Noble gas and isotope geochemistry in western Canadian Arctic watersheds: tracing groundwater recharge in permafrost terrain     

Nicholas Utting  Bernard Lauriol  Neil Mochnacz  Werner Aeschbach-Hertig  Ian Clark 《Hydrogeology Journal》2013,21(1):79-91

In Canada’s western Arctic, perennial discharge from permafrost watersheds is the surface manifestation of active groundwater flow systems with features including the occurrence of year-round open water and the formation of icings, yet understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic. Stable isotopes (δ¹⁸O, δD, δ¹³C_DIC), and noble gases have proved useful to study groundwater recharge and flow of groundwater which discharges along rivers in Canada’s western Arctic. In these studies of six catchments, groundwater recharge was determined to be a mix of snowmelt and precipitation. All systems investigated show that groundwater has recharged through organic soils with elevated P_CO2, which suggests that recharge occurs largely during summer when biological activity is high. Noble gas concentrations show that the recharge temperature was between 0 and 5 °C, which when considered in the context of discharge temperatures, suggests that there is no significant imbalance of energy flux into the subsurface. Groundwater circulation times were found to be up to 31 years for non-thermal waters using the ³?H-³He method.  相似文献   

Climate change impacts and adaptation of commercial marine fisheries in Australia: a review of the science   总被引：2，自引：0，他引：2  

Neil J. Holbrook  Johanna E. Johnson 《Climatic change》2014,124(4):703-715

Commercial marine fishing contributes significantly to the Australian economy, and has great importance for coastal communities. However, climate change presents significant challenges for Australia’s fishing industries, now and into the future. With greater use of targeted information, the fishing industry will be better placed to minimise the negative impacts and take advantage of opportunities associated with the effects of climate change. The future of the fishing industry—specifically wild capture fisheries—will depend on its ability and capacity to apply appropriate adaptation strategies for its viability and sustainability in the long-term. Knowledge regarding expected long-term changes in species distributions, improved weather and seasonal climate forecasts and their influence on target species, and better understanding of species tolerances, can inform adaptation responses. This paper provides a review of recent advances in research addressing Australia’s priorities in relation to commercial marine fisheries’ responses to current and anticipated future climate change impacts, and considers barriers and adaptation options for fisheries management over the near-term planning horizon of 5–7 years.  相似文献   

Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications     

Neil C. Mitchell  Nathalie Dubois 《Marine Geophysical Researches》2014,35(1):1-20

If equatorial sediments form characteristic deposits around the equator, they may help to resolve the amount of northwards drift of the Pacific tectonic plate. Relevant to this issue, it has been shown that ²³⁰Th has been accumulating on the equatorial seabed faster than its production from radioactive decay in the overlying water column during the Holocene (Marcantonio et al. in Paleoceanography 16:260–267, 2001). Some researchers have argued that this reflects the deposition of particles with adsorbed ²³⁰Th carried by bottom currents towards the equator (“focusing”). If correct, this effect may combine with high pelagic productivity, which is also centered on the equator, to yield a characteristic signature of high accumulation rates marking the paleoequator in older deposits. Here we evaluate potential evidence that such an equatorial feature existed in the geological past. Seismic reflection data from seven meridional transects suggest that a band of equatorially enhanced accumulation of restricted latitude was variably developed, both spatially and temporally. It is absent in the interval 14.25–20.1 Ma but is well developed for the interval 8.55–14.25 Ma. We also examined eolian dust accumulation rate histories generated from scientific drilling data. A dust accumulation rate anomaly near the modern equator, which is not obviously related to the inter-tropical convergence zone, is interpreted as caused by focusing. Accumulation rates of Ba and P₂O₅ (proxies of export production) reveal a static equatorial signature, which suggests that the movement of the Pacific plate over the period 10–25 Ma was modest. The general transition from missing to well-developed focusing signatures around 14.25 Ma in the seismic data coincides with the mid-Miocene development of the western boundary current off New Zealand. This current supplies the Pacific with deep water from Antarctica, and could therefore imply a potential paleoceanographic or paleoclimatic origin. At 10.05–14.25 Ma, the latitudes of the seismic anomalies are up to ~2° different from the paleoequator predicted by Pacific plate-hotspot models, suggesting potentially a small change in the hotspot latitudes relative to the present day (although this inference depends on the precise form of the deposition around the equator). The Ba and P₂O₅ anomalies, on the other hand, are broadly compatible with plate models predicting slow northward plate movement over 10–25 Ma.  相似文献   

A 520 year record of summer sunshine for the eastern European Alps based on stable carbon isotopes in larch tree rings   总被引：1，自引：1，他引：0  

Polona Hafner  Danny McCarroll  Iain Robertson  Neil J. Loader  Mary Gagen  Giles HF Young  Roderick J. Bale  Eloni Sonninen  Tom Levanič 《Climate Dynamics》2014,43(3-4):971-980

A 520-year stable carbon isotope chronology from tree ring cellulose in high altitude larch trees (Larix decidua Mill.), from the eastern European Alps, correlates more strongly with summer temperature than with summer sunshine hours. However, when instrumental records of temperature and sunshine diverge after AD1980, the tree ring time series does not follow warming summer temperatures but more closely tracks summer sunshine trends. When the tree ring stable carbon isotope record is used to reconstruct summer temperature the reconstruction is not robust. Reconstructed temperatures prior to the twentieth century are higher than regional instrumental records, and the evolution of temperature conflicts with other regional temperature reconstructions. It is concluded that sunshine is the dominant control on carbon isotope fractionation in these trees, via the influence of photosynthetic rate on the internal partial pressure of CO₂, and that high summer (July–August) sunshine hours is a suitable target for climate reconstruction. We thus present the first reconstruction of summer sunshine for the eastern Alps and compare it with the regional temperature evolution.  相似文献   

Towards environmental management of water turbidity within open coastal waters of the Great Barrier Reef     

Rachael K. Macdonald  Peter V. Ridd  James C. Whinney  Piers Larcombe  David T. Neil 《Marine pollution bulletin》2013

Water turbidity and suspended sediment concentration (SSC) are commonly used as part of marine monitoring and water quality plans. Current management plans utilise threshold SSC values derived from mean-annual turbidity concentrations. Little published work documents typical ranges of turbidity for reefs within open coastal waters. Here, time-series turbidity measurements from 61 sites in the Great Barrier Reef (GBR) and Moreton Bay, Australia, are presented as turbidity exceedance curves and derivatives. This contributes to the understanding of turbidity and SSC in the context of environmental management in open-coastal reef environments. Exceedance results indicate strong spatial and temporal variability in water turbidity across inter/intraregional scales. The highest turbidity across 61 sites, at 50% exceedance (T₅₀) is 15.3 NTU and at 90% exceedance (T₉₀) 4.1 NTU. Mean/median turbidity comparisons show strong differences between the two, consistent with a strongly skewed turbidity regime. Results may contribute towards promoting refinement of water quality management protocols.  相似文献   

Effects of hydrophobicity on splash erosion of model soil particles by a single water drop impact     

Sujung Ahn  Stefan H. Doerr  Peter Douglas  Robert Bryant  Christopher A.E. Hamlett  Glen McHale  Michael I. Newton  Neil J. Shirtcliffe 《地球表面变化过程与地形》2013,38(11):1225-1233

Raindrop impact can be a major contributor to particle mobilization for soils and other granular materials. In previous work, water repellent soils, comprised of hydrophobic particles, have been shown to exhibit greater splash erosion losses under multiple drop impact. However, the underlying principle differences in splash behavior between hydrophobic and hydrophilic granular surfaces have not been studied to date. In this study the effects of particle hydrophobicity on splash behaviour by a single water drop impact were examined using high‐speed videography. Water drops (4 mm in diameter) were dropped on beds of hydrophilic and hydrophobic glass beads (sieved range: 350–400 µm), serving as model soil particles. The drop velocity on impact was 2.67 m s^‐1, which corresponds to ~30% of the terminal velocity of a raindrop of similar size. The resulting impact behaviour was measured in terms of the trajectories of particles ejected from the beds and their final resting positions. The response to the impacting water drop was significantly different between hydrophilic and hydrophobic particles in terms of the distance distribution, the median distance travelled by the particles and number of ejected particles. The greater ejection distances of hydrophobic particles were mainly the result of the higher initial velocities rather than differences in ejecting angles. The higher and longer ejection trajectories for hydrophobic particles, compared with hydrophilic particles, indicate that particle hydrophobicity affects splash erosion from the initial stage of rainfall erosion before a water layer may be formed by accumulating drops. The ~10% increase in average splash distance for hydrophobic particles compared with hydrophilic particles suggests that particle hydrophobicity can result in greater net erosion rate, which would be amplified on sloping surfaces, for example, by ridges in ploughed agricultural soils or hillslopes following vegetation loss by clearing or wildfire. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Comment on Rosenberg and Garcia: Estimating displacement along the Brenner Fault and orogen-parallel extension in the Eastern Alps, Int J Earth Sci (Geol Rundsch) (2011) 100:1129–1145     

Bernhard Fügenschuh  Neil S. Mancktelow  Stefan S. Schmid 《International Journal of Earth Sciences》2012,101(5):1451-1455

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Sources of groundwater pumpage in a layered aquifer system in the Upper Gulf Coastal Plain, USA     

Yun Huang  Bridget R. Scanlon  Jean-Philippe Nicot  Robert C. Reedy  Alan R. Dutton  Van A. Kelley  Neil E. Deeds 《Hydrogeology Journal》2012,20(4):783-796

Understanding groundwater-pumpage sources is essential for assessing impacts on water resources and sustainability. The objective of this study was to quantify pumping impacts and sources in dipping, unconfined/confined aquifers in the Gulf Coast (USA) using the Texas Carrizo-Wilcox aquifer. Potentiometric-surface and streamflow data and groundwater modeling were used to evaluate sources and impacts of pumpage. Estimated groundwater storage is much greater in the confined aquifer (2,200?km³) than in the unconfined aquifer (170?km³); however, feasibility of abstraction depends on pumpage impacts on the flow system. Simulated pre-development recharge (0.96?km³/yr) discharged through evapotranspiration (ET, ～37%), baseflow to streams (～57%), and to the confined aquifer (～6%). Transient simulations (1980–1999) show that pumpage changed three out of ten streams from gaining to losing in the semiarid south and reversed regional vertical flow gradients in ～40% of the entire aquifer area. Simulations of predictive pumpage to 2050 indicate continued storage depletion (41% from storage, 32% from local discharge, and 25% from regional discharge capture). It takes ～100?yrs to recover 40% of storage after pumpage ceases in the south. This study underscores the importance of considering capture mechanism and long-term system response in developing water-management strategies.  相似文献   

The disposal of radioactive wastes underground     

Neil Chapman  Alan Hooper 《Proceedings of the Geologists' Association. Geologists' Association》2012,123(1):46-63

Nuclear power is strategically and quantitatively an important contributor to global electricity generation capacity and produces a small amount of potentially highly hazardous wastes that require careful management. The accepted solution for disposing of higher activity and longer-lived radioactive wastes from the nuclear power industry and other sources is engineered emplacement in deep geological disposal facilities (GDFs), situated many hundreds of metres underground. The first purpose-built GDFs for the most active of these wastes (used nuclear fuel and high-level wastes) will be operational in about ten years time in a few countries, with most other countries (including the UK) developing such facilities during coming decades. This article reviews the conceptual basis for geological disposal, examines how long-term safety is provided, considers the geological challenges to developing GDFs and the uncertainties that have to be managed, and looks in more detail at some of the most advanced design concepts. Because the issue of forecasting GDF evolution and behaviour over very long time periods lies at the core of geological disposal, particular emphasis is placed on matching containment requirements with diminishing hazard potential over many thousands of years. The article concludes with a commentary on current developments in the UK geological disposal programme.  相似文献   

Estimates of recent Hg pollution in Northeast China using peat profiles from Great Hinggan Mountains     

Kunshan Bao  Ji Shen  Guoping Wang  Atindra Sapkota  Neil McLaughlin 《Environmental Earth Sciences》2016,75(6):536

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