| 43251. |
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| 43252. |
- Plunkett, Gill, et al.
(författare)
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Distal tephrochronology in volcanic regions: Challenges and insights from Kamchatkan lake sediments
- 2015
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Ingår i: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 134, s. 26-40
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Tidskriftsartikel (refereegranskat)abstract
- Kamchatka is one of the world's most active volcanic regions and has hosted many explosive eruptions during the Holocene. These eruptions had the potential to disperse tephra over wide areas, forming time-synchronous markers wherever those tephras are found. Recent research in Kamchatka has begun to focus on the geochemical analysis of individual glass shards in order to characterise tephra layers. We have applied this approach to the study of visible tephras from three lakes - one in central and two in northern Kamchatka - with the aim of identifying key tephras and potential issues in the application of distal (>100 km from an active volcano) tephra in volcanically complex regions. In total, 23 tephras from 22 tephra beds have been geochemically analysed, representing products from at least four volcanic systems in Kamchatka. We demonstrate that distal lake sediments in the region can yield reliable tephrostratigraphies, capturing tephra from eruptions that have the greatest potential to disperse volcanic ash beyond the region. We draw attention to issues relating to correlating and distinguishing key marker horizons from the highly active Shiveluch Volcano, namely the need to ensure inter-lab comparability of geochemical data and good chronological control of the proximal and distal tephras. Importantly, we have also extended the known distribution of two key tephra isochrons from the Ksudach volcano. Our work contributes valuable glass geochemical on data several key marker beds that will facilitate future tephra and palaeoenvironmental research within and beyond Kamchatka. (C) 2015 Elsevier B.V. All rights reserved.
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| 43253. |
- Podgorski, Joel E., et al.
(författare)
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Integrated interpretation of helicopter and ground-based geophysical data recorded within the Okavango Delta, Botswana
- 2015
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Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 114, s. 52-67
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Tidskriftsartikel (refereegranskat)abstract
- Integration of information from the following sources has been used to produce a much better constrained and more complete four-unit geological/hydrological model of the Okavango Delta than previously available: (i) a 3D resistivity model determined from helicopter time-domain electromagnetic (HTEM) data recorded across most of the delta, (ii) 2D models and images derived from ground-based electrical resistance tomographic, transient electromagnetic, and high resolution seismic reflection/refraction tomographic data acquired at four selected sites in western and north-central regions of the delta, and (iii) geological details extracted from boreholes in northeastern and southeastern parts of the delta. The upper heterogeneous unit is the modern delta, which comprises extensive dry and freshwater-saturated sand and lesser amounts of clay and salt. It is characterized by moderate to high electrical resistivities and very low to low P-wave velocities. Except for images of several buried abandoned river channels, it is non-reflective. The laterally extensive underlying unit of low resistivities, low P-wave velocity, and subhorizontal reflectors very likely contains saline-water-saturated sands and clays deposited in the huge Paleo Lake Makgadikgadi (PLM), which once covered a 90,000 km(2) area that encompassed the delta, Lake Ngami, the Mababe Depression, and the Makgadikgadi Basin. Examples of PLM sediments are intersected in many boreholes. Low permeability clay within the PLM unit seems to be a barrier to the downward flow of the saline water. Below the PLM unit, freshwater-saturated sand of the Paleo Okavango Megafan (POM) unit is distinguished by moderate to high resistivities, low P-wave velocity, and numerous subhorizontal reflectors. The POM unit is interpreted to be the remnants of a megafan based on the arcuate nature of its front and the semi-conical shape of its upper surface in the HTEM resistivity model. Moderate to high resistivity subhorizontal layers are consistent with this interpretation. The deepest unit is the basement with very high resistivity, high P-wave velocity, and low or complex reflectivity. The interface between the POM unit and basement is a prominent seismic reflector. (C) 2015 Elsevier B.V. All rights reserved.
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| 43254. |
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| 43255. |
- Podgorski, Joel E., et al.
(författare)
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Processing and inversion of commercial helicopter time-domain electromagnetic data for environmental assessments and geologic and hydrologic mapping
- 2013
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Ingår i: Geophysics. - 0016-8033 .- 1942-2156. ; 78:4, s. E149-E159
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Tidskriftsartikel (refereegranskat)abstract
- Helicopter time-domain electromagnetic (HTEM) surveying has historically been used for mineral exploration, but over the past decade it has started to be used in environmental assessments and geologic and hydrologic mapping. Such surveying is a cost-effective means of rapidly acquiring densely spaced data over large regions. At the same time, the quality of HTEM data can suffer from various inaccuracies. We developed an effective strategy for processing and inverting a commercial HTEM data set affected by uncertainties and systematic errors. The delivered data included early time gates contaminated by transmitter currents, noise in late time gates, and amplitude shifts between adjacent flights that appeared as artificial lineations in maps of the data and horizontal slices extracted from inversion models. Multiple processing steps were required to address these issues. Contaminated early time gates and noisy late time gates were semiautomatically identified and eliminated on a record-by-record basis. Timing errors between the transmitter and receiver electronics and inaccuracies in absolute amplitudes were corrected after calibrating selected HTEM data against data simulated from accurate ground-based TEM measurements. After editing and calibration, application of a quasi-3D spatially constrained inversion scheme significantly reduced the artificial lineations. Residual lineations were effectively eliminated after incorporating the transmitter and receiver altitudes and line-to-line amplitude factors in the inversion process. The final inverted model was very different from that generated from the original data provided by the contractor. For example, the average resistivity of the thick surface layer decreased from similar to 1800 to similar to 30 Omega m, the depths to the layer boundaries were reduced by 15%-23%, and the artificial lineations were practically eliminated. Our processing and inversion strategy is entirely general, such that with minor system-specific modifications it could be applied to any HTEM data set, including those recorded many years ago.
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| 43256. |
- Poelzer, Gregory A, et al.
(författare)
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The Societal Dimension of SLO in European Mining
- 2022
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Ingår i: The Palgrave Handbook of Social License to Operate and Energy Transitions. - Cham : Springer Nature. - 9783030747251 - 9783030747251
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Bokkapitel (refereegranskat)abstract
- Future sustainability challenges require building public trust at both the local and societal levels. Significant attention has gone into understanding social license to operate (SLO) in company to community relationships, but the connection between industry and broader society is less well-defined. As the mining industry increasingly finds itself at the center of societal debates, the necessity to define societal SLO grows. And, as both national and supernational authorities attempt to meet climate and sustainability goals, understanding the key values and expectations needed to achieve SLO at both the local and societal levels is vital for success.
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| 43257. |
- Poeplau, Christopher
(författare)
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Meta-studies in land use science: Current coverage and prospects
- 2016
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Ingår i: AMBIO: A Journal of the Human Environment. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 45, s. 15-28
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Forskningsöversikt (refereegranskat)abstract
- Land use science has traditionally used case-study approaches for in-depth investigation of land use change processes and impacts. Meta-studies synthesize findings across case-study evidence to identify general patterns. In this paper, we provide a review of meta-studies in land use science. Various meta-studies have been conducted, which synthesize deforestation and agricultural land use change processes, while other important changes, such as urbanization, wetland conversion, and grassland dynamics have hardly been addressed. Meta-studies of land use change impacts focus mostly on biodiversity and biogeochemical cycles, while meta-studies of socioeconomic consequences are rare. Land use change processes and land use change impacts are generally addressed in isolation, while only few studies considered trajectories of drivers through changes to their impacts and their potential feedbacks. We provide a conceptual framework for linking meta-studies of land use change processes and impacts for the analysis of coupled human-environmental systems. Moreover, we provide suggestions for combining meta-studies of different land use change processes to develop a more integrated theory of land use change, and for combining meta-studies of land use change impacts to identify tradeoffs between different impacts. Land use science can benefit from an improved conceptualization of land use change processes and their impacts, and from new methods that combine meta-study findings to advance our understanding of human-environmental systems.
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| 43258. |
- Poeplau, Christopher, et al.
(författare)
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Sensitivity of soil carbon fractions and their specific stabilization mechanisms to extreme soil warming in a subarctic grassland
- 2017
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 23, s. 1316-1327
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial carbon cycle feedbacks to global warming are major uncertainties in climate models. For in-depth understanding of changes in soil organic carbon (SOC) after soil warming, long-term responses of SOC stabilization mechanisms such as aggregation, organo-mineral interactions and chemical recalcitrance need to be addressed. This study investigated the effect of 6 years of geothermal soil warming on different SOC fractions in an unmanaged grassland in Iceland. Along an extreme warming gradient of + 0 to similar to+ 40 degrees C, we isolated five fractions of SOC that varied conceptually in turnover rate from active to passive in the following order: particulate organic matter (POM), dissolved organic carbon (DOC), SOC in sand and stable aggregates (SA), SOC in silt and clay (SC-rSOC) and resistant SOC (rSOC). Soil warming of 0.6 degrees C increased bulk SOC by 22 +/- 43% (0-10 cm soil layer) and 27 +/- 54% (20-30 cm), while further warming led to exponential SOC depletion of up to 79 +/- 14% (0-10 cm) and 74 +/- 8% (20-30) in the most warmed plots (similar to+ 40 degrees C). Only the SA fraction was more sensitive than the bulk soil, with 93 +/- 6% (0-10 cm) and 86 +/- 13% (20-30 cm) SOC losses and the highest relative enrichment in C-13 as an indicator for the degree of decomposition (+ 1.6 +/- 1.5 parts per thousand in 0-10 cm and + 1.3 +/- 0.8 parts per thousand in 20-30 cm). The SA fraction mass also declined along the warming gradient, while the SC fraction mass increased. This was explained by deactivation of aggregate-binding mechanisms. There was no difference between the responses of SC-rSOC (slow-cycling) and rSOC (passive) to warming, and C-13 enrichment in rSOC was equal to that in bulk soil. We concluded that the sensitivity of SOC to warming was not a function of age or chemical recalcitrance, but triggered by changes in biophysical stabilization mechanisms, such as aggregation.
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| 43259. |
- Poggio, Laura, et al.
(författare)
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Legacy data for 3D modelling of peat properties with uncertainty estimation in Dava bog - Scotland
- 2020
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Ingår i: Geoderma regional. - : Elsevier. - 2352-0094. ; 22
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Tidskriftsartikel (refereegranskat)abstract
- Peatlands are an important potential sink or source of carbon and play a significant role in climate change regulation. Understanding peatland as 3D-landforms is as important as mapping their spatial extent. The main aim of this work was to estimate a 3D representation of peat properties and assess the associated spatial uncertainty, to provide baseline information for climate and land use change analyses. In this study a combination of 3D Generalized Additive Models and 3D geostatistics was applied to a raised basin bog using legacy data to map carbon content. The study presents a novel approach based on methods providing quantification of the spatial uncertainty and the possibility to model complex relationships. The approach fully exploits the 3D spatial relationships between the survey points while supported by environmental variables. The methods proved to be general and highly flexible. The results of this study showed that it is possible to model peat properties to obtain a detailed volumetric assessment of the peat, including carbon stocks from a limited set of legacy data. The estimates of spatial uncertainty are important when including the results in further environmental and climate-change models or for decision making to provide alternatives and prioritisation. (c) 2020 Elsevier B.V. All rights reserved.
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| 43260. |
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