http://hdl.handle.net/10023/1940 2013-06-20T07:22:32Z http://hdl.handle.net/10023/3660 Abstract: From the formation of Rodinia at the end of the Mesoproterozoic to the commencement of Pangea breakup at the end of the Paleozoic, the South China craton first formed and then occupied a position adjacent to Western Australia and northern India. Early Neoproterozoic suprasubduction zone magmatic arc-backarc assemblages in the craton range in age from ca. 1000 Ma to 820 Ma and display a sequential northwest decrease in age. These relations suggest formation and closure of arc systems through southeast-directed subduction, resulting in progressive northwestward accretion onto the periphery of an already assembled Rodinia. Siliciclastic units within an early Paleozoic succession that transgresses across the craton were derived from the southeast and include detritus from beyond the current limits of the craton. Detrital zircon age spectra require an East Gondwana source and are very similar to the Tethyan Himalaya and younger Paleozoic successions from Western Australia, suggesting derivation from a common source and by inference accumulation in linked basins along the northern margin of Gondwana, a situation that continued until rifting and breakup of the craton in the late Paleozoic. Description: This work was supported by NERC [Grant ID NE/J021822/1] 2013-01-01T00:00:00Z Cawood, Peter Anthony Wang, Yuejun Xu, Yajun Zhao, Guochun From the formation of Rodinia at the end of the Mesoproterozoic to the commencement of Pangea breakup at the end of the Paleozoic, the South China craton first formed and then occupied a position adjacent to Western Australia and northern India. Early Neoproterozoic suprasubduction zone magmatic arc-backarc assemblages in the craton range in age from ca. 1000 Ma to 820 Ma and display a sequential northwest decrease in age. These relations suggest formation and closure of arc systems through southeast-directed subduction, resulting in progressive northwestward accretion onto the periphery of an already assembled Rodinia. Siliciclastic units within an early Paleozoic succession that transgresses across the craton were derived from the southeast and include detritus from beyond the current limits of the craton. Detrital zircon age spectra require an East Gondwana source and are very similar to the Tethyan Himalaya and younger Paleozoic successions from Western Australia, suggesting derivation from a common source and by inference accumulation in linked basins along the northern margin of Gondwana, a situation that continued until rifting and breakup of the craton in the late Paleozoic. http://hdl.handle.net/10023/3585 Abstract: The Qilian Orogen records early Paleozoic collisional suturing of the Qaidam Block and the Central Qilian Block to the North China Craton. The composition and U-Pb age of detrital zircons and the composition of Cr-spinels from the Early Silurian Lujiaogou and Angzanggou formations in the northern part of orogen indicate derivation from evolving oceanic and continental source terranes. Heavy-mineral chemistry indicates the incorporation of suprasubduction zone-type ophiolitic detritus in addition to continent-derived material. Integrating these chemical and age data with regional data on the duration of subduction-related magmatic activity, syn- and postcollisional granitic rocks, and high-pressure metamorphic rocks constrains the transformation from oceanic subduction to continental collision to 450-440 Ma. The collision resulted in a flood of detritus into the northern part of the orogen from the Central Qilian Block, which masked input from the intervening magmatic arc, implying rapid exposure of the block. 2012-01-01T00:00:00Z Yang, Jianghai Du, Yuansheng Cawood, Peter A. Xu, Yajun The Qilian Orogen records early Paleozoic collisional suturing of the Qaidam Block and the Central Qilian Block to the North China Craton. The composition and U-Pb age of detrital zircons and the composition of Cr-spinels from the Early Silurian Lujiaogou and Angzanggou formations in the northern part of orogen indicate derivation from evolving oceanic and continental source terranes. Heavy-mineral chemistry indicates the incorporation of suprasubduction zone-type ophiolitic detritus in addition to continent-derived material. Integrating these chemical and age data with regional data on the duration of subduction-related magmatic activity, syn- and postcollisional granitic rocks, and high-pressure metamorphic rocks constrains the transformation from oceanic subduction to continental collision to 450-440 Ma. The collision resulted in a flood of detritus into the northern part of the orogen from the Central Qilian Block, which masked input from the intervening magmatic arc, implying rapid exposure of the block. http://hdl.handle.net/10023/3576 Abstract: Continental crust is the archive of Earth history. The spatial and temporal distribution of Earth's record of rock units and events is heterogeneous; for example, ages of igneous crystallization, metamorphism, continental margins, mineralization, and seawater and atmospheric proxies are distributed about a series of peaks and troughs. This distribution reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. The physio-chemical resilience of zircons and their derivation largely from felsic igneous rocks means that they are important indicators of the crustal record. Furthermore, detrital zircons, which sample a range of source rocks, provide a more representative record than direct analysis of grains in igneous rocks. Analysis of detrital zircons suggests that at least ∼60%–70% of the present volume of the continental crust had been generated by 3 Ga. Such estimates seek to take account of the extent to which the old crustal material is underrepresented in the sedimentary record, and they imply that there were greater volumes of continental crust in the Archean than might be inferred from the compositions of detrital zircons and sediments. The growth of continental crust was a continuous rather than an episodic process, but there was a marked decrease in the rate of crustal growth at ca. 3 Ga, which may have been linked to the onset of significant crustal recycling, probably through subduction at convergent plate margins. The Hadean and Early Archean continental record is poorly preserved and characterized by a bimodal TTG (tonalites, trondhjemites, and granodiorites) and greenstone association that differs from the younger record that can be more directly related to a plate-tectonic regime. The paucity of this early record has led to competing and equivocal models invoking plate-tectonic– and mantle-plume–dominated processes. The 60%–70% of the present volume of the continental crust estimated to have been present at 3 Ga contrasts markedly with the <10% of crust of that age apparently still preserved and requires ongoing destruction (recycling) of crust and subcontinental mantle lithosphere back into the mantle through processes such as subduction and delamination. 2013-01-01T00:00:00Z Cawood, Peter Anthony Hawkesworth, Chris Dhuime, Bruno Philippe Marcel Continental crust is the archive of Earth history. The spatial and temporal distribution of Earth's record of rock units and events is heterogeneous; for example, ages of igneous crystallization, metamorphism, continental margins, mineralization, and seawater and atmospheric proxies are distributed about a series of peaks and troughs. This distribution reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. The physio-chemical resilience of zircons and their derivation largely from felsic igneous rocks means that they are important indicators of the crustal record. Furthermore, detrital zircons, which sample a range of source rocks, provide a more representative record than direct analysis of grains in igneous rocks. Analysis of detrital zircons suggests that at least ∼60%–70% of the present volume of the continental crust had been generated by 3 Ga. Such estimates seek to take account of the extent to which the old crustal material is underrepresented in the sedimentary record, and they imply that there were greater volumes of continental crust in the Archean than might be inferred from the compositions of detrital zircons and sediments. The growth of continental crust was a continuous rather than an episodic process, but there was a marked decrease in the rate of crustal growth at ca. 3 Ga, which may have been linked to the onset of significant crustal recycling, probably through subduction at convergent plate margins. The Hadean and Early Archean continental record is poorly preserved and characterized by a bimodal TTG (tonalites, trondhjemites, and granodiorites) and greenstone association that differs from the younger record that can be more directly related to a plate-tectonic regime. The paucity of this early record has led to competing and equivocal models invoking plate-tectonic– and mantle-plume–dominated processes. The 60%–70% of the present volume of the continental crust estimated to have been present at 3 Ga contrasts markedly with the <10% of crust of that age apparently still preserved and requires ongoing destruction (recycling) of crust and subcontinental mantle lithosphere back into the mantle through processes such as subduction and delamination. http://hdl.handle.net/10023/3575 Abstract: Detrital zircon spectra reflect the tectonic setting of the basin in which they are deposited. Convergent plate margins are characterized by a large proportion of zircon ages close to the depositional age of the sediment, whereas sediments in collisional, extensional and intracratonic settings contain greater proportions with older ages that reflect the history of the underlying basement. These differences can be resolved by plotting the distribution of the difference between the measured crystallization ages (CA) of individual zircon grains present in the sediment and the depositional age (DA) of the sediment. Application of this approach to successions where the original nature of the basin and/or the link to source are no longer preserved constrains the tectonic setting in which the sediment was deposited. 2012-10-01T00:00:00Z Cawood, P. A. Hawkesworth, C. J. Dhuime, B. Detrital zircon spectra reflect the tectonic setting of the basin in which they are deposited. Convergent plate margins are characterized by a large proportion of zircon ages close to the depositional age of the sediment, whereas sediments in collisional, extensional and intracratonic settings contain greater proportions with older ages that reflect the history of the underlying basement. These differences can be resolved by plotting the distribution of the difference between the measured crystallization ages (CA) of individual zircon grains present in the sediment and the depositional age (DA) of the sediment. Application of this approach to successions where the original nature of the basin and/or the link to source are no longer preserved constrains the tectonic setting in which the sediment was deposited. http://hdl.handle.net/10023/3564 Abstract: Alluvial riverbed elevation responds to the balance between sediment supply and transport capacity, which is largely dependent on climate and its translation into fluvial discharge. We examine these relations using U.S. Geological Survey streamflow and channel measurements in conjunction with basin characteristics for 915 reference ("least disturbed") measurement stations across the conterminous United States for the period A.D. 1950–2011. We find that (1) 68% of stations have bed elevation change (BEC) trends (p < 0.05) with median values of +0.5 cm/yr for aggradation and –0.6 cm/yr for degradation, with no obvious relation to drainage basin structure, physiography, or lithology; (2) BEC correlates with drainage basin area; (3) high-flow variability (Q90/Q50, where Q is discharge and 90 and 50 are annual flow percentiles) translates directly into the magnitude, though not the direction, of BEC, after accounting for the scale dependence; (4) Q90/Q50 declines systematically from dry to wet climates, producing disproportionately high rates of BEC in drier regions; and (5) marked increases in precipitation and streamflow occurred disproportionately at dry sites, while streamflow declined disproportionately at wet sites. Climatic shifts in streamflow have the potential to increase/decrease sediment flux and thus affect riverbed elevation by altering flood frequency. These unforeseen responses of bed elevation to climate and climate change have important implications for sediment budgets, longitudinal profiles, ecology, and river management. Description: This work was partially supported by a Natural Environment Research Council Ph.D. studentship to Slater. 2013-05-01T00:00:00Z Slater, Louise Jeanne Elizabeth Singer, Michael Bliss Alluvial riverbed elevation responds to the balance between sediment supply and transport capacity, which is largely dependent on climate and its translation into fluvial discharge. We examine these relations using U.S. Geological Survey streamflow and channel measurements in conjunction with basin characteristics for 915 reference ("least disturbed") measurement stations across the conterminous United States for the period A.D. 1950–2011. We find that (1) 68% of stations have bed elevation change (BEC) trends (p < 0.05) with median values of +0.5 cm/yr for aggradation and –0.6 cm/yr for degradation, with no obvious relation to drainage basin structure, physiography, or lithology; (2) BEC correlates with drainage basin area; (3) high-flow variability (Q90/Q50, where Q is discharge and 90 and 50 are annual flow percentiles) translates directly into the magnitude, though not the direction, of BEC, after accounting for the scale dependence; (4) Q90/Q50 declines systematically from dry to wet climates, producing disproportionately high rates of BEC in drier regions; and (5) marked increases in precipitation and streamflow occurred disproportionately at dry sites, while streamflow declined disproportionately at wet sites. Climatic shifts in streamflow have the potential to increase/decrease sediment flux and thus affect riverbed elevation by altering flood frequency. These unforeseen responses of bed elevation to climate and climate change have important implications for sediment budgets, longitudinal profiles, ecology, and river management. http://hdl.handle.net/10023/3502 Abstract: The Antarctic continent contains the majority of the global ice volume and plays an important role in a changing climate. The nature and causes of Antarctic climate variability are, however, poorly understood beyond interannual time scales due to the paucity of long, reliable meteorological observations. This study analyzes decadal-interdecadal climate variability over Antarctica using a network of annually resolved ice core records and various instrumental and tropical proxy data for the 19th and 20th centuries. During the 20th century, Antarctic ice core records indicate strong linkages to sea surface temperature (SST) variations in the tropical Pacific and Atlantic on decadal-interdecadal time scales. Antarctic surface temperature anomalies inferred from the ice cores are consistent with the associated changes in atmospheric circulation and thermal advection. A set of atmospheric general circulation model experiments supports the idea that decadal SST variations in the tropics force atmospheric teleconnections that affect Antarctic surface temperatures. When coral and other proxies for tropical climate are used to extend the analysis back to 1799, a similar Antarctic-tropical Pacific linkage is found, with evidence for a weaker connection during the first half of the 19th century. Over the past 50 years, a change in the phase of Pacific and Atlantic interdecadal variability may have contributed to the rapid warming of the Antarctic Peninsula and West Antarctica. 2012-11-01T00:00:00Z Okumura, Yuko Schneider, David Deser, Clara Wilson, Rob The Antarctic continent contains the majority of the global ice volume and plays an important role in a changing climate. The nature and causes of Antarctic climate variability are, however, poorly understood beyond interannual time scales due to the paucity of long, reliable meteorological observations. This study analyzes decadal-interdecadal climate variability over Antarctica using a network of annually resolved ice core records and various instrumental and tropical proxy data for the 19th and 20th centuries. During the 20th century, Antarctic ice core records indicate strong linkages to sea surface temperature (SST) variations in the tropical Pacific and Atlantic on decadal-interdecadal time scales. Antarctic surface temperature anomalies inferred from the ice cores are consistent with the associated changes in atmospheric circulation and thermal advection. A set of atmospheric general circulation model experiments supports the idea that decadal SST variations in the tropics force atmospheric teleconnections that affect Antarctic surface temperatures. When coral and other proxies for tropical climate are used to extend the analysis back to 1799, a similar Antarctic-tropical Pacific linkage is found, with evidence for a weaker connection during the first half of the 19th century. Over the past 50 years, a change in the phase of Pacific and Atlantic interdecadal variability may have contributed to the rapid warming of the Antarctic Peninsula and West Antarctica. http://hdl.handle.net/10023/3376 Abstract: Thermodynamic calculations and inorganic precipitation experiments indicate a relationship between aragonite Mg/Ca and water temperature. This offers a route to reconstruct seawater temperatures from fossil corals. Fundamental to this is the assumption that Mg2+ exchanges for Ca2+ within carbonate. We present X-ray Absorption Fine Structure (XAFS) data to indicate the structural state of Mg in modern Porites coral skeletons. We show Mg is not in aragonite, but hosted by a disordered Mg-bearing material. Mg may be predominantly hosted in organic materials or as a highly disordered inorganic phase, e. g., a nanoparticulate form of Mg carbonate or hydroxide. Reported correlations between seawater temperature and coral Mg/Ca are unlikely to be consistent between corals and hence analysis of Mg/Ca in fossils is unlikely to produce accurate climate reconstructions. We anticipate XAFS will be applied widely to environmental proxies and become an important tool in identifying those that reconstruct accurate climates. 2008-04-19T00:00:00Z Finch, Adrian A. Allison, Nicola Thermodynamic calculations and inorganic precipitation experiments indicate a relationship between aragonite Mg/Ca and water temperature. This offers a route to reconstruct seawater temperatures from fossil corals. Fundamental to this is the assumption that Mg2+ exchanges for Ca2+ within carbonate. We present X-ray Absorption Fine Structure (XAFS) data to indicate the structural state of Mg in modern Porites coral skeletons. We show Mg is not in aragonite, but hosted by a disordered Mg-bearing material. Mg may be predominantly hosted in organic materials or as a highly disordered inorganic phase, e. g., a nanoparticulate form of Mg carbonate or hydroxide. Reported correlations between seawater temperature and coral Mg/Ca are unlikely to be consistent between corals and hence analysis of Mg/Ca in fossils is unlikely to produce accurate climate reconstructions. We anticipate XAFS will be applied widely to environmental proxies and become an important tool in identifying those that reconstruct accurate climates. http://hdl.handle.net/10023/3016 Abstract: Hydraulic gold mining in the Sierra Nevada, California (1853–1884) displaced ~1.1 billion m3 of sediment from upland placer gravels that were deposited along piedmont rivers below dams where floods can remobilize them. This study uses topographic and planimetric data from detailed 1906 topographic maps, 1999 photogrammetric data, and pre- and post-flood aerial photographs to document historic sediment erosion and deposition along the lower Yuba River due to individual floods at the reach scale. Differencing of 3 × 3-m topographic data indicates substantial changes in channel morphology and documents 12.6 × 106 m3 of erosion and 5.8 × 106 m3 of deposition in these reaches since 1906. Planimetric and volumetric measurements document spatial and temporal variations of channel enlargement and lateral migration. Over the last century, channels incised up to ~13 m into mining sediments, which dramatically decreased local flood frequencies and increased flood conveyance. These adjustments were punctuated by event-scale geomorphic changes that redistributed sediment and associated contaminants to downstream lowlands. 2010-07-19T00:00:00Z Ghoshal, S. James, L.A. Singer, Michael B. Aalto, R. Hydraulic gold mining in the Sierra Nevada, California (1853–1884) displaced ~1.1 billion m3 of sediment from upland placer gravels that were deposited along piedmont rivers below dams where floods can remobilize them. This study uses topographic and planimetric data from detailed 1906 topographic maps, 1999 photogrammetric data, and pre- and post-flood aerial photographs to document historic sediment erosion and deposition along the lower Yuba River due to individual floods at the reach scale. Differencing of 3 × 3-m topographic data indicates substantial changes in channel morphology and documents 12.6 × 106 m3 of erosion and 5.8 × 106 m3 of deposition in these reaches since 1906. Planimetric and volumetric measurements document spatial and temporal variations of channel enlargement and lateral migration. Over the last century, channels incised up to ~13 m into mining sediments, which dramatically decreased local flood frequencies and increased flood conveyance. These adjustments were punctuated by event-scale geomorphic changes that redistributed sediment and associated contaminants to downstream lowlands. http://hdl.handle.net/10023/2586 Abstract: The optically stimulated luminescence (OSL) characteristics of a suite of quartz and feldspar samples from a range of modern glaciofluvial sediments have been explored to determine the use of OSL as a depositional pathway tracer. Paraglacial and subglacial source material and various glaciofluvial deposits have been analysed from the glacial catchments of Bergsetbreen, Fåbergstølsbreen, and Nigardsbreen as well as the Fåbergstølsgrandane sandur, Jostedalen, Norway. The OSL distribution signatures have been characterised through exploration of sample skewness, kurtosis and overdispersion, and dose distributions of the different depositional settings and source materials are distinct for both quartz and feldspar. Residual ages are greatest for feldspar, indicating significant potential age overestimation where feldspar is used to date glaciofluvial deposits. Sample dose distributions and overdispersion characteristics are driven by source sediment properties, whereas residual ages are controlled by transport and depositional processes. Those transport and depositional processes which result in significant light exposure, also influence dose distributions, and processes that sort sediments least effectively have the highest residual doses. Sample OSL characteristics, transport distance and grain size distributions have been investigated using factor analysis, as a means of predicting sediment source, facies, depositional process and deposit type. Although the depositional processes of the quartz samples can be clearly differentiated based upon OSL characteristics, factor analyses of feldspar and grain size characteristics are inconclusive. The application of quartz OSL to the Norwegian samples was limited by its very poor luminescence sensitivity. Quartz is the preferred mineral for OSL, however, despite the plethora of successful quartz OSL applications, the precise origin of the UV/blue luminescence emission, measured during OSL, remains unclear. The origins of this emission and controls on its intensity were explored using a variety of spectroscopic techniques including photoluminescence, cathodoluminescence, radioluminescence (RL), ionoluminescence (IL) and x-ray excited optical luminescence (XEOL). Exciting sample luminescence at a range of energies enables exploration of the different donor centres responsible for the luminescence emission. Cathodoluminescence and RL emission spectra are similar, comprising broad emissions at 1.5, 2.0 and 2.7 eV (detection in the UV part of the spectrum was not possible for these experiments). Ionoluminescence emission spectra were dominated by the ~ 3.3 eV emission, which is a component of the signal conventionally monitored during OSL. This emission depleted as a function of dose, to the benefit of the red emission (1.8-2.0 eV) for all samples throughout IL, and similar observations were made for the 3.4 eV emission observed from the XEOL emission spectra. The XEOL spectra are dominated by an emission at ~ 3.8 eV, not widely reported for quartz, which has tentatively been attributed to peroxy linkages. Differences between the IL and XEOL emission spectra are interpreted as evidence for the presence of multiple excited states. Description: Electronic version excludes material for which permission has not been granted by the rights holder 2012-06-20T00:00:00Z King, Georgina The optically stimulated luminescence (OSL) characteristics of a suite of quartz and feldspar samples from a range of modern glaciofluvial sediments have been explored to determine the use of OSL as a depositional pathway tracer. Paraglacial and subglacial source material and various glaciofluvial deposits have been analysed from the glacial catchments of Bergsetbreen, Fåbergstølsbreen, and Nigardsbreen as well as the Fåbergstølsgrandane sandur, Jostedalen, Norway. The OSL distribution signatures have been characterised through exploration of sample skewness, kurtosis and overdispersion, and dose distributions of the different depositional settings and source materials are distinct for both quartz and feldspar. Residual ages are greatest for feldspar, indicating significant potential age overestimation where feldspar is used to date glaciofluvial deposits. Sample dose distributions and overdispersion characteristics are driven by source sediment properties, whereas residual ages are controlled by transport and depositional processes. Those transport and depositional processes which result in significant light exposure, also influence dose distributions, and processes that sort sediments least effectively have the highest residual doses. Sample OSL characteristics, transport distance and grain size distributions have been investigated using factor analysis, as a means of predicting sediment source, facies, depositional process and deposit type. Although the depositional processes of the quartz samples can be clearly differentiated based upon OSL characteristics, factor analyses of feldspar and grain size characteristics are inconclusive. The application of quartz OSL to the Norwegian samples was limited by its very poor luminescence sensitivity. Quartz is the preferred mineral for OSL, however, despite the plethora of successful quartz OSL applications, the precise origin of the UV/blue luminescence emission, measured during OSL, remains unclear. The origins of this emission and controls on its intensity were explored using a variety of spectroscopic techniques including photoluminescence, cathodoluminescence, radioluminescence (RL), ionoluminescence (IL) and x-ray excited optical luminescence (XEOL). Exciting sample luminescence at a range of energies enables exploration of the different donor centres responsible for the luminescence emission. Cathodoluminescence and RL emission spectra are similar, comprising broad emissions at 1.5, 2.0 and 2.7 eV (detection in the UV part of the spectrum was not possible for these experiments). Ionoluminescence emission spectra were dominated by the ~ 3.3 eV emission, which is a component of the signal conventionally monitored during OSL. This emission depleted as a function of dose, to the benefit of the red emission (1.8-2.0 eV) for all samples throughout IL, and similar observations were made for the 3.4 eV emission observed from the XEOL emission spectra. The XEOL spectra are dominated by an emission at ~ 3.8 eV, not widely reported for quartz, which has tentatively been attributed to peroxy linkages. Differences between the IL and XEOL emission spectra are interpreted as evidence for the presence of multiple excited states. http://hdl.handle.net/10023/2408 Abstract: We present an approach for dealing with coarse-resolution Earth observations (EO) in terrestrial ecosystem data assimilation schemes. The use of coarse-scale observations in ecological data assimilation schemes is complicated by spatial heterogeneity and nonlinear processes in natural ecosystems. If these complications are not appropriately dealt with, then the data assimilation will produce biased results. The "disaggregation" approach that we describe in this paper combines frequent coarse-resolution observations with temporally sparse fine-resolution measurements. We demonstrate the approach using a demonstration data set based on measurements of an Arctic ecosystem. In this example, normalized difference vegetation index observations are assimilated into a "zero-order" model of leaf area index and carbon uptake. The disaggregation approach conserves key ecosystem characteristics regardless of the observation resolution and estimates the carbon uptake to within 1% of the demonstration data set "truth." Assimilating the same data in the normal manner, but without the disaggregation approach, results in carbon uptake being underestimated by 58% at an observation resolution of 250 m. The disaggregation method allows the combination of multiresolution EO and improves in spatial resolution if observations are located on a grid that shifts from one observation time to the next. Additionally, the approach is not tied to a particular data assimilation scheme, model, or EO product and can cope with complex observation distributions, as it makes no implicit assumptions of normality. 2011-04-29T00:00:00Z Hill, T. C. Quaife, T. Williams, M. We present an approach for dealing with coarse-resolution Earth observations (EO) in terrestrial ecosystem data assimilation schemes. The use of coarse-scale observations in ecological data assimilation schemes is complicated by spatial heterogeneity and nonlinear processes in natural ecosystems. If these complications are not appropriately dealt with, then the data assimilation will produce biased results. The "disaggregation" approach that we describe in this paper combines frequent coarse-resolution observations with temporally sparse fine-resolution measurements. We demonstrate the approach using a demonstration data set based on measurements of an Arctic ecosystem. In this example, normalized difference vegetation index observations are assimilated into a "zero-order" model of leaf area index and carbon uptake. The disaggregation approach conserves key ecosystem characteristics regardless of the observation resolution and estimates the carbon uptake to within 1% of the demonstration data set "truth." Assimilating the same data in the normal manner, but without the disaggregation approach, results in carbon uptake being underestimated by 58% at an observation resolution of 250 m. The disaggregation method allows the combination of multiresolution EO and improves in spatial resolution if observations are located on a grid that shifts from one observation time to the next. Additionally, the approach is not tied to a particular data assimilation scheme, model, or EO product and can cope with complex observation distributions, as it makes no implicit assumptions of normality. http://hdl.handle.net/10023/2407 Abstract: The atmosphere and biosphere interact strongly in the planetary boundary layer. Understanding the mechanisms controlling the coupled atmosphere-biosphere system allows improved scaling between observations at the stand scale ( e. g., flux towers) and those at larger scales, e. g., airborne or satellite measurements. Simulation of the joint atmosphere-biosphere system permits the study of feedbacks occurring within the coupled system. In this paper, two well-tested models, one a process-based biosphere model ( SPA) and the other a planetary boundary layer model ( CAPS), were coupled to allow simulation of atmosphere-biosphere feedbacks and interactions with a focus on ecological controls. As part of the validation process, the biosphere model was tested using eddy covariance, surface meteorology, and soil data collected during a 120 day period at a boreal black spruce site during the 1994 BOREAS field campaign. The coupled atmosphere-biosphere model was also validated with radiosonde data above the black spruce site, demonstrating that atmosphere and biosphere models can be coherently combined. We show that negative feedbacks at the black spruce site have strong moderating effects. The feedbacks reduce the mean impact of LAI changes on the atmospheric surface layer by 21% for latent energy, 64% for air temperature, and 44% for water mixing ratio. We show that both radiative and hydraulic limitations imposed by the vegetation structure strongly affected the interactions within the atmosphere-biosphere system, while the impact of the canopy roughness length was weak. 2008-08-12T00:00:00Z Hill, T. C. Williams, M. Moncrieff, J. B. The atmosphere and biosphere interact strongly in the planetary boundary layer. Understanding the mechanisms controlling the coupled atmosphere-biosphere system allows improved scaling between observations at the stand scale ( e. g., flux towers) and those at larger scales, e. g., airborne or satellite measurements. Simulation of the joint atmosphere-biosphere system permits the study of feedbacks occurring within the coupled system. In this paper, two well-tested models, one a process-based biosphere model ( SPA) and the other a planetary boundary layer model ( CAPS), were coupled to allow simulation of atmosphere-biosphere feedbacks and interactions with a focus on ecological controls. As part of the validation process, the biosphere model was tested using eddy covariance, surface meteorology, and soil data collected during a 120 day period at a boreal black spruce site during the 1994 BOREAS field campaign. The coupled atmosphere-biosphere model was also validated with radiosonde data above the black spruce site, demonstrating that atmosphere and biosphere models can be coherently combined. We show that negative feedbacks at the black spruce site have strong moderating effects. The feedbacks reduce the mean impact of LAI changes on the atmospheric surface layer by 21% for latent energy, 64% for air temperature, and 44% for water mixing ratio. We show that both radiative and hydraulic limitations imposed by the vegetation structure strongly affected the interactions within the atmosphere-biosphere system, while the impact of the canopy roughness length was weak. http://hdl.handle.net/10023/2406 Abstract: The planetary boundary layer (PBL) provides an important link between the scales and processes resolved by global atmospheric sampling/modeling and site-based flux measurements. The PBL is in direct contact with the land surface, both driving and responding to ecosystem processes. Measurements within the PBL (e. g., by radiosondes, aircraft profiles, and flask measurements) have a footprint, and thus an integrating scale, on the order of; similar to 1-100 km. We use the coupled atmosphere-biosphere model (CAB) and a Bayesian data assimilation framework to investigate the amount of biosphere process information that can be inferred from PBL measurements. We investigate the information content of PBL measurements in a two-stage study. First, we demonstrate consistency between the coupled model (CAB) and measurements, by comparing the model to eddy covariance flux tower measurements (i.e., water and carbon fluxes) and also PBL scalar profile measurements (i.e., water, carbon dioxide, and temperature) from Canadian boreal forest. Second, we use the CAB model in a set of Bayesian inversions experiments using synthetic data for a single day. In the synthetic experiment, leaf area and respiration were relatively well constrained, whereas surface albedo and plant hydraulic conductance were only moderately constrained. Finally, the abilities of the PBL profiles and the eddy covariance data to constrain the parameters were largely similar and only slightly lower than the combination of both observations. 2011-07-01T00:00:00Z Hill, T. C. Williams, M. Woodward, F. I. Moncrieff, J. B. The planetary boundary layer (PBL) provides an important link between the scales and processes resolved by global atmospheric sampling/modeling and site-based flux measurements. The PBL is in direct contact with the land surface, both driving and responding to ecosystem processes. Measurements within the PBL (e. g., by radiosondes, aircraft profiles, and flask measurements) have a footprint, and thus an integrating scale, on the order of; similar to 1-100 km. We use the coupled atmosphere-biosphere model (CAB) and a Bayesian data assimilation framework to investigate the amount of biosphere process information that can be inferred from PBL measurements. We investigate the information content of PBL measurements in a two-stage study. First, we demonstrate consistency between the coupled model (CAB) and measurements, by comparing the model to eddy covariance flux tower measurements (i.e., water and carbon fluxes) and also PBL scalar profile measurements (i.e., water, carbon dioxide, and temperature) from Canadian boreal forest. Second, we use the CAB model in a set of Bayesian inversions experiments using synthetic data for a single day. In the synthetic experiment, leaf area and respiration were relatively well constrained, whereas surface albedo and plant hydraulic conductance were only moderately constrained. Finally, the abilities of the PBL profiles and the eddy covariance data to constrain the parameters were largely similar and only slightly lower than the combination of both observations. http://hdl.handle.net/10023/2295 Abstract: One of the most profound events in biospheric evolution was the emergence of animals, which is thought to have occurred some 600-650 Ma. Here we report on the discovery of phosphatised body fossils that we interpret as ancient sponge-like fossils and term them Otavia antiqua gen. et sp. nov. The fossils are found in Namibia in rocks that range in age between about 760 Ma and 550 Ma. This age places the advent of animals some 100 to 150 million years earlier than proposed, and prior to the extreme climatic changes and postulated stepwise increases in oxygen levels of Ediacaran time. These findings support the predictions based on genetic sequencing and inferences drawn from biomarkers that the first animals were sponges. Further, the deposition and burial of Otavia as sedimentary particles may have driven the large positive C-isotopic excursions and increases in oxygen levels that have been inferred for Neoproterozoic time. 2012-01-01T00:00:00Z Brain, C. K. 'Bob' Prave, Anthony R. Hoffmann, Karl-Heinz Fallick, Anthony E. Botha, Andre Herd, Donald A. Sturrock, Craig Young, Iain Condon, Daniel J. Allison, Stuart G. One of the most profound events in biospheric evolution was the emergence of animals, which is thought to have occurred some 600-650 Ma. Here we report on the discovery of phosphatised body fossils that we interpret as ancient sponge-like fossils and term them Otavia antiqua gen. et sp. nov. The fossils are found in Namibia in rocks that range in age between about 760 Ma and 550 Ma. This age places the advent of animals some 100 to 150 million years earlier than proposed, and prior to the extreme climatic changes and postulated stepwise increases in oxygen levels of Ediacaran time. These findings support the predictions based on genetic sequencing and inferences drawn from biomarkers that the first animals were sponges. Further, the deposition and burial of Otavia as sedimentary particles may have driven the large positive C-isotopic excursions and increases in oxygen levels that have been inferred for Neoproterozoic time. http://hdl.handle.net/10023/2002 Abstract: In easternmost Bhutan the South Tibetan detachment (STD) is a ductile shear zone that juxtaposes the Radi (or Sakteng) klippe of the Tethyan Sedimentary Series from underlying high-grade Greater Himalayan rocks. In situ LA-ICPMS U-Th-Pb analysis of metamorphic monazite from the immediate footwall and hanging wall of the STD within the shear zone at the base of the klippe, constrains north vergent normal shear to between 25 and 20 Ma. Coeval thrusting on the Main Central Thrust during this time supports a phase of channel flow-viscous wedge model activity, lasting only similar to 3 Ma. Geochronologic data from the eastern Himalaya indicate alternating mechanisms for extrusion of the metamorphic core of the orogen from the Late Oligocene through to the Late Miocene, switching from channel flow-viscous wedge behavior to critical taper-frictional wedge behavior, each phase lasting approximately only 2 to 5 Ma. The tectonic evolution of the eastern Himalaya is comparable to central and western Himalayan tectonics during the Early Miocene, but during the Middle Miocene metamorphism and magmatism in the eastern Himalaya migrated toward the orogenic hinterland, a process not widely documented elsewhere in the Himalaya, thus highlighting the need for an orogenic model in three spatial dimensions. Citation: Chambers, J., R. Parrish, T. Argles, N. Harris, and M. Horstwood (2011), A short-duration pulse of ductile normal shear on the outer South Tibetan detachment in Bhutan: Alternating channel flow and critical taper mechanics of the eastern Himalaya, Tectonics, 30, TC2005, doi:10.1029/2010TC002784. 2011-03-11T00:00:00Z Chambers, Jennifer Parrish, Randall Argles, Tom Harris, Nigel Horstwood, Matthew In easternmost Bhutan the South Tibetan detachment (STD) is a ductile shear zone that juxtaposes the Radi (or Sakteng) klippe of the Tethyan Sedimentary Series from underlying high-grade Greater Himalayan rocks. In situ LA-ICPMS U-Th-Pb analysis of metamorphic monazite from the immediate footwall and hanging wall of the STD within the shear zone at the base of the klippe, constrains north vergent normal shear to between 25 and 20 Ma. Coeval thrusting on the Main Central Thrust during this time supports a phase of channel flow-viscous wedge model activity, lasting only similar to 3 Ma. Geochronologic data from the eastern Himalaya indicate alternating mechanisms for extrusion of the metamorphic core of the orogen from the Late Oligocene through to the Late Miocene, switching from channel flow-viscous wedge behavior to critical taper-frictional wedge behavior, each phase lasting approximately only 2 to 5 Ma. The tectonic evolution of the eastern Himalaya is comparable to central and western Himalayan tectonics during the Early Miocene, but during the Middle Miocene metamorphism and magmatism in the eastern Himalaya migrated toward the orogenic hinterland, a process not widely documented elsewhere in the Himalaya, thus highlighting the need for an orogenic model in three spatial dimensions. Citation: Chambers, J., R. Parrish, T. Argles, N. Harris, and M. Horstwood (2011), A short-duration pulse of ductile normal shear on the outer South Tibetan detachment in Bhutan: Alternating channel flow and critical taper mechanics of the eastern Himalaya, Tectonics, 30, TC2005, doi:10.1029/2010TC002784. http://hdl.handle.net/10023/1938 Abstract: The Irrawaddy (Ayeyarwady) River of Myanmar is ranked as having the fifth-largest suspended load and the fourth-highest total dissolved load of the world's rivers, and the combined Irrawaddy and Salween ( Thanlwin) system is regarded as contributing 20% of the total flux of material from the Himalayan-Tibetan orogen. The estimates for the Irrawaddy are taken from published quotations of a nineteenth-century data set, and there are no available published data for the Myanmar reaches of the Salween. Apart from our own field studies in 2005 and 2006, no recent research documenting the sediment load of these important large rivers has been conducted, although their contribution to biogeochemical cycles and ocean geochemistry is clearly significant. We present a reanalysis of the Irrawaddy data from the original 550-page report of Gordon covering 10 yr of discharge ( 1869-1879) and 1 yr of sediment concentration measurements ( 1877-1878). We describe Gordon's methodologies, evaluate his measurements and calculations and the adjustments he made to his data set, and present our revised interpretation of nineteenth-century discharge and sediment load with an estimate of uncertainty. The 10-yr average of annual suspended sediment load currently cited in the literature is assessed as being underestimated by 27% on the basis of our sediment rating curve of the nineteenth-century data. On the basis of our sampling of suspended load, the nineteenth-century concentrations are interpreted to be missing about 18% of their total mass, which is the proportion of sediment recovered by a 0.45-mm filter. The new annual Irrawaddy suspended sediment load is MT. Our revised estimate of the annual sediment load 364 +/- 60 from the Irrawaddy-Salween system for the nineteenth century ( 600 MT) represents more than half the present-day Ganges-Brahmaputra flux to the Indian Ocean. Since major Chinese rivers have reduced their load due to damming, the Irrawaddy is likely the third-largest contributor of sediment load in the world. 2007-11-01T00:00:00Z Robinson, Ruth Alison Joyce Bird, M I Win Oo, N Hoey, T B Maung Aye, M Higgitt, D L Lu, X X Sandar Aye, Khin Swe, A Tun, T Lhaing Win, S The Irrawaddy (Ayeyarwady) River of Myanmar is ranked as having the fifth-largest suspended load and the fourth-highest total dissolved load of the world's rivers, and the combined Irrawaddy and Salween ( Thanlwin) system is regarded as contributing 20% of the total flux of material from the Himalayan-Tibetan orogen. The estimates for the Irrawaddy are taken from published quotations of a nineteenth-century data set, and there are no available published data for the Myanmar reaches of the Salween. Apart from our own field studies in 2005 and 2006, no recent research documenting the sediment load of these important large rivers has been conducted, although their contribution to biogeochemical cycles and ocean geochemistry is clearly significant. We present a reanalysis of the Irrawaddy data from the original 550-page report of Gordon covering 10 yr of discharge ( 1869-1879) and 1 yr of sediment concentration measurements ( 1877-1878). We describe Gordon's methodologies, evaluate his measurements and calculations and the adjustments he made to his data set, and present our revised interpretation of nineteenth-century discharge and sediment load with an estimate of uncertainty. The 10-yr average of annual suspended sediment load currently cited in the literature is assessed as being underestimated by 27% on the basis of our sediment rating curve of the nineteenth-century data. On the basis of our sampling of suspended load, the nineteenth-century concentrations are interpreted to be missing about 18% of their total mass, which is the proportion of sediment recovered by a 0.45-mm filter. The new annual Irrawaddy suspended sediment load is MT. Our revised estimate of the annual sediment load 364 +/- 60 from the Irrawaddy-Salween system for the nineteenth century ( 600 MT) represents more than half the present-day Ganges-Brahmaputra flux to the Indian Ocean. Since major Chinese rivers have reduced their load due to damming, the Irrawaddy is likely the third-largest contributor of sediment load in the world. http://hdl.handle.net/10023/1934 Abstract: Structural and 40Ar/39Ar data from the Yunkaidashan Belt document kinematic and tectonothermal characteristics of early Mesozoic Indosinian orogenesis in the southern part of the South China Block. The Yunkaidashan Belt is tectonically divided from east to west into the Wuchuang-Sihui shear zone, Xinyi-Gaozhou block, and the Fengshan-Qinxi shear zone. Indosinian structural elements ascribed to the Indosinian orogeny include D2 and D3 deformation. The early D2 phase is characterized by folding and thrusting with associated foliation and lineation development, related to NW-SE transpression under amphibolite- to greenschist-facies conditions. This event is heterogeneously overprinted by D3 deformation characterized by a gentle-dipping S-3 foliation, subhorizontally to shallowly plunging L3 lineation, some reactived-D2 folds and low-angle normal faults. The D3 fabrics suggest a sinistral transtensional regime under greenschist-facies metamorphism. The timing of the D2 and D3 events have been constrained to the early to middle Triassic (similar to 248-220 Ma) and late Triassic (similar to 220-200 Ma) respectively on the basis of 40Ar/39Ar geochronology and regional geological relations. The change from oblique thrusting (D2) to sinistral transtension (D3) may reflect oblique convergence and crustal thickening followed by relaxation of the overthickened crust. In combination with the regional relations from Xuefengshan to Yunkaidashan and on to Wuyishan, the early phase of the Indosinian orogeny constituted a large-scale positive flower structure and is related to the intracontinental convergence during the assembly of Pangea in which the less competent South China Orogen was squeezed between the more competent North China and Indosinian Blocks. 2007-12-14T00:00:00Z Wang, Yuejun Fan, Weiming Cawood, Peter Anthony Ji, Shaocheng Peng, Touping Chen, Xinyue Structural and 40Ar/39Ar data from the Yunkaidashan Belt document kinematic and tectonothermal characteristics of early Mesozoic Indosinian orogenesis in the southern part of the South China Block. The Yunkaidashan Belt is tectonically divided from east to west into the Wuchuang-Sihui shear zone, Xinyi-Gaozhou block, and the Fengshan-Qinxi shear zone. Indosinian structural elements ascribed to the Indosinian orogeny include D2 and D3 deformation. The early D2 phase is characterized by folding and thrusting with associated foliation and lineation development, related to NW-SE transpression under amphibolite- to greenschist-facies conditions. This event is heterogeneously overprinted by D3 deformation characterized by a gentle-dipping S-3 foliation, subhorizontally to shallowly plunging L3 lineation, some reactived-D2 folds and low-angle normal faults. The D3 fabrics suggest a sinistral transtensional regime under greenschist-facies metamorphism. The timing of the D2 and D3 events have been constrained to the early to middle Triassic (similar to 248-220 Ma) and late Triassic (similar to 220-200 Ma) respectively on the basis of 40Ar/39Ar geochronology and regional geological relations. The change from oblique thrusting (D2) to sinistral transtension (D3) may reflect oblique convergence and crustal thickening followed by relaxation of the overthickened crust. In combination with the regional relations from Xuefengshan to Yunkaidashan and on to Wuyishan, the early phase of the Indosinian orogeny constituted a large-scale positive flower structure and is related to the intracontinental convergence during the assembly of Pangea in which the less competent South China Orogen was squeezed between the more competent North China and Indosinian Blocks. http://hdl.handle.net/10023/1931 Abstract: The Huangshi foreland basin developed on the southern margin of the Dabie Mountains as a result of tectonic loading during Triassic collisional suturing between the North China and South China cratons. Modal and detrital zircon data for Jurassic samples within the basin suggest a multicomponent source with input from both the South China Craton and Dabie Orogen. Samples are predominantly quartz arenites derived, on the basis of framework compositions, from a recycled orogen source. Detrital zircons range in age from Archean to Triassic with a dominant component in the late Paleoproterozoic between 1.9-1.7 Ga and subsidiary components at 2.6-2.2 Ga, 0.8-0.7 Ga, 0.5-0.4 Ga, and 0.33-0.2 Ga. Age data integrated with cathodoluminescence and trace element data for the zircons indicate that the Archean and Proterozoic detritus was derived from igneous and metamorphic sources that overlap with time-equivalent pulses of such activity within the South China Craton. Phanerozoic zircon ages overlap the times of the Ordovician, Carboniferous and Triassic high-pressure metamorphism in the Dabie Mountains. The provenance record, integrated with paleocurrent and regional relations, enables a paleogeographic reconstruction in which the Huangshi Basin was fed by a major axial flowing trunk river system carrying detritus from eastern and southern sources within the South China Craton and was also fed by short south flowing tributaries supplying some detritus from the evolving Dabie Orogen. The dominance of cratonic-derived detritus within the provenance record of the Huangshi Basin contrasts with that of the Hefei foreland basin that lies to the north of the Dabie Mountains, which is dominated by Neoproterozoic - Mesozoic detritus derived directly from the Dabie Mountains and lacks any significant older Paleoproterozoic or Archean components. Easterly extensions of the Dabie-Sulu collisional suture and of the resultant Huangshi Basin occur in Korea and Japan over an along strike length of some 2000 km. Citation: Yang, J., P. A. Cawood, and Y. Du (2010), Detrital record of mountain building: Provenance of Jurassic foreland basin to the Dabie Mountains, Tectonics, 29, TC4011, doi: 10.1029/2009TC002600. 2010-07-27T00:00:00Z Yang, Jianghai Cawood, Peter Anthony Du, Yuansheng The Huangshi foreland basin developed on the southern margin of the Dabie Mountains as a result of tectonic loading during Triassic collisional suturing between the North China and South China cratons. Modal and detrital zircon data for Jurassic samples within the basin suggest a multicomponent source with input from both the South China Craton and Dabie Orogen. Samples are predominantly quartz arenites derived, on the basis of framework compositions, from a recycled orogen source. Detrital zircons range in age from Archean to Triassic with a dominant component in the late Paleoproterozoic between 1.9-1.7 Ga and subsidiary components at 2.6-2.2 Ga, 0.8-0.7 Ga, 0.5-0.4 Ga, and 0.33-0.2 Ga. Age data integrated with cathodoluminescence and trace element data for the zircons indicate that the Archean and Proterozoic detritus was derived from igneous and metamorphic sources that overlap with time-equivalent pulses of such activity within the South China Craton. Phanerozoic zircon ages overlap the times of the Ordovician, Carboniferous and Triassic high-pressure metamorphism in the Dabie Mountains. The provenance record, integrated with paleocurrent and regional relations, enables a paleogeographic reconstruction in which the Huangshi Basin was fed by a major axial flowing trunk river system carrying detritus from eastern and southern sources within the South China Craton and was also fed by short south flowing tributaries supplying some detritus from the evolving Dabie Orogen. The dominance of cratonic-derived detritus within the provenance record of the Huangshi Basin contrasts with that of the Hefei foreland basin that lies to the north of the Dabie Mountains, which is dominated by Neoproterozoic - Mesozoic detritus derived directly from the Dabie Mountains and lacks any significant older Paleoproterozoic or Archean components. Easterly extensions of the Dabie-Sulu collisional suture and of the resultant Huangshi Basin occur in Korea and Japan over an along strike length of some 2000 km. Citation: Yang, J., P. A. Cawood, and Y. Du (2010), Detrital record of mountain building: Provenance of Jurassic foreland basin to the Dabie Mountains, Tectonics, 29, TC4011, doi: 10.1029/2009TC002600. http://hdl.handle.net/10023/1031 Abstract: A suite of quartz samples of different provenances, irradiation, thermal and depositional histories were analysed using spectroscopic ionoluminescence (IL) to investigate variations in emission spectra as a function of cumulative radiation dosing. Protons were selected for implantation to mimic the effect of natural radiation over geological timescales. All samples exhibited depletion in the UV-violet emission (3.2-3.4 eV) with increasing cumulative dose, whilst the red emission (1.8-1.9 eV) increased. A power-law relationship exists between the two emissions. It is inferred that the luminescence emission of quartz is indicative of its radiation history, and spectral analyses could be used to determine the utility of different quartz samples for optically stimulated luminescence dating (OSL) where the detection range is limited to 3.4-4.6 eV. 2011-01-01T00:00:00Z King, Georgina Finch, Adrian Anthony Robinson, Ruth Alison Joyce Hole, D E A suite of quartz samples of different provenances, irradiation, thermal and depositional histories were analysed using spectroscopic ionoluminescence (IL) to investigate variations in emission spectra as a function of cumulative radiation dosing. Protons were selected for implantation to mimic the effect of natural radiation over geological timescales. All samples exhibited depletion in the UV-violet emission (3.2-3.4 eV) with increasing cumulative dose, whilst the red emission (1.8-1.9 eV) increased. A power-law relationship exists between the two emissions. It is inferred that the luminescence emission of quartz is indicative of its radiation history, and spectral analyses could be used to determine the utility of different quartz samples for optically stimulated luminescence dating (OSL) where the detection range is limited to 3.4-4.6 eV.