Holocene valley-floor deposition and incision in a small drainage basin in western Colorado, USA     

Lawrence S. Jones  Margaret Rosenburg  Kathleen McKee  Jenna Hunter 《Quaternary Research》2010,74(2):199-206

The valley floor of a 33.9 km² watershed in western Colorado experienced gradual sedimentation from before ∼ 6765 to ∼ 500 cal yr BP followed by deep incision, renewed aggradation, and secondary incision. In contrast, at least four terraces and widespread cut-and-fill architecture in the valley floor downstream indicate multiple episodes of incision and deposition occurred during the same time interval. The upper valley fill history is atypical compared to other drainages in the Colorado Plateau.One possible reason for these differences is that a bedrock canyon between the upper and lower valley prevented headward erosion from reaching the upper valley fill. Another possibility is that widespread, sand-rich, clay-poor lithologies in the upper drainage limited surface runoff and generally favored alluviation, whereas more clay-rich lithologies in the lower drainage resulted in increased surface runoff and more frequent incision. Twenty-two dates from valley fill charcoal indicate an approximate forest fire recurrence interval of several hundred years, similar to that from other studies in juniper-piñon woodlands. Results show that closely spaced vertical sampling of alluvium in headwater valleys where linkages between hillslope processes and fluvial activity are relatively direct can provide insight about the role of fires in alluvial chronologies of semi-arid watersheds.  相似文献   

Delta13C and delta15N shifts in benthic invertebrates exposed to sewage from McMurdo Station, Antarctica     

Conlan KE  Rau GH  Kvitek RG 《Marine pollution bulletin》2006,52(12):1695-1707

In an effort to identify biomonitors for contamination of Antarctic marine benthos by sewage, this study determines whether the US Antarctic Program’s McMurdo Station produces a benthic sewage footprint and whether resident megafauna are assimilating sewage-derived material. We identified strong C and N isotopic gradients in benthic sediment as a function of downstream distance from McMurdo Station’s point-source sewage addition. Sediment C and N isotope ratios approached marine background levels at the sampling end-point 612 m downcurrent. Based on isotope abundances in their tissues, at least some sewage C and N were assimilated by the sedentary, suspension feeding soft coral Alcyonium antarcticum, ascidian Cnemidocarpa verrucosa and bivalve Laternula elliptica. However, as inferred by tissue-sediment differences in downstream isotope trends, such assimilation was not in proportion to sewage exposure and input, therefore implying non-generalist feeding behavior by these species. In contrast, the motile, generalist feeding sea urchin Sterechinus neumayeri, sea star Odontaster validus and ribbon worm Parborlasia corrugatus showed isotopic evidence of sewage C and N assimilation roughly in proportion to sewage input. We recommend these generalist feeders for further use as biomonitors at this site now that sewage treatment has been implemented. As these species are circumpolar in distribution, they may also prove useful elsewhere in the Antarctic.  相似文献   

Reducing long-term remedial costs by transport modeling optimization   总被引：1，自引：0，他引：1  

Becker D  Minsker B  Greenwald R  Zhang Y  Harre K  Yager K  Zheng C  Peralta R 《Ground water》2006,44(6):864-875

The Department of Defense (DoD) Environmental Security Technology Certification Program and the Environmental Protection Agency sponsored a project to evaluate the benefits and utility of contaminant transport simulation-optimization algorithms against traditional (trial and error) modeling approaches. Three pump-and-treat facilities operated by the DoD were selected for inclusion in the project. Three optimization formulations were developed for each facility and solved independently by three modeling teams (two using simulation-optimization algorithms and one applying trial-and-error methods). The results clearly indicate that simulation-optimization methods are able to search a wider range of well locations and flow rates and identify better solutions than current trial-and-error approaches. The solutions found were 5% to 50% better than those obtained using trial-and-error (measured using optimal objective function values), with an average improvement of approximately 20%. This translated into potential savings ranging from 600,000 dollars to 10,000,000 dollars for the three sites. In nearly all cases, the cost savings easily outweighed the costs of the optimization. To reduce computational requirements, in some cases the simulation-optimization groups applied multiple mathematical algorithms, solved a series of modified subproblems, and/or fit "meta-models" such as neural networks or regression models to replace time-consuming simulation models in the optimization algorithm. The optimal solutions did not account for the uncertainties inherent in the modeling process. This project illustrates that transport simulation-optimization techniques are practical for real problems. However, applying the techniques in an efficient manner requires expertise and should involve iterative modification to the formulations based on interim results.  相似文献   

Chemical and isotopic evidence for the nature of the fluid in CH4-containing sediments of the Håkon Mosby Mud Volcano     

A. Lein  P. Vogt  K. Crane  A. Egorov  M. Ivanov 《Geo-Marine Letters》1999,19(1-2):76-83

The pore waters of CH₄-containing sediments of the Håkon Mosby Mud Volcano were rich in NH⁺ ₄, Br^-, and I^-; exhibited a high total alkalinity; but were poor in Cl^-and SO^2- ₄. The geological evidence and our data suggest that organic matter decomposition in preglacial or early interglacial sediments took place during early diagenesis (bacterial processes) and during metamorphism (thermogenic processes under the 3100-m-thick layer of glacial sediments), accompanied by mud volcano fluid generation. It is argued that the CH₄of the mud volcano sediments has a mixed, biogenic and thermogenic, origin.  相似文献   

SW Barents Sea continental margin heat flow and Håkon Mosby Mud Volcano     

O. Eldholm  E. Sundvor  P. R. Vogt  B. O. Hjelstuen  K. Crane  A. K. Nilsen  T. P. Gladczenko 《Geo-Marine Letters》1999,19(1-2):29-37

The high thermal gradient and heat flow >1000?mW?m^-2 on Håkon Mosby Mud Volcano are ascribed to rapid transport of pore water, mud, and gas in a narrow, deep conduit within a 3.1-km-thick glacial sediment unit. The instability is caused by rapid loading of dense glacial sediments on less dense oozes. Changes in pressure–temperature conditions by sudden, large-scale downslope mass movement may induce structural deformation, opening transient pathways from the base of the glacial sediments to the sea floor. This model may also explain slope maxima elsewhere on the margin.  相似文献   

The relationship between turbidity and spectral optical depth     

John Davies  Kathleen Stewart 《大气与海洋》2013,51(2):256-260

Abstract

Spectral and spectrally integrated direct beam irradiances measured in Hamilton during the summer of 1981 were used to examine the relationship between the aerosol optical depth τ_a and Unsworth and Monteith's turbidity coefficient τ_A, which is a measure of spectrally averaged optical depth. Good correlation was obtained between τ_a at a wavelength of 0.67 μm and τ_A, thus confirming experimentally Blanchet's (1982) conclusion from a numerical study.  相似文献   

A decision aid tool for equity issues analysis in emission permit allocations     

Kathleen Vaillancourt  Jean-Philippe Waaub 《Climate Policy》2013,13(5):487-501

Abstract

In the long term, the Kyoto Protocol will be insufficient to stabilize the greenhouse gas (GHG) concentrations in the atmosphere; quantified commitments will also be essential for major developing countries (and the US). International cooperation mechanisms, such as permit trading systems, can help achieve global economic efficiency. However, the initial allocation of emission permits raises many debates on equity. The main objective is to propose a decision aid tool for decision makers, which is capable of providing relevant information on various equitable permit allocation schemes and burden sharing. A dynamic multicriteria model is proposed to share the global quantity of permits among 15 regions, taking into account multiple definitions of equity and regional interests. The World-MARKAL energy model is used to compute the gross reduction cost (before permit exchanges) for each region. Afterward, it is possible to calculate their net reduction costs (after permit exchanges) according to different allocation schemes. A realistic simulation of the tool provides examples of results, i.e. ranges of permit allocations and net costs for each region. Finally, some recommendations are proposed to policy makers to design a decision process adapted to the global context of negotiations.  相似文献   

Constraining and enabling factors to using long-term climate information in decision-making     

Lindsey Jones  Clara Champalle  Sabrina Chesterman  Laura Cramer  Todd A. Crane 《Climate Policy》2013,13(5):551-572

We carry out a structured review of the peer-reviewed literature to assess the factors that constrain and enable the uptake of long-term climate information in a wide range of sectoral investment and planning decisions. Common applications of long-term climate information are shown to relate to urban planning and infrastructure, as well as flood and coastal management. Analysis of the identified literature highlights five categories of constraints: disconnection between users and producers of climate information, limitations of climate information, financial and technical constraints, political economy and institutional constraints and finally psycho-social constraints. Five categories of enablers to the uptake of long-term climate information in decision-making are also identified: collaboration and bridge work, increased accessibility of climate information, improvement in the underlying science, institutional reform and windows of opportunity for building trust.

Policy relevance

Our review suggests that stand-alone interventions aimed at promoting the uptake of climate information into decision-making are unlikely to succeed without genuine and sustained relationships between producers and users. We also highlight that not every decision requires consideration of long-term climate information for successful outcomes to be achieved. This is particularly the case in the context of developing countries, where the immediacy of development challenges means that decision makers often prioritize short-term interventions. Care should therefore be taken to ensure that information is targeted towards investments and planning decisions that are relevant to longer-term timescales.  相似文献   

Projected changes in vertical temperature profiles for Australasia     

Ji  Fei  Evans  Jason P.  Di Virgilio  Giovanni  Nishant  Nidhi  Di Luca  Alejandro  Herold  Nicholas  Downes  Stephanie M.  Tam  Eugene  Beyer  Kathleen 《Climate Dynamics》2020,55(9-10):2453-2468

The vertical temperature profile in the atmosphere reflects a balance between radiative and convective processes and interactions with the oceanic and land surfaces. Changes in vertical temperature profiles can affect atmospheric stability, which in turn can impact various aspects of weather systems. In this study, we analyzed recent-past trends of temperature over the Australian region using a homogenized monthly upper-air temperature dataset and four reanalysis datasets (NCEP, ERA-Interim, JRA-55 and MERRA). We also used outputs of 12 historical and future regional climate model (RCM) simulations from the NSW/ACT (New South Wales/Australian Capital Territory) Regional Climate Modelling (NARCliM) project and 6 RCM simulations from the CORDEX (Coordinated Regional Downscaling Experiment) Australasian project to investigate projected changes in vertical temperature profiles. The results show that the currently observed positive trend in the troposphere and negative trend in the lower stratosphere will continue in the future with significant warming over the whole troposphere and largest over the middle to upper troposphere. The increasing temperatures are found to be latitude-dependent with clear seasonal variations, and a strong diurnal variation for the near surface layers and upper levels in tropical regions. Changes in the diurnal variability indicate that near surface layers will be less stable in the afternoon leading to conditions favoring convective systems and more stable in the early morning which is favorable for temperature inversions. The largest differences of future changes in temperature between the simulations are associated with the driving GCMs, suggesting that large-scale circulation plays a dominant role in regional atmospheric temperature change.

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Exploration of bounded motion near binary systems comprised of small irregular bodies     

Loic Chappaz  Kathleen C. Howell 《Celestial Mechanics and Dynamical Astronomy》2015,123(2):123-149

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