| 2. |
- Johnsen, Sigfus J., et al.
(author)
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A "deep" ice core from east Greenland
- 1992
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In: MoG Geoscience. ; 29
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Journal article (peer-reviewed)abstract
- Pilot studies on the Renland peninsula in Scoresbysund Fjord, East Greenland, indicated that the relatively small and separate Renland ice cap meets most of the criteria defining a favourable ice-core drill-site. In 1988, a Nordic expedition recovered a continuous surface-to-bedrock ice core from the summit. This relatively short core reaches deep into the past, probably throughout the last glaciation and through most of the preceding interglacial, Eem, 125,000 years B.P. The core contains detailed information on temporal changes of the coastal environment, and serves as a valuable complement to the new deep ice cores being drilled in Central Greenland. Core analyses suggest that (1) during Eemian time the East Greenland climate was at least 5ÔC warmer than now, and the precipitation 20% higher; (2) during the last glacial period, the precipitation decreased to a minimum, perhaps only 20% of the present value; (3) the post-glacial climatic optimum was 2,5ÔC warmer than now; (4) the long-term variability of the record is relatively low, due to isostatic movements in the area; and (5) from 70,000 years B.P. the Greenland glacial climate alternated between two quasi-stable stages. The latter point may reflect a chaotic feature of climate. If so, climate predictions will be difficult to access.
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| 3. |
- Kissling, W. Daniel, et al.
(author)
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Building essential biodiversity variables (EBVs) of species distribution and abundance at a global scale
- 2018
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In: Biological Reviews. - : Wiley. - 1464-7931 .- 1469-185X. ; 93:1, s. 600-625
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Journal article (peer-reviewed)abstract
- © 2017 Cambridge Philosophical Society. Much biodiversity data is collected worldwide, but it remains challenging to assemble the scattered knowledge for assessing biodiversity status and trends. The concept of Essential Biodiversity Variables (EBVs) was introduced to structure biodiversity monitoring globally, and to harmonize and standardize biodiversity data from disparate sources to capture a minimum set of critical variables required to study, report and manage biodiversity change. Here, we assess the challenges of a 'Big Data' approach to building global EBV data products across taxa and spatiotemporal scales, focusing on species distribution and abundance. The majority of currently available data on species distributions derives from incidentally reported observations or from surveys where presence-only or presence-absence data are sampled repeatedly with standardized protocols. Most abundance data come from opportunistic population counts or from population time series using standardized protocols (e.g. repeated surveys of the same population from single or multiple sites). Enormous complexity exists in integrating these heterogeneous, multi-source data sets across space, time, taxa and different sampling methods. Integration of such data into global EBV data products requires correcting biases introduced by imperfect detection and varying sampling effort, dealing with different spatial resolution and extents, harmonizing measurement units from different data sources or sampling methods, applying statistical tools and models for spatial inter- or extrapolation, and quantifying sources of uncertainty and errors in data and models. To support the development of EBVs by the Group on Earth Observations Biodiversity Observation Network (GEO BON), we identify 11 key workflow steps that will operationalize the process of building EBV data products within and across research infrastructures worldwide. These workflow steps take multiple sequential activities into account, including identification and aggregation of various raw data sources, data quality control, taxonomic name matching and statistical modelling of integrated data. We illustrate these steps with concrete examples from existing citizen science and professional monitoring projects, including eBird, the Tropical Ecology Assessment and Monitoring network, the Living Planet Index and the Baltic Sea zooplankton monitoring. The identified workflow steps are applicable to both terrestrial and aquatic systems and a broad range of spatial, temporal and taxonomic scales. They depend on clear, findable and accessible metadata, and we provide an overview of current data and metadata standards. Several challenges remain to be solved for building global EBV data products: (i) developing tools and models for combining heterogeneous, multi-source data sets and filling data gaps in geographic, temporal and taxonomic coverage, (ii) integrating emerging methods and technologies for data collection such as citizen science, sensor networks, DNA-based techniques and satellite remote sensing, (iii) solving major technical issues related to data product structure, data storage, execution of workflows and the production process/cycle as well as approaching technical interoperability among research infrastructures, (iv) allowing semantic interoperability by developing and adopting standards and tools for capturing consistent data and metadata, and (v) ensuring legal interoperability by endorsing open data or data that are free from restrictions on use, modification and sharing. Addressing these challenges is critical for biodiversity research and for assessing progress towards conservation policy targets and sustainable development goals.
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| 4. |
- Quinn, K., et al.
(author)
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Weibel-Induced Filamentation during an Ultrafast Laser-Driven Plasma Expansion
- 2012
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In: Physical Review Letters. - American Physical Society. - 0031-9007 .- 1079-7114. ; 108:13, s. 135001-
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Journal article (peer-reviewed)abstract
- The development of current instabilities behind the front of a cylindrically expanding plasma has been investigated experimentally via proton probing techniques. A multitude of tubelike filamentary structures is observed to form behind the front of a plasma created by irradiating solid-density wire targets with a high-intensity (I∼1019 W/cm2), picosecond-duration laser pulse. These filaments exhibit a remarkable degree of stability, persisting for several tens of picoseconds, and appear to be magnetized over a filament length corresponding to several filament radii. Particle-in-cell simulations indicate that their formation can be attributed to a Weibel instability driven by a thermal anisotropy of the electron population. We suggest that these results may have implications in astrophysical scenarios, particularly concerning the problem of the generation of strong, spatially extended and sustained magnetic fields in astrophysical jets.
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