Trace element geochemistry of K-rich impact spherules from howardites   总被引：1，自引：0，他引：1  

Jean-Alix Barrat  Akira Yamaguchi  Richard C. Greenwood  Claire Bollinger  Marcel Bohn  Ian A. Franchi 《Geochimica et cosmochimica acta》2009,73(19):5944-5958

The howardite–eucrite–diogenite (HED) achondrites are a group of meteorites that probably originate from the asteroid Vesta. Howardites are complex polymict breccias that sometimes contain, in addition to various rock debris, impact melt glasses which show an impressive range of compositions. In this paper we report on the geochemistry and O isotopes of a series of 6 Saharan polymict breccias (4 howardites and 2 polymict eucrites), and on the trace element abundances of high-K impact spherules found in two of them, Northwest Africa (NWA) 1664 and 1769, which are likely paired.The high-K impact spherules found in the howardites NWA 1664 and NWA 1769 display remarkable trace element patterns. Compared to eucrites or howardites, they all show prominent enrichments in Cs, Rb, K, Li and Ba, strong depletion in Na, while the REE and other refractory elements are unfractionated. These features could not have been generated during impact melting of their host howardites, nor other normal HED target materials. The involvement of Na-poor rocks, and possibly rocks of granitic composition, appears likely. Although these lithologies cannot be well constrained at present, our results demonstrate that the surface of Vesta is certainly more diverse than previously thought. Indeed, despite the large number of available HED meteorites (about 1000 different meteorites), the latter are probably not sufficient to describe the whole surface of their parent body.  相似文献   

Can the spread of non-native oysters (Crassostrea gigas) at the early stages of population expansion be managed?     

Claire Guy  Dai Roberts 《Marine pollution bulletin》2010,60(7):1059-1064

The Pacific oyster (Crassostrea gigas) was introduced into Strangford Lough, Northern Ireland in the 1970s. It was assumed that local environmental conditions would not facilitate successful reproduction. However, in the 1990s there were reports of C. gigas outside licensed aquaculture sites and this investigation set out to ascertain the current distribution, years of likely recruitment and population structure of the species. C. gigas were found distributed widely throughout the northern basin during surveys; the frequency distribution suggesting C. gigas is not recruiting every year. Establishment of feral populations of C. gigas elsewhere have linked to habitat change. A pilot cull was initiated to assess the success rate of early intervention. This paper demonstrates the potential benefits of responding rapidly to initial reports of non-native species in a way that may curtail establishment and expansion. The method advocated in simple and can be recommended to the appropriate regulatory authorities.  相似文献   

Natural and Anthropogenic Geohazards in Greater London Observed from Geological and ERS-1/2 and ENVISAT Persistent Scatterers Ground Motion Data: Results from the EC FP7-SPACE PanGeo Project     

Francesca Cigna  Hannah Jordan  Luke Bateson  Harry McCormack  Claire Roberts 《Pure and Applied Geophysics》2015,172(11):2965-2995

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Fluid flow and sediment entrainment in the Garonne River bore and tidal bore collision          下载免费PDF全文

Claire E. Keevil  Hubert Chanson  David Reungoat 《地球表面变化过程与地形》2015,40(12):1574-1586

A detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred. The measured bore, within the Arcins Channel of the Garonne River (France), was undular in nature and was followed by well‐defined secondary wave motion. Due to the local river geometry a collision between the Arcins channel tidal bore and the bore which formed within the main Garonne River channel was observed about 800 m upstream of the sampling site. This bore collision generated a transient standing wave with a black water mixing zone. Following this collision the bore from the main Garonne River channel propagated ‘backward’ to the downstream end of the Arcins channel. Velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level. The instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore. Large Reynolds shear stresses were observed during and after the tidal bore passage, including during the 'backward' bore propagation. Large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion, consistent with the murky appearance of the flood tide waters. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Process oriented use of geostatistics to analyse creeping para‐glacial features          下载免费PDF全文

Eric Bardou  Guillaume Favre‐Bulle  Claire Faucheux  Nicolas Jeannée  Pascal Ornstein 《地球表面变化过程与地形》2015,40(9):1191-1201

Complex para‐glacial systems may show signs of destabilization leading to frequent and potentially hazardous debris‐flows. Understanding creeping permafrost displacement over a period of time is therefore crucial for hazard management and risks assessment. This paper presents our methodology for estimating creeping permafrost displacement based upon data derived from various survey methods and demonstrates its relevance on the Glacier Bonnard system in southern Switzerland. Geostatistical processing allowed estimation of the displacement intensity over the area of interest, as well as assessment of the interpolation quality. Although the local measurement network needs to be refined, the results largely improve the understanding of the Bonnard para‐glacial system, though highlighting the need to locally refine the measurement network. In the present case, the destabilized front advances at ~1 m/a and the upstream creeping part at ~0.4 m/a. Variance analysis also provide objective thresholds that could be used to distinguish underlying physical processes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Identifying sources of organic matter in sediments of shallow lakes using multiple geochemical variables     

William F. Kenney  Mark Brenner  Jason H. Curtis  Claire L. Schelske 《Journal of Paleolimnology》2010,44(4):1039-1052

We analyzed ²¹⁰Pb-dated sediment cores from four relatively shallow lakes (z_max < 10 m) in the Upper Ocklawaha River Basin, Florida, USA to compare primary producer community structure before and after anthropogenic impacts. We measured physical and chemical sediment variables including density, organic matter (OM), water-soluble phosphorus, polyphosphate (Poly-P), total P (TP), total carbon to total nitrogen mass ratios of OM (TC:TN), biogenic silica (diatoms, sponge spicules), total amorphous silica, and stable carbon and nitrogen isotope ratios of bulk OM. Principal component analysis showed that diatom biogenic silica, TC:TN, Poly-P and TP displayed discernible stratigraphic changes associated with the shift in the primary producer community. We applied k-means cluster analysis to these variables to identify macrophyte-derived, transitional, and phytoplankton-derived sediments. Our approach provides an objective method for identifying sediment sources that may be applied to shallow lakes in other regions. The four study lakes shifted from a macrophyte-dominated state to a transitional state before major anthropogenic disturbances, and became phytoplankton-dominated after ~1950.  相似文献   

Discussion of: Development of carbonate platforms on an extensional (rifted) margin: the Valanginian–Albian record of the Prebetic of Alicante (SE Spain), by J.M. Castro et al., Cretaceous Research 29 (2008), 848–860     

B. Granier  V. Perthuisot   《Cretaceous Research》2009,30(4):1019-1026

The original reconstruction (Granier, 1987, and subsequent revisions) of the Early Cretaceous tectono-sedimentary evolution of the northeastern border of the Citrabetic basin in the Alicante province (Spain) was made possible by the integration of sedimentological and palaeontological data. Its findings are based on direct evidence (synsedimentary fractures, reworking, etc.) that differentiates it significantly from the model proposed by Castro et al. (2008). Errors in their analysis of both the sequence and timing of events are corrected. In addition, their negligence with regard to citations of previous work in the region is discussed. In the Citrabetic basin a thick dominantly-siliciclastic wedge developed at the start of the Valanginian, as a consequence of the major transgression that flooded the "Upper Jurassic" carbonate platform. A rift phase occurred later in Valanginian times; the related block-faulting and fracturing persisted up to early Aptian times. At the edges of the blocks and in the starved basins they delimit, the synrift series is characterized by condensed sedimentation (ferruginous oolites, glauconite). This block-faulting initiated the migration of Triassic salts which possibly reached an apogee in Albian times.  相似文献   

Charting the territory: Exploring stakeholder reactions to the prospect of seafloor exploration and mining in Australia     

Claire Mason  Gillian Paxton  Joanna Parr  Naomi Boughen 《Marine Policy》2010

Geological surveys of Australia’s marine territory have revealed significant potential for development of a marine resource industry. As onshore mineral deposits become harder to find, less accessible to their market and more challenging to extract, seafloor exploration and mining becomes an economically viable option. However, evidence from industry and environmental literature suggests that social acceptance will be important in determining the future of this industry in Australia. This paper reports on findings from research investigating the social viability of seafloor mining in Australia. A combination of interviews and focus groups were used to explore industry and community reactions to the possible development of seafloor mining in Australia. Although stakeholders’ reactions were variable, the majority of the participants were reluctant to see development of seafloor mining in Australia, primarily because of concerns about the industry’s potential environmental impact. All stakeholders sought further information about the benefits and costs associated with the industry suggesting that they did not yet have a fixed attitude towards the industry. Stakeholders favoured a precautionary approach towards the industry, supported by rigorous scientific analysis of the potential environmental impacts, transparent and socially responsive management processes and meaningful engagement with stakeholders.  相似文献   

Estimates of water vapor flux and canopy conductance of Scots pine at the tree level utilizing different xylem sap flow methods   总被引：8，自引：0，他引：8  

B. Köstner  P. Biron  R. Siegwolf  A. Granier 《Theoretical and Applied Climatology》1996,53(1-3):105-113

Summary During the Hartheim Experiment (HartX) 1992 conducted in the upper Rhine Valley, Germany, three different methods were used to measure sap flow in Scots pine trees via heating of water transported in the xylem: (1) constant heating applied radially in the sapwood (Granier-system-G), (2) constant heating of a stem segment (ermák-system-C), and (3) regulated variable heating of a stem segment that locally maintains a constant temperature gradient in the trunk (ermák/Schulze-system-CS). While the constant heating methods utilize changes in the induced temperature gradient to quantify sap flux, the CS-system estimates water flow from the variable power requirement to maintain a 2 or 3 degree Kelvin temperature gradient over a short distance between inserted electrodes and reference point. The C- and CS-systems assume that all transported water is encompassed and equally heated by the electrodes. In this case, flux rate is determined from temperature difference or energy input and the heat capacity of water. Active sapwood area need not be determined exactly. In contrast, the G-system requires an empirical calibration of the sensors that allows conversion of temperature difference into sap flow density. Estimates of sapwood area are used to calculate the total flux. All three methods assume that the natural fluctuation in temperature of the trunk near the point of insertion of heating and sensing elements is the same as that where reference thermocouples are inserted.Using all three systems, 24 trees were simultaneously monitored during the HartX campaign. Tree size within the stand ranged between 18 and 61 cm circumference at breast height, while sample trees ranged between 24 and 55 cm circumference. The smallest trees could only be measured by utilizing the G-system. Sap flow rates of individual trees measured at breast height increased rapidly in the morning along with increases in irradiance and vapor pressure deficit (D), decreased slowly during the course of the afternoon with continued increase inD, and decreased more slowly during the night.Ignoring potential effects introduced by the different methods, maximum flow rates of individual trees ranged between 0.5 and 2.5 kg H₂O h^–1 tree^–1 or 0.3 and 0.6 mm h^–1 related to projected crown area of trees and daily sums of sap flow for individual trees varied between 4.4 and 24 kg H₂O tree^–1 d^–1 or 1.1 and 6.0 mm d^–1. Maximum sap flow rates per sapwood area of trees varied least for the G-system (11–17 g cm^–2 h^–1) and was of similar magnitude as the C- (8–21 g cm^–2 h^–1) and CS-system (4–14 g cm^–2 h^–1).Regressions of total tree conductance (g _t ) derived from sap flow estimates demonstrated the same linear increase of conductance with increasing irradiance, however decrease of conductance with increasingD under non-limiting light conditions was different for the three systems with strongest reduction ofg _t measured with the CS-system followed by the C- and G-system. This led to different estimates of daily sap flow rates especially during the second part of the measurement period.Variation in sap flow rates is explained on the basis of variation in leaf area index of individual trees, heterogeneity in soil conditions, and methodological differences in sap flow measurements. Despite the highly uniform plantation forest at the scale of hectares, the heterogeneity in tree size and soil depth at the scale of square meters still make it difficult to appropriately and efficiently select sample trees and to scale-up water flux from individual trees to the stand level.With 5 Figures  相似文献   

The PROWQM physical–biological model with benthic–pelagic coupling applied to the northern North Sea     

Jae-Young Lee  Paul Tett  Ken Jones  Sarah Jones  Patrick Luyten  Claire Smith  Karen Wild-Allen   《Journal of Sea Research》2002,48(4):57

PROWQM, a 1-D depth resolving model which couples physical and microbiological processes in the water column with sedimentation/resuspension and benthic mineralisation processes, has been used to simulate seasonal changes of chlorophyll, nutrients and oxygen at the PROVESS north site (59°20′N 1°00′E) in the North Sea. PROWQM is derived from the 3-D model COHERENS, and improves COHEREN's benthic and pelagic biology.The physical sub-model of PROWQM implicitly solves turbulence closure equations forced by climatological, or realistic high-frequency, meteorological and tidal data. The pelagic biological sub-model 2MPPD includes a ‘diatomy’ microplankton (mp1) and a ‘flagellatey’ (or microbial loop) microplankton (mp2), the cycling of silicon and nitrogen, slow-sinking detritus, and fast-sinking phytodetritus. Phytodetritus is formed by shear-driven aggregation of particulate material, using a simple algorithm for bulk processes that is derived by considering the interactions of single cells. The microplankton compartments include heterotrophic bacteria and protozoa as well as phytoplankton, and most microplankton rates are specified with the aid of a ‘heterotroph fraction’ parameter, which was 0.125 for mp1 and 0.6 for mp2. The microbiological system is closed by mesozooplankton grazing pressures imposed as time varying series determined from observed zooplankton abundance. The benthic boundary sub-model includes a superficial fluff layer and a nutrient element reservoir in the consolidated sediment. Particulate material in the fluff layer can be resuspended (in response to bed stress by near-bed flows), mineralised or carried by bioturbation into the underlying, consolidated, sediment, where it is mineralised and its nutrients returned to the water-column at rates mainly dependent on (implicit) macrobenthic pumping. Benthic denitrification can occur when mineralisation rates exceed oxygen supply.Verification of the PROWQM numerical implementation used test cases and checks for nutrient element conservation. Simulations with realistic forcing, for a range of parameter values, were compared with historic observations in the NOWESP data set and during FLEX76, and with those made during the PROVESS cruises in autumn 1998. PROWQM provided a good simulation of the seasonal succession from a diatom-dominated spring bloom to summer dominance by small flagellates. The simulations included sedimentation of organic matter from the spring bloom, and qualitatively realistic behaviour of the fluff layer, but decay rates were too slow and there was almost no denitrification. The simulated surface mixed layer was too shallow during the summer. Simulated annual net microplankton primary production was in between 59 and 91 g C m⁻² y⁻¹. A large proportion of mineralisation, 28–47% of nitrogen and 40–67% of silicon mineralisation, took place as a result of the decay of sinking and resuspended detritus whilst in the water column.PROWQM is discussed in relation to other models that have been used to simulate this part of the North Sea, in particular the simpler ECOHAM1 and the more complex ERSEM, and in relation to PROWQM's evolution from COHERENS.  相似文献