bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution of Subduction Zone Curvature and its Dependence on the Trench Velocity and the Slab to Upper Mantle Viscosity Ratio
Authors: Schellart W. P.
Published: May 2011

Three‐dimensional laboratory models of upper mantle subduction are presented investigating the effect of the trench velocity (vt) and the slab to upper mantle viscosity ratio (ηSP/ηUM) on trench curvature and slab curvature. One set of experiments varies ηSP/ηUM from 66 to 1375. Another set of experiments modifies vt through applying different velocities at the trailing plate. The results show that the radius of trench curvature (RTC) progressively decreases with continuous trench retreat due to quasi‐toroidal mantle return flow from the subslab region around the lateral slab edges and toward the mantle wedge region, but starts to increase when trench retreat changes to trench advance due to quasi‐toroidal return flow in the opposite direction. Furthermore, RTC increases with increasing ηSP/ηUM (i.e., progressively stronger slabs are progressively less curved) following a cubic root function. The force required to curve the slab and trench varies with progressive subduction, but is only 0.1–2.5% of the total negative buoyancy force of the slab, while the viscous dissipation rate due to progressive slab curvature is only 0.01–0.60% of the potential energy release rate. Comparison of trench curvature in the models (scaled slab width w = 750 km) with that of the Scotia subduction zone (w ≈ 800 km) indicates that for the Scotia subduction zone the effective ηSP/ηUM is of the order 1–2 × 102. Finally, the elastic sphere indentation model for arc curvature is revisited, demonstrating that four main predictions are not met by observations, implying that the model should be rejected.
SVM‐PGSL coupled approach for statistical downscaling to predict rainfall from GCM output
Authors: Ghosh Subimal
Published: May 2011

Hydrological impacts of climate change are assessed by downscaling the General Circulation Model (GCM) outputs of predictor variables to local or regional scale hydrologic variables (predictand). Support Vector Machine (SVM) is a machine learning technique which is capable of capturing highly nonlinear relationship between predictor and predictand and thus performs better than conventional linear regression in transfer function‐based downscaling modeling. SVM has certain parameters the values of which need to be fixed appropriately for controlling undertraining and overtraining. In this study, an optimization model is proposed to estimate the values of these parameters. As the optimization model, for selection of parameters, contains SVM as one of its constraints, analytical solution techniques are difficult to use in solving it. Probabilistic Global Search Algorithm (PGSL), a probabilistic search technique, is used to compute the optimum parameters of SVM. With these optimum parameters, training of SVM is performed for statistical downscaling. The obtained relationship between large‐scale atmospheric variables and local‐scale hydrologic variables (e.g., rainfall) is used to compute the hydrologic scenarios for multiple GCMs. The uncertainty resulting from the use of multiple GCMs is further modeled with a modified reliability ensemble averaging method. The proposed methodology is demonstrated with the prediction of monsoon rainfall of Assam and Meghalaya meteorological subdivision of northeastern India. The results obtained from the proposed model are compared with earlier developed SVM‐based downscaling models, and improved performance is observed.
Effect of near‐bed turbulence on chronic detachment of epilithic biofilm: Experimental and modeling approaches
Authors: Graba Myriam , Moulin Frédéric Y. , Boulêtreau Stéphanie , Garabétian Frédéric , Kettab Ahmed , Eiff Olivier , Sánchez‐Pérez José Miguel , Sauvage Sabine
Published: May 2011

The biomass dynamics of epilithic biofilm, a collective term for a complex microorganism community that grows on gravel bed rivers, was investigated by coupling experimental and numerical approaches focusing on epilithic biofilm‐flow interactions. The experiment was conducted during 65 days in an artificial rough open‐channel flow, where filtered river water circulated at a constant discharge. To characterize the effect of near‐bed turbulence on the chronic detachment process in the dynamics of epilithic biofilm, local hydrodynamic conditions were measured by laser Doppler anemometry and turbulent boundary layer parameters inferred from double‐averaged quantities. Numerical simulations of the EB biomass dynamics were performed using three different models of chronic detachment based upon three different descriptors for the flow conditions: Discharge Q, friction velocity u*, and roughness Reynolds number k+. Comparisons of numerical simulation results with experimental data revealed chronic detachment to be better simulated by taking the roughness Reynolds number as the external physical variable forcing chronic detachment. Indeed, the loss of epilithic matter through the chronic detachment process is related not only to hydrodynamic conditions, but also to change in bottom roughness. This suggests that changes in the behavior and dimensions of river bed roughness must be considered when checking the dynamics of epilithic biofilm in running waters.
Widespread influence of resuspended sediments on oceanic particulate organic carbon: Insights from radiocarbon and aluminum contents in sinking particles
Authors: Hwang Jeomshik , Druffel Ellen R. M. , Eglinton Timothy I.
Published: May 2011

Particulate organic carbon (POC) in the ocean often exhibits more depleted radiocarbon contents (lower Δ 14C values) than expected if its sole source were POC recently synthesized by primary production and export from the overlying surface waters. An examination of available Δ14C data sets for sinking POC show that this phenomenon is both common and globally widespread. Also, a strong correlation is found to exist between Δ14C values of organic carbon and aluminum content in sinking particles that is consistent over a range of oceanic settings. Together, these findings imply that aged organic carbon associated with lithogenic material from sediment resuspension is responsible for the observed low Δ 14C values as opposed to other processes such as incorporation of dissolved inorganic carbon or dissolved organic carbon into POC at depth. An estimate based on POC flux‐weighted Δ14C values shows that about 35% of sinking POC at the locations studied is derived from resuspended sediment. Our results suggest that resuspension of sediment and its subsequent lateral transport is an important component of the oceanic carbon cycle and should be considered in models of oceanic carbon export and burial.
Coherent pattern and timing of the carbon isotope excursion and warming during Eocene Thermal Maximum 2 as recorded in planktic and benthic foraminifera
Authors: Stap Lucy , Lourens Lucas , van Dijk Arnold , Schouten Stefan , Thomas Ellen
Published: May 2011

Eocene Thermal Maximum 2 (ETM2; ∼53.7 Ma) occurred approximately 2 Myr after the Paleocene‐Eocene Thermal Maximum (∼55.5 Ma) and was characterized by a deep‐sea warming of >3°C, associated with massive release of carbon into the ocean‐atmosphere system. We performed single‐specimen stable isotope analyses of the planktic foraminiferal genera Acarinina (surface dweller) and Subbotina (thermocline dweller) from Ocean Drilling Program Sites 1265, 1267, and 1263 (Walvis Ridge, SE Atlantic Ocean) and compared high‐resolution planktic and benthic stable isotope records to constrain the surface warming and the bathymetric pathway of the carbon isotope excursion during ETM2. Tests of the thermocline dweller Subbotina are absent from sediment deposited during the peak of ETM2. The Acarinina carbon and oxygen isotope records of Sites 1263, 1265, and 1267 are strikingly similar, despite some test recrystallization and large differences in burial depths. Sea surface temperature (SST) estimates based on δ18O isotope values of Acarinina indicate a SST increase of ∼2°C, significantly less than the >3°C estimated for bottom water warming. The maximum negative carbon isotope excursion for Acarinina was ∼1.7‰, slightly more than in the deep sea (∼1.4‰). The planktic and benthic isotope records do not show time lags, indicating that during ETM2 the isotopically depleted carbon injected into the ocean‐atmosphere system was rapidly mixed within all oceanic carbon reservoirs.
Signal linearity of an extended range pulse counting detector: Applications to accurate and precise U‐Pb dating of zircon by laser ablation quadrupole ICP‐MS
Authors: Shaulis Barry , Lapen Thomas J. , Toms Andrew
Published: May 2011

Element concentration and isotope ratio measurements by single‐collector mass spectrometry often require the detection system to handle ion beams with very large intensity ratios. In order to obtain accurate and reproducible element concentration and isotope ratio data, the detection system must have a linear response with respect to the intensity of the incident ion beam. An extended range scaling pulse counting detector equipped on a Varian 810 quadrupole inductively coupled plasma–mass spectrometer (ICP‐MS) was tested for linearity across count rates of ∼2000 to 110,000,000 cps with different concentrations of natural U solutions. We also tested detector linearity by the laser ablation analysis of 206Pb/238U, 207Pb/235U, and 207Pb/206Pb ratios in well‐characterized 416–1565 Ma zircon standards. Results indicate that there is no correlation between the measured isotope ratio and ion intensity for the solution tests or the tests of natural zircon standards. The results of these tests confirm the suitability of this instrument for isotope ratio measurements that require a substantial dynamic range without having to switch between pulse counting and analog modes on electron multipliers or switching between electron multiplier to Faraday detectors.
Triangulated finite difference methods for global‐scale electromagnetic induction simulations of whole mantle electrical heterogeneity
Authors: Weiss C. J.
Published: May 2011

Long‐period, global‐scale electromagnetic induction data have long been recognized as containing potentially useful information for constraining our understanding of the dynamics and physiochemical state of Earth's deep interior. A key component to realizing the potential of this data set is the ability to compute the induction response of a fully 3‐D Earth mantle in global spherical geometries. In this contribution a novel finite difference method is described which preserves many algorithmic advantages of staggered grid discretizations in Cartesian computational electromagnetics but is generalized for the sphere by introducing a hybrid, tensor product mesh consisting of concentrically nested, triangulated, spherical shells topologically connected node‐for‐node in the radial direction. Such a discretization allows for a flexible distribution of mesh nodes in the lateral sense and avoids the problems associated with excessive node density near the poles which results from conformally mapping the standard Cartesian mesh. Modified finite difference templates for spherical geometries are derived and presented, as is a comparison with integral equation solutions for a simple double‐hemisphere test model. As a first step toward applying the algorithm for mantle induction studies, results of a conservative, thermally activated mantle heterogeneity model confirm that mantle structure remains observable in the presence of the strongly conductive ocean and may manifest important, diagnostic signatures in the orientation of the horizontal component of induced magnetic field.
Better mathematical constraints on ages of Carboniferous stage boundaries using radiometric tuff dates and cyclostratigraphy
Authors: Peterson John A.
Published: May 2011

Using more geologically reasonable constraints on radiometric dates from tuffs in a cyclic mixed carbonate‐siliciclastic succession in the Donets Basin, Ukraine, newer and more geologically accurate ages of stage boundaries are calculated for the Carboniferous period. These calculations assume astronomically forced (Milankovitch) cyclicity and use radiometric dates of ash layers in the stratigraphic record. Unlike previous work, measurement uncertainties are propagated through calculations to provide mathematically constrained uncertainty in the ages of the boundaries. This work uses more realistic errors in the known dates of zircons in the ash layers and does not assume an a priori value for the Milankovitch long‐eccentricity period. These calculations are compatible with other previous methods of determining the boundaries and represent improvement over existing age constraints.
Diagenetic sensitivity of paleoenvironmental proxies: A rock magnetic study of Australian continental margin sediments
Authors: Abrajevitch Alexandra , Kodama Kazuto
Published: May 2011

A rock magnetic study of the upper 40 m of the Ocean Drilling Program Site 133‐820A recovered at the outer edge of the northeastern Australian continental margin shows that downcore variations in magnetic parameters are diagenetically driven and correlate with the changes in global sea level. We identified intervals enriched in single‐domain (SD) magnetite in the studied section. Unlike previous studies that postulated a detrital source, we show that the bulk of the SD fraction is biologically produced and is likely to be authigenic. The abundance of SD magnetite thus cannot be used as an indicator for provenance or sediment transport mechanisms. The biogenic magnetite was preserved during the high sedimentation rate periods, likely due to a short residence time in the corrosive zone of active iron reduction. The presence of the biogenic magnetite thus can be used as an indicator for a low degree of reductive dissolution. More advanced dissolution during the periods of slow sedimentation, coincident with sea level highstands, resulted in significant changes in the composition of the detrital assemblage, particularly in relative abundances of different mineral phases. The overall stability of the detrital magnetic minerals toward dissolution varies in the studied section as hematite > magnetite > goethite. Due to the higher stability of hematite, reductive diagenesis in general will lead to the lowering of the goethite/hematite (G/H) ratio, which can be mistaken for an increased aridity in the sedimentary source areas in the conventional interpretation for this proxy. The sensitivity of the G/H proxy to diagenesis should be taken into account in paleoenvironmental studies.
Concentrated perchlorate at the Mars Phoenix landing site: Evidence for thin film liquid water on Mars
Authors: Cull Selby C. , Arvidson Raymond E. , Catalano Jeffrey G. , Ming Douglas W. , Morris Richard V. , Mellon Michael T. , Lemmon Mark
Published: May 2011

NASA's Phoenix mission, which landed on the northern plains of Mars in 2008, returned evidence of the perchlorate anion distributed evenly throughout the soil column at the landing site. Here, we use spectral data from Phoenix's Surface Stereo Imager to map the distribution of perchlorate salts at the Phoenix landing site, and find that perchlorate salt has been locally concentrated into subsurface patches, similar to salt patches that result from aqueous dissolution and redistribution on Earth. We propose that thin films of liquid water are responsible for translocating perchlorate from the surface to the subsurface, and for concentrating it in patches. The thin films are interpreted to result from melting of minor ice covers related to seasonal and long‐term obliquity cycles.
Upstream Pc3‐4 waves: Experimental evidence of propagation to the nightside plasmapause/plasmatrough
Authors: Ponomarenko P. V. , Waters C. L. , St‐Maurice J.‐P.
Published: May 2011

Compressional magnetohydrodynamic (MHD) waves in the Pc3‐4 frequency range (≃10–50 mHz) are generally believed to be generated upstream of the Earth's bow‐shock in reflected proton beams. Inside the closed field‐line geometry, these waves are conventionally considered to be a dayside phenomenon. However, recent studies suggest that some of the nighttime Pc4 pulsations may in fact have an upstream origin. In this letter, we report synchronous variations of the Pc3‐4 spectra near post‐dawn cusp and nightside plasmapause/plasmatrough as observed by HF radar and ground magnetometers. The measured Pc3‐4 frequency closely follows that of the upstream waves theoretically predicted based on the dynamics of the interplanetary magnetic field, which presents the most convincing evidence to date of upstream‐generated Pc3‐4 waves propagating to the nightside magnetosphere in the closed field‐line geometry. We conclude the letter with a brief discussion of a possible propagation scenario.
Characteristics of storm time electric fields in the inner magnetosphere derived from Cluster data
Authors: Matsui H. , Puhl‐Quinn P. A. , Bonnell J. W. , Farrugia C. J. , Jordanova V. K. , Khotyaintsev Yu. V. , Lindqvist P.‐A. , Georgescu E. , Torbert R. B.
Published: May 2011

Storm‐time electric fields in the inner magnetosphere measured by Cluster are reported in this study. First, we show two events around the time when Dst index is at a minimum. The electric field possibly related to subauroral ion drifts and/or undershielding is measured inside the inner edge of the electron plasma sheet in the eveningside. For the second event observed in the nightside, the electric field is partly related to dipolarization and is considered as inductive. An electric field without coincident magnetic signatures is also observed. Spatial coherence of the electric field is not large when we check multispacecraft data. It is inferred that the electric field in the magnetotail penetrates inside the region 1 current, while it is not clear about the electric field within the region 2 current from our data. Then superposed epoch analyses using 71 storms are performed. Electric fields at R = 3.5–6RE and less than 25 degrees of magnetic latitudes are enhanced around the minimum Dst at all magnetic local times. Electric fields during the recovery phase decay on a time scale shorter than that of Dst index, which could be interpreted in terms of the relation between electric field and ring current during that storm phase. AC electric fields are generally larger than DC electric fields, indicating that the former component might play some role in accelerating ring current particles. These results will be useful to update our empirical electric field model.
Forecasting the local ionospheric foF2 parameter 1 hour ahead during disturbed geomagnetic conditions
Authors: Chen C. , Wu Z. S. , Xu Z. W. , Sun S. J. , Ding Z. H. , Ban P. P.
Published: May 2011

Using the support vector machine (SVM), an empirical local ionospheric forecasting model over Lanzhou (ELIFMOL) has been developed to predict the critical frequency of the F2 layer (foF2) during disturbed geomagnetic conditions. This study focuses on the reliable prediction of foF2 during geomagnetic storms, which is important for practical applications as well as for further understanding of the storm dynamics. In this paper, we investigate whether foF2 during disturbed geomagnetic conditions at a single station can be well predicted one hour ahead by using some inputs to an SVM network, such as the latest foF2 observations, hourly quiet time foF2 (foF2QT), time, and the hourly time‐weighted accumulation series derived from the geomagnetic index (ap(τ)). The input observation data cover the period of January 1958 to December 2000 at Lanzhou (36.1°N, 104.0°E) in China. The foF2 forecasted by the ELIFMOL are compared with the monthly median values and with those by the STORMMEDIAN model, the persistence model, and the STORMfoF2QT model during geomagnetic storms occurring from 2001 to 2006. As for the data sets used in this paper, the results show that the performance of ELIFMOL is better than that of the latter models.
Radiation belt electron precipitation due to geomagnetic storms: Significance to middle atmosphere ozone chemistry
Authors: Rodger Craig J. , Clilverd Mark A. , Seppälä Annika , Thomson Neil R. , Gamble Rory J. , Parrot Michel , Sauvaud Jean‐André , Ulich Thomas
Published: May 2011

Geomagnetic storms triggered by coronal mass ejections and high‐speed solar wind streams can lead to enhanced losses of energetic electrons from the radiation belts into the atmosphere, both during the storm itself and also through the poststorm relaxation of enhanced radiation belt fluxes. In this study we have analyzed the impact of electron precipitation on atmospheric chemistry (30–90 km altitudes) as a result of a single geomagnetic storm. The study conditions were chosen such that there was no influence of solar proton precipitation, and thus we were able to determine the storm‐induced outer radiation belt electron precipitation fluxes. We use ground‐based subionospheric radio wave observations to infer the electron precipitation fluxes at L = 3.2 during a geomagnetic disturbance which occurred in September 2005. Through application of the Sodankylä Ion and Neutral Chemistry model, we examine the significance of this particular period of electron precipitation to neutral atmospheric chemistry. Building on an earlier study, we refine the quantification of the electron precipitation flux into the atmosphere by using a time‐varying energy spectrum determined from the DEMETER satellite. We show that the large increases in odd nitrogen (NOx) and odd hydrogen (HOx) caused by the electron precipitation do not lead to significant in situ ozone depletion in September in the Northern Hemisphere. However, had the same precipitation been deposited into the polar winter atmosphere, it would have led to >20% in situ decreases in O3 at 65–80 km altitudes through catalytic HOx cycles, with possible additional stratospheric O3 depletion from descending NOx beyond the model simulation period.
Is DE2 the source of the ionospheric wave number 3 longitudinal structure?
Authors: Kil H. , Paxton L. J. , Lee W. K. , Ren Z. , Oh S.‐J. , Kwak Y.‐S.
Published: May 2011

This study examines the connection of the wave number 3 (wave‐3) longitudinal structure in the ionospheric plasma density with diurnal eastward propagating zonal wave number 2 tide (DE2) by examining the annual and diurnal variations of the wave‐3 structures in the plasma density and vertical E × B drift. For this purpose, we have utilized the mean plasma density and vertical ion velocity derived from the first Republic of China satellite data during 1999–2004 under Kp < 4 condition. Good correlation between the wave‐3 longitudinal structures in the plasma density and vertical E × B drift indicates that the vertical E × B drift (or E‐region dynamo electric field) is responsible for the creation of the wave‐3 plasma density structure. The annual variation of the amplitude of the ionospheric wave‐3 structure in the plasma density and vertical E × B drift shows two peaks near December and May, which is consistent with the annual variation of the DE2 amplitude. However, the diurnal variation of the ionospheric wave‐3 structure does not show the eastward phase shift of 120°/24 LT that is predicted by DE2. The amplitude of the ionospheric wave‐3 structure is greater than might be predicted by the comparison of the amplitude of the DE3 and DE2 winds. Another mechanism in addition to DE2 is necessary in order to explain the formation of the ionospheric wave‐3 longitudinal structure.
Formation of a hydrothermal reservoir due to anhydrite precipitation in an arc volcano hydrothermal system
Authors: Kawada Yoshifumi , Yoshida Shigeo
Published: May 2011

Anhydrite precipitation strongly affects the circulation of hydrothermal systems by changing the permeability structure of the oceanic crust. For example, a hydrothermal reservoir capped by anhydrite precipitates was found beneath the caldera floor of Suiyo Seamount of the Izu‐Bonin Arc. We interpret the precipitation to be due to alternating layers of lavas and tephras, typical of arc volcanos, because the layering gives rise to the mixing of high‐temperature hydrothermal fluids with low‐temperature seawater at layer boundaries. We thus perform two‐dimensional numerical simulations of subseafloor fluid flow in a two‐layer porous medium to model the shallowest part of the discharge zone near the summit of an arc volcano. The upper layer is set to be more permeable than the lower one. High‐temperature Ca2+‐rich hydrothermal fluid flows in from the bottom, and low‐temperature SO42−‐rich seawater flows in from the seafloor. The two fluids meet at the layer boundary, precipitating anhydrite, which serves as the ceiling of a hydrothermal reservoir. Anhydrite precipitates form also in the upper layer, serving as conduit walls for upwelling hydrothermal fluid. When the permeability of the upper layer is in the range 10−10–10−12 m2, which is typical for unconsolidated volcanic pumice, the pattern of the circulation stabilizes in about 0.5–40 years. The circulation structure and the timescale of its formation are similar to those of the hydrothermal system on Suiyo Seamount.
A flow‐dependent estimate for the sampling error
Authors: Stiller Olaf
Published: May 2011

A pragmatic method is presented for obtaining a flow‐dependent estimate of the sampling error which arises when comparing line measurements (whose horizontal extent is quasi one‐dimensional (1‐D)) with model grid box averages (whose horizontal extent is 2‐D). The errors are computed from synthetic data which share important statistical properties with the observed field and which can be generated from the information obtained from the 1‐D measurements. Flow dependency is obtained through a statistical measure (or “score”) which is linked to the sampling error through a quasi‐empirical relationship that is obtained from the synthetic data. The success of the method particularly depends on how well the employed score differentiates situations with different error magnitudes. A score is proposed which is based on local estimates of the structure function maximum (i.e., the maximum over neighborhoods of different spatial extent) and therefore exploits information from different space scales. Since the proposed method is heuristic (in the sense that the adequacy of the synthetic data cannot be inferred from first principles), a large part of this paper is devoted to demonstrating the robustness of this method in the context of data from scanning satellite instruments for which 1‐D estimates can be compared directly with the corresponding 2‐D averages.
Front‐like behavior in the Arctic wintertime upper stratosphere and lower mesosphere
Authors: Thayer J. P. , Greer K. , Harvey V. L.
Published: May 2011

Synoptic scale disturbances in the Arctic wintertime middle atmosphere are investigated using Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) satellite temperature observations and U.K. Meteorological Office (MetO) assimilated analyses. A representative data set on 13 February 2002 is used as a case study. The observed strong vertical and horizontal thermal gradients in the Arctic winter upper stratosphere and mesosphere are evocative to front‐like behavior in the troposphere. The observations from the SABER instrument and the MetO data of temperature and geopotential suggest that baroclinic instability is a process involved in enhancing the disturbance. Contrary to tropospheric baroclinic development, the ageostrophic circulation associated with the middle atmosphere disturbance is indirect and is driven by eddy momentum flux convergence due to vertically propagating planetary waves. Investigating perturbation geopotential through the Arctic middle atmosphere prior to and during the event, a dominant zonal wave number 1 planetary wave propagating into the upper stratosphere is observed. The observations suggest that, through this planetary wave action, the middle atmosphere becomes highly baroclinic and can promote baroclinic instability that can enhance temperatures to the extreme levels characteristic of these disturbances near the stratopause and in the lower mesosphere.
Synoptic controls on precipitation pathways and snow delivery to high‐accumulation ice core sites in the Ross Sea region, Antarctica
Authors: Sinclair K. E. , Bertler N. A. N. , Trompetter W. J.
Published: May 2011

Dominant storm tracks to two ice core sites on the western margin of the Ross Sea, Antarctica (Skinner Saddle (SKS) and Evans Piedmont Glacier), are investigated to establish key synoptic controls on snow accumulation. This is critical in terms of understanding the seasonality, source regions, and transport pathways of precipitation delivered to these sites. In situ snow depth and meteorological observations are used to identify major accumulation events in 2007–2008, which differ considerably between sites in terms of their magnitude and seasonal distribution. While snowfall at Evans Piedmont Glacier occurs almost exclusively during summer and spring, Skinner Saddle receives precipitation year round with a lull during the months of April and May. Cluster analysis of daily back trajectories reveals that the highest‐accumulation days at both sites result from fast‐moving air masses, associated with synoptic‐scale low‐pressure systems. There is evidence that short‐duration pulses of snowfall at SKS also originate from mesocyclone development over the Ross Ice Shelf and local moisture sources. Changes in the frequency and seasonal distribution of these mechanisms of precipitation delivery will have a marked impact on annual accumulation over time and will therefore need careful consideration during the interpretation of stable isotope and geochemical records from these ice cores.
Visible and near‐infrared multispectral analysis of geochemically measured rock fragments at the Opportunity landing site in Meridiani Planum
Authors: Weitz Catherine M. , Farrand William H. , Johnson Jeffrey R. , Fleischer Iris , Schröder Christian , Yingst Aileen , Jolliff Brad , Gellert Ralf , Bell Jim , Herkenhoff Kenneth E. , Klingelhöfer Göstar , Cohen Barbara , Calvin Wendy , Rutherford Malcolm , Ashley James
Published: May 2011

We have used visible and near‐infrared Panoramic Camera (Pancam) spectral data acquired by the Opportunity rover to analyze 15 rock fragments at the Meridiani Planum landing site. These spectral results were then compared to geochemistry measurements made by the in situ instruments Mössbauer (MB) and Alpha Particle X‐ray Spectrometer (APXS) to determine the feasibility of mineralogic characterization from Pancam data. Our results suggest that dust and alteration rinds coat many rock fragments, which limits our ability to adequately measure the mineralogy of some rocks from Pancam spectra relative to the different field of view and penetration depths of MB and APXS. Viewing and lighting geometry, along with sampling size, also complicate the spectral characterization of the rocks. Rock fragments with the same geochemistry of sulfate‐rich outcrops have similar spectra, although the sulfate‐rich composition cannot be ascertained based upon Pancam spectra alone. FeNi meteorites have spectral characteristics, particularly ferric oxide coatings, that generally differentiate them from other rocks at the landing site. Stony meteorites and impact fragments with unknown compositions have a diverse range of spectral properties and are not well constrained nor diagnostic in Pancam data. Bounce Rock, with its unique basalt composition, is easily differentiated in the Pancam data from all other rock types at Meridiani Planum. Our Pancam analyses of small pebbles adjacent to these 15 rock fragments suggests that other rock types may exist at the landing site but have not yet been geochemically measured.
Nitrate response of a lowland catchment: On the relation between stream concentration and travel time distribution dynamics
Authors: van der Velde Y. , de Rooij G. H. , Rozemeijer J. C. , van Geer F. C. , Broers H. P.
Published: May 2011

Nitrate pollution of surface waters is widespread in lowland catchments with intensive agriculture. For identification of effective nitrate concentration reducing measures the nitrate fluxes within catchments need to be quantified. In this paper we applied a mass transfer function approach to simulate catchment‐scale nitrate transport. This approach was extended with time‐varying travel time distributions and removal of nitrate along flow paths by denitrification to be applicable for lowland catchments. Numerical particle tracking simulations revealed that transient travel time distributions are highly irregular and rapidly changing, reflecting the dynamics of rainfall and evapotranspiration. The solute transport model was able to describe 26 years of frequently measured chloride and nitrate concentrations in the Hupsel Brook catchment (6.6 km2 lowland catchment in the Netherlands) with an R2 value of 0.86. Most of the seasonal and daily variations in concentrations could be attributed to temporal changes of the travel time distributions. A full sensitivity analysis revealed that measurements other than just surface water nitrate and chloride concentrations are needed to constrain the uncertainty in denitrification, plant uptake, and mineralization of organic matter. Despite this large uncertainty, our results revealed that denitrification removes more nitrate from the Hupsel Brook catchment than stream discharge. This study demonstrates that a catchment‐scale lumped approach to model chloride and nitrate transport processes suffices to accurately capture the dynamics of catchment‐scale surface water concentration as long as the model includes detailed transient travel time distributions.
Integrated modeling of groundwater–surface water interactions in a tile‐drained agricultural field: The importance of directly measured flow route contributions
Authors: Rozemeijer J. C. , van der Velde Y. , McLaren R. G. , van Geer F. C. , Broers H. P. , Bierkens M. F. P.
Published: May 2011

Understanding the dynamics of groundwater–surface water interaction is needed to evaluate and simulate water and solute transport in catchments. However, direct measurements of the contributions of different flow routes from specific surfaces within a catchment toward the surface water are rarely available. For this study, we physically separated the tile drain discharge toward a 43.5 m ditch transect from the groundwater–plus–overland flow routes. Direct groundwater flow and ephemeral overland flow were jointly captured in three sheet pile in‐stream reservoirs, while the effluent from three tile drain outlets was collected in vessels. Our flux measurements showed that, in response to a rainfall event, the tile drain contribution to the total ditch discharge decreased from 80% to 28%. We used these flow route measurements to calibrate a field‐scale integrated water transport model. The HydroGeoSphere code was used because it simultaneously solves the flow regimes in the variably saturated domain, the tile drain domain, and the surface flow domain. This simultaneous solution is needed for a correct representation of the mutual interactions between groundwater flow, tile drain flow, and ditch water flow. Our model produced a flow distribution between the flow paths which deviated only 2% from the measured flow distribution. A sensitivity analysis showed that model parameters related to tile drain entrance resistance and to the resistance to water flow through the surface water system controlled the water flow route distribution but with little effect on groundwater levels. This indicates that a model calibration based on groundwater levels alone does not necessarily produce a correct representation of the flow route contributions.
Groundwater flow, transport, and residence times through topography‐driven basins with exponentially decreasing permeability and porosity
Authors: Cardenas M. Bayani , Jiang Xiao‐Wei
Published: May 2011

In this paper, we investigate the effects of systematic and local heterogeneity on groundwater flow, transport, and residence time distributions (RTDs) of basins where groundwater flow is topography driven. Systematic heterogeneity is represented by an exponentially depth‐decreasing hydraulic conductivity and porosity, and local heterogeneity is represented by the dispersivity. The RTDs for both a simple basin with one flow system and a basin with nested local and regional systems gradually evolve to a power law RTD with more pronounced systematic heterogeneity. Exponential decrease of poromechanical properties enhances shallow circulation and subdues deep and regional flows leading to longer flushing times for the large part of the domain, while the shallower portions flush solutes rapidly. Therefore, deeper basins lead to more persistent and pronounced power law RTDs when the poromechanical properties systematically decrease with depth. Separate contributions to the RTD due to stagnation zones associated with local flow cells and due to deeper immobile zones were identified; each leads to a different tailing behavior. Local heterogeneity slightly enhances the power law RTD by causing the tailing to begin earlier but does not affect the late time portion of the RTD. Systematic depth‐dependent heterogeneity is an important factor controlling the circulation and associated RTDs of subsurface fluids. It contributes significantly to generation of power law RTDs.
Pore‐scale simulation of density‐driven convection in fractured porous media during geological CO2sequestration
Authors: Chen Cheng , Zhang Dongxiao
Published: May 2011

Global warming is attributed to the excessive emission of greenhouse gases, one of whose main components is carbon dioxide (CO2). A promising long‐term solution for mitigating global warming is geological CO2sequestration, which is the capture and storage of enormous amounts of CO2in underground reservoirs in order to reduce CO2build up in the atmosphere. In this study, a pore‐scale lattice Boltzmann method was used to simulate density‐driven convection in a porous medium with a fracture, to study geological CO2sequestration in deep saline aquifers. The CO2‐brine interface was located at the top of the domain. Both fracture width and body force were varied to generate differentRanumbers in order to investigate the effect ofRaon the convection. All simulated data can be fitted by the same trend, implying that the characteristic length of the system was dominated by the fracture width. WhenRawas high enough, increasingRadid not reduce the critical time for the onset of instability apparently. Also, it did not increase the maximum peak vertical velocity noticeably. Therefore, there existed asymptotic values for the critical time and maximum peak vertical velocity. With highRanumbers, the high‐frequency oscillation of turbulence greatly enhanced the dissolution of CO2into brine. After the onset of convective instability, the brine with a high CO2concentration intruded into the underlying unaffected brine, which increased the interfacial area between the CO2‐rich brine and unaffected brine, and consequently favored the migration of CO2into the fracture and porous medium. This study is the first pore‐scale one investigating density‐driven convection during geological CO2sequestration in deep saline aquifers, whereas most existing research is focused on the field scale and the dissolved CO2concentration at the top boundary is usually assumed to be saturated.
Methionine and protein metabolism in non-alcoholic steatohepatitis: evidence for lower rate of transmethylation of methionine
Authors: Kalhan Satish C. , Edmison John , Marczewski Susan , Dasarathy Srinivasan , Gruca Lourdes L. , Bennett Carole , Duenas Clarita , Lopez Rocio
Published: May 2011

Hepatic metabolism of methionine is the source of cysteine, the precursor of glutathione, the major intracellular antioxidant in the body. Methionine also is the immediate precursor of SAM (S-adenosylmethionine) the key methyl donor for phosphatidylcholine synthesis required for the export of VLDL (very-low-density lipoprotein) triacylglycerols (triglycerides) from the liver. We have examined the kinetics of methionine, its transmethylation and trans-sulfuration with estimates of whole body rate of protein turnover and urea synthesis in clinically stable biopsy-confirmed subjects with NASH (non-alcoholic steatohepatitis). Subjects with NASH were more insulin-resistant and had significantly higher plasma concentrations of usCRP (ultrasensitive C-reactive protein), TNFα (tumour necrosis factor α) and other inflammatory cytokines. There was no significant effect of insulin resistance and NASH on whole body rate of protein turnover [phenylalanine Ra (rate of appearance)] and on the rate of urea synthesis. The rates of methylation of homocysteine and transmethylation of methionine were significantly lower in NASH compared with controls. There was no difference in the rate of trans-sulfuration of methionine between the two groups. Enteric mixed nutrient load resulted in a significant increase in all the measured parameters of methionine kinetics. Heterozygosity for MTHFR (5,10-methylene-tetrahydrofolate reductase) (677C→T) did not have an impact on methionine metabolism. We speculate that, as a result of oxidant stress possibly due to high fatty acid oxidation, the activity of methionine adenosyltransferase is attenuated resulting in a lower rate of transmethylation of methionine and of SAM synthesis. These results are the first evidence for perturbed metabolism of methionine in NASH in humans and provide a rationale for the development of targeted intervention strategies.
Charles Henry Brian Priestley 1915 - 1998
Authors: Garratt J. R. , Webb E. K. , McCarthy S.
Published: May 2011

Charles Henry Brian Priestley (known as Bill) was born and educated in England. After completing the Mathematical Tripos at the University of Cambridge, he joined the Meteorological Office in 1939. In 1946, aged 31 years, he took up an Australian appointment with the Council for Scientific and Industrial Research (CSIR, later to become CSIRO) to establish and develop a group to undertake research in meteorological physics. Thereafter he was based in Melbourne, Australia. The group earned world recognition, particularly for its investigations of turbulent transfer in the lower atmosphere, and evolved to become the CSIRO Division of Atmospheric Research. Priestley's own early research focused on large-scale atmospheric systems, including substantial work on global-scale transport, and later on small-scale atmospheric convection and heat transfer, in which he established some significant results. He had a leading role in the development of the atmospheric sciences in Australia, and was strongly involved in international meteorology. His career with CSIRO extended to 1977, and he finally retired from all professional commitments in the mid-1980s. After several years of declining health, he died on 18 May 1998, seven weeks before he turned 83.
Rossiter Henry Crozier 1943 - 2009
Authors: Oldroyd Benjamin P. , Mayo Oliver
Published: May 2011

Ross Crozier, population geneticist and leader in the study of the evolutionary genetics of social insects, was born on 4 January 1943 in Jodhpur, India. He died of a heart attack in his office at James Cook University in Townsville on 12 November 2009. He is survived by his wife Yuen Ching Kok, who was his inseparable companion and collaborator in life as in the laboratory. Crozier was a pioneer in the application of molecular genetic markers to the analysis of social insect populations, and generated much of the theory that made these analyses possible. Ross and Ching Crozier produced the first sequence of the honey bee mitochondrial genome?the second insect mitochondria to be fully sequenced. From the sequence Crozier produced fundamental insights into the nature of DNA evolution, particularly directional mutation pressure towards particular nucleotides. Crozier contributed massively to the development of kin selection theory, which remains the most potent explanatory theory for the evolution of social behaviour in insects.
The early embryo response to intracellular reactive oxygen species is developmentally regulated
Authors: Bain Nathan T. , Madan Pavneesh , Betts Dean H.
Published: May 2011

In vitro embryo production (IVP) suffers from excessive developmental failure. Its inefficiency is linked, in part, to reactive oxygen species (ROS) brought on by high ex vivo oxygen (O2) tensions. To further delineate the effects of ROS on IVP, the intracellular ROS levels of early bovine embryos were modulated by: (1) varying O2 tension; (2) exogenous H2O2 treatment; and (3) antioxidant supplementation. Although O2 tension did not significantly affect blastocyst frequencies (P > 0.05), 20% O2 accelerated the rate of first cleavage division and significantly decreased and increased the proportion of permanently arrested 2- to 4-cell embryos and apoptotic 9- to 16-cell embryos, respectively, compared with embryos cultured in 5% O2 tension. Treatment with H2O2, when applied separately to oocytes, zygotes, 2- to 4-cell embryos or 9- to 16-cell embryos, resulted in a significant (P < 0.05) dose-dependent decrease in blastocyst development in conjunction with a corresponding increase in the induction of either permanent embryo arrest or apoptosis in a stage-dependent manner. Polyethylene glycol–catalase supplementation reduced ROS-induced embryo arrest and/or death, resulting in a significant (P < 0.05) increase in blastocyst frequencies under high O2 culture conditions. Together, these results indicate that intracellular ROS may be signalling molecules that, outside an optimal range, result in various developmentally regulated modes of embryo demise.
Vitrification of bovine blastocysts pretreated with sublethal hydrostatic pressure stress: evaluation of post-thaw in vitro development and gene expression
Authors: Filho E. Siqueira , Caixeta E. S. , Pribenszky C. , Molnar M. , Horvath A. , Harnos A. , Franco M. M. , Rumpf R.
Published: May 2011

Sublethal stress treatment has been reported to enhance gametes’ performance in subsequent procedures, such as cryopreservation. The aim of the present study was to evaluate the effect of different equilibration times between the termination of a sublethal hydrostatic pressure (HP) stress treatment and the initiation of vitrification on the post-thaw survival, continued in vitro development, hatching rate and gene expression of selected candidate genes of in vitro-produced (IVP) expanded bovine blastocysts. Day 7 IVP blastocysts were subjected to 600 bar pressure for 60 min at 32°C. Immediately after pressure treatment (HP0h) or after 1 or 2 h incubation (HP1h and HP2h groups, respectively), embryos were either vitrified and warmed using the open pulled straw method, followed by 72 h in vitro culture or were stored at –80°C until gene expression analysis. Re-expansion and hatching rates after vitrification–warming were significantly (P < 0.05) higher in the HP0h (88 and 76%, respectively) and HP1h (90 and 75%, respectively) groups than in the untreated (82 and 63%, respectively) and HP2h groups (79 and 70%, respectively). Moreover, the HP1h group showed further improvement in the speed of re-expansion and resumption of normal in vitro development. Cumulative analysis of all genes (SC4MOL, HSP1A1A, SOD2 and GPX4) revealed a similar pattern of expression, with a tendency for peak transcript abundance 1 h after HP treatment. Application of HP stress treatment was found to be efficient in increasing the in vitro developmental competence of vitrified bovine embryos.