‘Diatoms and pH reconstruction’ (1990) revisited     

H. John B. Birks  Gavin L. Simpson 《Journal of Paleolimnology》2013,49(3):363-371

The 167 sample lake-water pH-diatom calibration data-set created as part of the Palaeolimnology Programme within the Surface Water Acidification Project (SWAP) is re-analysed numerically using nine different numerical methods, six based on simple two-way weighted-averaging (WA), and the other three involving Gaussian logit regression (GLR) and maximum-likelihood (ML) calibration, the modern analogue technique, or weighted-averaging partial least-squares regression and calibration. Root mean squared error of prediction and maximum bias were estimated for all nine methods based on 10,000 internal and 10,000 external cross-validations involving a training-set, an optimisation-set, and a test-set. The results show that WA with a monotonic deshrinking spline equals or slightly outperforms WA with linear inverse deshrinking, especially in external cross-validation. Methods that employ tolerance downweighting generally have an inferior performance except when combined with monotonic deshrinking. It appears that simple two-way WA extensively used in SWAP cannot be significantly bettered. Thanks to increased computing power, better software, and more rigorous cross-validations, GLR shows good performance, especially in external cross-validation.  相似文献   

Comprehensive evaluation of heavy metal contamination in surface and core sediments of Taihu Lake, the third largest freshwater lake in China   总被引：5，自引：2，他引：3  

Enfeng Liu  Gavin F. Birch  Ji Shen  Hezhong Yuan  Enlou Zhang  Yanmin Cao 《Environmental Earth Sciences》2012,67(1):39-51

The spatial and temporal variations of Fe, K, Co, V, Cr, Cu, Ni, Zn, and Pb were determined in the sediments of Taihu Lake, the third largest freshwater lake in China and categorized into natural origin (Fe, K, Co, and V) and human contamination (Cr, Cu, Ni, Zn, and Pb) groups by principal component analysis. Most of the metals were positively correlated with the clay content (<4???m) and negatively correlated with the >16???m fraction, indicating the dominant role of grain size in regulating metals concentrations. Geochemical normalization and enrichment factors (EFs) were introduced to reduce the confounding of variable grain size and to quantify anthropogenic contributions. Higher EF values for Cr, Cu, Ni, and Zn occurred in the north Zhushan, Meiliang, and Gonghu Bays, indicating a high level of human contamination from the northern cities, such as Wuxi and Changzhou. Higher EF values of Pb were also present in the southwest and east lake areas, denoting the existence of additional anthropogenic sources. Chrome, Cu, Ni, Zn, and Pb showed increasing EF values in the top layers of sediment cores, indicating enhancing contamination since 1970s with rapid economy development in the catchment. These results indicate that geochemical normalization is a necessary and effective method in quantifying heavy metals contamination, and that historic sediment should be used as background values in calculating EFs. Potential risks of the heavy metals were assessed linking the consensus-based sediment quality guidelines and human contamination. Concentrations of Ni and Cr are greater than the threshold effect concentration (TEC) values, even in the sediments before 1970s, due to higher background concentrations in terrestrial parent materials. Concentrations of Ni and Cr are generally lower than the probable effect concentration (PEC) values, and concentrations of Cu and Zn are below the TEC values in the open lake areas. Whereas, concentrations of Ni and Cr are surpassing the PEC values and Cu and Zn are surpassing the TEC values in the north bays due to the high level of human contamination, where they were with EFs over 1.2, denoting higher potential eco-risks.  相似文献   

A Bayesian palaeoenvironmental transfer function model for acidified lakes     

Philip B. Holden  Anson W. Mackay  Gavin L. Simpson 《Journal of Paleolimnology》2008,39(4):551-566

A Bayesian approach to palaeoecological environmental reconstruction deriving from the unimodal responses generally exhibited by organisms to an environmental gradient is described. The approach uses Bayesian model selection to calculate a collection of probability-weighted, species-specific response curves (SRCs) for each taxon within a training set, with an explicit treatment for zero abundances. These SRCs are used to reconstruct the environmental variable from sub-fossilised assemblages. The approach enables a substantial increase in computational efficiency (several orders of magnitude) over existing Bayesian methodologies. The model is developed from the Surface Water Acidification Programme (SWAP) training set and is demonstrated to exhibit comparable predictive power to existing Weighted Averaging and Maximum Likelihood methodologies, though with improvements in bias; the additional explanatory power of the Bayesian approach lies in an explicit calculation of uncertainty for each individual reconstruction. The model is applied to reconstruct the Holocene acidification history of the Round Loch of Glenhead, including a reconstruction of recent recovery derived from sediment trap data. The Bayesian reconstructions display similar trends to conventional (Weighted Averaging Partial Least Squares) reconstructions but provide a better reconstruction of extreme pH and are more sensitive to small changes in diatom assemblages. The validity of the posteriors as an apparently meaningful representation of assemblage-specific uncertainty and the high computational efficiency of the approach open up the possibility of highly constrained multiproxy reconstructions.  相似文献   

A Study of the 2015 Mw 8.3 Illapel Earthquake and Tsunami: Numerical and Analytical Approaches     

Mauricio Fuentes  Sebastián Riquelme  Gavin Hayes  Miguel Medina  Diego Melgar  Gabriel Vargas  José González  Angelo Villalobos 《Pure and Applied Geophysics》2016,173(6):1847-1858

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Experimental validation of a simplified model for rolling isolation systems          下载免费PDF全文

P. Scott Harvey Jr.  Gérard‐Philippe Zéhil  Henri P. Gavin 《地震工程与结构动力学》2014,43(7):1067-1088

Rolling isolation systems (RISs) protect mission‐critical equipment and valuable property from earthquake hazards by decoupling the dynamic responses of vibration‐sensitive objects from horizontal floor motions. These responses involve the constrained rolling of steel balls between bowl‐shaped surfaces. The light damping of steel balls rolling between steel plates can be augmented by adhering thin rubber sheets to the plates, thereby increasing the rolling resistance and decreasing the displacement demand on the RIS. An assessment of the ability of lightly‐ and heavily‐damped RISs to mitigate the hazard of seismically induced failures requires high‐fidelity models that can adequately capture the systems' intrinsic nonlinear behavior. The simplified model presented in this paper is applicable to RISs with any potential energy function, is amenable to both lightly‐ and heavily‐damped RISs, and is validated through the successful prediction of peak responses for a wide range of disturbance frequencies and intensities. The validated model can therefore be used to compute the spectra of peak floor motions for which displacement demands equal capacity. These spectra are compared with representative floor motion spectra provided by the American Society of Civil Engineers 7–10. The damping provided by rolling between thin viscoelastic sheets increases the allowable floor motion intensity by a factor of 2–3, depending on the period of motion. Acceleration responses of isolation systems with damping supplied in this fashion do not grow with increased damping, even for short‐period excitations. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Detecting changing river temperatures in England and Wales          下载免费PDF全文

Harriet G. Orr  Gavin L. Simpson  Sophie des Clers  Glenn Watts  Mike Hughes  Jamie Hannaford  Michael J. Dunbar  Cédric L. R. Laizé  Rob L. Wilby  Richard W. Battarbee  Rob Evans 《水文研究》2015,29(5):752-766

Changes in water temperature can have important consequences for aquatic ecosystems, with some species being sensitive even to small shifts in temperature during some or all of their life cycle. While many studies report increasing regional and global air temperatures, evidence of changes in river water temperature has, thus far, been site specific and often from sites heavily influenced by human activities that themselves could lead to warming. Here we present a tiered assessment of changing river water temperature covering England and Wales with data from 2773 locations. We use novel statistical approaches to detect trends in irregularly sampled spot measurements taken between 1990 and 2006. During this 17‐year period, on average, mean water temperature increased by 0.03 °C per year (±0.002 °C), and positive changes in water temperature were observed at 2385 (86%) sites. Examination of catchments where there has been limited human influence on hydrological response shows that changes in river flow have had little influence on these water temperature trends. In the absence of other systematic influences on water temperature, it is inferred that anthropogenically driven climate change is driving some of this trend in water temperature. © 2014 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.  相似文献   

Intraplate deformation adjacent to the Macquarie Ridge south of New Zealand—The tectonic evolution of a complex plate boundary     

Gavin P. Hayes  Kevin P. Furlong  Charles J. Ammon 《Tectonophysics》2009,463(1-4):1-14

The distribution of relocated seismicity and the evolving shape of fracture zones through time in the oceanic crust of the Australian Plate adjacent to the Australia:Pacific plate boundary south of New Zealand are used to constrain the deformation of this region of the Australian Plate, here called the Puysegur Block. Relocated seismicity reveals a broad distribution of earthquakes in the Puysegur Block on both inter- and intraplate structures, including two great (M8+) earthquakes in the region over the past twenty years, one of which occurred over 130 km from the plate boundary. Plate reconstructions from the Late Oligocene through Early–Mid Miocene allow us to determine the undeformed shape of fracture zones in the Puysegur Block, formed during the Paleogene when the plate boundary was dominantly a divergent mid-ocean ridge system. Comparing these reconstructions to the present-day shape of the fracture zones allows us to map the deformation that has occurred within the Puysegur Block since the fracture zones formed. These two sets of independent observations delineate a broad zone of deformation extending ~ 150 km into the plate interior from the Macquarie Ridge Complex, the modern plate boundary structure through the region. The persistence of this deformation through time indicates a link with the evolution of the plate boundary over the past ~ 25 Ma from divergence to translation and subduction of the Australian Plate further north at the Puysegur Trench. We infer that this deformation may be a result of stresses in the Puysegur Block resulting from the impingement of the subducting plate on the thickened lithosphere of southern New Zealand. Such a collision may resist subduction, and if resistance remains substantial, further deformation internal to the Puysegur Block may lead to a southward migration of the Australia:Pacific subduction interface and the capturing of this section of lithosphere onto the Pacific Plate.  相似文献   

Population biology of coral trout species in eastern Torres Strait: Implications for fishery management     

Ashley J. Williams  Leanne M. Currey  Gavin A. Begg  Cameron D. Murchie  Aaron C. Ballagh 《Continental Shelf Research》2008

Coral trout (Plectropomus spp.) are the main target species for commercial fishers in the eastern Torres Strait Reef Line Fishery (ETS RLF). The four species of coral trout known to occur in Torres Strait: Plectropomus leopardus, Plectropomus maculatus, Plectropomus areolatus and Plectropomus laevis are currently managed as a single species in Torres Strait, as there is no species-specific biological information available for the region which could be used to assess whether species differ in their response to fishing pressure. The aim of our study was to determine whether it is appropriate (biologically) to manage coral trout in the ETS RLF as a single species group or whether different management arrangements are required for some species. We used catch data and biological data from samples collected by commercial fishers to examine the distribution within Torres Strait and estimate a range of biological parameters for P. leopardus, P. maculatus and P. areolatus. Insufficient P. laevis samples were collected to reliably examine this species. Results indicated that the population biology, particularly the reproductive biology, of P. areolatus was substantially different to both P. leopardus and P. maculatus. Although it is difficult to predict the response to fishing, P. areolatus may be more vulnerable to fishing than P. leopardus and P. maculatus, due to the larger size at sex change observed for this species and the very low proportion of males protected by the current minimum size limit. Therefore, while the common management arrangements for P. leopardus and P. maculatus appear to be adequate for these species, separate management arrangements are needed for the sustainable harvest of P. areolatus populations in the ETS. Specifically, we recommend the introduction of a maximum size limit for P. areolatus, in addition to the current minimum size limit, which may allow a proportion of males some protection from fishing.  相似文献   

Effects of gravity on the structure of post-shock accretion flows in magnetic cataclysmic variables     

Mark Cropper  Kinwah Wu  Gavin Ramsay  Aysegul Kocabiyik 《Monthly notices of the Royal Astronomical Society》1999,306(3):684-690

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A search for electron cyclotron maser emission from compact binaries     

Gavin Ramsay  Catherine Brocksopp  Kinwah Wu  Bruce Slee  Curtis J. Saxton 《Monthly notices of the Royal Astronomical Society》2007,382(1):461-465

Unipolar induction (UI) is a fundamental physical process, which occurs when a conducting body transverses a magnetic field. It has been suggested that UI is operating in RX J0806+15 and RX J1914+24, which are believed to be ultracompact binaries with orbital periods of 5.4 and 9.6 min, respectively. The UI model predicts that those two sources may be electron cyclotron maser sources at radio wavelengths. Other systems in which UI has been predicted to occur are short period extrasolar terrestrial planets with conducting cores. If UI is present, circularly polarized radio emission is predicted to be emitted. We have searched for this predicted radio emission from short period binaries using the Very Large Array (VLA) and Australian Telescope Compact Array (ATCA). In one epoch, we find evidence for a radio source, coincident in position with the optical position of RX J0806+15. Although we cannot completely exclude that this is a chance alignment between the position of RX J0806+15 and an artefact in the data reduction process, the fact that it was detected at a significance level of 5.8σ and found to be transient suggests that it is more likely that RX J0806+15 is a transient radio source. We find an upper limit on the degree of circular polarization to be ∼50 per cent. The inferred brightness temperature exceeds 10¹⁸ K, which is too high for any known incoherent process, but is consistent with maser emission and UI being the driving mechanism. We did not detect radio emission from ES Cet, RX J1914+24 or Gliese 876.  相似文献