http://hdl.handle.net/1842/1630 Thu, 13 Jun 2013 01:24:37 GMT 2013-06-13T01:24:37Z http://hdl.handle.net/1842/6262 Title: Diatom-based Late Quaternary precipitation record for lowland tropical South America Authors: Fitzpatrick, Katharine Anne Abstract: The late Quaternary palaeoclimatic history of the lowland Southern Hemisphere Tropics of South America (SHTSA) has been little studied and analysis of key climatic events, such as the Last Glacial Maximum (centred ~ 21,000 years ago (21 cal. ka BP)) and the glacial-Holocene transition is limited. Studies from the SH tropical Andes and the Atlantic seaboard demonstrate a strengthening of the South American summer monsoon during the LGM, in tune with the ~ 20 kyr precession orbital cycle. However, palynological studies from SHTSA suggest a drier LGM. There are difficulties in interpreting different palaeoenvironmental proxy records and the extent to which they reflect changes in temperature, precipitation, and/or atmospheric CO2 concentrations. In particular, the palaeoenvironmental significance of palynological data is often unclear. Also, high frequency, millennial-scale events have not been captured in records from the lowland SHTSA due to a lack of high resolution temporal records. Diatoms have been used widely in other parts of the world to reconstruct lake level change and therefore provide an independent proxy for precipitation, and an understanding of the modern diatom ecology is essential for accurate palaeoreconstruction. The main rationale of this thesis is to address the uncertainty of the glacial-Holocene climate in South America. To this end, this thesis aims to: (a) investigate the distribution, ecology, and flora of diatom taxa at Laguna La Gaiba (17°45’S, 57°40’W) (LLG) in the heart of lowland tropical South America, where very few modern diatom studies exist; (b) determine whether modern diatom assemblages at LLG will provide a useful analogue for palaeoenvironmental reconstructions, in particular, lake depth reconstruction; (c) provide a detailed late Quaternary lake level reconstruction for the lowland interior of SHTSA, based upon fossil diatom analysis of a sedimentary core in LLG. Descriptive, quantitative and multivariate analyses were applied to modern diatom assemblages and environmental variables to ascertain the modern diatom environment of LLG. Diatom, pollen, and geochemical analyses, chronologically constrained by 18 AMS 14C dates, were performed on a sediment core extracted from LLG. Key findings indicate: (1) Aulacoseira ambigua, A. ambigua var. robusta. A. distans and A. granulata var. angustissima were the most abundant species. Shallowwater species, such as Staurosira and Eunotia spp., dominated the shallows and littoral zone, whilst deep-water species, such as Aulacoseira sp., dominated in open water; (2) The highest percent variance in the diatom data was explained by depth and pH; (3) Analysis of fossil diatom assemblages from the LLG core demonstrated that the Last Glacial Maximum (LGM) and late glacial period (prior to 12.5 kyr BP) was drier than present. This corroborates and significantly strengthens pollen-based palaeo-hydrological reconstructions from the same core; (4) An abrupt shift from 12.5 kyr BP from shallow water to deep water diatoms signals major flooding of LLG associated with the transition from relatively drier glacial conditions to wetter Holocene conditions and also highlights an anomalously wet period centred over 12.2 kyr BP that falls within the Younger Dryas chronozone; (5) Deep-water diatoms remain high throughout the Holocene, which means that the mid-Holocene aridity inferred from the pollen data (expansion of seasonally-dry tropical forest) is not captured by the diatom data. These results not only present the modern diatom ecology of a little studied area in lowland Bolivia, but also highlight the potential of diatoms as a proxy for past lake level fluctuations, improving the understanding of late Quaternary palaeoclimate of tropical South America. Used as part of a multiproxy reconstruction, this record has provided a more complete picture of the variation between regions of late Quaternary climate change in South America, as evidence of a dry LGM climate contrasts with the robust, well-dated climate archives of the central Andes and E Brazil. This suggests the climate in the continental interior of SHTSA was not driven by the precesionally-forced monsoon cycle but is in step with changes in glacialinterglacial cycle boundary conditions. Mon, 25 Jun 2012 00:00:00 GMT http://hdl.handle.net/1842/6262 2012-06-25T00:00:00Z http://hdl.handle.net/1842/6253 Title: Field spectroscopy and spectral reflectance modelling of Calluna vulgaris Authors: MacArthur, Alasdair Archibald Abstract: Boreal peatlands store carbon sequestered from the atmosphere over millennia and the importance of this and the other ecosystem services these areas provide is now widely recognised. However, a changing climate will affect these environments and, consequently, the services they provide to the global population. The rate and direction of environmental change to peatlands is currently unclear and they have not yet been included in many climate models. This may in part be due to the ecological heterogeneity and spatial extent of these areas and the sparse sampling survey methods currently adopted. Hyperspectral remote sensing from satellite platforms may in future offer an approach to surveying and do so at the high spectral and spatial resolutions necessary to infer ecological change in these peatlands. However, work is required to develop methods of analysis to determine if hyperspectral data can be used to measure the overstorey vegetation of these areas. This will require an understanding of how annual and inter-annual cyclical changes affect the peatland plant canopy reflectances that would be recorded by hyperspectral sensors and how these reflectances can be related to state variable of interest to climate scientists, ecologists and peatland managers. There are significant areas of peatland within Scotland and, as it is towards the southern extreme of the boreal peatlands, these may be an early indicator of environment change to the wider boreal region. Calluna vulgaris, a hardy dwarf shrub, is the dominant overstorey species over much of these peatlands and could serve as a proxy for ecological, and consequently, environmental change. However, little has been done to understand how variations in leaf pigments or canopy structural parameters influence the spectral reflectance of Calluna through annual and inter-annual growth and senescence cycles. Nor has much work been done to develop methods of analysis to enable images acquired by hyperspectral remote sensing to be utilised to monitor change to these Calluna dominated peatlands over time. To advance understanding of the optical properties of Calluna leaves and canopies and develop methods to analyse hyperspectral images laboratory, field and modelling studies have been carried out in time series over a number of years. The leaf and canopy parameters significantly affecting reflectance have been identified and quantified. Differences between published Chlorophyll(a+b) in vivo absorption spectra and those determined were found. Carotenoids and Anthocyanins were also identified and quantified. The absorption spectra of these pigments were incorporated into a canopy reflectance model and this was coupled to a Calluna growth model. This combined model enabled the reflectance of Calluna canopies to be modelled in daily increments through annual and inter-annual growth and senescence cycles. Reasonable results were achieved in spectral regions where reflectance changed systematically but only for homogeneous Calluna stands. However, it was noted during this research that the area of support for the spectral measurements appeared to differ from that assumed from the specification provided by the spectroradiometer manufacturers. The directional response functions (DRFs) of two spectroradiometers were investigated and wavelength, or wavelength region, specific spatial dependences were noted. The effect that the DRFs of the spectroradiometers would have on reflectances recorded from Calluna canopies was investigated through a modelling study. Errors and inaccuracies in the spectra that would be recorded from these canopies, and commonly used biochemical indices derived from them, have been quantified. Mon, 25 Jun 2012 00:00:00 GMT http://hdl.handle.net/1842/6253 2012-06-25T00:00:00Z http://hdl.handle.net/1842/6244 Title: Nitrogen fluxes at the landscape scale: a case study in Scotland Authors: Vogt, Esther Abstract: Nitrogen (N) fluxes show a substantial variability at the landscape scale. Emissions are transferred by atmospheric, hydrological and anthropogenic dispersion between different landscape elements or ecosystems, e.g. farms, fields, forests or moorland. These landscape N fluxes can cause impacts to the environment, such as loss of biodiversity. The aim of this study is to illustrate how landscape N fluxes can be quantified by integrating atmospheric and fluvial fluxes in a Scottish landscape of 6 km x 6 km that contains intensively managed poultry farming, extensively managed beef and sheep farming, semi-natural moorland and woodland. Atmospheric ammonia (NH3) emissions of two deep pit free range layer poultry houses were estimated by high time-resolution measurements of NH3 concentrations and meteorological variables downwind of layer poultry houses and the application of an inverse Gaussian plume model. Atmospheric NH3 concentrations and deposition fluxes across the study landscape were studied at a resolution of 25 m x 25 m. The approach combined a detailed landscape inventory of all farm activities providing high resolution NH3 emission estimates for atmospheric dispersion modelling and an intensive measurement programme of spatial NH3 concentrations for verifying modelled NH3 concentrations. The spatially diverse emission pattern resulted in a high spatial variability of modelled mean annual NH3 concentrations (0.3 to 77.9 μg NH3 m-3) and dry deposition fluxes (0.1 to >100 kg NH3-N ha-1 yr-1) within the landscape. Annual downstream fluxes and variation in spatial concentration of dissolved inorganic nitrogen (NH4 + and NO3 -) and dissolved organic nitrogen (DON) were studied in the two main catchments within the study landscape (agricultural grassland vs. semi-natural moorland catchment). The grassland catchment was associated with an annual downstream total dissolved nitrogen (TDN) flux of 14.4 kg N ha-1 yr-1, which was 66% higher than the flux of 8.7 kg ha-1 yr-1 from the moorland catchment. This difference was largely due to the NO3 - flux being one order of magnitude higher in the grassland catchment. The contribution of DON to the TDN flux varied between the catchments with 49% in the grassland and 81% in the moorland catchment. Fluvial and atmospheric N fluxes were combined to derive N budgets of the two catchments. Agricultural activities accounted for the majority of N input to the catchments, with atmospheric deposition also playing a significant role, especially in the moorland catchment. Both catchments showed large stream export fluxes compared to their net import which suggests that their capacity of N storage is limited. This thesis quantifies major N fluxes in a study landscape and shows their large spatial variability. Agricultural activities dominate landscape N dynamics. The work demonstrates the importance of considering landscape N variability when attempting to reduce the environmental impact of agricultural activities. Mon, 25 Jun 2012 00:00:00 GMT http://hdl.handle.net/1842/6244 2012-06-25T00:00:00Z http://hdl.handle.net/1842/6242 Title: Satellite investigations of ice-ocean interactions in the Amundsen Sea sector of West Antarctica Authors: McMillan, Malcolm John Abstract: This thesis analyses satellite-based radar data to improve our understanding of the interactions between the Antarctic Ice Sheet and the ocean in the Amundsen Sea Sector of West Antarctica. Over the last two decades, the European Remote Sensing (ERS) Satellites have provided extensive observations of the marine and cryospheric environments of this region. Here I use this data record to develop new datasets and methods for studying the nature and drivers of ongoing change in this sector. Firstly, I develop a new bathymetric map of the Amundsen Sea, which serves to provide improved boundary conditions for models of (1) ocean heat transfer to the ice sheet margin, and (2) past ice sheet behaviour and extent. This new map augments sparse ship-based depth soundings with dense gravity data acquired from ERS altimetry and achieves an RMS depth accuracy of 120 meters. An evaluation of this technique indicates that the inclusion of gravity data improves the depth accuracy by up to 17 % and reveals glaciologically-important features in regions devoid of ship surveys. Secondly, I use ERS synthetic aperture radar observations of the tidal motion of ice shelves to assess the accuracy of tide models in the Amundsen Sea. Tide models contribute to simulations of ocean circulation and are used to remove unwanted signals from estimates of ice shelf flow velocities. The quality of tide models directly affects the accuracy of such estimates yet, due to a lack of in situ records, tide model accuracy in this region is poorly constrained. Here I use two methods to determine that tide model accuracy in the Amundsen Sea is of the order of 10 cm. Finally, I develop a method to map 2-d ice shelf flow velocity from stacked conventional and multiple aperture radar interferograms. Estimates of ice shelf flow provide detail of catchment stability, and the processes driving glaciological change in the Amundsen Sea. However, velocity estimates can be contaminated by ocean tide and atmospheric pressure signals. I minimise these signals by stacking interferograms, a process which synthesises a longer observation period, and enhances long-period (flow) displacement signals, relative to rapidly-varying (tide and atmospheric pressure) ones. This avoids the reliance upon model predictions of tide and atmospheric pressure, which can be uncertain in remote regions. Ice loss from Amundsen Sea glaciers forms the largest component of Antarctica’s total contribution to sea level, yet because present models cannot adequately characterise the processes driving this system, future glacier evolution is uncertain. Observations and models implicate the ocean as the driver of glaciological change in this region and have focussed attention on improving our understanding of the nature of ice-ocean interactions in the Amundsen Sea. This thesis contributes datasets and methods that will aid historical reconstructions, current monitoring and future modelling of these processes. Mon, 25 Jun 2012 00:00:00 GMT http://hdl.handle.net/1842/6242 2012-06-25T00:00:00Z