A Textural Record of Solidification and Cooling in the Skaergaard Intrusion, East Greenland   总被引：2，自引：0，他引：2  

Holness  Marian B.; Tegner  Christian; Nielsen  Troels F. D.; Stripp  Gemma; Morse  Stearns A. 《Journal of Petrology》2007,48(12):2359-2377

The clinopyroxene–plagioclase–plagioclase dihedralangle, _cpp, in gabbroic cumulates records the time-integratedthermal history in the sub-solidus and provides a measure oftextural maturity. Variations in _cpp through the Layered Seriesof the Skaergaard intrusion, East Greenland, demonstrate thatthe onset of crystallization of clinopyroxene (within LZa),Fe–Ti oxides (at the base of LZc) and apatite (at thebase of UZb) as liquidus phases in the bulk magma is recordedby a stepwise increase in textural maturity, related to an increasein the contribution of latent heat to the total heat loss tothe surroundings and a reduction in the specific cooling rateat the crystallization front of the intrusion. The onset ofboth liquidus Fe–Ti oxide and apatite crystallizationis marked by a transient increase in textural maturity, probablylinked to overstepping before nucleation. Textural maturationat pyroxene–plagioclase–plagioclase triple junctionseffectively ceases in the uppermost parts of the Layered Seriesas a result of the entire pluton cooling below the closure temperaturefor dihedral angle change, which is 1075°C. Solidificationof the Layered Series of the Skaergaard intrusion occurred viathe upwards propagation of a mush zone only a few metres thick. KEY WORDS: magma; partial melting; asthenosphere; olivine; mantle  相似文献   

Halogen oxide measurements at Masaya Volcano,Nicaragua using active long path differential optical absorption spectroscopy     

Christoph Kern  Holger Sihler  Leif Vogel  Claudia Rivera  Martha Herrera  Ulrich Platt 《Bulletin of Volcanology》2009,71(6):659-670

Active Long Path Differential Optical Absorption Spectroscopy (LP-DOAS) measurements of halogen oxides were conducted at Masaya Volcano, in Nicaragua from April 14 to 26, 2007. The active LP-DOAS system allowed night-time halogen measurements and reduced the ClO detection limit by an order of magnitude when compared to previous passive DOAS measurements, as wavelengths below 300 nm could be used for the DOAS retrievals. BrO was detected with an average BrO/SO₂ molecular ratio of approximately 3 × 10⁻⁵ during the day. However, BrO values were below the detection limit of the instrument for all night-time measurements, a strong indication that BrO is not directly emitted, but rather the result of photochemical formation in the plume itself according to the autocatalytic “bromine explosion” mechanism. Despite the increased sensitivity, both ClO and OClO could not be detected. The achieved upper limits for the X/SO₂ ratios were 5 × 10⁻³ and 7 × 10⁻⁶, respectively. A rough calculation suggests that ClO and OClO should be present at similar abundances in volcanic plumes. Since the DOAS technique is orders of magnitude more sensitive for OClO than for ClO, this indicates that OClO should always be detectable in plumes in which ClO is found. However, further LP-DOAS studies are needed to conclusively clarify the role of chlorine oxides in volcanic plumes.  相似文献   

A meshless method to simulate solute transport in heterogeneous porous media     

Paulo A. Herrera  Marco Massabó  Roger D. Beckie 《Advances in water resources》2009

We derive a meshless numerical method based on smoothed particle hydrodynamics (SPH) for the simulation of conservative solute transport in heterogeneous geological formations. We demonstrate that the new proposed scheme is stable, accurate, and conserves global mass. We evaluate the performance of the proposed method versus other popular numerical methods for the simulation of one- and two-dimensional dispersion and two-dimensional advective–dispersive solute transport in heterogeneous porous media under different Pèclet numbers. The results of those benchmarks demonstrate that the proposed scheme has important advantages over other standard methods because of its natural ability to control numerical dispersion and other numerical artifacts. More importantly, while the numerical dispersion affecting traditional numerical methods creates artificial mixing and dilution, the new scheme provides numerical solutions that are “physically correct”, greatly reducing these artifacts.  相似文献   

On board short-time high temperature heat treatment of ballast water: a field trial under operational conditions   总被引：2，自引：1，他引：1  

Quilez-Badia G  McCollin T  Josefsen KD  Vourdachas A  Gill ME  Mesbahi E  Frid CL 《Marine pollution bulletin》2008,56(1):127-135

A ballast water short-time high temperature heat treatment technique was applied on board a car-carrier during a voyage from Egypt to Belgium. Ballast water from three tanks was subjected for a few seconds to temperatures ranging from 55 degrees C to 80 degrees C. The water was heated using the vessel's heat exchanger steam and a second heat exchanger was used to pre-heat and cool down the water. The treatment was effective at causing mortality of bacteria, phytoplankton and zooplankton. The International Maritime Organization (IMO) standard was not agreed before this study was carried out, but comparing our results gives a broad indication that the IMO standard would have been met in some of the tests for the zooplankton, in all the tests for the phytoplankton; and probably on most occasions for the bacteria. Passing the water through the pump increased the kill rate but increasing the temperature above 55 degrees C did not improve the heat treatment's efficacy.  相似文献   

The impact of ditch blocking on the hydrological functioning of blanket peatlands   总被引：1，自引：0，他引：1       下载免费PDF全文

Joseph Holden  Sophie M. Green  Andy J. Baird  Richard P. Grayson  Gemma P. Dooling  Pippa J. Chapman  Christopher D. Evans  Mike Peacock  Graeme Swindles 《水文研究》2017,31(3):525-539

Ditch blocking in blanket peatlands is common as part of peatland restoration. The effects of ditch blocking on flow regimes and nearby water tables were examined in a field trial. After an initial 6‐month monitoring period, eight ditches had peat dams installed 10 m apart along their entire length (dammed), four of these ditches were also partially infilled through bank reprofiling (reprofiled). Four ditches were left open with no dams or reprofiling (open). These 12 ditches and the surrounding peat were monitored for 4 more years. An initial five‐fold reduction in discharge occurred in the dammed and the reprofiled ditches with the displaced water being diverted to overland flow and pathways away from the ditches. However, there was a gradual change over time in ditch flow regime in subsequent years, with the overall volume of water leaving the dammed and the reprofiled ditches increasing per unit of rainfall to around twice that which occurred in the first year after blocking. Hence, monitoring for greater than one year is important for understanding hydrological impacts of peatland restoration. Overland flow and flow in the upper ~4 cm of peat was common and occurred in the inter‐ditch areas for over half of the time after ditch blocking. There was strong evidence that topographic boundaries of small ditch catchments, despite being defined using a high‐resolution Light Detection And Ranging‐based terrain model, were not always equivalent to actual catchment areas. Hence, caution is needed when upscaling area‐based fluxes, such as aquatic carbon fluxes, from smaller scale studies including those using ditches and small streams. The effect of ditch blocking on local water tables was spatially highly variable but small overall (time‐weighted mean effect <2 cm). Practitioners seeking to raise water tables through peatland restoration should first be informed either by prior measurement of water tables or by spatial modelling to show whether the peatland already has shallow water tables or whether there are locations that could potentially undergo large water‐table recoveries.  相似文献   

Water‐level dynamics in natural and artificial pools in blanket peatlands          下载免费PDF全文

Joseph Holden  Catherine S. Moody  T. Edward Turner  Rebecca McKenzie  Andy J. Baird  Mike F. Billett  Pippa J. Chapman  Kerry J. Dinsmore  Richard P. Grayson  Roxane Andersen  Clare Gee  Gemma Dooling 《水文研究》2018,32(4):550-561

Perennial pools are common natural features of peatlands, and their hydrological functioning and turnover may be important for carbon fluxes, aquatic ecology, and downstream water quality. Peatland restoration methods such as ditch blocking result in many new pools. However, little is known about the hydrological function of either pool type. We monitored six natural and six artificial pools on a Scottish blanket peatland. Pool water levels were more variable in all seasons in artificial pools having greater water level increases and faster recession responses to storms than natural pools. Pools overflowed by a median of 9 and 54 times pool volume per year for natural and artificial pools, respectively, but this varied widely because some large pools had small upslope catchments and vice versa. Mean peat water‐table depths were similar between natural and artificial pool sites but much more variable over time at the artificial pool site, possibly due to a lower bulk specific yield across this site. Pool levels and pool‐level fluctuations were not the same as those of local water tables in the adjacent peat. Pool‐level time series were much smoother, with more damped rainfall or recession responses than those for peat water tables. There were strong hydraulic gradients between the peat and pools, with absolute water tables often being 20–30 cm higher or lower than water levels in pools only 1–4 m away. However, as peat hydraulic conductivity was very low (median of 1.5 × 10^?5 and 1.4 × 10^?6 cm s^?1 at 30 and 50 cm depths at the natural pool site), there was little deep subsurface flow interaction. We conclude that (a) for peat restoration projects, a larger total pool surface area is likely to result in smaller flood peaks downstream, at least during summer months, because peatland bulk specific yield will be greater; and (b) surface and near‐surface connectivity during storm events and topographic context, rather than pool size alone, must be taken into account in future peatland pool and stream chemistry studies.  相似文献   

Erratum to: Potential impacts of increased coastal flooding in California due to sea-level rise     

Matthew Heberger  Heather Cooley  Pablo Herrera  Peter H. Gleick  Eli Moore 《Climatic change》2012,112(2):523-523

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Numerical modelling and analysis of the influence of local variation in the thickness of a coal seam on surrounding stresses: Application to a practical case     

M.I. lvarez-Fernndez  C. Gonzlez-Nicieza  A.E. lvarez-Vigil  G. Herrera García  S. Torno 《International Journal of Coal Geology》2009,79(4):157-166

One of the factors with the most influence in the carrying out of underground coal mining work is the stress state, especially when such work is carried out at great depths. One of the mining methods in which the influence of stresses becomes most patent is that of sublevel caving. For that reason, a variety of authors have studied many of the causes which condition the stress state of mining work of this kind at a general level.However, diverse types of conditioning factors exist at a local level that may substantially vary recorded pressures in the surroundings of the workings. Using numerical models, this paper analyses the specific case of a coal seam mined by the sublevel caving method at a depth of 1000 m which suffers significant increases in stress and major deformations in certain advance headings as a result of variations in the geometry and dimensions of the load itself, in particular, thinning.The results of the research carried out were validated by measuring the stresses in the area under study. Furthermore, on the basis of a retrospective analysis of what was observed in the mine, another series of predictive models were analyzed to establish the existing relation between the increase in stress due to thinning of the seam and the depth at which such thinning is situated.  相似文献   

Robust projections of Fire Weather Index in the Mediterranean using statistical downscaling   总被引：2，自引：2，他引：0  

J. Bedia  S. Herrera  D. San Martín  N. Koutsias  J. M. Gutiérrez 《Climatic change》2013,120(1-2):229-247

The effect of climate change on wildfires constitutes a serious concern in fire-prone regions with complex fire behavior such as the Mediterranean. The coarse resolution of future climate projections produced by General Circulation Models (GCMs) prevents their direct use in local climate change studies. Statistical downscaling techniques bridge this gap using empirical models that link the synoptic-scale variables from GCMs to the local variables of interest (using e.g. data from meteorological stations). In this paper, we investigate the application of statistical downscaling methods in the context of wildfire research, focusing in the Canadian Fire Weather Index (FWI), one of the most popular fire danger indices. We target on the Iberian Peninsula and Greece and use historical observations of the FWI meteorological drivers (temperature, humidity, wind and precipitation) in several local stations. In particular, we analyze the performance of the analog method, which is a convenient first choice for this problem since it guarantees physical and spatial consistency of the downscaled variables, regardless of their different statistical properties. First we validate the method in perfect model conditions using ERA-Interim reanalysis data. Overall, not all variables are downscaled with the same accuracy, with the poorest results (with spatially averaged daily correlations below 0.5) obtained for wind, followed by precipitation. Consequently, those FWI components mostly relying on those parameters exhibit the poorest results. However, those deficiencies are compensated in the resulting FWI values due to the overall high performance of temperature and relative humidity. Then, we check the suitability of the method to downscale control projections (20C3M scenario) from a single GCM (the ECHAM5 model) and compute the downscaled future fire danger projections for the transient A1B scenario. In order to detect problems due to non-stationarities related to climate change, we compare the results with those obtained with a Regional Climate Model (RCM) driven by the same GCM. Although both statistical and dynamical projections exhibit a similar pattern of risk increment in the first half of the 21st century, they diverge during the second half of the century. As a conclusion, we advocate caution in the use of projections for this last period, regardless of the regionalization technique applied.  相似文献   

Large biases and inconsistent climate change signals in ENSEMBLES regional projections   总被引：1，自引：1，他引：0  

Marco Turco  Antonella Sanna  Sixto Herrera  Maria-Carmen Llasat  José Manuel Gutiérrez 《Climatic change》2013,120(4):859-869

In this paper we analyze some caveats found in the state-of-the-art ENSEMBLES regional projections dataset focusing on precipitation over Spain, and highlight the need of a task-oriented validation of the GCM-driven control runs. In particular, we compare the performance of the GCM-driven control runs (20C3M scenario) with the ERA40-driven ones (“perfect” boundary conditions) in a common period (1961–2000). Large deviations between the results indicate a large uncertainty/bias for the particular RCM-GCM combinations and, hence, a small confidence for the corresponding transient simulations due to the potential nonlinear amplification of biases. Specifically, we found large biases for some RCM-GCM combinations attributable to RCM in-house problems with the particular GCM coupling. These biases are shown to distort the corresponding climate change signal, or “delta”, in the last decades of the 21st century, considering the A1B scenario. Moreover, we analyze how to best combine the available RCMs to obtain more reliable projections.  相似文献