de sedimentação e a idade dos perfis foram avaliadas utilizando-se o modelo Constant Rate of Supply. Verificou-se que a utilização do modelo Constant Rate of Supply para a determinação das idades dos perfis forneceu resultados satisfatórios e da mesma ordem da grandeza das idades reais das represas Bortolan e Poço Fundo, 60 anos e 67 anos, respectivamente. Os valores obtidos para a taxa de sedimentação foram maiores para a represa Bortolan, devido ao assoreamento da represa, à urbanização e ocupação extensiva do solo para fins agrícolas e industriais. Analisando os resultados obtidos para a concentração dos elementos U, 226Ra, 210Pb, Mn, Mo, Ni, P e Zn, pode-se afirmar que os elementos que apresentaram contribuições antrópicas na represa Bortolan são o Mn, P e Zn. As maiores concentrações obtidas foram encontradas nas secções superficiais, indicando que o maior aporte ocorreu mais recentemente, a partir do ano de 1997. Os resultados obtidos para U e Ni não variaram ao longo dos perfis e são da mesma ordem de grandeza de dados da literatura para a mesma represa, indicando que esses valores podem ser considerados como níveis basais da região. Em particular, os resultados de concentração de U para a represa Bortolan foram elevados, visto que a região do planalto de Poços de Caldas é caracterizada por ser uma anomalia radioativa. O Mo não apresentou variação significativa ao longo dos perfis da represa Bortolan e sua concentração média também é da mesma ordem de grandeza do valor médio mundial para solo. Portanto, para esse elemento não foi verificado um aporte antrópico. Para os resultados de concentração dos elementos analisados no perfil da represa de Poço Fundo, pode-se afirmar que todos são próximos das concentrações médias mundiais e inferiores aos resultados obtidos na represa Bortolan. / The Poços de Caldas Plateau, located in the southwest of Minas Gerais, is the greatest intrusion that occurred in Brazil, formed by processes of volcanism and weathering, which occurred about 60-80 million years ago. These processes were responsible by the formation of zirconium and molybdenum mineralizations and various radioactive anomalies. More recently, the presence in the region of several anthropogenic sources, amongst them, the uranium mining from Industrias Nucleares Brasileiras - Caldas, contributed to the entry of several natural radionuclides in the water bodies of Ribeirão das Antas. The aim of this study was to use sediment profiles and sedimentation rates to reconstruct the insertion of radionuclides and possible contaminants in the Bortolan and Poço Fundo dams over the years. In these profiles, the concentration of the natural radionuclides U, 226Ra and 210Pb, and the Mn, Mo, Ni, Zn and P elements were determined by Gamma Spectrometry, Inductively Coupled Plasma - Atomic Emission Spectrometry and Spectrophotometry. The sedimentation rate and age of the profiles were evaluated using the Constant Rate of Supply. model. It was verified that the use of the Constant Rate of Supply. model to determine the ages of the sediment profiles gave satisfactory results, of the same order of magnitude of the real ages of the Bortolan and Poço Fundo dams, 60 years and 67 years, respectively. The values obtained for the sedimentation rate were higher for the Bortolan dam, due to silting of the dam, urbanization and extensive land occupation for agricultural and industrial activities. The results obtained for the concentration of the analyzed elements showed that Mn, P and Zn presented anthropogenic contributions in the Bortolan dam. The highest concentrations obtained were found in the superficial sections, indicating that the largest contribution occurred more recently, from the year of 1997 until now. The results obtained for U and Ni did not vary along the profiles and are of the same order of magnitude of literature data for sediments of Bortolan dam, indicating that these values can be considered as the base line for the region. In particular, the results of U concentration for the sediments of Bortolan dam were higher than natural background, since the region of Poços de Caldas plateau is characterized by a radioactive anomaly. The Mo did not present significant variation along the profiles of the Bortolan dam and its average concentration is also of the same order of magnitude of the world average value for soil. Therefore, for this element an anthropogenic contribution was not verified. The results obtained for the concentration of the elements analyzed in the Poço Fundo dam profile are of the same order of magnitude as the world average value for soil and lower than the results obtained in the Bortolan dam sediment profile.

Sulfide is commonly present in domestic and industrial wastewater. As it is toxic, corrosive and odorous, it often needs to be removed prior to discharge to sewer or in the sewer system itself, and certainly before discharging into the environment. The scope of this thesis was to develop and demonstrate a novel, low energy electrochemical technique for the removal and recovery of sulfide from wastewater. In addition, this study aimed to evaluate the influence of inorganic sulfur species on organics oxidation in bioelectrochemical systems. The results demonstrate that sulfide oxidation to elemental sulfur can generate net electrical power in an electrochemical system. However, while the process effectively removed the sulfide from the wastewater, the elemental sulfur was deposited on the electrodes and deactivated them over time. Sulfide removal rate decreased from its initial value 80±2% to 62±4% after 8 days of operation when a lab scale reactor operated continuously in fuel cell mode (external resistance 10 Ω) with a loading rate of 0.43 ± 0.04 kg-S m-3 d-1 of total anodic compartment (TAC). The removal rate was constant for the following 50 days of operation and significantly decreased to about 10% after 90 days. On average, the power production was 5±1 W m-3 TAC with the coulombic efficiency of 88±5% but the maximum power production capacity of the reactor was 78 W m-3 TAC using potassium ferricyanide cathode. However, the deposited sulfur could be effectively removed and recovered as a concentrated sulfide/polysulfide solution by reversing the polarity of the electrode with low electrical energy input. The results also demonstrate that microbial consortia that developed due to the organic electron donors in the wastewater, negatively affected the performance of the sulfide removal process. The microorganisms were using the electrodeposited sulfur as a preferred electron acceptor over soluble sulfate and the electrode. This process was converting sulfur back to sulfide irrespective of the electrochemical conditions. In batch systems, the sulfide produced in this way could be re-oxidized at the anode and therefore the obtained coulombic efficiency was 97±2% for acetate oxidation. However, in continuous systems, depending on the operational conditions and wastewater characteristics, the sulfide could leave the system in the effluent. By applying cell polarity reversals at a sufficiently high frequency, it was possible to avoid biofilm formation and hence the re-generation of sulfide from the deposited sulfur. To confirm the effectiveness of the electrochemical sulfide removal in real wastewater, the process was demonstrated on the effluent of an anaerobic digester of a paper mill. Sulfide was removed from 44±7 to 8±2 mg-S L-1 at a removal rate of 0.845±0.133 kg-S m-3 TAC d-1 and a recovery rate of 75±4% with the voltage input of 0.52 to 1.3 V. Periodic switching in every 24 hours intervals between anode and cathode was an effective technique to maintain a good sulfide removal performance and avoid unwanted biofilm formation at the anode. Sulfide present in the wastewater could therefore be effectively removed from the liquid phase and harvested as elemental sulfur deposit on the electrode.

<p>The Swedish government has decided that waste containing more than 0.1% mercury is to</p><p>be placed in a permanent repository in the bedrock1,10. To minimize the risk of spreading</p><p>mercury, elemental mercury must first be converted into a practically insoluble</p><p>compound. In a PhD investigation of stabilization attempts at SAKAB AB in Kumla</p><p>favorable conditions for conversion of mercury to cinnabar (the sparingly soluble sulphide</p><p>form of mercury and the naturally occurring mineral) was found. In a long-term study of</p><p>diffusion of mercury it was found that water solubility of mercury varied much, from 0.05</p><p>to 5 μmolL-1.</p><p>To be able to study the water solubility of mercury as detailed as possible a speciation</p><p>method was developed and verified. This investigation includes how different parameters,</p><p>like matrix properties and Hg0/solution ratios effects the solubility of mercury and how the</p><p>different species are distributed in the water phase. The total solubility of mercury is very</p><p>dependent of both the matrix properties and the Hg0/solution ratio.</p><p>Aqueous elemental mercury (Hg0</p><p>aq) is not as matrix dependent as the oxidized species.</p><p>However, trends show that a higher Hg0/solution ratio contributes to a higher solubility of</p><p>Hg0</p><p>aq. Factors like time, pH, ionic strength and degree of stirring, greatly effects the total</p><p>solubility of mercury. The concentration of the oxidized mercury species generated from</p><p>elemental mercury increases over time and is very dependent on the properties of the</p><p>matrix. After 18 hours the solubility of Hg0</p><p>aq ranges from 0.2 to 0.7 μmolL-1, depending</p><p>on Hg0/solution ratio. The solubility for the oxidized species has a much larger variation,</p><p>ranging from 0.1 to 28.6 μmolL-1. Among other things, because the composition and</p><p>redox potential of the matrix plays an important role in what mercuric complexes can be</p><p>expected to form, and contribute to the solubility.</p> / <p>Det har beslutats av regeringen att senast år 2010 skall kvicksilverhaltigt avfall med en</p><p>kvicksilverhalt på mer än 0.1% slutförvaras i en stabiliserad from djupt ner i berggrunden.</p><p>I en doktorsavhandling som genomförts på SAKAB AB i Kumla har det konstaterats att</p><p>det är möjligt att överföra elementärt kvicksilver till cinnober, den stabila sulfidformen av</p><p>kvicksilver som för övrigt är ett naturligt förekommande mineral. Experiment som pågått</p><p>under lång tid för att studera det elementära kvicksilvrets diffusion under olika</p><p>omständigheter har också utförts. De uppmätta halterna i vattenfasen har varierat mycket,</p><p>från 0.05 till 5 μmolL-1. Det är vad som ligger till grund för det här arbetet.</p><p>För att kvicksilvers löslighet skall kunna studeras fullt ut har en specierings metod</p><p>vidareutvecklats och verifierats att den fungerar. Studien innefattar hur lösligheten av</p><p>kvicksilver påverkas av olika parametrar, som till exempel; matriser med olika egenskaper</p><p>och olika kvicksilver/vatten kvoter, samt hur fördelningen mellan oxiderade species och</p><p>det elementära kvicksilvret är i vattenfasen (Hg0</p><p>aq). Den totala lösligheten av kvicksilver</p><p>beror dels av matrisens egenskaper och mängden kvicksilver i förhållande till mängden</p><p>vätska. Lösligheten av Hg0</p><p>aq är inte lika beroende av matrisen som de oxiderade species.</p><p>Däremot finns trender som visar att högre Hg0/lösning kvot bidrar till en aningen högre</p><p>löslighet av Hg0</p><p>aq. Tid, konduktivitet, pH och omrörning spelar stor roll för vilken</p><p>totalhalt och hur stor andel oxiderade species man får i vattenfasen. Lösligheten av Hg0</p><p>aq,</p><p>efter 18 timmar, varierar mellan 0.2 till 0.7 μmolL-1, beroende på Hg0/lösning kvoten.</p><p>Efter 18 timmar är lösligheten för de oxiderade species mycket mer varierande, från 0.1</p><p>till 28.6 μmolL-1. Detta beror bland annat på att matrisens sammansättning och redoxpotential</p><p>spelar en viktig roll för vilka komplex som kan bildas med kvicksilverjonerna</p><p>och på så sätt bidra till en ökad löslighet.</p>

<p>Poor food quality can have large negative effects on zooplankton growth and this can also affect food web interactions. The main aims of this thesis were to study the importance of different food quality aspects in <i>Daphnia</i>, to identify potentially important differences among zooplankton taxa, and to put food quality research into a natural context by identifying the importance of food quality and quantity in lakes of different nutrient content.</p><p>In the first experiment, the RNA:DNA ratio was positively related to the somatic growth rate of <i>Daphnia</i>, supporting a connection between P content, RNA content, and growth rate. The second experiment showed that EPA was important for <i>Daphnia</i> somatic growth, and 0.9 µg EPA mg C^-1 was identified as the threshold below which negative effects on <i>Daphnia</i> growth occurred.</p><p>A field survey identified patterns in the PUFA content of zooplankton that could be explained by taxonomy and trophic position. <i>Cladocera</i> enriched EPA and ARA relative to seston, and <i>Copepoda</i> primarily enriched DHA. In a whole-lake experiment, gentle fertilization of an oligotrophicated reservoir increased the seston P content and the biomass of high quality phytoplankton (<i>Cryptophyceae</i>, high EPA content). This was followed by increases in zooplankton and fish biomasses.</p><p>An empirical model based on data from a literature survey predicted that food quantity is most important for zooplankton growth in oligotrophic lakes, and that food quality factors are more important in eutrophic lakes. Thus, zooplankton growth, and energy transfer efficiency in the food web, is predicted to be highest in mesotrophic lakes. The results predict that the strength and nature of food quantity and quality limitation of <i>Daphnia</i> growth varies with lake trophic state, and that some combination of food quantity and/or quality limitation should be expected in nearly all lakes.</p>

Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2009.

<p>The aim of the project was to study the manufacturing of synthetic soda ash (sodium carbonate, Na2CO3) on an industrial scale. Currently all Soda ash that is used in South Africa for manufacturing glass is imported at a high cost, and the company Nampak Wiegand Glass (South Africa) is investigating the possibility to locally manufacture synthetic soda ash. About 75% of soda ash is synthetically produced from either the Leblanc process, Solvay process, Modified Solvay (Dual) process or dry lime process. This study concentrated on the Solvay process on a laboratory scale for eventual input into a larger pilot plant. The produced material was analyzed using analytical techniques such as FTIR (Fourier Transform Infrared spectroscopy), Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Atomic Emission spectroscopy (ICP-AES). There are certain standard requirements for impurities in the soda ash, and this needed to be measured and determined what changes to the process will bring the impurities to the required minimum standard. Environmental issues around the manufacturing process were also studied. After completing of the laboratory experiments and the extraction of required data from the results, Nampak will use the information to decide on a followup to the building of a small pilot plant to further test and develop the engineering and economical aspects of a full plant. If successful a full scale manufacturing plant can be developed in South Africa for producing soda ash.&nbsp / This study thus will not only help Nampak Wiegand Glass in finalizing the decision to go ahead, but its result will also benefit other companies that use the soda ash in oil refining, water treatment, pulp and paper, chemical industry etc. Some parts of the work done will be proprietary to Nampak and subject to confidentiality agreement.</p>

In the first phase of this project, four decades of monthly resolved geochemical variations from two massive heads of Montastraea were used to explore the reproducibility of the geochemical signal in these two corals from Looe Key, Florida. The coral d18O and d13C records of the two corals have statistically indistinguishable mean values, which is not the case for the coral Sr/Ca records implying that nonenvironmental factors are influencing coral Sr/Ca. Calibration equations relating coral geochemistry variations to environmental variations at Looe Key are different from previously published equations for Montastraea. These calibration differences are not related to growth-related kinetic effects, but may reflect variations in seawater chemistry in the coastal waters of the Florida Keys. Additional studies are needed to identify the causes of the observed geochemical variability. In the second phase of this study, fourteen decades of monthly resolved geochemical variations in another Montastraea coral from Looe Key, Florida were compared to records of sea-surface temperature (SST). Coral Sr/Ca and d18O variations have a weak relationship with variations in SST and skeletal extension rates; however, many events in the Sr/Ca and d18O records are coincident with anomalies in SST, growth, or precipitation. Strong coupling exists between Sr/Ca and d18O in both anomaly and mean annual perspectives, which reflects the combined influence of SST and growth related processes on the geochemical signal. Separating these impacts proved to be problematic due to modest agreements with each forcing variable. In the final phase of this study, geochemical records from three, mid-Holocene(~5 ka) fossil Montastraea corals from the Dry Tortugas, Florida were compared with geochemical records from modern Montastraea corals from the same region to investigate temporal changes in climate. Stable isotopic records show significant changes through time, which can be interpreted in terms of environmental variation; however, large inter-coral variability between modern specimens of Montastraea precludes meaningful assessment of Sr/Ca. The pattern and mean d18O values in the fossil corals reflects changes in both temperature and salinity are reminiscent of centennial-scale variability present in other records from this region.