No description available.

Earth’s climate system has experienced significant changes throughout its history. Tropical, glacial and interglacial conditions have persisted across the globe during the Tertiary, and the present interglacial period with strong seasonality and episodes of warming and cooling has existed for the last several thousand years. However, rapid warming during the last century has highlighted the importance of understanding past climate behaviour, in order to predict the likely effects of such warming on our future climate. This has led to the use of proxies, such as sediment cores, tree rings, ice and carbonates, which provide high resolution palaeoclimate archives. Studies using a variety of proxies from around the globe have developed a network of site specific climate information, offering insights of climate fluctuations on a millennial scale, and identifying changing oceanic conditions as a major influence on global climate change. Coral skeletons are particularly sensitive recorders of ambient seawater conditions as they record fluctuations of oxygen and carbon in their aragonitic skeletons, which are caused by perturbations of sea surface temperature (SST) and sea surface salinity (SSS). Therefore, tropical oceans themselves provide a crucial record of climate change. Many of the coupled atmospheric-oceanographic processes that drive the global climate system occur in the Indo-Pacific, making it a particularly important region for data collection. Porites corals from the Indo-Pacific have been studied in detail and have revealed high resolution SST and SSS records, yet comprehensive investigations using other coral species are minimal. This study expands upon the current understanding of coral proxies by investigating three coral species of different ages, and provides new insights into the palaeoclimate history of the Indo-Pacific. Goniastrea retiformis, Platygyra pini and Platygyra lamellina corals have been retrieved from Timor Leste in the Indo-Pacific, and analysed using stable and radiogenic isotopic techniques. Sclerochronology was used to determine that the 4.5 year old, modern G. retiformis coral was living from 2006-mid 2010. Uranium-thorium (U/Th) analysis provided a mid Holocene age of 4.5 ± 0.092 (2σ) ka for the fossil P. pini. Uranium-lead (U/Pb) techniques were used to obtain a 2.7 ± 0.34 (2σ) Ma age for the fossil P. lamellina. A rigorous diagenetic screening process of X-ray diffraction (XRD), petrographic analysis of thin sections, and scanning electron microscopy (SEM) has been carried out to ascertain the extent of preservation in each coral. X-ray images allow annual density bands to be located and unique micromilling paths were developed for the three samples. This enabled us to obtain the first δ¹⁸O and δ¹³C stable isotope results for a G. retiformis coral, and the first fossil coral results for the Platygyra genus. Cross spectral analysis has been used to verify the periodicity of seasonal fluctuations visible in the data, and confirmed that these coral species are suitable for use as climate proxies. G. retiformis is an abundant reef coral distributed throughout the tropical Pacific, and has a robust skeletal configuration making it suitable for use as a climate proxy. The 4.5 year long record has revealed that δ¹⁸O and δ¹³C values range from -4.62‰ ± 0.03‰ (2σ) to -6.11‰ ± 0.02‰ (2σ), and 1.57‰ to -2.53‰, with means of -5.35‰ and -1.02‰, respectively. These values are in agreement with the average δ¹⁸O range of -5.1 to -5.6‰ in modern corals throughout the Indo-Pacific, predominantly of the Porites genus. Statistical analysis of the isotopic data has revealed a quasi-biennial signal in G. retiformis, typical of the temporal interaction between El Niño Southern Oscillation (ENSO) and the South Asian monsoon. Results have also been compared to the Southern Oscillation Index (SOI) in order to assess potential relationships between coral isotopes and ENSO. This has shown an accurate record of El Niño and La Niña events for the first half of the ~ 4.5 year record, from 2006 to mid 2008. Climate processes such as local rainfall and the Indian Ocean Dipole (IOD) are also reflected in the record, to varying extents. The use of Platygyra corals as climate proxies is limited to three investigations using modern samples, despite the fact that this genus has a much broader latitudinal range than the extensively studied Porites genus. This thesis provides the first examination of fossil samples, and provides analysis of both pristine and altered specimens. The 4.5 ka P. pini coral has allowed investigation of the palaeoclimate record in a sample that has been exposed to diagenesis. XRD, petrographic and SEM analyses have revealed widespread secondary aragonite growth, dissolution and secondary calcite within the coral, which would have occurred due to marine and freshwater diagenesis. However, primary growth textures have been retained in some areas of the coral. δ¹⁸O and δ¹³C values range from -3.47‰ ± 0.03‰ (2σ) to -5.45‰ ± 0.02‰ (2σ), and 3.43‰ to -0.49‰, with means of -4.82‰ and 1.12‰, respectively. These values are significantly more positive that the mean δ¹⁸O of four Platygyra corals from the Pacific region, which range from -4.82‰ to -5.10‰. There are two reasonable explanations for this. Secondary aragonite, which is detected throughout the milled section of coral, causes positive shifts in coral δ¹⁸O, an effect which is likely to have altered the geochemical record of this particular coral. But the fact that SST in the southern Indo Pacific Warm Pool (IPWP) during the mid Holocene were 1.2° C cooler than present must also be acknowledged, as cooler temperatures also impart a shift toward higher δ¹⁸O, due to equilibrium fractionation processes. SST reconstruction using the temperature dependence equation from a modern Platygyra coral reveals an SST range of 18.5-27.6° C, and mean of 24.7° C. The present day mean annual SST of 28° C suggests that mid Holocene temperatures less than 26.8° C are unrealistically cool, highlighting the fact that isotopic fractionation during diagenesis has affected coral chemistry. However, the presence of interannual periodicity indicates that ENSO was operating, and the magnitude of isotopic fluctuation through the 10 year record is similar to that found in modern and other Holocene corals. We suggest that although absolute isotopic and SST values are unreliable, prohibiting the extraction of high resolution climate records, insights into the behaviour of broad scale, seasonal and interannual climate processes may still be obtained. A strong annual periodicity has been detected when analysing the stable isotopic values recorded in the 2.7 Ma P. lamellina coral. This indicates that seasonal SST fluctuations were the dominant influence on this coral. Ranges of -4.67‰ ± 0.03‰ (2σ) to -5.48‰ ± 0.02‰ (2σ) and 0.88‰ to -1.12‰ for δ¹⁸O and δ¹³C, respectively, are similar to modern Platygyra coral results, suggesting that this coral has been preserved in pristine condition. Palaeo-SSTs have been reconstructed using a modern Platygyra temperature dependence equation, providing a range of 24-27.7° C and a mean of 25.9° C. Foraminiferal data from sediment cores in the greater Indo-Pacific suggest that mean annual SSTs at this time were ~ 2-3° C cooler than present. The coral record I present supports this statement, providing new insights into our understanding of tropical palaeoclimates. This coral has been entrained within a turbidite deposit on the sea floor that has subsequently been uplifted during the emergence of Timor, with U/Pb dating allowing further constraints of the stratigraphic age of the deposit. Tectonic narrowing is postulated to have caused major changes to the Indonesian Throughflow (ITF) from 4-2 Ma, and been a driver of major global climate change beginning in the late Pliocene. This means that fossil Platygyra corals Timor Leste could provide unique time slices of information about this important time in global climate history. This study confirms that G. retiformis, P. pini and P. lamellina corals are excellent candidates for further, detailed investigations. They provide the opportunity to develop new coral proxies which are both abundant throughout the tropics and distributed over a wide latitudinal range. Their prevalence in both modern and fossil reefs means that once modern samples of each species have been calibrated against modern SST and SSS, these corals will provide reliable, quantitative palaeoclimate proxies, with potential for data capture throughout the Indo-Pacific and mid latitudes. Geochemical coral archives are a crucial tool in the study of climate processes, and we believe that these species are ideally suited to enhancing and refining our current understanding of earth’s climate system.

Thesis (Ph. D.)--University of California, San Diego, 1998. / Vita. Includes bibliographical references.

Tree-rings are natural archives of the climate variation experienced by trees during their life span. Because trees actively discriminate against 13C versus 12C in atmospheric carbon dioxide due to environmental forcing inducing higher assimilation of 12C in optimal conditions for growth, the ratio between these two isotopes represents a record of climate variability occurring at the time of the wood formation. Therefore, the delta13C can be used to reconstruct palaeoclimate from when the trees sampled were living. As the instrumental period from meteorological methods to measure climate is relatively short (last 150 years), the calibration between delta13C time series and climatic data can be used to improve the understanding of climate variability through longer periods. The main objective of this study is to produce a consistent methodology for the reconstruction of climate and environmental forcing on trees from the high resolution delta13C time series over the period 1997-2009 at three study sites in Europe where extensive eddy covariance measurements have been conducted. This atmospheric measurement technique permits a very fine resolution to observe the exchange of gases between the atmosphere and a land surface with additional applications in meteorology. At Hyytiala, dendrometer and microcore measurements were used to test if a methodology can be developed to predict the occurrence of radial growth during years when dendrological data are missing. The modeling of the intra-annual rate of growth is then performed via the Gompertz equation. Integration of cell life time to match climate information with time delta13C series is also assessed. The delta13C signature from both inter- and intra-annual resolution are tested against three weather variables: photosynthetically active radiation, temperature and precipitation. The results show stronger linear responses from the delta13C time series of the most northern site (Hyytiala, Finland) to the weather variables while the two other study sites (Norunda, Sweden and Loobos, the Netherlands) did not show significant linear relationships at both annual and intra-annual resolution. The approach developed in this study represents a first step in developing a generic method accessible for non-specialists in dendroclimatology for the use of delta13C time series as climate archives.

A stalagmite was collected in the Salón de la Permencia of the Majaguas Cave, that is a part of the Majaguas-Cantera Cave System in Cuba. The use of this stalagmite as a natural climate archive is advantageous not only because stalagmites can record continuous episodes of growth that are thousands of years in duration but also because they are easily and reliably dated, using U/Th dating methods. With this method, the stalagmite was reliably dated to 100 ka and was still active when removed from the cave for analysis. The stable isotopes of oxygen and carbon from this stalagmite from Western Cuba presents information of significant influencing factors on Caribbean precipitation records, and past climatic events during the Pleistocene. Due to the lack of high- resolution records for Western Cuba, this study verifies and adds to our knowledge of past climate variability for the Cuban region and the Caribbean as a whole. The δ18O data in MCS-01 shows a pattern that is very similar to the D-O and Heinrich events clearly recorded in the NGRIP ice core, especially at ~82ka and between 78-70ka. This study provides a continuous precipitation record for the area during the Pleistocene, allowing a greater understanding of the climate drivers that have had an impact on past precipitation patterns in this region.

Through stable isotope analysis of human tooth dentine, this thesis investigates breastfeeding and weaning patterns in relation to rickets in a sample of sub-adults (n=12) interred in the nineteenth century sub-adult cemetery located at the Church of the Trinitarias in Madrid, Spain. The main objectives of this research are to create early life feeding histories for each individual using dentine serial sectioning techniques and apply these histories to investigate the relationship between breastfeeding, weaning, and vitamin D deficiency. The early life feeding histories allows for the determination of the onset and complete age of weaning at an individual level. These stable isotope data are then used to estimate general trends in breastfeeding and weaning practices in nineteenth century Spain. The results of this study indicate that the onset age of weaning for most of the individuals in this sample was between 10 and 14 months of age. The age at which breastmilk consumption stopped entirely was more difficult to estimate, however, in individuals that did show evidence of completed weaning, it was estimated to occur around the age of three. These ages are slightly higher than those discussed in historical sources for nineteenth century Spain. When these results are compared to contemporaneous, more industrialized, European countries the comparison shows that the initialization of weaning occurred slightly later and was a more gradual process in this Spanish sample. The results also demonstrate that there is no direct relationship between weaning patterns and the occurrence of skeletal vitamin D deficiency. It may be that the high prevalence of vitamin D deficiency is linked with the nuances of breastfeeding and other biocultural variables, such as a lack of sun exposure, an inadequate weaning diet, or childcare practices. / Thesis / Master of Arts (MA)

Yes / Here we present a novel method which allows the measurement of the stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) from much smaller samples of dentine than previously possible without affecting the quality parameters. The reconstruction of the diet of past populations using isotopic analysis of bone collagen is a well-established tool. However, because of remodelling of bone throughout life, this gives a blurred picture of the diet. The analysis of δ13C and δ15N from tiny increments of dentine utilizes tissue that does not remodel and permits comparison, at the same age, of those who survived infancy with those who did not at high temporal resolution. This new method has been tested on archaeological teeth from two sites: three molar teeth from the 19th Century Kilkenny Union Workhouse Famine cemetery, Ireland; and three from the Anglian (5-7th centuries AD) cemetery at West Heslerton, Yorkshire, England, selected on the basis of their varied preservation. The methods of incremental dentine sectioning described in Beaumont et al (2013)[1] were carried out and a sub-section removed prior to denaturing and lyophilisation. The two sample sets, dentine and collagen from each section, were measured by isotope ratio mass spectrometry. The profiles produced from each of the six teeth studied show close correlation in isotope ratios indicating that demineralized dentine which has not been denatured and lyophilised produces isotope ratios comparable with dentine collagen. This finding allows analysis of extremely small samples of dentine which could previously not be measured using current instruments and methods.

Lizard ecology through time is largely unknown. Understanding ecology is important because of today’s drastic climate change, but this is not a unique event. Early Cenozoic hyperthermals were comparable to the perturbations currently experienced by living species. Understanding ecology through time must acknowledge the dynamic relationship between an organism and its environment on multiple scales. Ecological inferences can be based on form equaling function, correlating certain features (e.g. leaf-shaped dentition) with certain behaviors (e.g. herbivorous diet). Though this applies to specific taxa, there are confounding examples. Ecology can also be inferred through indirect means, but these are disconnected from the taxon of interest. Stable isotope geochemistry, however, provides an independent test. I analyzed stable isotope ratios (δ¹⁸O, δ¹³C) from enamel, providing new data on the connection between morphology, diet, and environment. I find a trophic separation in δ¹³C, and indications of aridity through δ¹⁸O. I applied this framework to extinct lizards from an Early Eocene (Wa4) assemblage, a key time between two major global warming events (Paleocene-Eocene Thermal Maximum and Early Eocene Climatic Optimum). I identify xenosaurid and glyptosaurine squamates and alethinophidian snakes. The xenosaurid is one of the youngest representatives of Restes rugosus, and I provide the first testable hypothesis of its ecology. These δ¹⁸O values corroborate hypotheses of a wet, tropical environment, and the δ¹³C values indicate an insectivorous or carnivorous diet for both taxa. My study provides an independent test of ecology of both extant and fossil lizards, with implications for differing survivorship throughout the early Cenozoic. / MS / We know little about the diet and habitat of lizards. We have a limited knowledge of these characteristics in living species, but these represents a fraction of the total number of all lizard species that have ever lived. There are several ways to try to understand the ecology of an animal. We can observe it directly, we can infer things about it from comparisons to other living species, or we can make inferences through indirect proxies. All of these methods have their limitations, however. I am interested in how lizard ecology changes through geologic time as preserved in the fossil record. This requires understanding the ecology of extinct lizards. For my thesis, I quantified ecology using stable isotope ratios in both living and extinct lizard species. Through my analyses, I was able to differentiate their diets and habitats. My examination of lizard fossils from ~54 million years ago identifies two lizards and one snake, and analyses of the fossil lizards indicate they were carnivorous or insectivorous and lived in a tropical climate. These stable isotope analyses not only have the potential to infer diet and habitat, but also track illegal pet trade and determine if an organism is warm or cold blooded.

Floodplains are among the most productive and biologically diverse freshwater ecosystems on earth. The exchange of nutrients and biota that occurs within these systems during seasonal inundation is essential in maintaining floodplain and river health. Anthropogenic structures, such as weirs, channels, and dams, have altered the natural flood hydrology of floodplain systems minimizing the frequency, strength and duration of flood events. This reduction ultimately leads to the isolation of important floodplain habitat, such as off-channel lakes, from the main channel, decreasing connectivity. Although some studies have examined the productivity of off-channel floodplain lakes in relation to connectivity, most are limited to tropical or highly degraded systems. Northern floodplains are not as well understood, with most of the research limited to the spring, summer, and fall seasons, when waterbodies are free of ice. With research limited to ice free seasons, there is not a full understanding of the year-round processes that occur within these off-channel lake habitats. This knowledge is crucial as the winter season is often when conditions within these habitats are at their most extreme. Such conditions prevent many fish species from permanent settlement; however, no research has been attempted to understand fish presence within these habitats during the winter season. In tropical systems, hypoxia-tolerant species and juveniles utilize these habitats as refuge from intolerant predators, so such habitat may be used similarly in more northern systems. The purpose of this research was to understand the connectivity, limnology and suitability as fish habitat of off-channel floodplain lakes in the Saskatchewan River Delta (SRD), SK, during winter months. I determined the degree of connectivity to the main channel for 26 individual lakes within the SRD by two modern methods: remote sensing imagery, and stable isotopes (δ18O, δ2H). Both of these techniques proved effective at determining connectivity of individual lakes and showed good agreement, with lakes arranged into five connectivity categories using remote sensing imagery. Winter limnological conditions within these lakes were significantly influenced by their degree of connectivity, with lakes that were more connected having characteristics similar to that of the river, with higher levels of dissolved oxygen (DO), nitrates (NO3-NO2), pH, and lower levels of nutrients (TN,TP). Lakes that were less connected were characterized by low levels of DO and nutrients, and high levels of ammonia/ammonium (NH3-NH4), conditions that are not favourable for the survival of many fish species. Some of the more hypoxia-tolerant species found within the SRD appear, however, to use these habitats in the winter. This was supported by detection of fish presence using environmental DNA; five fish species were detected in many of the 26 lakes sampled, but only in lakes with NH3-NH4 levels below 1.77 mg/L and volumes greater than 178000 m3. Together, these analyses suggest the influence of a spring/summer flood pulse on limnology is not limited to the months following a flood event, but rather extends well into the ice-cover season. This knowledge is critical as it points to controls on key processes (e.g. nutrient cycling, provision of fish habitat) during the period when lake conditions are most severe. As a result of human induced climate change, and from increased water demands for agriculture and hydropower, the natural flood pulse is expected to further decrease in size and frequency in large river-wetlands such as the SRD. This will reduce the connection between the floodplain and the main channel, with profound impacts on the SRD ecosystem as a whole. Lakes that currently experience frequent inundation will likely have conditions characteristic of infrequently flooded lakes, with low DO and nutrients and high NH3-NH4. Lakes which currently experience infrequent inundation will likely dry up completely due to decreased water renewal.

The high sensitivity of high latitudes to global climate changes is the stimulus for the study of ancient Arctic ecosystems under greenhouse conditions. With an increasing number of studies, including the most recent Intergovernmental Panel on Climate Change (IPCC) report highlighting Pliocene climate as key example for the study of Earth system sensitivity to higher levels of atmospheric CO₂, the need for accurate proxy records for this period is crucial. In order to investigate Pliocene climate, I used stable isotopic studies of fossil molluscs, moss and wood from two fossil forest deposits in the Canadian High Arctic. Temperatures were determined for an Early Pliocene (4-5 Ma) fossil forest site located on Ellesmere Island using 'clumped' and stable isotopic analysis of mollusc shells and stable isotope values of fossil wood. Mollusc inferred growing season (May-Sept) temperatures derived using two independent techniques were estimated to be 11-16° C warmer than present (1950-1990) Ellesmere Island temperatures. Tree ring inferred growing season (June-July) temperatures (JJ) were 10-16° C and mean annual temperatures (MAT) were 18-20° C warmer than present (1950-1990). Mean annual and growing season (JJ) temperatures were also determined using fossil wood from a younger (2.4-2.8 Ma) late Pliocene-early Pleistocene site on Bylot Island. This deposit represents the remains of a flora that grew during an interglacial warm period during the transition to large-scale Northern Hemisphere glaciation that occurred between 2.5 to 3 million years ago. Mean annual temperatures were ~12° C and growing season temperatures were ~13° C warmer than present (1923-2010). The interglacial setting of the Bylot Island site and the warm temperatures suggests that prior to using such sites as true analogues of future conditions we may need to consider how close the feedbacks operating then were to the feedbacks we might expect in the future. However, that temperatures so much warmer than present existed in the high Arctic during a period when levels of atmospheric CO₂ were at nearpresent levels indicates that we may be moving beyond our ability to use the Pliocene as an example of the future.