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281.
Moninya Roughan Helen S. MacdonaldMark E. Baird Tim M. Glasby 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(5):628-644
Understanding the transport and distribution of marine larvae by ocean currents is one of the key goals of population ecology. Here we investigate circulation in the East Australian Current (EAC) and its impact on the transport of larvae and coastal connectivity. A series of Lagrangian particle trajectory experiments are conducted in summer and winter from 1992-2006 which enables us to investigate seasonal and inter-annual variability. We also estimate a mean connectivity state from the average of each of the individual realisations. Connectivity patterns are related to the movement of five individual larval species (two tropical, two temperate and one invasive species) and are found to be in qualitative agreement with historical distribution patterns found along the coast of SE Australia.We use a configuration of the Princeton Ocean Model to investigate physical processes in the ocean along the coast of SE Australia where the circulation is dominated by the EAC, a vigorous western boundary current. We assimilate hydrographic fields from a ∼10?\km global analysis into a ∼3?\km resolution continental shelf model to create a high-resolution hindcast of ocean state for each summer and winter from 1992-2006. Particles are released along the coast of SE Australia, and at various isobaths across the shelf (25-1000 m) over timescales ranging from 10-90 days. Upstream of the EAC separation point across-shelf release location dominates the particle trajectory length scales, whereas seasonality dominates in the southern half of the domain, downstream of the separation point.Lagrangian probability density functions show dispersion pathways vary with release latitude, distance offshore and the timescale of dispersion. Northern (southern) release sites are typified by maximum (minimum) dispersal pathways. Offshore release distance also plays a role having the greatest impact at the mid-latitude release sites. Maximum alongshore dispersion occurs at the mid-latitude release sites such as Sydney. Seasonal variability is also greatest at mid-latitudes, associated with variations in the separation point of the EAC. Climatic variations such as El Niño and La Niña are also shown to play a role in dictating the connectivity patterns. La Niña periods have a tendency to increase summer time connectivity (particularly with offshore release sites) while El Niño periods are shown to increase winter connectivity.The EAC acts as a barrier to the onshore movement of particles offshore, which impacts on the connectivity of offshore release sites. Consequentially particles released inshore of the EAC jet exhibit a greater coastal connectivity than those released offshore of the EAC front. The separation point of the EAC also dictates connectivity with more sites being connected (with lower concentration) downstream of the separation point of the EAC. These results can provide a useful guide to the potential connectivity of marine populations, or the spread of invasive pests (via ballast water or release of propagules from established populations). 相似文献
282.
Helen Bennion Richard W. Battarbee Carl D. Sayer Gavin L. Simpson Thomas A. Davidson 《Journal of Paleolimnology》2011,45(4):533-544
The potential of palaeolimnological methods for establishing reference conditions and restoration targets for lakes has been
recognised for some time, and has received renewed interest in recent years with the introduction of the EU Water Framework
Directive. This paper considers some of the issues associated with the role of lake sediments in establishing reference conditions
and defining recovery targets. We discuss the problem of attributing variation in the sediment record to human activity rather
than to natural causes or random variability, and the need for the concepts of pristine and reference conditions to be differentiated.
We address the question of expressing quantitatively the degree of change that has taken place between the reference and the
present day and the problem of accounting for changes that may have taken place between the reference and the present, such
as climate change, that may limit the use of the reference condition as a restoration target. Finally we consider the use
of past habitat structure and inferred ecological functioning as targets for restoration, and the potential role that multi-proxy
palaeoecological studies can play in defining such targets. 相似文献
283.
284.
A knowledge of pre-disturbance conditions is important for setting realistic restoration targets for lakes. For European waters
this is now a requirement of the European Council Water Framework Directive where ecological status must be assessed based
on the degree to which present day conditions deviate from reference conditions. Here, we employ palaeolimnological techniques,
principally inferences of total phosphorus from diatom assemblages (DI-TP) and classification of diatom composition data from
the time slice in sediment cores dated to ~1850 AD, to define chemical and ecological reference conditions, respectively,
for a range of UK lake types. The DI-TP results from 169 sites indicate that reference TP values for low alkalinity lakes
are typically <10 μg L−1 and in many cases <5 μg L−1, whilst those for medium and high alkalinity lakes are in the range 10–30 and 20–40 μg L−1, respectively. Within the latter two alkalinity types, the deeper waters (>3 m mean depth) generally had lower reference
TP concentrations than the shallow sites. A small group of shallow marl lakes had concentrations of ~30 μg L−1. Cluster analysis of diatom composition data from 106 lakes where the key pressure of interest was eutrophication identified
three clusters, each associated with particular lake types, suggesting that the typology has ecological relevance, although
poor cross matching of the diatom groups and the lake typology at type boundaries highlights the value of a site-specific
approach to defining reference conditions. Finally the floristic difference between the reference and present day (surface
sample) diatom assemblages of each site was estimated using the squared chord distance dissimilarity coefficient. Only 25
of the 106 lakes experienced insignificant change and the findings indicate that eutrophication has impacted all lake types
with >50% of sites exhibiting significant floristic change. The study illustrates the role of the sediment record in determining
both chemical and ecological reference conditions, and assessing deviation from the latter. Whilst restoration targets may
require modification in the future to account for climate induced alterations, the long temporal perspective offered by palaeolimnology
ensures that such changes are assessed against a sound baseline. 相似文献
285.
Helen Miller Carol J. Cotterill Tom Bradwell 《Proceedings of the Geologists' Association. Geologists' Association》2014
High resolution airborne LiDAR (light detection and ranging) and multibeam bathymetry data, supplemented by geomorphological and geological field mapping are used to derive the glacial and post-glacial history of Troutbeck Valley (English Lake District) at a catchment scale. The results inform wider regional and ice sheet wide glacial reconstructions and demonstrate the effectiveness of an integrated approach combining geomorphological and sedimentological signatures with remote sensing. The holistic catchment approach is used to reconstruct palaeo-ice flow and behaviour of a small part of the last British and Irish Ice Sheet, identifying a series of depositional environments that accompanied both ice advance, ice retreat and post-glacial deposition within the Lake District. Drumlins are mapped in the lower catchment and show multiple regional (wider-extent) ice flow events and a sedimentology consistent with deposition by lodgement processes during the Main Late Devensian Stadial. Other subglacial deposits include till sequences formed under variable basal conditions beneath an advancing ice mass. Retreat features include a suite of recessional moraines formed by still-stands or small readvances of an outlet glacier. Following deglaciation, major sediment redistribution led to formation of a large fan delta via paraglacial and post-glacial fluvial sedimentation. This study indicates that an integrated approach, using geomorphology, sedimentology and remote sensing on a catchment scale, is capable of deriving a more in-depth understanding of regional ice sheet reconstructions and highlights the complexity of palaeo-ice sheet dynamics at a range of spatial scales. 相似文献
286.
Heiner Denker Ludger Timmen Christian Voigt Stefan Weyers Ekkehard Peik Helen S. Margolis Pacôme Delva Peter Wolf Gérard Petit 《Journal of Geodesy》2018,92(5):487-516
The frequency stability and uncertainty of the latest generation of optical atomic clocks is now approaching the one part in \(10^{18}\) level. Comparisons between earthbound clocks at rest must account for the relativistic redshift of the clock frequencies, which is proportional to the corresponding gravity (gravitational plus centrifugal) potential difference. For contributions to international timescales, the relativistic redshift correction must be computed with respect to a conventional zero potential value in order to be consistent with the definition of Terrestrial Time. To benefit fully from the uncertainty of the optical clocks, the gravity potential must be determined with an accuracy of about \(0.1\,\hbox {m}^{2}\,\hbox {s}^{-2}\), equivalent to about 0.01 m in height. This contribution focuses on the static part of the gravity field, assuming that temporal variations are accounted for separately by appropriate reductions. Two geodetic approaches are investigated for the derivation of gravity potential values: geometric levelling and the Global Navigation Satellite Systems (GNSS)/geoid approach. Geometric levelling gives potential differences with millimetre uncertainty over shorter distances (several kilometres), but is susceptible to systematic errors at the decimetre level over large distances. The GNSS/geoid approach gives absolute gravity potential values, but with an uncertainty corresponding to about 2 cm in height. For large distances, the GNSS/geoid approach should therefore be better than geometric levelling. This is demonstrated by the results from practical investigations related to three clock sites in Germany and one in France. The estimated uncertainty for the relativistic redshift correction at each site is about \(2 \times 10^{-18}\). 相似文献
287.
Gerardo Herrera Rosa María Mateos Juan Carlos García-Davalillo Gilles Grandjean Eleftheria Poyiadji Raluca Maftei Tatiana-Constantina Filipciuc Mateja Jemec Auflič Jernej Jež Laszlo Podolszki Alessandro Trigila Carla Iadanza Hugo Raetzo Arben Kociu Maria Przyłucka Marcin Kułak Michael Sheehy Xavier M. Pellicer Charise McKeown Graham Ryan Veronika Kopačková Michaela Frei Dirk Kuhn Reginald L. Hermanns Niki Koulermou Colby A. Smith Mats Engdahl Pere Buxó Marta Gonzalez Claire Dashwood Helen Reeves Francesca Cigna Pavel Liščák Peter Pauditš Vidas Mikulėnas Vedad Demir Margus Raha Lídia Quental Cvjetko Sandić Balazs Fusi Odd Are Jensen 《Landslides》2018,15(2):359-379
Landslides are one of the most widespread geohazards in Europe, producing significant social and economic impacts. Rapid population growth in urban areas throughout many countries in Europe and extreme climatic scenarios can considerably increase landslide risk in the near future. Variability exists between European countries in both the statutory treatment of landslide risk and the use of official assessment guidelines. This suggests that a European Landslides Directive that provides a common legal framework for dealing with landslides is necessary. With this long-term goal in mind, this work analyzes the landslide databases from the Geological Surveys of Europe focusing on their interoperability and completeness. The same landslide classification could be used for the 849,543 landslide records from the Geological Surveys, from which 36% are slides, 10% are falls, 20% are flows, 11% are complex slides, and 24% either remain unclassified or correspond to another typology. Most of them are mapped with the same symbol at a scale of 1:25,000 or greater, providing the necessary information to elaborate European-scale susceptibility maps for each landslide type. A landslide density map was produced for the available records from the Geological Surveys (LANDEN map) showing, for the first time, 210,544 km2 landslide-prone areas and 23,681 administrative areas where the Geological Surveys from Europe have recorded landslides. The comparison of this map with the European landslide susceptibility map (ELSUS 1000 v1) is successful for most of the territory (69.7%) showing certain variability between countries. This comparison also permitted the identification of 0.98 Mkm2 (28.9%) of landslide-susceptible areas without records from the Geological Surveys, which have been used to evaluate the landslide database completeness. The estimated completeness of the landslide databases (LDBs) from the Geological Surveys is 17%, varying between 1 and 55%. This variability is due to the different landslide strategies adopted by each country. In some of them, landslide mapping is systematic; others only record damaging landslides, whereas in others, landslide maps are only available for certain regions or local areas. Moreover, in most of the countries, LDBs from the Geological Surveys co-exist with others owned by a variety of public institutions producing LDBs at variable scales and formats. Hence, a greater coordination effort should be made by all the institutions working in landslide mapping to increase data integration and harmonization. 相似文献
288.
Lique Camille Johnson Helen L. Plancherel Yves Flanders Robert 《Climate Dynamics》2015,45(5-6):1235-1252
Climate Dynamics - The impact of climate warming on the ocean near Greenland is investigated with a high resolution coupled global climate model. The ocean around Greenland exhibits a strong... 相似文献
289.
The period of vibration is a fundamental parameter in the force‐based design of structures as this parameter defines the spectral acceleration and thus the base shear force to which the building should be designed. This paper takes a critical look at the way in which seismic design codes around the world have allowed the designer to estimate the period of vibration for use in both linear static and dynamic analysis. Based on this review, some preliminary suggestions are made for updating the clauses related to the estimation of the periods of vibration in Eurocode 8. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
290.
Julian Clifton Leanne C. Cullen Jessica Haapkylä Richard K.F. Unsworth 《Ocean & Coastal Management》2010,53(11):700-702
The ecological consequences of coral mining can be severe, with immediate reduction in reef-associated biodiversity and longer term implications for linked habitats such as mangrove forests and seagrass meadows. However, research into the effects of coral mining must take into account other environmental processes which may affect reef communities and the socio-economic context within which coral mining takes place if appropriate and proportionate management responses are to be identified. This article builds upon recently published research detailing the adverse effects of coral mining in Indonesia to illustrate the significance of these points. We use the previous paper to demonstrate that accurate identification of the ecological impacts of coral mining requires the use of appropriate control sites and recognizing natural stresses which may account for short-term variability in ecological parameters. We also underline the need to appreciate that government institutions can directly or indirectly facilitate coral mining, whilst proposed alternative income-generating activities intended to reduce coral mining should be tailored to the local economic, cultural and environmental context if they are to gain community support. This demonstrates the value of an integrated approach to analyzing marine resource usage which combines information from the natural and social sciences to address environmental problems such as coral mining. 相似文献