Advance,deglacial and sea‐level chronology for Foxe Peninsula,Baffin Island,Nunavut          下载免费PDF全文

Daniel J. Utting  John C. Gosse  Samuel E. Kelley  Kayla J. Vickers  Brent C. Ward  Michelle S. Trommelen 《Boreas: An International Journal of Quaternary Research》2016,45(3):439-454

The impact of the Laurentide Ice Sheet (LIS) deglaciation on Northern Hemisphere early Holocene climate can be evaluated only once a detailed chronology of ice history and sea‐level change is established. Foxe Peninsula is ideally situated on the northern boundary of Hudson Strait, and preserves a chronostratigraphy that provides important glaciological insights regarding changes in ice‐sheet position and relative sea level before and after the 8.2 ka cooling event. We utilized a combination of radiocarbon ages, adjusted with a new locally derived ΔR, and terrestrial in‐situ cosmogenic nuclide (TCN) exposure ages to develop a chronology for early‐Holocene events in the northern Hudson Strait. A marine limit at 192 m a.s.l., dated at 8.1–7.9 cal. ka BP, provides the timing of deglaciation following the 8.2 ka event, confirming that ice persisted at least north of Hudson Bay until then. A moraine complex and esker morphosequence, the Foxe Moraine, relates to glaciomarine outwash deltas and beaches at 160 m a.s.l., and is tightly dated at 7.6 cal. ka BP with a combination of shell dates and exposure ages on boulders. The final rapid collapse of Foxe Peninsula ice occurred by 7.1–6.9 cal. ka BP (radiocarbon dates and TCN depth profile age on an outwash delta), which supports the hypothesis that LIS melting contributed to the contemporaneous global sea‐level rise known as the Catastrophic Rise Event 3 (CRE‐3).  相似文献   

Groundwater transport of crater-lake brine at Poa´s Volcano, Costa Rica     

Ward E. Sanford  Leonard F. Konikow  Gary L. Rowe  Jr.  Susan L. Brantley 《Journal of Volcanology and Geothermal Research》1995,64(3-4)

Poa´s Volcano is an active stratovolcano in Costa Rica that has a lake in its active crater. The crater lake has high temperatures (50–90 °C), high acidity (pH ≈ 0.0), and a high dissolved-solids content (100 g/kg). The volcano has numerous freshwater springs on its flanks, but a few on the northwestern flank are highly acidic (pH = 1.6–2.5) and have high dissolved-solids concentrations (2–22 g/kg). This study analyzes the regional groundwater system at Poa´s and demonstrates the likelihood that the water discharging from the acidic springs in the Rio Agrio watershed originates at the acidic crater lake. Both heat and solute transport are analyzed on a regional scale through numerical simulations using the HST3D finite-difference model, which solves the coupled equations for fluid flow, heat transport, and solute transport. The code allows fluid viscosity and density to be functions of both temperature and solute concentration. The simulations use estimates for recharge to the mountain and a range of values and various distributions of permeability and porosity. Several sensitivity analyses are performed to test how the uncertainty in many of the model parameters affects the simulation results. These uncertainties yield an estimated range of travel times from the crater lake to the Rio Agrio springs of 1–30 years, which is in close agreement with the results of tritium analyses of the springs. Calculated groundwater fluxes into and out of the crater lake are both about several hundred kg/s. These fluxes must be accounted for in water budgets of the crater lake.  相似文献   

The Anak Krakatau question     

I. W. B. Thornton  S. A. Ward  R. A. Zann  T. R. New 《GeoJournal》1993,29(4):421-425

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Statistics of atmospheric turbulence within and above a corn canopy   总被引：1，自引：2，他引：1  

J. D. Wilson  D. P. Ward  G. W. Thurtell  G. E. Kidd 《Boundary-Layer Meteorology》1982,24(4):495-519

Two three-dimensional split-film anemometers were used to measure turbulence statistics within and above a corn canopy. Normalised profiles of mean windspeed, root-mean-square velocity, momentum flux, and heat flux were constructed from half-hourly averages by dividing within-canopy measurements by the simultaneous canopy-top measurement. With the exception of the heat flux, these profiles showed consistent shape from day to day. Time series of the three velocity components were recorded on magnetic tape and subsequently analysed to obtain Eulerian time and length scales and the power spectrum of each component at several heights. The timescale was found to have a local minimum value at the top of the canopy. However the length scale L _wformed from the timescale and the root-mean-square vertical velocity varied with height as L _w 0.1 z. The power-spectra were non-dimensionalised to facilitate comparison of spectra at different heights and times. All spectra had -5/3 regions spanning at least two decades in frequency.  相似文献   

Gravity changes accompanying volcanic activity at Pacaya volcano, Guatemala     

Albert Eggers  Jeffery Krausse  Harold Rush  James Ward 《Journal of Volcanology and Geothermal Research》1976,1(3):229-236

Gravity changes of up to 1.2 ± 0.1 mgal (1 standard deviation) were measured at three points within 400 m of an active vent on Pacaya volcano, Guatemala during eleven days of January, 1975. For five continuous days gravity varied inversely with the average muzzle velocity of ejecta, the frequency of volcanic explosions, and the frequency of volcanic earthquakes. The gravity changes are most reasonably interpreted as the product of intravolcanic movements of magma with masses one to two orders of magnitude larger than any flow ever erupted from the volcano. However, elevation changes and/or combination of elevation and mass distribution changes could also have been an important factor in effecting the observed gravity variations. Because we lack elevation control on the gravity stations, we are unable to unequivocally conclude which factor or which combination of factors produced the gravity changes. The study indicates the possibility of gravity monitoring of hazardous volcanoes as a predictive tool, and as an added means for investigating the internal mechanism of volcanic eruptions.  相似文献   

Late quaternary solution of Chalk at Basingstoke,Hants     

D.J. Ward  J. Cooper 《Proceedings of the Geologists' Association. Geologists' Association》1976,87(1):101-102

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Intra-city migration to squatter settlements in Mexico City     

Peter M. Ward 《Geoforum》1976,7(5-6)

The paper describes spatially the zonal movements of residents to three squatter settlements established at different time periods in Mexico City. In addition, moves are related to the dynamics of the low income housing system and previous theories of intra-city squatter migration behaviour are evaluated. The data corroborate the concept that the traditionally accepted pattern of centre to periphery, tenement to squatter settlement movements has altered. Direct movement into the periphery on the part of incoming migrants is increasingly important, and older established squatter areas are the most important suppliers of population in recent invasions. The implications for the distribution and structure of housing opportunities for future low-income populations in Mexico City are discussed.  相似文献   

Effect of ammonium jarosite on early life stages of a saltwater fish,Cyprinodon variegatus     

G.S Ward  G.C Cramm  P.R Parrish  S.R Petrocelli 《Marine pollution bulletin》1982,13(6):191-195

Embryos and juveniles of the sheepshead minnow (Cyprinodon variegatus), a saltwater fish, were exposed to ammonium jarosite, a waste product of the processing of zinc ore, during a 28-day posthatch, flow-through toxicity test. Exposure to measured ammonium jarosite concentrations ≤ 290 ppm had no significant effect on the hatching success of embryos. However, slight delays in hatching were observed in test concentrations ≥ 140 ppm. Although exposure to test concentrations ≥ 140 ppm significantly decreased the ability of juvenile fish to uncurl after hatching, juvenile mortality was significantly increased only in test concentrations ≥ 230 ppm. There was no effect on growth of juvenile fish in jarosite concentrations ≤ 230 ppm. The estimated maximum acceptable toxicant concentration (MATC), based on measured concentrations, was > 140< 230 ppm.  相似文献   

The effect of pressure on the ionization of boric acid in sodium chloride and seawater from molal volume data at 0 and 25°C     

Gary K Ward  Frank J Millero 《Geochimica et cosmochimica acta》1975,39(12):1595-1604

The apparent molal volume, φ_V of boric acid, B(OH)₃ and sodium borate, NaB(OH)₄, have been determined in 35%. salinity seawater and 0·725 molal NaCl solutions at 0 and 25°C from precise density measurements. Similar to the behavior of nonelectrolytes and electrolytes in pure water, the φ_V of B(OH)₃ is a linear function of added molality and the φ_V of NaB(OH)₄ is a linear function of the square root of added molarity in seawater and NaCl solutions. The partial molal volumes, $\text{V}\text{?}\text{1}$, of B(OH)₃ and NaB(OH)₄ in seawater and NaCl were determined from the φ_V's by extrapolating to infinite dilution in the medium. The $\text{V}\text{?}\text{1}$ of B(OH)₃ is larger in NaCl and seawater than pure water apparently due to the ability of electrolytes to dehydrate the nonelectrolyte B(OH)₃. The $\text{V}\text{?}\text{1}$ of NaB(OH)₄ in itself, NaCl and seawater is larger than the expected value at 0·725 molal ionic strength due to ion pair formation [Na⁺ + B(OH)₄^? → NaB(OH)₄⁰]. The volume change for the formation of NaB(OH)₄⁰ in itself and NaCl was found to be equal to 29·4 ml mol^?1 at 25°C and 0·725 molal ionic strength. These large $\text{Δ}\text{V}\text{?}\text{1}$'s indicate that at least one water molecule is released when the ion pair is formed [Na⁺ + B(OH)₄^? → H₂O + NaOB(OH)₂⁰]. The observed $\text{V}\text{?}\text{1}$ in seawater and the $\text{Δ}\text{V}\text{?}\text{1}$ (NaB⁰) in water and NaCl were used to estimate $\text{Δ}\text{V}\text{?}\text{1 (MgB}{}^{\mathrm{+}}\text{) = Δ}\text{V}\text{?}\text{1 (CaB}{}^{\mathrm{+}}\text{) = 38·4 ml mol}{}^{\mathrm{?1}}$ for the formation of MgB⁺ and CaB⁺. The volume change for the ionization of B(OH)₃ in NaCl and seawater was determined from the molal volume data. Values of $\text{Δ}\text{V}\text{?}\text{1 = ?29·2 and ?25·9 ml mol}{}^{\mathrm{?1}}$ were found in seawater and $\text{Δ}\text{V}\text{?}\text{1 = ?21·6 and ?26·4}$ in NaCl, respectively, at 0 and 25°C. The effect of pressure on the ionization of B(OH)₃ in NaCl and seawater at 0 and 25°C determined from the volume change is in excellent agreement with direct measurements in artificial seawater (culberson and Pytkowicz, 1968; Disteche and Disteche, 1967) and natural seawater (Culberson and Pytkowicz, 1968).  相似文献   

Dynamic response of a staggered wall-beam structure     

A. L. Mee  I. J. Jordaan  M. A. Ward 《地震工程与结构动力学》1974,3(4):353-364

A method for the dynamic analysis of staggered wall-beam frames is developed using consistent mass terms which are derived and given in simple terms. The method uses effective stiffnesses for wall-beam elements developed in an earlier paper. Experiments using a nine storey 1 : 15 scale perspex model are described. The first three natural frequencies of the model were obtained using two methods: sinusoidal external excitation of the structure with the base fixed and white noise excitation employing a single degree-of-freedom shake table, in the latter method with and without the addition of mass throughout the model. Agreement between analytical predictions of the first three natural frequencies and mode shapes and experimentally determined values is considered satisfactory, particularly for the first two modes. The lumped mass assumption gave reasonable results for these two cases, whereas the consistent mass theory gave reasonable results for the first three natural frequencies.  相似文献