The Dakhleh Glass: Product of an impact airburst or cratering event in the Western Desert of Egypt?     

Gordon R. OSINSKI  Johanna KIENIEWICZ  Jennifer R. SMITH  Mark B. E. BOSLOUGH  Mark ECCLESTON  Henry P. SCHWARCZ  Maxine R. KLEINDIENST  Albert F. C. HALDEMANN  Charles S. CHURCHER 《Meteoritics & planetary science》2008,43(12):2089-2107

Abstract— Impact cratering is a ubiquitous geological process on the terrestrial planets. Meteorite impact craters are the most visible product of impact events, but there is a growing recognition that large aerial bursts or airbursts should occur relatively frequently throughout geological time. In this contribution, we report on an unusual impact glass‐the Dakhleh Glass (DG)–which is distributed over an area of ?400 km ²of the Dakhleh Oasis, Egypt. This region preserves a rich history of habitation stretching back to over 400,000 years before the emergence of Homo sapiens. We report on observations made during recent fieldwork and subsequent analytical analyses that strengthen previous suggestions that the DG formed during an impact event. The wide distribution and large size of DG specimens (up to ?50 cm across), the chemistry (e.g., CaO and Al₂O₃ contents up to ?25 and ?18 wt, respectively), the presence of lechatelierite and burnt sediments, and the inclusion of clasts and spherules in the DG is inconsistent with known terrestrial processes of glass formation. The age and other textural characteristics rule out a human origin. Instead, we draw upon recent numerical modeling of airbursts to suggest that the properties of DG, coupled with the absence of a confirmed crater, can best be explained by melting of surficial sediments as a result of a large airburst event. We suggest that glass produced by such events should, therefore, be more common in the rock record than impact craters, assuming that the glass formed in a suitable preserving environment.  相似文献   

Development of a generic concept to analyze the accessibility of emergency facilities in critical road infrastructure for disaster scenarios: exemplary application for the 2017 wildfires in Chile and Portugal     

Guth  Johanna  Wursthorn  Sven  Braun  Andreas Ch.  Keller  Sina 《Natural Hazards》2019,97(3):979-999

Natural Hazards - Natural hazards such as earthquakes, floods, or wildfires pose a serious threat to road infrastructure. Especially in emergency situations, the society depends on the road...  相似文献   

Latest Cretaceous storm-generated sea grass accumulations in the Maastrichtian type area,the Netherlands – preliminary observations     

John W.M. Jagt  Mart Deckers  Stephen K. Donovan  René Fraaije  Stijn Goolaerts  Raymond van der Ham  Malcolm B. Hart  Elena A. Jagt-Yazykova  Johanna van Konijnenburg-van Cittert  Sjir Renkens 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(5):590-598

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Impact of different energies of precipitating particles on NOx generation in the middle and upper atmosphere during geomagnetic storms     

Esa Turunen  Pekka T. Verronen  Annika Seppälä  Craig J. Rodger  Mark A. Clilverd  Johanna Tamminen  Carl-Fredrik Enell  Thomas Ulich 《Journal of Atmospheric and Solar》2009,71(10-11):1176-1189

Energetic particle precipitation couples the solar wind to the Earth's atmosphere and indirectly to Earth's climate. Ionisation and dissociation increases, due to particle precipitation, create odd nitrogen (NO_x) and odd hydrogen (HO_X) in the upper atmosphere, which can affect ozone chemistry. The long-lived NO_x can be transported downwards into the stratosphere, particularly during the polar winter. Thus, the impact of NO_x is determined by both the initial ionisation production, which is a function of the particle flux and energy spectrum, as well as transport rates. In this paper, we use the Sodankylä Ion and Neurtal Chemistry (SIC) model to simulate the production of NO_x from examples of the most representative particle flux and energy spectra available today of solar proton events (SPE), auroral energy electrons, and relativistic electron precipitation (REP). Large SPEs are found to produce higher initial NO_x concentrations than long-lived REP events, which themselves produce higher initial NO_x levels than auroral electron precipitation. Only REP microburst events were found to be insignificant in terms of generating NO_x. We show that the Global Ozone Monitoring by Occultation of Stars (GOMOS) observations from the Arctic winter 2003–2004 are consistent with NO_x generation by a combination of SPE, auroral altitude precipitation, and long-lived REP events.  相似文献   

Temporospatial dynamics and public health significance of bacterial flora identified on a major leatherback turtle (Dermochelys coriacea) nesting beach in the Southern Caribbean          下载免费PDF全文

Ayanna Carla N. Phillips  Johanna Coutou  Stacy Rajh  Neville Stewart  Antonio Watson  Adam Jehu  Hamish Asmath  Francis Dziva  Chandrashekhar Unakal  Ridley Holder  Raymond Raoul Carthy 《Marine Ecology》2017,38(2)

Grande Riviere beach, on the island of Trinidad, supports the largest nesting population of leatherback turtles in the Caribbean region. Throughout the nesting season, nests are naturally disturbed by newly nesting females, resulting in egg breakage and loss of some nest viability. This environment is ideal for the growth and proliferation of microorganisms. The range of bacterial flora present in beach sand and egg shells was examined, with emphasis on bacteria that may pose a threat to public and animal health. The extent to which the bacterial load and genera on the beach changed throughout the season was also assessed. Twenty‐five genera were identified, with Pseudomonas spp. found to be the most predominant environmental bacteria. Four genera identified possess zoonotic potential, while five additional genera are known to be of public and animal health significance. Distinct shifts in the density and distribution of bacteria were observed along the beach from early to peak nesting season. Shifts were seen across heavily traversed zones, thus highlighting the potential exposure threats posed to beach visitors and animals alike. Further studies aimed at speciating this population of bacteria, as well as isolating potential fungal pathogens may mitigate this threat. Identification of bacterial agents that are specifically pathogenic to leatherback turtles, turtle eggs, hatchlings and those who may interact with these animals will serve to enhance and guide efforts to better conserve this species and protect the health of all who visit this ecologically significant site.  相似文献   

Period analysis for the peculiar variable FG sagittae     

Johanna Jurcsik  László Szabados 《Astrophysics and Space Science》1989,153(1):45-54

The analysis of the available photoelectric observations covering the interval 1970–1987 was performed. The rapid secular variation of the physical parameters of the star makes the analysis of the whole data set impossible. From the yearly observations (2–3 cycles long) only one period can be determined, the variation of these periods shows a 4–5 year periodicity. The analysis of 2–5 years of observations shows two close frequency components with a nearly constant frequency ratio but with varying amplitudes. The two frequency fits, however, do not describe all the characteristics of the light curve. New photoelectric observations carried out between 1980 and 1987 are also published.  相似文献   

The last glaciation of the Arctic volcanic island Jan Mayen     

Astrid Lyså  Eiliv A. Larsen  Johanna Anjar  Naki Akçar  Morgan Ganerød  Asbjørn Hiksdal  Roelant Van Der Lelij  Christof Vockenhuber 《Boreas: An International Journal of Quaternary Research》2021,50(1):6-28

The volcanic island of Jan Mayen, remotely located in the Norwegian-Greenland Sea, was covered by a contiguous ice cap during the Late Weichselian. Until now, it has been disputed whether parts of the island south of the presently glaciated Mount Beerenberg area were ever glaciated. Based on extensive field mapping we demonstrate that an ice cap covered all land areas and likely also extended onto the shallow shelf areas southeast and east of the island. Chronological interpretations are based on K-Ar and ⁴⁰Ar/³⁹Ar dating of volcanic rocks, cosmogenic nuclide (³⁶Cl) surface exposure dating of bedrock and glacial erratics, and radiocarbon dating. We argue that ice growth started after 34 ka and that an initial deglaciation started some 21.5–19.5 ka in the southern and middle parts of the island. In the northern parts, closer to the present glaciers, the deglaciation might have started later, as evidenced by the establishment of vegetation 17–16 cal. ka BP. During full glaciation, the ice cap was likely thickest over the southern part of the island. This may explain a seemingly delayed deglaciation compared with the northern parts despite earlier initial deglaciation. In a broader context, the new knowledge of the Late Weichselian of the island contributes to the understanding of glaciations surrounding the North Atlantic and its climate history.  相似文献   

Visualizing flood risk,enabling participation and supporting climate change adaptation using the Geoweb: the case of coastal communities in Nova Scotia,Canada     

Andrea Minano  Peter A. Johnson  Johanna Wandel 《GeoJournal》2018,83(3):413-425

Impacts of climate change have been observed in natural systems and are expected to intensify in future decades (IPCC in Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change IPPC, Geneva, 2014). Governments are seeking to establish adaptive measures for minimizing the effects of climate change on vulnerable citizen groups, economic sectors and critical infrastructure (Adger et al. in Global Environ Change 15(2):77–86, 2005. doi: 10.1016/j.gloenvcha.2004.12.005; Smit and Wandel in Global Environ Change 16(3):282–292, 2006. doi: 10.1016/j.gloenvcha.2006.03.008). Coastal areas are particularly vulnerable to changing conditions due to rising sea levels and storm event intensification that produce new flood exposures (Richards and Daigle in Government of Prince Edward Island, Halifax, Nova Scotia, 2011 http://www.gov.pe.ca/photos/original/ccscenarios.pdf). However, communities oftentimes lack access to locally-relevant climate change information that can support adaptation planning. This research introduces the use of a Geoweb tool for supporting local climate change adaptation efforts in coastal Canadian communities. The Geoweb tool (called “AdaptNS”) is a web-based visualization tool that displays interactive flood exposure maps generated using local climate change projections of sea level rise and storm surge impacts between the years 2000 and 2100. AdaptNS includes participatory features that allow users to identify and share specific locations to protect against present and future coastal flood events. By soliciting feedback from community members, AdaptNS is shown to support local adaptation through the provision of flood exposure visuals, as a platform for identifying adaptation priorities, and as an avenue to communicate local risks to external entities that could facilitate local adaptation initiatives (e.g. upper levels of government). Future Geoweb research directions include improving the visualization of climate change projection uncertainties, the expansion of informational and participation capabilities, and understanding the potential for long-term adoption of Geoweb tools in adaptation decision-making.  相似文献   

In situ oxygen,magnesium, and silicon isotopic compositions of the FUN inclusion Vigarano 1623-5     

Johanna Marin-Carbonne  Kevin D. McKeegan  Andrew M. Davis  Glenn J. MacPherson  Ruslan A. Mendybaev  Frank M. Richter 《Meteoritics & planetary science》2023,58(4):546-571

Oxygen, magnesium, and silicon isotopic abundances in Vigarano 1623-5 were studied using secondary ion mass spectrometry to investigate correlations between isotopic and petrologic properties of this unique forsterite-bearing FUN inclusion. Vigarano 1623-5 displays large, correlated mass-dependent fractionation effects, tightly linked to mineralogy within distinct petrologic units of the inclusion. The pyroxene-rich and melilite-rich interior parts of the inclusion display highly mass-fractionated isotopic compositions of oxygen, magnesium, and silicon, consistent with Rayleigh distillation during evaporation of a melt with initial oxygen composition close to a solar composition. However, the chemical composition, enriched in magnesium and silicon, suggests a precursor already fractionated by prior melt evaporation. A discontinuous igneous rim was produced by a flash-melting event followed by isotopic exchange in the rim melilite with planetary-like oxygen, mechanical fragmentation, and reassembly with an accretionary rim of heterogeneous materials. Al-rich minerals in 1623-5 show evidence for having crystallized with live ²⁶Al but at less than the “canonical” level of most CV calcium-aluminum-rich inclusions. However, well-defined ²⁶Al-²⁶Mg isochrons are not found and temporal implications are ambiguous.  相似文献   

Climate change impacts and adaptation of commercial marine fisheries in Australia: a review of the science   总被引：2，自引：0，他引：2  

Neil J. Holbrook  Johanna E. Johnson 《Climatic change》2014,124(4):703-715

Commercial marine fishing contributes significantly to the Australian economy, and has great importance for coastal communities. However, climate change presents significant challenges for Australia’s fishing industries, now and into the future. With greater use of targeted information, the fishing industry will be better placed to minimise the negative impacts and take advantage of opportunities associated with the effects of climate change. The future of the fishing industry—specifically wild capture fisheries—will depend on its ability and capacity to apply appropriate adaptation strategies for its viability and sustainability in the long-term. Knowledge regarding expected long-term changes in species distributions, improved weather and seasonal climate forecasts and their influence on target species, and better understanding of species tolerances, can inform adaptation responses. This paper provides a review of recent advances in research addressing Australia’s priorities in relation to commercial marine fisheries’ responses to current and anticipated future climate change impacts, and considers barriers and adaptation options for fisheries management over the near-term planning horizon of 5–7 years.  相似文献