Middle to late Holocene environmental changes in western Ireland inferred from fluctuations in preservation of biological variables in lake sediment   总被引：1，自引：1，他引：0  

S. Murnaghan  D. Taylor  E. Jennings  C. Dalton  K. Olaya-Bosch  B. O’Dwyer 《Journal of Paleolimnology》2012,48(2):433-448

Knowledge of natural variability in aquatic ecosystems is vital for assessing the nature and amplitude of human-induced change, and for predicting future anthropogenic impacts. Distinguishing between naturally and anthropogenically caused variability in lake sediment records can be problematic, however, because both drivers can produce similar ecological effects. Standard sediment-based approaches for reconstructing past environmental changes tend to focus on qualitative and quantitative variations in palaeoenvironmental indicators, with little significance attached to their complete absence. We used multiple variables in radiometrically dated sediment cores collected from two sites in Lough Mask, a lake in western Ireland. Results suggest that the Lough Mask sediment record has been a sensitive recorder of past climate variability, especially changing precipitation, since the middle Holocene. Variations in the presence of aquatic siliceous microfossils and calcareous macrofossils, and changing sediment lithology and geochemistry, indicate a quasi-cyclic response to oscillations in climate conditions that correspond generally with palaeoclimate findings from elsewhere in NW Europe, including other sites in Ireland. We conclude that during much of the middle to late Holocene, prolonged periods of relatively high rainfall in the catchment reduced nutrient inputs to the lake, particularly silica and calcite. Diatom productivity consequently declined, whereas dissolution of frustules was enhanced. During relatively dry climate periods, availability of these nutrients increased, diatom productivity was higher, and dissolution was reduced. Relatively early human impacts are evident in the sediment record beginning ca. 1,000?BP. The results highlight the aquatic and taphonomic effects of complex interactions among past variations in catchment conditions, climate and water chemistry. The complexity of these interactions and their effects, mediated through the characteristics of Lough Mask and its catchment, pose problems for conventional interpretation of palaeolimnological data and their use in computer-based simulations of future changes in stresses on aquatic ecosystems and their consequent impacts.  相似文献   

Handbook of Geotourism edited by Ross Dowling and David Newsome,Edward Elgar Publishing,Cheltenham (2018). 499p. ISBN 978 1 78536 885 1 (cased). ISBN 978 1 78536 886 8 (eBook). Price £190.     

Eleanor Brown 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(5):657-658

  相似文献   

Opinion II     

Kenneth V. B. Jennings 《Ground Water Monitoring & Remediation》1987,7(1):36-38

  相似文献   

Collapse of a model for ductile reinforced concrete frames under extreme earthquake motions     

Haruo Takizawa  Paul C. Jennings 《地震工程与结构动力学》1980,8(2):117-144

  相似文献   

Plutonium, ²⁴¹Am and ¹³⁷Cs ratios,inventories and vertical profiles in Washington and Oregon continental shelf sediments     

T.M. Beasley  R. Carpenter  C.D. Jennings 《Geochimica et cosmochimica acta》1982,46(10):1931-1946

Continental shelf sediments from nine locations off Washington and Oregon have ^239,240Pu inventories which average 8.0 ± 2.6 mCi/km². The Columbia River and seawaters advecting over the shelf supply Pu which is removed to underlying sediments, principally through scavenging by inorganic paniculate matter. Mass balance calculations argue that less than 20 percent of the advected Pu need be scavenged from the water column to balance river input and total shelf sediment inventories. The percentage of the Pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment/water distribution coefficients.No marked separation of Pu from ¹³⁷Cs is observed with depth in Pacific shelf sediments as has been reported in Atlantic coastal sediments. This interocean distinctness can be explained by differences in particle mixing and downward diffusion of Cs in sediments of varying porosities. The transuranic inventories and Pu/Cs ratios in the Pacific sediments do not support the hypothesis of Livingston and Bowen that Pu is remobilized within the sediment column by ‘complexone’ formation with (principally) organic substances.Excess ²¹⁰Pb/^239,240Pu inventory ratios in eight representative cores from the Washington shelf average 100 ± 19, even though absolute values of both inventories vary by much larger factors. This reasonably constant ratio, for a given water depth, permits estimation of total Pu inventories and prediction of sites of unusual Pu accumulation from data on the more easily measured natural radionuclide.  相似文献   

Hysteretic response of a nine-storey reinforced concrete building     

H. Iemura  P. C. Jennings 《地震工程与结构动力学》1974,3(2):183-201

The Millikan Library on the campus of the California Institute of Technology was strongly shaken during the San Fernando earthquake of 9 February 1971. The building was not damaged structurally, but the observed E-W response of the building showed a fundamental period of about 1.0 sec, significantly longer than the 0.66 sec observed in pre-earthquake vibration tests. In this study, the response of the fundamental mode was treated as that of a single-degree-of-freedom hysteretic structure, and four simple models, two stationary and two with changing properties, were examined to see if they could describe the observed response. It was found that an equivalent linear model and a bilinear hysteretic model both could match the response, provided their properties were changed during the earthquake. (Four changes were used.) A linear model with constant properties and a stationary, bilinear hysteretic model did not give nearly as good agreement as the non-stationary models. The results indicated, in general, a degrading of the stiffness and energy dissipation capacity of the building, with the suggestion that the changes were sudden rather than gradual.  相似文献   

Multicomponent solute transport with sorption and soluble complexation     

David J. Kirkner  Thomas L. Theis  Aaron A. Jennings 《Advances in water resources》1984,7(3):120-125

A numerical algorithm for predicting the migration of multiple subsurface pollutants has been developed accounting for dispersion, convection, soluble complexation and solid phase accumulations (sorption). The basis of the model is a finite element solution of the mass transport equation. The essence of the algorithm is the treatment of the sorption terms as implicit functions of the total soluble concentrations facilitating a general and modularized treatment of solution phase and solid phase chemistry. Examples are presented illustrating the effects of soluble complexation and competitive sorption on the transport of multicomponent solutions.  相似文献   

Small-particle concentration fluctuations at a coastal site     

M. Vana  S. G. Jennings  C. Kleefeld  A. Mirme  E. Tamm 《Atmospheric Research》2002,63(3-4)

Aerosol size spectra (d=10 nm–10 μm) were measured with an electrical aerosol spectrometer (EAS) at Mace Head on the west coast of Ireland. Several small aerosol particle (diameter 10–32 nm) concentration bursts were observed during the measurement period. Relationships between the events, air mass trajectories, tide height, and meteorological parameters are examined. Series of bursts were observed when a spectral transformation due to subsequent particle growth from 10 to 56–100 nm can be identified in an Eulerian experiment. Particle growth rates of between 1 and 3 nm/h were determined. These bursts appear in cold and comparatively clean arctic or polar air masses with temperature and relative humidity fluctuations, and do not correlate with low tide in some cases. These episodes, similar to those frequently found in the continental boundary layer, are thought to occur over a wide area and, for clear detection, require stable airflow for a few days. Elevated small-particle concentration events are more common during low tide or shortly after, and are typically associated with low wind speeds. Here, the increased shore exposure during low tide is thought to influence the nucleation and the subsequent growth of these aerosol particles. The occurrences of the bursts are found to depend on local wind direction. The highest d=10–32 nm particle concentrations appeared for wind sectors furthest from the tidal regions when the wind direction was 150–160°(south-easterly). Most of the events occurred during daytime when solar irradiation is most intense.  相似文献   

Patch scale aggregation of heterogeneous land surface cover for mesoscale meteorological models     

A. Johannes Dolman  Eleanor M. Blyth 《Journal of Hydrology》1997,190(3-4):252-268

Theoretical studies dealing with aggregation of surface parameters at small scale are reviewed. Finding effective parameters for surface resistance is possible for most cases by taking simple geometric or arithmetic averages of the component resistances. The use of more sophisticated techniques such as the blending height improves the calculations. Resistances for heat and water vapour behave differently in heterogeneous terrain. A simple surface energy balance model is adapted to show the behaviour of the roughness length of heat and water vapour in heterogeneous terrain. It is suggested that this simple parameterization can adequately take into account the effect of variation in surface cover on the fluxes of heat and water vapour.  相似文献   

The micro-erosion meter: Use and limitations     

A. P. Spate  J. N. Jennings  D. I. Smith  M. A. Greenaway 《地球表面变化过程与地形》1985,10(5):427-440

Detection of anomalies in measurements of low rates of limestone surface lowering with a traversing micro-erosion meter (MEM) led to temperature-controlled laboratory and field investigations of some sources of error in the method. Regressions for the correction of temperature change in the instrument and in the stud-rock interface were obtained. Probe erosion tests permitted a correction to be devised and also provided information whereby a measure of operational irregularity was adopted. Corrections and error terms were applied to field measurements from two southern New South Wales karsts and a collection of Australian limestone slabs exposed at one site. Examination of these results and of published MEM rates from other parts of the world validated the MEM method. Marine platforms are lowered at such gross rates that these error sources may be neglected there. However limestone lowering in terrestrial environments cannot be assumed to proceed at rates which permit this and recommendations are made about procedures to ensure that investigations are prosecuted within the limitations of the method.  相似文献