The Great Ice Age: Climate Change and Life.: By R.C.L. Wilson, S.A. Drury and J. L. Chapman.     

Bryan C. Storey 《New Zealand geographer》2000,56(2):63-64

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Do Low CO₂ Concentrations Affect Pollen-Based Reconstructions of LGM Climates? A Response to “Physiological Significance of Low Atmospheric CO₂ for Plant–Climate Interactions” by Cowling and Sykes     

John W. Williams  Thompson Webb  III  Bryan N. Shurman  Patrick J. Bartlein 《Quaternary Research》2000,53(3):402

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Drivers of peatland water table dynamics in the central Andes,Bolivia and Peru     

David J. Cooper  Jeremy Sueltenfuss  Eduardo Oyague  Karina Yager  Daniel Slayback  E. Marcelo Cabero Caballero  Jaime Argollo  Bryan G. Mark 《水文研究》2019,33(13):1913-1925

Cushion plant dominated peatlands are key ecosystems in tropical alpine regions of the Andes in South America. The cushion plants have formed peat bodies over thousands of years that fill many valley bottoms, and the forage produced by the plants is critical for native and nonnative domesticated mammals. The sources and flow paths of water supporting these peatlands remain largely unknown. Some studies have suggested that glacier meltwater streams support some peatlands, and that the ongoing loss of glaciers and their meltwaters could lead to the loss or diminishment of peatlands. We analysed the hydrologic regime of 10 peatlands in four mountain regions of Bolivia and Peru using groundwater monitoring. Groundwater levels in peatlands were relatively stable and within 20 cm of the ground surface during the rainy season, and many sites had water tables 40–90 cm below the ground surface in the dry season. Topographic and groundwater elevations in the peatlands demonstrated that the water source of all 10 peatlands was hillslope groundwater flowing from lateral moraines, talus, colluvium, or bedrock aquifers into the peatlands. There was little to no input from streams, whether derived from glacier melt or other sources, and glacier melt could not have recharged the hillslope aquifers supporting peatlands. We measured the stable water isotopes in water samples taken during different seasons, distributed throughout the catchments, and the values are consistent with this interpretation. Our findings indicate that peatlands in the study region are recharged by hillslope groundwater discharge rather than stream water and may not be as vulnerable to glacial decline as other studies have indicated. However, both glaciers and peatlands are susceptible to changing thermal and precipitation regimes that could affect the persistence of peatlands.  相似文献   

Three hundred years of snowpack variability in southwestern British Columbia reconstructed from tree-rings     

Bryan J. Mood  Bethany Coulthard  Dan J. Smith 《水文研究》2020,34(25):5123-5133

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Transverse mixing and surface heat exchange in the Waikato River: A comparison of two models     

J. Christopher Rutherford  Bryan L. Williams  Ray A. Hoare 《新西兰海洋与淡水研究杂志》2013,47(3-4):435-452

Abstract

Two mathematical models of different complexity were used to study transverse dispersion and surface heat transfer in the lower Waikato River. A simple analytical streamtube model (HPLUME) gave adequate temperature predictions in a reach where the channel was fairly regular but performed poorly where there were extensive shallows. In the latter reach, a two‐dimensional numerical model (SYSTEM21) gave good temperature and flow predictions once properly calibrated. Model calibration proved to be difficult in the Waikato River because the natural river temperature varied significantly along the channel. A search method was developed to estimate both the transverse dispersion and surface heat exchange coefficients from measured plume temperature profiles based on the observation that transverse variations in natural temperature were small. This method was used to calibrate SYSTEM21 in two separate reaches. Coefficient estimates were sensitive to measurement errors and slight departures in homogeneity of natural temperature and it would be desirable to corroborate the estimates of E_z using dye tests. In the upper reach, the average transverse dispersion coefficient was E_z/hu? = 1 which is high but within the range of published values. A sharp bend and buoyant spreading contributed to the high E_z value. E_z increased with river flow because both h and u? increase with flow. In the lower reach, E_z/hu? = 0.1 which is lower than expected but islands may have affected the model calibration. The surface heat exchange coefficient averaged K = 84–167 W m^?2 s^?1 °C^?1 which falls within the range of published values. No significant relationship could be found between surface heat exchange coefficient and meteorological variables.  相似文献   

Crustal and thermal structure of the Thomson Orogen: constraints from the geochemistry,zircon U–Pb age,and Hf and O isotopes of subsurface granitic rocks     

C. Siégel  S. E. Bryan  C. M. Allen  D. J. Purdy  A. J. Cross  I. T. Uysal 《Australian Journal of Earth Sciences》2013,60(7-8):967-986

Abstract

The origin of elevated geothermal gradients in the subsurface Thomson Orogen and the nature of the crustal basement beneath it, whether oceanic or continental, remain enigmatic. Previous studies have demonstrated that a higher crustal radiogenic input is required to explain these anomalous thermal gradients. In this study, we have investigated the nature and age of this crustal input by undertaking geochemical, geochronological and Hf and O isotope analyses of buried granitic rocks as well as evaluating the heat-producing potential of metasedimentary rocks. The mineralogy, composition and Neoproterozoic/Cambrian to Devonian age of the low to moderate heat-producing I- and S-type granitic rocks strongly contrast with the Carboniferous A-type high-heat-producing granites of the Big Lake Suite, which have been suggested to be an important contributor to the elevated geothermal gradients, near the southwest corner of the Thomson Orogen. These differences suggest the Big Lake Suite rocks do not extend into the Queensland part of the temperature anomaly. Heat production of the metasedimentary rocks is also low to moderate. Based on Hf isotope compositions of zircons characterised by mantle-like oxygen signature (?_Hf(t) = –12 to +2), we propose the temperature anomaly results from the occurrence of Mesoproterozoic and/or Paleoproterozoic high-heat-producing rocks beneath the Thomson Orogen. Precambrian crust, therefore, lies well east of the Tasman line. The results do not support a Neoproterozoic to Cambrian oceanic crust, as previously suggested, but instead point to a continental substrate for the Thomson Orogen. Hf isotopes indicate an overall trend towards more isotopically juvenile compositions with a progressive reduction in the contribution of older crustal sources to granitic magmas towards the present time. Different Hf isotopic signatures for the Lachlan (?_Hf(t) = –13 to +15), Thomson (?_Hf(t) = –14 to +5) and Delamerian (?_Hf(t) = –7 to +4) orogens highlight lateral variations in the age structures of crustal basement beneath these orogens.  相似文献   

Operational Coefficient of Consolidation Around a Pile Group Driven in Clay/Silt     

Bryan A. McCabe  Brian G. Sexton  Barry M. Lehane 《Geotechnical and Geological Engineering》2013,31(1):183-197

Although finite element packages facilitating coupled consolidation analyses are increasingly in use, many practitioners still favour linear uncoupled analysis out of familiarity with the use of coefficients of consolidation. However, coefficients of consolidation measured by any single means tend to exhibit significant variation, with mean results from different laboratory and field tests also varying widely, leaving uncertainty over the correct values to apply to field problems. In this paper, a finite difference approach is used to back-calculate operational coefficients of consolidation from pore pressure measurements pertinent to a pile group driven in clay–silt. The research shows that this method is capable of successfully capturing the process of pore pressure dissipation, and that the operational coefficient of consolidation around the pile group is higher than that derived from piezocone dissipation tests in the same material.  相似文献   

Seasonal and inter-annual variability of water quality in the Uruguay River,Argentina     

Juan C. Colombo  Carlos N. Skorupka  Claudio Bilos  Leandro Tatone  Natalia Cappelletti  M. Carolina Migoya 《水文科学杂志》2013,58(6):1155-1163

Abstract

Water quality of the Uruguay River was evaluated with multi-parametric (temperature, turbidity, conductivity, pH, dissolved oxygen) and sediment trap data (particle flux, total organic carbon and nitrogen contents) and correlated to precipitation, river discharge and El Niño Southern Oscillation (ENSO) indices for the period 2006–2011. Hydro-meteorological parameters averaged 24–85% variability with coincident precipitation (200–400 mm month^-1), discharge (7000–28 000 m³ s^-1) and turbidity peaks (50–80 NTU) in the austral spring, and absolute maxima during the El Niño 2009 episode. Spectral analysis of discharge and sea-surface temperature anomaly (SSTA) showed consistent variance maxima at approx. 3 and 1.5 years. Deseasonalized discharge was significantly correlated to SSTA. During river floods, pH decreased (from 7.5 to 6.6) and particle dynamics peaked (turbidity: 15–80 NTU; vertical fluxes: 20–200 g m^-2 d^-1; total solid load: <1000 to 100 000 t d^-1),whereas TOC remained stable (3.2 ± 0.8%) and C/N ratios increased (10–12) due to the higher contribution of terrestrial detritus.  相似文献   

Modeling the morphodynamic response of tidal embayments to sea-level rise     

van Maanen  Barend  Coco  Giovanni  Bryan  Karin R.  Friedrichs  Carl T. 《Ocean Dynamics》2013,63(11):1249-1262

Sea-level rise has a strong influence on tidal systems, and a major focus of climate change effect studies is to predict the future state of these environmental systems. Here, we used a model to simulate the morphological evolution of tidal embayments and to explore their response to a rising sea level. The model was first used to reproduce the formation of channels and intertidal flats under a stable mean water level in an idealised and initially unchannelled tidal basin. A gradual rise in sea level was imposed once a well-developed channel network had formed. Simulations were conducted with different sea-level rise rates and tidal ranges. Sea-level rise forced headward erosion of the tidal channels, driving a landward expansion of the channel network and channel development in the previously non-inundated part of the basin. Simultaneously, an increase in channel drainage width in the lower part of the basin occurred and a decrease in the overall fraction of the basin occupied by channels could be observed. Sea-level rise thus altered important characteristics of the tidal channel network. Some intertidal areas were maintained despite a rising sea level. However, the size, shape, and location of the intertidal areas changed. In addition, sea-level rise affected the exchange of sediment between the different morphological elements. A shift from exporting to importing sediment as well as a reinforcement of the existing sediment export was observed for the simulations performed here. Sediment erosion in the inlet and the offshore transport of sediment was enhanced, resulting in the expansion of the ebb-tidal delta. Our model results further emphasise that tidal embayments can exhibit contrasting responses to sea-level rise.

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Contribution of groundwater to the outflow from ungauged glacierized catchments: a multi‐site study in the tropical Cordillera Blanca,Peru          下载免费PDF全文

Michel Baraer  Jeffrey McKenzie  Bryan G. Mark  Ryan Gordon  Jeffrey Bury  Thomas Condom  Jesus Gomez  Sara Knox  Sarah K. Fortner 《水文研究》2015,29(11):2561-2581

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