Climate change is expected to include changes to rainfall patterns. For southern England, this is likely to include decreased summer and increased winter rainfall patterns by the end of the 21st century. The aim of this research was to investigate the effects of altered precipitation patterns on ecosystem properties both above- and below-ground using a grassland experimental system in southeast England. The DIRECT experiments were established in 2008 and continued through 2013. This included three experiments assessing the effects of rainfall change on ecosystem functioning. The first crossed a summer rainfall reduction/winter rainfall increase scenario with plant functional trait diversity. The second considered the effects of two more extreme rainfall change scenarios, one an extended drought and one a shorter, more severe drought with occasional downpours. The third crossed rainfall change with increased nitrogen deposition in line with current levels experienced in parts of Europe. By concurrently measuring a broad range of above- and below-ground properties during the 2012 and 2013 growing seasons, I assessed the effects of changes in annual precipitation patterns. Drought during the growing season was linked to increased grass dominance and reduced ecosystem respiration, photosynthesis, and net ecosystem exchange, despite increases in winter precipitation. Effects on ecosystem functioning were most severe under extreme drought scenarios. Plant functional trait identity and diversity influenced response to drought, with increased diversity linked to higher plant cover in drought conditions. Increased nitrogen appeared to magnify the effects of drought on plant cover, while moderating the effects on CO2 flux. These results suggests that the levels of precipitation change predicted for England will negatively affect biodiversity and carbon cycling in grasslands, but factors such as trait diversity and nutrient inputs must be taken into account to understand the range of possible outcomes for ecosystem functioning.

Natural rubber is in high demand for the manufacture of tyres, and rubber plantations are expanding globally. Southeast Asia is the epicentre of rubber cultivation, where deforestation to make way for rubber has been occurring for decades. This process has caused substantial biodiversity loss and carbon emissions. Expansion has recently shifted northwards into mainland Southeast Asia (the Indo-Burma biodiversity hotspot) due to the development of hardier rubber varieties that can survive longer dry seasons and cooler climates. The northward shift has been exacerbated by replacement of rubber with oil palm further south. Profitability and extent of rubber are comparable to oil palm, but rubber has received far less attention and scrutiny from civil society. Future demand for natural rubber is predicted to require 4.3 – 8.5 million ha of additional plantation area by 2024, relative to a 2010 baseline. Profits accruing from logging and conversion of forest to rubber in Cambodia are shown to be very high. The carbon prices that would be needed for a REDD+ program in Indo- Burma to match costs of forest conservation where rubber is a threat, are $30 – 51 tCO2-1. These prices are far higher than those currently paid on carbon markets or through carbon funds, highlighting the importance of supply-chain initiatives, environmental governance and full valuation of ecosystem services for defending forests from conversion to rubber. Agroforestry methods for cultivating rubber in Thailand were found to produce yields comparable to monocultural methods, while providing modest benefits for bird and butterfly diversity. Agroforests did not support any species of conservation concern, and contiguous forests are irreplaceable for the conservation of forest biodiversity. Functional diversity of birds was found not to differ between rubber agroforests and monocultures, and species that feed primarily on nectar and fruit were extremely scarce in both types of rubber plantation.

A multi-proxy age model protocol was established using Labrador Sea sediment cores U1305 (57°N,48°W) and U1302 (50°N,45°W). These cores provided centennial-scale surface and deep-water records spanning the last interglacial (153-100ka). Ice rafted debris (IRD) counts and meltwater-runoff proxy Ba/Ca were used to investigate ice sheet instabilities; planktonic foraminiferal assemblages, planktonic δ18O and multi-species Mg/Ca records were used to reconstruct temperature and salinity; and fluctuations in Atlantic meridional overturning circulation (AMOC) were inferred from benthic δ13C. Intense cold and ice rafting accompanied Heinrich events H11 (135–130ka) and H12 (140ka), as well as a previously unrecognised Heinrich event (H13; 150–148ka), during which benthic and planktonic δ13C values indicate reduced AMOC and nutrient-rich Antarctic bottom-water (AABW) incursions. During H11, three warm phases preceded cooling and massive IRD pulses. Strongly depleted U1302 planktonic δ18O accompanied all IRD-rich cold periods, particularly H11, attributed to sea-ice formation and enhanced meltwater input. No Younger Dryas-like event was observed. Last interglacial temperatures were 2–5°C warmer in U1305, but similar to modern values at U1302, suggesting differing latitudinal responses to increased insolation (129–126ka). A diatom mat deposited ~128.7–128.6ka in U1305 indicates a proximal subarctic convergence front. Palaeotemperature reconstructions reveal two last interglacial warm maxima. The first (128.5–126.5ka) had the most diverse foraminiferal assemblages and was coeval with continued Greenland ice-sheet melt. A previously reported red layer, linked to a Laurentide outburst flood, has been dated to ~126.5ka and marks the culmination of localised intra-interglacial cooling. Subsequent AABW incursion events suggest rapid AMOC weakening and instability. Mg/Ca results reveal a second warming (123–117ka) associated with a vigorous AMOC, and was attributed to a stronger Irminger Current. IRD, SST and isotopic evidence indicate a prominent cold event ~117ka, followed by surface cooling and ice rafting linked to the North Atlantic cold events C26–C23.

Albugo candida is a plant pathogen that has been reported on many host species. While multiple host-specific races have long been recognized in A. candida, the genetic variation of these races has never been explored in nature and little is known about how the pathogen has adapted to its many hosts. Recently, evidence of genetic exchanges between races suggested that hybridization played an important role in the evolution of A. candida races. The authors also demonstrated that host-specific races of A. candida can co-occur, provided the immune system of the host is compromised by a compatible race. This immunosuppression by A. candida had previously been shown to allow growth of other pathogens. To study both these phenomena (the evolution of and the host immunosuppression imposed by A. candida), a capture array was designed to sequence 187 loci (~660,000 bp) from A. candida and loci from 47 other plant pathogens. In Chapter 3, I explain the rationale and methodology behind this approach. I show that it is cost-effective and that it may be used to identify microorganisms directly from a leaf and make inference about pathogen abundance within samples. In Chapter 4, genetic diversity of A. candida is analysed at a 400 kb contig and 32 diversity-tracking genes. Races are identified based on genetic divergence and recombination is investigated within and between races. In Chapter 5, I investigate genetic diversity at heterozygous sites to study the ploidy level and the reproductive mode of A. candida races as well as to detect mixed A. candida infections and loss-of-heterozygosity events. In this thesis, I demonstrate that A. candida races adapt to their hosts using complex mechanisms and that some may, in the long term, speciate. I also provide a novel method which may be used to interrogate microbial diversity directly from the field.

Albugo candida is a plant pathogen that has been reported on many host species. While multiple host-specific races have long been recognized in A. candida, the genetic variation of these races has never been explored in nature and little is known about how the pathogen has adapted to its many hosts. Recently, evidence of genetic exchanges between races suggested that hybridization played an important role in the evolution of A. candida races. The authors also demonstrated that host-specific races of A. candida can co-occur, provided the immune system of the host is compromised by a compatible race. This immunosuppression by A. candida had previously been shown to allow growth of other pathogens. To study both these phenomena (the evolution of and the host immunosuppression imposed by A. candida), a capture array was designed to sequence 187 loci (~660,000 bp) from A. candida and loci from 47 other plant pathogens. In Chapter 3, I explain the rationale and methodology behind this approach. I show that it is cost-effective and that it may be used to identify microorganisms directly from a leaf and make inference about pathogen abundance within samples. In Chapter 4, genetic diversity of A. candida is analysed at a 400 kb contig and 32 diversity-tracking genes. Races are identified based on genetic divergence and recombination is investigated within and between races. In Chapter 5, I investigate genetic diversity at heterozygous sites to study the ploidy level and the reproductive mode of A. candida races as well as to detect mixed A. candida infections and loss-of-heterozygosity events. In this thesis, I demonstrate that A. candida races adapt to their hosts using complex mechanisms and that some may, in the long term, speciate. I also provide a novel method which may be used to interrogate microbial diversity directly from the field.

Shelf seas represent only 10 % of the ocean area, but support 30 % of oceanic primary production. There are few measurements of biological production at high spatial and temporal resolution in such physically dynamic systems. Here, I use dissolved oxygento- argon (O2/Ar) ratios and triple oxygen isotopes (δ(17O), δ(18O)) to estimate net and gross biological production seasonally in the Celtic Sea between summer 2014 and summer 2015, as part of the NERC Shelf-Sea Biogeochemistry programme. O2/Ar was measured continuously using a shipboard membrane inlet mass spectrometer. Discrete water samples from hydrocasts were used to measure O2/Ar, δ(17O) and δ(18O) depth profiles. The data were combined with wind-speed based gas exchange parameterisations to calculate biological air-sea oxygen fluxes. These fluxes were corrected for non-steady state and diapycnal diffusion to give net community production (N(O2/Ar)) and gross O2 production (G(17O)). N(O2/Ar) was highest in spring at (33±41) mmol m-2 d-1, and G(17O) was highest in summer at (494±370) mmol m-2 d-1, while autumn was net heterotrophic with N(O2/Ar) = (–14±28) mmol m-2 d-1. During spring, biological production was spatially heterogeneous, highlighting the importance of high resolution biological production measurements. The ratio of N(O2/Ar) to G(17O), ƒ(O2), was highest in spring at 0.18±0.03 corresponding to 0.34±0.06 in carbon equivalents; about 0.05 in summer and < 0 in autumn/winter. Statistical measurement uncertainties increase when terms other than air-sea exchange fluxes are included in the calculations. Additionally, electron transfer rate derived from fast repetition rate fluorometry measurements was compared with G(17O), but no simple relationship was found. This study characterised the seasonal biological patterns in production rates and shows that the Celtic Sea is a net carbon sink in spring and summer. Such measurements can help reconcile the differences between satellite and in situ productivity estimates, and improve our understanding of the biological carbon pump.

In this thesis, new Holocene palaeoclimate information from speleothems is presented from three regions (central Peloponnese Greece, south west Turkey and the eastern forelands of the Zagros Mountains, Iran) where the spatial distribution of Holocene climate records is low. This study uses a multi-proxy approach with particular emphasis on petrography and stable isotope analysis. Holocene growth of stalagmite KTR-2 (11,900 yr BP to 6700 yr BP) from Limnon Cave in the central Peloponnese is broadly coincident with the formation of Sapropel 1. The early Holocene was generally wetter than at present. A record of the 8.2 kyr event was obtained from KTR-2 using high resolution trace element ICP-MS and micromilled stable isotope samples. Arid conditions are implied by δ18O and trace elements, with aridity probably beginning ~9000 yr BP. δ13C data suggests precipitation may have been strongly seasonal during the 8.2 kyr event. Distinct grey coloured layers in HY-8, a stalagmite from Sirtlanini Cave, SW Turkey, represent fire events occurring above the cave; there is however, no suggestion that the fires occurred during periods of relatively enhanced aridity. The palaeoclimate record spans ~5600 yr BP to the present day, but does not indicate any significant long term reduction in precipitation. The HY-8 δ18O record suggests the 4.2 kyr anomaly was a two-step aridity event occurring between 4290 and 3850 yr BP. A distinct pluvial event from 4890-4290 yr BP is also recorded by δ18O, as is evidence for the Little Ice Age (630-280 yr BP). The Holocene section of stalagmite KT-3, from the eastern forelands of the Zagros Mountains in Iran, grew from 9400 yr BP to present. The early Holocene until ~7000 yr BP was wetter than the present day. Multiple proxies show falling precipitation amounts from ~7000 yr BP, plateauing from ~3000 yr BP to present. There is very little short term fluctuation in δ18O but the overall trend has a profile similar to the decline of solar insolation in the Holocene, which appears to be responsible for the long term reduction in winter precipitation. In KT-3, the correlation between Ba/Ca and δ13C fluctuations might be a more sensitive indicator of moisture. A significant positive δ13C excursion could be recording the 8.2 kyr event. Additionally, this thesis presents a specific petrographic study from two different, but discontinuously grown, Turkish stalagmites. These stalagmites grew very differently and within different epochs. Petrography has been used to interpret and relate fabrics to their environment of formation and identified micro-dissolution as a prominent feature of growth. A link between these micro-dissolution events and stratigraphically inverted U-series dates is proposed.

No description available.

The extent to which transitions from dominantly viscous to dominantly brittle magma deformation regulate eruptive activity has not been widely explored in volcanology. Within this thesis, investigations combining experiments, petrology and geophysical signals are presented to help decipher and understand the role of brittle deformation during lava dome eruptions. Lava domes are commonly associated with explosions and dome collapse events, both of which generate volcanic ash. In order to recognise and discriminate fragmentation mechanisms from ash samples, the physical properties and mineralogy of natural ash produced during a typical Vulcanian explosion and a dome collapse event were compared. Measurements of the componentry of several thousand ash particles were conducted using QEMSCAN® Particle Mineralogical Analysis, a rapid automated SEM-EDS mapping technique. Analysis of images obtained by QEMSCAN® reveals that the relative distribution of plagioclase and glass present along the ash particle boundaries varied for both generation mechanisms. Deconvolution of particle size distributions and particle shape analyses shows that ash ejected in Vulcanian explosions has a more complex fragmentation and transport history, while ash produced in pyroclastic flows shows the dominance of a single process. These results suggest mechanism-dependent controls on the surface composition and componentry of volcanic ash – future work is required to discriminate fragmentation mechanisms from ash characteristics through the use of QEMSCAN® data. Explosive fragmentation at lava dome volcanoes is likely to be triggered by tensile failure of magma following stress accumulation. In order to investigate pressure-driven fracturing of conduit magma, Brazilian tensile tests were conducted on lava samples from Santiaguito volcano at ambient and magmatic temperatures. These tests reveal that deformation style becomes sensitive to small changes in temperature and strain rate at temperatures of 750-800 °C. Higher temperatures generated increasingly viscous deformation, while faster strain rates promoted more brittle behaviour. Experimental constraints on the strain rate and strain leading to failure can be compared to natural deformation timescales recorded in cycles of inflation preceding explosions at Santiaguito, which shows that a viscous component accompanies deformation and suggests that fractures propagate away from a pressure source prior to explosive eruption. Following fracture propagation, any remaining energy is likely to be accommodated by fault slip along the fracture plane. These faulting events are investigated using a high-velocity rotary shear apparatus, showing that the response to faulting generates temperatures sufficient to produce frictional melt within ~10 cm of slip under the slip rates and normal stresses constrained through monitoring of the volcanic behaviour at Santiaguito. The range of mechanical response to slip events in the volcanic conduit and their relation to concurrent seismic signals are investigated in greater detail during the extrusion of a lava spine at Mt Unzen (Japan). Examination of textures at the spine margins and similarity of the seismic signals that accompanied its extrusion has determined that spine emplacement proceeds by incremental fault slip events in the shallow edifice. Waveform analysis together with spine growth observations allow calculation of the average slip distance (8.9 cm) and slip velocity (0.75 m.s-1). These calculations are combined with results from laboratory measurements in a high-velocity rotary shear apparatus to define the range of depths where average faulting events would induce viscous remobilisation (at >275m) and frictional melting along the fault plane (at >500 m). The frictional properties of the dome rocks and the viscosity of the frictional melt in the fault zone suggest that at shallow depths frictional melts act as a viscous brake to fault slip, potentially augmenting stick-slip spine growth. Taken together, the failure, faulting and fragmentation of dome-forming magma demonstrates that our interpretation of eruptive activity at lava dome volcanoes requires a fundamental understanding of brittle processes.

No description available.