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191.
Aradhna K. Tripati Robert A. Eagle Andrew Morton Julian A. Dowdeswell Katie L. Atkinson Yannick Bahé Caroline F. Dawber Emma Khadun Ruth M.H. Shaw Oliver Shorttle Lavaniya Thanabalasundaram 《Earth and Planetary Science Letters》2008,265(1-2):112-122
The widely accepted age estimate for the onset of glaciation in the Northern Hemisphere ranges between 2 and 15 million years ago (Ma). However, recent studies indicate the date for glacial onset may be significantly older. We report the presence of ice-rafted debris (IRD) in ~ 44 to 30 Ma sediments from the Greenland Sea, evidence for glaciation in the North Atlantic during the Middle Eocene to Early Oligocene. Detailed sedimentological evidence indicates that glaciers extended to sea level in the region, allowing icebergs to be produced. IRD may have been sourced from tidewater glaciers, small ice caps, and/or a continental ice sheet. 相似文献
192.
Emma Newton Howell G M Edwards David Wynn-Williams Julian A Hiscox 《Astronomy& Geophysics》2000,41(5):5.28-5.31
Emma Newton , Howell G M Edwards , David Wynn-Williams and Julian A Hiscox review the combination of biology, geology and physics necessary to search for life off Earth. 相似文献
193.
Ravi V. Kolhatkar Matthew A. Lahvis Ian Hers John T. Wilson Emma Luo Parisa Jourabchi 《Ground Water Monitoring & Remediation》2019,39(4):41-51
Vapor intrusion (VI) involves migration of volatile contaminants from subsurface through unsaturated soil into overlying buildings. In 2015, the US EPA recommended an approach for screening VI risks associated with gasoline releases from underground storage tank (UST) sites. Additional assessment of the VI risk from petroleum hydrocarbons was deemed unnecessary for buildings separated from vapor sources by more than recommended vertical screening distances. However, these vertical screening distances did not apply to potential VI risks associated with releases of former leaded gasoline containing 1,2-dichloroethane (1,2-DCA), because of a lack of empirical data on the attenuation of 1,2-DCA in soil gas. This study empirically evaluated 144 paired measurements of 1,2-DCA concentrations in soil gas and groundwater collected at 47 petroleum UST sites combined with BioVapor modeling. This included (1) assessing the frequency of 1,2-DCA detections in soil gas below 10−6 risk-based screening levels at different vertical separation distances and (2) comparing the US EPA recommended vertical screening distances with those predicted by BioVapor modeling. Vertical screening distances were predicted for different soil types using aerobic biodegradation rate constants estimated from the measured soil-gas data combined with conservative estimates of source concentrations. The modeling indicates that the vertical screening distance of 6 feet (1.8 m) recommended for dissolved-phase sources is applicable for 1,2-DCA below certain threshold concentrations in groundwater, while 15 feet (4.6 m) recommended for light nonaqueous phase liquid (LNAPL) sources is applicable for sites with clay and loam soils in the vadose zone, but not sand, if 1,2-DCA concentrations in groundwater exceed 150 μg/L. This dependence of the predicted vertical screening distances on soil type places added emphasis on proper soil characterization for VI screening at sites with 1,2-DCA sources. The soil-gas data suggests that a vertical screening distance of 15 feet (4.6 m) is necessary for both dissolved-phase and LNAPL sources. 相似文献
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Lewis J. Alcott Alexander J. Krause Emma U. Hammarlund Christian J. Bjerrum Florian Scholz Yijun Xiong Andrew J. Hobson Lesley Neve Benjamin J. W. Mills Christian Mrz Bernhard Schnetger Andrey Bekker Simon W. Poulton 《Geostandards and Geoanalytical Research》2020,44(3):581-591
The development and application of geochemical techniques to identify redox conditions in modern and ancient aquatic environments has intensified over recent years. Iron (Fe) speciation has emerged as one of the most widely used procedures to distinguish different redox regimes in both the water column and sediments, and is the main technique used to identify oxic, ferruginous (anoxic, Fe(II) containing) and euxinic (anoxic, sulfidic) water column conditions. However, an international sediment reference material has never been developed. This has led to concern over the consistency of results published by the many laboratories that now utilise the technique. Here, we report an interlaboratory comparison of four Fe speciation reference materials for palaeoredox analysis, which span a range of compositions and reflect deposition under different redox conditions. We provide an update of extraction techniques used in Fe speciation and assess the effects of both test portion mass, and the use of different analytical procedures, on the quantification of different Fe fractions in sedimentary rocks. While atomic absorption spectroscopy and inductively coupled plasma‐optical emission spectrometry produced comparable Fe measurements for all extraction stages, the use of ferrozine consistently underestimated Fe in the extraction step targeting mixed ferrous–ferric minerals such as magnetite. We therefore suggest that the use of ferrozine is discontinued for this Fe pool. Finally, we report the combined data of four independent Fe speciation laboratories to characterise the Fe speciation composition of the reference materials. These reference materials are available to the community to provide an essential validation of in‐house Fe speciation measurements. 相似文献
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Patterns in community structure and functioning of motile epibenthic fauna were investigated in shallow (0–1 m) sediment habitats along the Skagerrak–Baltic estuarine gradient (salinity range from 4 to 34). The study area was divided into five regions, reflecting different sea-basins along the 1260 km coastline, and fauna was collected at six sites within each region. Ten replicate samples of motile epibenthic fauna were taken randomly at each site with a portable drop trap (bottom area 1 m2) in June and September in 2004. 相似文献
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Laurie Boithias Yves Auda Stéphane Audry Jean-Pierre Bricquet Alounsavath Chanhphengxay Vincent Chaplot Anneke de Rouw Thierry Henry des Tureaux Sylvain Huon Jean-Louis Janeau Keooudone Latsachack Yann Le Troquer Guillaume Lestrelin Jean-Luc Maeght Pierre Marchand Pierre Moreau Andrew Noble Anne Pando-Bahuon Kongkeo Phachomphon Khambai Phanthavong Alain Pierret Olivier Ribolzi Jean Riotte Henri Robain Emma Rochelle-Newall Saysongkham Sayavong Oloth Sengtaheuanghoung Norbert Silvera Nivong Sipaseuth Bounsamay Soulileuth Xaysatith Souliyavongsa Phapvilay Sounyaphong Sengkeo Tasaketh Chanthamousone Thammahacksa Jean-Pierre Thiebaux Christian Valentin Olga Vigiak Marion Viguier Khampaseuth Xayyathip 《水文研究》2021,35(5):e14126
Mountain regions of the humid tropics are characterized by steep slopes and heavy rains. These regions are thus prone to both high surface runoff and soil erosion. In Southeast Asia, uplands are also subject to rapid land-use change, predominantly as a result of increased population pressure and market forces. Since 1998, the Houay Pano site, located in northern Lao PDR (19.85°N 102.17°E) within the Mekong basin, aims at assessing the long-term impact of the conversion of traditional slash-and-burn cultivation systems to commercial perennial monocultures such as teak tree plantations, on the catchment hydrological response and sediment yield. The instrumented site monitors hydro-meteorological and soil loss parameters at both microplot (1 m2) and small catchment (0.6 km2) scales. The monitored catchment is part of the network of critical zone observatories named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Houay Pano are (1) rainfall, (2) air temperature, air relative humidity, wind speed, and global radiation, (3) catchment land use, (4) stream water level, suspended particulate matter, bed particulate matter and stones, (5) soil surface features, and (6) soil surface runoff and soil detachment. The dataset has already been used to interpret suspended particulate matter and bed particulate matter sources and dynamics, to assess the impact of land-use change on catchment hydrology, soil erosion, and sediment yields, to understand bacteria fate and weed seed transport across the catchment, and to build catchment-scale models focused on hydrology and water quality issues. The dataset may be further used to, for example, assess the role of headwater catchments in large tropical river basin hydrology, support the interpretation of new variables measured in the catchment (e.g., contaminants other than faecal bacteria), and assess the relative impacts of both climate and land-use change on the catchment. 相似文献