Analysis of snowpack dynamics during the spring melt season for a sub‐alpine site using point measurements and numerical modeling          下载免费PDF全文

Mark S. Pleasants  Thijs J. Kelleners  Noriaki Ohara 《水文研究》2017,31(25):4568-4585

Snowpack dynamics through October 2014–June 2017 were described for a forested, sub‐alpine field site in southeastern Wyoming. Point measurements of wetness and density were combined with numerical modeling and continuous time series of snow depth, snow temperature, and snowpack outflow to identify 5 major classes of distinct snowpack conditions. Class (i) is characterized by no snowpack outflow and variable average snowpack temperature and density. Class (ii) is characterized by short durations of liquid water in the upper snowpack, snowpack outflow values of 0.0008–0.005 cm hr^?1, an increase in snowpack temperature, and average snow density between 0.25–0.35 g cm^?3. Class (iii) is characterized by a partially saturated wetness profile, snowpack outflow values of 0.005–0.25 cm hr^?1, snowpack temperature near 0 °C, and average snow density between 0.25–0.40 g cm^?3. Class (iv) is characterized by strong diurnal snowpack outflow pattern with values as high as 0.75 cm hr^?1, stable snowpack temperature near 0 °C, and stable average snow density between 0.35–0.45 g cm^?3. Class (v) occurs intermittently between Classes (ii)–(iv) and displays low snowpack outflow values between 0.0008–0.04 cm hr^?1, a slight decrease in temperature relative to the preceding class, and similar densities to the preceding class. Numerical modeling of snowpack properties with SNOWPACK using both the Storage Threshold scheme and Richards' equation was used to quantify the effect of snowpack capillarity on predictions of snowpack outflow and other snowpack properties. Results indicate that both simulations are able to predict snow depth, snow temperature, and snow density reasonably well with little difference between the 2 water transport schemes. Richards' equation more accurately simulates the timing of snowpack outflow over the Storage Threshold scheme, especially early in the melt season and at diurnal timescales.  相似文献   

Flooding of the continental shelves as a contributor to deglacial CH4 rise     

Andy Ridgwell  Mark Maslin  Jed O. Kaplan 《第四纪科学杂志》2012,27(8):800-806

The transition from the last glacial and beginning of Bølling–Allerød and Pre‐Boreal periods in particular is marked by rapid increases in atmospheric methane (CH₄) concentrations. The CH₄ concentrations reached during these intervals, ～650–750 ppb, is twice that at the last glacial maximum and is not exceeded until the onset of industrialization at the end of the Holocene. Periods of rapid sea‐level rise as the Last Glacial Maximum ice sheets retreated and associated with ‘melt‐water pulses’ appear to coincide with the onset of elevated concentrations of CH₄, suggestive of a potential causative link. Here we identify and outline a mechanism involving the flooding of the continental shelves that were exposed and vegetated during the glacial sea‐level low stand and that can help account for some of these observations. Specifically, we hypothesize that waterlogging (and later, flooding) of large tracts of forest and savanna in the Tropics and Subtropics during the deglacial transition and early Holocene would have resulted in rapid anaerobic decomposition of standing biomass and emission of methane to the atmosphere. This novel mechanism, akin to the consequences of filling new hydroelectric reservoirs, provides a mechanistic explanation for the apparent synchronicity between rate of sea‐level rise and occurrence of elevated concentrations of ice core CH₄. However, shelf flooding and the creation of transient wetlands are unlikely to explain more than ～60 ppb of the increase in atmospheric CH₄ during the deglacial transition, requiring additional mechanisms to explain the bulk of the glacial to interglacial increase. Similarly, this mechanism has the potential also to play some role in the rapid changes in atmospheric methane associated with the Dansgaard–Oeschger cycles. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Moving boulders in flash floods and estimating flow conditions using boulders in ancient deposits          下载免费PDF全文

Jan Alexander  Mark J. Cooker 《Sedimentology》2016,63(6):1582-1595

Boulders moving in flash floods cause considerable damage and casualties. More and bigger boulders move in flash floods than predicted from published theory. The interpretation of flow conditions from the size of large particles within flash flood deposits has, until now, generally assumed that the velocity (or discharge) is unchanging in time (i.e. flow is steady), or changes instantaneously between periods of constant conditions. Standard practice is to apply theories developed for steady flow conditions to flash floods, which are however inherently very unsteady flows. This is likely to lead to overestimates of peak flow velocity (or discharge). Flash floods are characterised by extremely rapid variations in flow that generate significant transient forces in addition to the mean‐flow drag. These transient forces, generated by rapid velocity changes, are generally ignored in published theories, but they are briefly so large that they could initiate the motion of boulders. This paper develops a theory for the initiation of boulder movement due to the additional impulsive force generated by unsteady flow, and discusses the implications.  相似文献   

Inter-annual rainfall variability in the eastern Antilles and coupling with the regional and intra-seasonal circulation     

Mark R. Jury 《Theoretical and Applied Climatology》2016,126(3-4):727-737

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High-Ti,bright-CL rims in volcanic quartz: a result of very rapid growth     

Ayla S. Pamukcu  Mark S. Ghiorso  Guilherme A. R. Gualda 《Contributions to Mineralogy and Petrology》2016,171(12):105

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Identification of Uranyl Minerals Using Oxygen K‐Edge X‐Ray Absorption Spectroscopy          下载免费PDF全文

Jesse D. Ward  Mark Bowden  C. Tom Resch  Steven Smith  Bruce K. McNamara  Edgar C. Buck  Gregory C. Eiden  Andrew M. Duffin 《Geostandards and Geoanalytical Research》2016,40(1):135-148

Although most of the world's uranium exists as pitchblende or uraninite, this mineral can be weathered to a great variety of secondary uranium minerals, most containing the uranyl cation. Anthropogenic uranium compounds can also react in the environment, leading to spatial–chemical alterations that could be useful for nuclear forensics analyses. Soft X‐ray absorption spectroscopy (XAS) has the advantages of being non‐destructive, element‐specific and sensitive to electronic and physical structure. The soft X‐ray probe can also be focused to a spot size on the order of tens of nanometres, providing chemical information with high spatial resolution. However, before XAS can be applied at high spatial resolution, it is necessary to find spectroscopic signatures for a variety of uranium compounds in the soft X‐ray spectral region. To that end, we collected the near edge X‐ray absorption fine structure (NEXAFS) spectra of a variety of common uranyl‐bearing minerals, including uranyl carbonates, oxyhydroxides, phosphates and silicates. We find that uranyl compounds can be distinguished by class (carbonate, oxyhydroxide, phosphate or silicate) based on their oxygen K‐edge absorption spectra. This work establishes a database of reference spectra for future spatially resolved analyses. We proceed to show scanning X‐ray transmission microscopy (STXM) data from a schoepite particle in the presence of an unknown contaminant.  相似文献   

Generalised observations of wave characteristics on near‐horizontal shore platforms: Synthesis of six case studies from the North Island,New Zealand          下载免费PDF全文

Hiroki Ogawa  Mark E. Dickson  Paul S. Kench 《New Zealand geographer》2016,72(2):107-121

Most field studies of wave processes on shore platforms in front of eroding cliffs focus on a single site, revealing aspects of wave dynamics at that location. Here, we analyse data from six platforms around northeastern New Zealand and describe the fundamental control of shore platform width, gradient and elevation on wave processes, including greater attenuation of short‐period waves at lower tidal stages and increases in longer period wave energy towards the cliff toe. These data suggest that empirical formulae developed from coral‐reef environments provide better predictions of wave height on platforms than formulae currently used in shore platform models.  相似文献   

Stochastic groundwater modeling of a sedimentary aquifer: evaluation of the impacts of abstraction scenarios under conditions of reduced recharge     

Sandow Mark Yidana  Millicent Obeng Addai  Daniel Kwadwo Asiedu  Bruce Banoeng-Yakubo 《Arabian Journal of Geosciences》2016,9(17):684

A transient finite difference groundwater flow model has been calibrated for the Nasia sub-catchment of the White Volta Basin. This model has been validated through a stochastic parameter randomization process and used to evaluate the impacts of groundwater abstraction scenarios on resource sustainability in the basin. A total of 1500 equally likely model realizations of the same terrain based on 1500 equally likely combinations of the data of the key aquifer input parameters were calibrated and used for the scenario analysis. This was done to evaluate model non-uniqueness arising from uncertainties in the key aquifer parameters especially hydraulic conductivity and recharge by comparing the realizations and statistically determining the degree to which they differ from each other. Parameter standard deviations, computed from the calibrated data of the key parameters of hydraulic conductivity and recharge, were used as a yardstick for evaluating model non-uniqueness. All model realizations suggest horizontal hydraulic conductivity estimates in the range of 0.03–78.4 m/day, although over 70 % of the area has values in the range of 0.03–14 m/day. Low standard deviations of the horizontal hydraulic conductivity estimates from the 1500 solutions suggest that this range adequately reflects the properties of the material in the terrain. Lateral groundwater inflows and outflows appear to constitute significant components of the groundwater budgets in the terrain, although estimated direct vertical recharge from precipitation amounts to about 7 % of annual precipitation. High potential for groundwater development has been suggested in the simulations, corroborating earlier estimates of groundwater recharge. Simulation of groundwater abstraction scenarios suggests that the domain can sustain abstraction rates of up to 200 % of the current estimated abstraction rates of 12,960 m³/day under the current recharge rates. Decreasing groundwater recharge by 10 % over a 20-year period will not significantly alter the results of this abstraction scenario. However, increasing abstraction rates by 300 % over the period with decreasing recharge by 10 % will lead to drastic drawdowns in the hydraulic head over the entire terrain by up to 6 m and could cause reversals of flow in most parts of the terrain.  相似文献   

A Cambrian mixed carbonate–siliciclastic platform in SW Gondwana: evidence from the Western Sierras Pampeanas (Argentina) and implications for the early Paleozoic paleogeography of the proto-Andean margin     

Ramacciotti  Carlos D.  Casquet  César  Baldo  Edgardo G.  Galindo  Carmen  Pankhurst  Robert J.  Verdecchia  Sebastián O.  Rapela  Carlos W.  Fanning  Mark 《International Journal of Earth Sciences》2018,107(7):2605-2625

International Journal of Earth Sciences - The Western Sierras Pampeanas (WSP) of Argentina record a protracted geological history from the Mesoproterozoic assembly of the Rodinia supercontinent to...  相似文献   

Borehole diffusive flux apparatus for characterizing diffusive mass-transfer in subsurface systems     

Mark L. Brusseau  Kenneth C. Carroll  Zhilin Guo  Jon Mainhagu 《Environmental Earth Sciences》2018,77(18):648

The concept of the Borehole Diffusive Flux Apparatus (BDFA) is presented herein. The BDFA is an innovative apparatus designed to provide continuous direct access to an undisturbed column of sediment that can be monitored at multiple discrete vertical intervals to provide high-resolution characterization of local-scale mass transfer and attenuation. The conceptual basis and technical design of the device are presented, along with an example of borehole design and installation at a field site. Mathematical simulations are used to illustrate its application for two scenarios. The results of these simulations indicate that test periods of several weeks to a few months should be sufficient to obtain robust results. The device has the potential to improve our ability to characterize critical mass-transfer and attenuation processes and to quantify the associated rates. This information is key to the evaluation of remediation alternatives, for enhancing the accuracy of mathematical models, and to support more effective long-term management of large groundwater contaminant plumes present at many sites.  相似文献