Large discrepancies remain regarding the timing of Cenozoic paleoclimatic and paleoenvironmental transitions in the central Asia. The first order driving force behind these changes has been intensively debated. Global climate change, the uplift of Tibetan Plateau, and the evolution of Paratethys sea have been proposed as three major candidates. To understand the evolutionary history of climate and environment of the region and controlling factors responsible for these paleoclimatic and paleoenvironmental changes, a combined study utilizing multiple proxies, including microfossils, bulk carbonate carbon and oxygen isotopes, long chain alkenones, plant n-alkane-based indices (carbon preference index, average chain length and Paq) and compound-specific carbon and hydrogen isotopes of higher plant n-alkanes, was carried out on a long, continuous and well-dated section in Dahonggou, Qaidam Basin, northern Tibetan Plateau. A parallel study was also carried out in another relatively shorter section in the Xunhua Basin, northern Tibetan Plateau. Six intervals of paleoclimatic and paleoenvironmental transitions over an interval of ~35 Myr can be recognized in the studied sections, including Late Eocene-Early Oligocene gradual drying (prior to ~30 Ma), Middle Oligocene aridification (~30-26 Ma), Late Oligocene-Early Miocene wetting (~26-21 Ma), Early Miocene drying (~21-17 Ma), Middle Miocene climatic optimum (~17-13 Ma), and deteriorated climate since the late Middle Miocene (~13 Ma onwards). The reconstructed onsite C4 plant abundance including occurrence of C4 plants and their thriving and the followed decreasing, a sensitive indicator of available moisture level in the environment, agrees well with these intervals. Microfossils and long-chain alkenones suggest that a relic sea existed in the Qaidam Basin during the Middle Miocene, thus falsifying any hypothesis of significant variations in elevations of northern Tibetan Plateau prior to the Middle Miocene. The relatively stable elevations since the Eocene and before the Middle Miocene of, respectively, the central-southern part and northern part of the Plateau reveals an insignificant role of Tibetan Plateau uplift in controlling the evolution of central Asian climate and environment during the early Cenozoic. However, the Middle Miocene marine transgression and the rapid plateau-scale uplift since the late Middle Miocene probably contributed to the Middle Miocene climatic optimum and the initiated aridification afterwards in the central Asia. A comparison of proxy records in the northern Tibetan Plateau with the global benthic oxygen isotope record suggests a tight relation between the climatic/environmental transitions in the central Asia and global climatic changes. This lends support to the hypothesis that global climate, by controlling the moisture supply to the continental interior, played the dominant role in the evolution of climate and environment of central Asia during the Cenozoic time. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

The flux of carbon in to and out of the atmosphere exerts a fundamental control over the Earth's climate. The oceans contain almost two orders of magnitude more carbon than the atmosphere, and consequently, small fluctuations within the oceanic carbon reservoir can have very significant effects on air-sea CO₂ exchange, and the climate of the planet. Pelagic carbonates represent a major long-term flux of carbon from the surface ocean to deep-sea sediments. Within sediments, the biologically produced carbonates act as a longterm carbon store, but also as chemical recorders of past surface ocean conditions. Counterintuitively, despite the production and sedimentation of carbonate acting as a CO₂ sink, over periods shorter than the mixing-time of the ocean, the pH change associated with calcium carbonate precipitation enriches the surface waters in CO₂ and elevates the equilibrium value of gaseous exchange with the atmosphere. Coccolithophores, ubiquitous marine photosynthetic plankton, produce calcium carbonate plates, coccoliths, which account for around one third of all marine calcium carbonate production. Sedimentary coccoliths therefore represent a valuable repository of surface ocean geochemical data, as well as a very significant carbon-cycle flux. This thesis examines how the mass of calcium carbonate produced by coccolithophores has changed in response to rising levels of atmospheric CO₂. A -40% increase in average coccolith mass over the last 230 years, paralleling anthropogenic CO₂ release, is demonstrated within a high-accumulation rate North Atlantic sediment core. Additionally, a flow-cytometry method is presented, which enables the automatic separation of coccoliths from clay particles in sedimentary samples, representing the first step in a coccolith cleaning procedure, which should ultimately enable down-core measurements of coccolith trace-element/calcium ratios. Complementing this work I describe results from continuous dissolution analysis of cultured coccoliths which allows a first-order evaluation of trace-element partitioning into coccoliths produced by the species Coccoliths pelagicus, and present a conceptual methodology to allow the determination of single-species coccolith chemical data.

This thesis provides an analysis of the diminishing sea ice trend in the Arctic Ocean by examining the NPS 1/12-degree pan-Arctic coupled ice-ocean model. While many previous studies have analyzed changes in ice extent and concentration, this research focuses on ice thickness as it gives a better indication of ice volume variability. The skill of the model is examined by comparing its output to sea ice thickness data gathered during the last two decades. The first dataset used is the collection of draft measurements conducted by U.S. Navy submarines between 1986 and 1999. The second is electromagnetic (EM) induction ice thickness measurements gathered using a helicopter by the Alfred Wegener Institute in April 2003. Last, model output is compared with data collected by NASAâ s ICESat program using a laser altimeter mounted on a satellite of the same name. The NPS model indicates an accelerated thinning trend in Arctic sea ice during the last decade. The validation of model output with submarine, EM and ICESat data supports this result. This lends credence to the postulation that the Arctic not only might, but is likely to be ice-free during the summer in the near future.

Tree-ring records from long-lived trees are instrumental for understanding climate variability during the Common Era. Some of the oldest and most valuable conifers used to reconstruct past climate exhibit strip-bark morphology, in which vertical segments of the tree have died in response to environmental stress. This form of localized stem mortality, also referred to as partial cambial dieback, is particularly common on conifers growing in xeric, cold, or exposed environments. Some studies note that strip-bark trees have increasing ring-width trends relative to trees with a fully living stem circumference, but there is substantial uncertainty as to what extent partial cambial dieback can influence tree-ring records and subsequent climate reconstructions. This dissertation explores the environmental drivers of partial cambial dieback on Siberian pine (Pinus sibirica Du Tour) from Mongolia, the effect of cambial dieback on the radial growth and physiology of affected trees, and methods for reducing strip-bark biases in tree-ring records. Chapter 1 assesses the causes and radial growth impacts of partial cambial dieback on Siberian pine trees growing on an ancient lava flow in central Mongolia. Using a combination of field observations and dendrochronological methods, this chapter demonstrates that strip-bark trees from this site exhibit dieback primarily on the southern side of stems, and that dieback was most common during a cold and dry period in the mid-19th century. Given the directionality and timing of dieback on these strip-bark trees, it is hypothesized that localized mortality events are linked to physiological injuries spurred from solar heating combined with unfavorable climatic conditions. This chapter also reveals that strip-bark trees from this site have increasing radial growth trends relative to trees with a full circular morphology (“whole-bark” trees). Strip-bark trees showed an especially rapid increase in ring widths following the cambial dieback period in the mid-19th century, providing initial evidence that dieback events can lead to increasing ring widths in strip-bark Siberian pine. Chapter 2 seeks to discern the physiological mechanisms of increasing radial growth trends in the Siberian pine strip-bark trees using stable carbon and oxygen isotopes from tree rings. One simple hypothesis is that strip-bark trees show increasing ring-width trends because radial growth is restricted to a smaller stem area after cambial dieback events. Conversely, some studies have hypothesized that increasing ring widths in strip-bark trees reflect a CO2 fertilization effect on growth that is not readily apparent in whole-bark trees. This chapter finds that strip-bark and whole-bark trees responded similarly to increasing atmospheric CO2 and climate variability in their radial growth and leaf-level gas exchange inferred from tree-ring stable isotopes. However, strip-bark and whole-bark trees showed notably different behavior following documented cambial dieback events. After dieback events, strip-bark trees exhibited an increase in ring widths and an enrichment in stable carbon and oxygen isotopes that was not apparent in whole-bark trees. These results further support the notion that partial cambial dieback leads directly to increasing ring widths in strip-bark trees, and that this response could reflect an increase in the ratio of leaf to live stem area after dieback occurs. Chapters 1 and 2 demonstrate that partial cambial dieback events and morphological changes impact the radial growth and physiology of strip-bark trees. Therefore, prior to developing climate reconstructions, it is necessary to remove variance associated with these non-climatic, morphological changes in tree-ring series. Chapter 3 outlines two chronology development methods for reducing strip-bark biases in tree-ring records. These methods, applied to Siberian pine and Great Basin bristlecone pine (Pinus longaeva Bailey), successfully reduce a strip-bark bias without removing low-to-medium frequency climate variance inferred from whole-bark trees, which were not impacted by dieback activity. While one approach directly corrects the bias in strip-bark series using a whole-bark chronology as a target, another method is based on the development of a low-percentile chronology, which can be applied to a site collection where the stem morphology of individual trees is unknown. Some limitations and caveats of these methods are discussed in context of the analyzed tree species. The findings from this dissertation have significantly contributed to our understanding of the radial growth and physiological responses of Siberian pine to partial cambial dieback and environmental changes. This dissertation also provides new methods for removing strip-bark biases in tree-ring chronologies. The conclusions presented here have important implications regarding the potential effects of partial cambial dieback on tree-ring records from other tree species and climate reconstructions derived from them. Continued and detailed study of the causes and impacts of partial cambial dieback on other tree species will be critical for understanding the interactions between ancient trees and their environment, and for improving the reliability of climate reconstructions based fully or partly on strip-bark trees.

A dissertation submitted in the fulfilment of the requirements for the degree of Masters of Science (MSc) (Geography Archaeology and Environmental Studies) Faculty of Science. University of the Witwatersrand. Johannesburg, March 2016. / The southern African sardine run is an annually recurring phenomenon involving vast schools of sardines travelling northwards along the east coast of South Africa. Climate change is assumed responsible for recently observed changes in the occurrence of sardine runs, yet data have been absent to quantify any phenological changes over time. The National Library of South Africa has extensive archives of Kwa-Zulu Natal based newspapers which were scrutinized to determine the annual arrival of sardines at specific places along the east coast between 1946 and 2012. In particular, ‘The Natal Mercury’, ‘South Coast Herald’ and ‘South Coast Sun’ newspapers were consulted. This yielded an uninterrupted sardine run record spanning 66 consecutive years. This is the first such study examining historical fish phenology in the southern Hemisphere. A variety of environmental conditions is thought to influence the sardine runs and may include, oceanic temperatures, oceanic currents, visibility of the water, wind speed/direction and air temperature. We thus also demonstrate historical climate variability and change along the east coast for the period between 1936 and 2012, based on data obtained from the National Oceanic and Atmospheric Administration (NOAA) and the South African Weather Service. In particular, we examine the parameters: temperature, wind, the occurrence of westerly wave disturbances (i.e. cold fronts), the El Nino Southern Oscillation, and the Southern Oscillation Index. The sardine run data are then compared against the various climate parameters to ascertain which variables most influence their phenology. It is found that the sardine runs have become more temporally delayed during recent years, particularly since the late 1960s/early 1970s, and may be associated with considerable increases in Sea Surface Temperatures (SST) since that time. / TG2016

Climate change education, at both primary and secondary school levels, has been recognised as a key approach through which to enhance the knowledge and understanding of climate change among learners. The success of climate change education is largely dependent on the resources through which learners acquire knowledge of climate change, namely teachers and textbooks. This two dimensional study investigates FET geography teachers’ knowledge and perceptions of climate change, and provides a critique of the geography textbooks used most frequently by these teachers in climate change education. To investigate teachers’ understandings of climate change, the study employed a qualitative non-experimental research design, which encompassed semi-structured interviews conducted with 32 geography teachers in Gauteng province, South Africa. A number of key inconsistencies, misconceptions and gaps were found to exist in teachers’ knowledge and perceptions of climate change. The value of the nine FET level geography textbooks for climate change education was assessed, and critiqued using a classification process based on criteria developed by the researcher. This assessment revealed a number of shortfalls in the textbooks’ provision of relevant, accessible and accurate information on climate change. It is important that these flaws and shortfalls in both teachers’ knowledge and textbooks representations of climate change are rectified as they are likely to have implications for the ultimate success of climate change education in schools.

No description available.

No description available.

Global climate change is expected to increase the frequency of extreme and unpredictable weather in many parts of the world. As a result, a critical goal for biologists is to predict how organisms may come to cope with increased environmental variability. The key to making these predictions will be to understand how animals currently living in fluctuating environments are able to survive and reproduce under these conditions. Sociality (i.e. group living) and cooperative breeding (i.e. where more than two individuals care for young together) may both facilitate the colonization of highly fluctuating environments. However, the relative benefits of group living and engaging in alloparental care under variable conditions remain unclear. My dissertation examines the fitness consequences of living in one of the world’s most unpredictable habitats—the African savanna—in a population of free-living cooperatively breeding superb starlings (Lamprotornis superbus). In chapter 1, I examine whether adults benefit from living in large social groups of up to 50 individuals, which are among the largest known for any cooperatively breeding bird. In addition, I test whether group size serves to buffer against harsh environmental conditions. In chapter 2, I examine whether breeders gain reproductive benefits by having alloparents at their nest—I explore the type of reproductive benefits gained (i.e. improved reproductive success versus offspring care load-lightening), as well as whether these benefits occur in both harsh and benign conditions (i.e. temporal variability hypothesis), or are greatest under harsh conditions only (i.e. hard life hypothesis). In chapter 3, I explore whether offspring care load-lightening reduces the cost of reproduction incurred by breeders and alloparents by comparing four physiological mechanisms known to mediate reproductive costs. Lastly, in chapter 4 I test the long-standing assumption that cooperatively breeding species face reduced costs of reproduction by sharing offspring care relative to non-cooperatively breeding species. I compare the oxidative cost of reproduction in superb starlings to greater blue-eared glossy starlings (L. chalybaeus), a synoptic non-cooperatively breeding species. Taken together my dissertation findings demonstrate that group living and alloparental care do not solely buffer against harsh conditions in superb starlings, but instead provide individuals with the flexibility to modify their offspring care behavior according to environmental conditions, to the behavior of other group members, and to their physiological condition prior to breeding—this behavioral flexibility may in turn serve to mitigate fluctuations in the cost of living and breeding in variable environments.

The impact of the Madden Julian Oscillation (MJO), a major source of intraseasonal variability in the tropical atmosphere, on the Indonesia Seas is investigated using satellite-derived, reanalysis and mooring data. The MJO footprint on the Indonesian Seas is evident from the surface layer into the pycnocline. In the surface, MJO air-sea heat fluxes govern the intraseasonal sea surface temperature (SST) variations. Within the pycnocline, the MJO reduces the transfer of the Pacific water to the Indian Ocean, the Indonesian Throughflow (ITF). In addition to the ocean’s response, the oceanic feedback to the MJO is also examined. Warmer SST in the Indonesian Seas during the suppressed phase of the MJO promotes the MJO convective phase to propagate eastward over the maritime continent (MC). Intraseasonal SST variation accounts for 55 - 60% of the total non-seasonal SST variance across the Indonesian Seas. It is most energetic in Banda and Timor Seas, with its standard deviation varying between 0.4 – 0.5°C. Coupled to the MJO surface fluxes, the intraseasonal SST exhibits stronger variation in boreal winter than in summer. A slab ocean model indicates that MJO surface heat fluxes account for 69-78% of the intraseasonal SST variability. The SST increases by 1.1° - 2°C, on average, in response to intense surface heating and weak winds over the suppressed (dry) MJO phase, and then decreases by 1.8° - 2.1°C over the course of the ensuing MJO active phase that is characterized by enhanced convective cooling and westerly wind bursts. Intraseasonal variability is also significant in the Sulawesi Sea SST, but it is mostly derived from eddies and local winds. Over the period 1980 - 2012, we observe 86 significant MJO (Real-time Multi variate MJO index > 1) events occurring in the Indian Ocean, of which 51 events achieve eastward propagation (EP) over the MC, while 35 events attentuate in the eastern Indian Ocean, or show no propagation (NP) over the MC. Eastward propagation (EP) MJO events occur more frequently during La Niña years than during El Niño years. Analyses of SST across the Indonesian Seas during the suppressed phase of the MJO events indicate that the SST in Java, Banda, and Timor Seas attributed to the EP MJO events is warmer by 0.5oC that associated with the NP MJO events. The warmer SST corresponds with enhanced surface latent heat flux, sensible heat flux, and low-level moisture in the atmospheric boundary layer, driven by diurnal activity. The EP MJO events are more frequent during La Niña, as the SST response to MJO events is influenced by the thermocline depth: shallower thermocline during El Niño enables cooler subsurface water under the MJO forcing to reduce SST that then attenuates MJO activity, with deeper thermocline of La Niña having the opposite outcome. Moored velocity data in Makassar Strait between 2004 – August 2011 and August 2013 – August 2015 document substantial direct impacts of the MJO on the ITF, particularly with the surface layer (< 80 m ). A composite of the along-strait velocity within the surface layer for 10 MJO events observed during the observational period exhibits strong northward velocity within days, following the peak of MJO wind stress. The MJO forces both northward along-strait pressure gradient and the resultant of northward wind stress and turbulent stress at the base of the surface layer that, together with the seasonal forcing, maintain the reduction or even reversal of the ITF southward transport on timescales of 1-3 months during boreal winter.