Aquitard Distribution In A Northern Reach Of The Miami Valley Aquifer,Ohio, USA: Part 1. Three-Dimensional Geostatistical Evaluation Of Physical Heterogeneity     

Robert W. Ritzi  David F. Dominic  Kenneth W. Kausch 《Hydrogeology Journal》1996,4(2):12-24

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Multi-scale variability of beach profiles at Duck: A wavelet analysis   总被引：3，自引：0，他引：3  

Ying Li  Murray Lark  Dominic Reeve   《Coastal Engineering》2005,52(12):1133-1153

Beach profiles have been observed to change over a range of spatial and temporal scales; however techniques for quantifying this variability have not been fully established. In this paper, a wavelet technique is introduced as a method to study the multi-scale variability of beach profiles. The beach profile data comprising a 22-year time series surveyed at the US Army Corps of Civil Engineers Field Research Facility (FRF) at Duck are analysed using the adapted maximal overlap discrete wavelet transform (AMODWT). The analysis successfully identifies strong local features in the variability of beach profiles in time and space separately that cannot be isolated by traditional statistical methods. The analysis of spatial wavelet variances provides a new means of investigating the depth of closure. Analysis of variances by temporal scales shows that the combined effects of several temporal scales with one or two dominant scales can be seen at particular points across profiles whilst the dominant temporal scales are different at different portions of the profiles. The method allows for the extremely nonstationary behaviour of beach profile to be analysed into separate frequency bands that can facilitate the interpretation of morphological changes in terms of physical processes.  相似文献   

Recent Rapid Regional Climate Warming on the Antarctic Peninsula   总被引：15，自引：1，他引：15  

David G. Vaughan  Gareth J. Marshall  William M. Connolley  Claire Parkinson  Robert Mulvaney  Dominic A. Hodgson  John C. King  Carol J. Pudsey  John Turner 《Climatic change》2003,60(3):243-274

The Intergovernmental Panel on Climate Change (IPCC) confirmed that mean global warming was 0.6 ± 0.2 °C during the 20th century and cited anthropogenic increases in greenhouse gases as the likely cause of temperature rise in the last 50 years. But this mean value conceals the substantial complexity of observed climate change, which is seasonally- and diurnally-biased, decadally-variable and geographically patchy. In particular, over the last 50 years three high-latitude areas have undergone recent rapid regional (RRR) warming, which was substantially more rapid than the global mean. However, each RRR warming occupies a different climatic regime and may have an entirely different underlying cause. We discuss the significance of RRR warming in one area, the Antarctic Peninsula. Here warming was much more rapid than in the rest of Antarctica where it was not significantly different to the global mean. We highlight climate proxies that appear to show that RRR warming on the Antarctic Peninsula is unprecedented over the last two millennia, and so unlikely to be a natural mode of variability. So while the station records do not indicate a ubiquitous polar amplification of global warming, the RRR warming on the Antarctic Peninsula might be a regional amplification of such warming. This, however, remains unproven since we cannot yet be sure what mechanism leads to such an amplification. We discuss several possible candidate mechanisms: changing oceanographic or changing atmospheric circulation, or a regional air-sea-ice feedback amplifying greenhouse warming. We can show that atmospheric warming and reduction in sea-ice duration coincide in a small area on the west of the Antarctic Peninsula, but here we cannot yet distinguish cause and effect. Thus for the present we cannot determine which process is the probable cause of RRR warming on the Antarctic Peninsula and until the mechanism initiating and sustaining the RRR warming is understood, and is convincingly reproduced in climate models, we lack a sound basis for predicting climate change in this region over the coming century.  相似文献   

The palaeolimnology of Lake Fidler, a meromictic lake in south-west Tasmania and the significance of recent human impact     

Dominic Hodgson  Peter Tyler  Wim Vyverman 《Journal of Paleolimnology》1997,18(4):313-333

Three meromictic lakes in the World Heritage Area of south-west Tasmania possess unusual microbiological communities. Their meromixis is maintained by periodic incursions of brackish water from the nearby Gordon River which, in its lower reaches, is a salt-wedge estuary. In 1977 the construction of a dam in the middle reaches of the river restricted penetration of the salt-wedge and meromixis rapidly declined in all three lakes. A palaeolimnological study was carried out on one of the lakes, Lake Fidler, firstly to determine the history of meromixis and its associated microbiological communities, and secondly to assess whether the recent and rapid decline of meromixis is inconsistent with natural rates of development of the Gordon River meromictic lakes. One part of this study included the analysis of the stratigraphy of fossil diatoms from a 17-metre sediment core dating back 8000 yrs. Detrended Correspondence Analysis and Analog Matching were used to compare diatom species assemblages in core samples with diatom samples from a reference dataset consisting of a selection of lake and river sites in the lower Gordon River valley. Five distinct stratigraphic zones were identified in the core. These zones indicated specific stages in the development of the Gordon River lakes from river backwaters to ectogenically-maintained meromictic lakes which will, finally, become terrestrialised by encroaching rainforest. The onset of a stratified water column was identified by the emergence of a dominant freshwater algal flora which suggested that the lake had developed a mixolimnion and become meromictic ca. 2070 ± 50 ¹⁴C yrs ago. In the context of this long history of meromixis, the rapid demise in meromictic stability following construction of the dam is judged to be inconsistent with natural rates of development. The palaeolimnological studies, of which this paper is one part, prompt recommendations for a management strategy to prevent the further decay of these meromictic lakes in the World Heritage Area.  相似文献   

Structural variations in derivatives of the bacteriochlorophylls of Chlorobiaceae: impact of stratigraphic resolution on depth profiles as revealed by methanolysis     

Michael A. Wilson  Dominic A. Hodgson  Brendan J. Keely   《Organic Geochemistry》2004,35(11-12):1299

Bacteriochlorophylls c and d, recovered from two sedimentary sequences, were converted to bacteriophaeophorbide methyl esters by methanolysis and analysed by atmospheric pressure chemical ionisation liquid chromatography-multistage mass spectrometry (APCI LC-MSⁿ). The distributions in both settings, a moderately consolidated sediment from Kirisjes Pond, Antarctica, and in a finely laminated microbial mat from Les Salines de la Trinitat, Spain, show significant variations within a narrow depth interval. The overall bacteriophaeophorbide c to d ratios in the two sediments are different, as are the ratios of particular C-3¹ diastereoisomers, indicating distinct differences between the bacterial communities that contributed to each sediment. Furthermore, a shift towards more extensive alkylation in homologues within each sediment is consistent either with changing environmental conditions in the depositional environments, or development-related changes in the structure of the bacterial community, leading to increased competition for light or nutrients.  相似文献   

Relative sea-level history from the Lambert Glacier region, East Antarctica, and its relation to deglaciation and Holocene glacier readvance   总被引：1，自引：0，他引：1  

Elie Verleyen  Dominic A. Hodgson  Koen Sabbe 《Quaternary Research》2005,63(1):45-52

We present a relative sea-level (RSL) history, constrained by AMS radiocarbon-dated marine-freshwater transitions in isolation basins from a site adjacent to the Lambert Glacier, East Antarctica. The RSL data suggest an initial ice retreat between c. 15,370 and 12,660 cal yr B.P.. Within this period, meltwater pulse IA (mwp IA, between c. 14,600-14,200 and 14,100-13,700 cal yr B.P.) occurred; an exceptionally large ice melting event, inferred from far-field sea-level records. The RSL curve shows a pronounced highstand of approximately 8 m between c. 7570-7270 and 7250-6950 cal yr B.P. that is consistent with the timing of the RSL highstand in the nearby Vestfold Hills. This is followed by a fall in RSL to the present. In contrast to previous findings, the isolation of the lakes in the Larsemann Hills postdates the isolation of lakes with similar sill heights in the Vestfold Hills. An increase in RSL fall during the late Holocene may record a decline in the rate of isostatic uplift in the Larsemann Hills between c. 7250-6950 and 2847-2509 cal yr B.P., that occurred in response to a documented mid-Holocene glacier readvance followed by a late-Holocene retreat.  相似文献   

Flood frequencies reveal Holocene rapid climate changes (Lower Moulouya River,northeastern Morocco)     

Christoph Zielhofer  Jens Bussmann  Hanoun Ibouhouten  Katrin Fenech 《第四纪科学杂志》2010,25(5):700-714

Current high‐resolution palaeoenvironmental records reveal short‐term Holocene coolings. One of these major Holocene rapid climate changes occurred between 3.2 and 2.7 cal. ka BP. The sensitivity of river systems vis‐à‐vis slight and short‐term Holocene climatic variations is a subject of controversy in the scientific community. In this paper, we present a 4.0 to 1.4 cal ka BP palaeoflood record from the Lower Moulouya River (northeastern Morocco) to demonstrate the high sensitivity of semiarid rivers in the southwestern Mediterranean towards Holocene environmental changes. The Lower Moulouya flood deposits are characterised by thick, well‐stratified, predominantly clayey to silty overbank fine sediments. These cohesive sediments show evidence of excellent preservation conditions against fluvial erosion and contain a continuous record of mid to late Holocene flood sequences. The Moulouya palaeoflood record can be interpreted in the context of regional and global high‐resolution proxy data, revealing a strong coupling with Holocene rapid climate changes. The centennial‐scale Moulouya palaeohydrological history will be discussed with palaeoenvironmental data from the same record (palaeomagnetics, sedimentary charcoal record, anthracological analyses, snail analyses) to generate new ideas about the mid to late Holocene hydrological cycle in the southwestern Mediterranean. The deduced features of pronounced Lower Moulouya flooding and the decreased fire recurrence during Holocene cooling remain somewhat inconsistent with the interpretation of other palaeohydrological and paleaoecological records from the southwestern Mediterranean. However, enhanced Lower Moulouya flood frequencies between 3.2 and 2.7 cal. ka BP agree with increased floodplain aggradation in other major river systems of Mediterranean North Africa. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Statistical analysis and forecasts of long-term sandbank evolution at Great Yarmouth, UK   总被引：4，自引：1，他引：3  

Dominic E. Reeve  Jos M. Horrillo-Caraballo  Vanesa Magar 《Estuarine, Coastal and Shelf Science》2008,79(3):387-399

A data-driven model has been developed to analyse the long-term evolution of a sandbank system and to make ensemble predictions in a period of 8 years. The method uses a combination of empirical orthogonal function (EOF) analysis, (to define spatial and temporal patterns of variability), jack-knife resampling, (to generate an ensemble of EOFs), a causal auto-regression technique, (to extrapolate the temporal eigenfunctions), and straightforward statistical analysis of the resulting ensemble of predictions to determine a ‘forecast’ and associated uncertainty. The methodology has been applied to a very demanding site which includes a curved shoreline and a group of mobile nearshore sandbanks. The site is on the eastern coast of the UK and includes the Great Yarmouth sandbanks and neighbouring shoreline. A sequence of 33 high quality historical survey charts reaching back to 1848 have been used to analyse the patterns and to predict morphological evolution of the sandbank system. The forecasts demonstrate an improved skill relative to an assumption of persistence, but suffer in locations where there are propagating features in the morphology that are not well-described by EOFs.  相似文献   

Automated threshold selection methods for extreme wave analysis   总被引：2，自引：0，他引：2  

Paul Thompson  Yuzhi Cai  Dominic Reeve  Julian Stander 《Coastal Engineering》2009,56(10):1013-1021

The study of the extreme values of a variable such as wave height is very important in flood risk assessment and coastal design. Often values above a sufficiently large threshold can be modelled using the Generalized Pareto Distribution, the parameters of which are estimated using maximum likelihood. There are several popular empirical techniques for choosing a suitable threshold, but these require the subjective interpretation of plots by the user.In this paper we present a pragmatic automated, simple and computationally inexpensive threshold selection method based on the distribution of the difference of parameter estimates when the threshold is changed, and apply it to a published rainfall and a new wave height data set. We assess the effect of the uncertainty associated with our threshold selection technique on return level estimation by using the bootstrap procedure. We illustrate the effectiveness of our methodology by a simulation study and compare it with the approach used in the JOINSEA software. In addition, we present an extension that allows the threshold selected to depend on the value of a covariate such as the cosine of wave direction.  相似文献   

Advancing the interdisciplinary dialogue on climate justice     

Dominic Roser  Christian Huggel  Markus Ohndorf  Ivo Wallimann-Helmer 《Climatic change》2015,133(3):349-359

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