A high-resolution geophysical investigation of sediment distribution controlled by catchment size and tides in a multi-basin turbid outwash fjord: Simpson Bay,Prince William Sound,Alaska     

Christian J. Noll  Timothy M. Dellapenna  Andrea Gilkinson  Randall W. Davis 《Geo-Marine Letters》2009,29(1):1-16

Surficial sediment distribution within Simpson Bay is a function of antecedent bedrock and recently deposited glacial geology, as well as active physical processes both within Simpson Bay and Prince William Sound (PWS). Simpson Bay is a turbid, outwash fjord located in northeastern PWS, Alaska. Freshwater from heavy precipitation, and the melting of high alpine glaciers enter the bay through bay head rivers and small shoreline creeks. The catchment has a high watershed/basin surface area ratio (∼8:1), and easily erodible bedrock that contribute to high sediment loads. The system can be divided into three discrete basins, each with specific morphologic and circulatory characters. Side scan sonar, swath bathymetry, and seismic profiles reveal that bathymetric highs are areas of outcropping glacial surfaces. High backscatter coupled with surface grab samples reveal these surfaces to be composed of coarse sediment and bedrock outcrops. Bathymetric lows are areas of low backscatter, and grab samples reveal these areas to be ponded deposits of organic-rich estuarine muds. The data provide evidence of terminal morainal bank systems, and glacial grounding line deposits at the mouth of the bay and rocky outcrops were identified as subsurface extensions of aerial rocky promontories. Radioisotope analyses of short cores reveal that the bay has an average accumulation rate of approx. 0.5 cm year⁻¹, but that this varies in function of the watershed/basin surface area ratios of the different basins. The interaction of tidal currents and sediment source drives sediment distribution in Simpson Bay. Hydrographic data reveal high spatial variability in surface and bottom currents throughout the bay. Subsurface currents are tide dominated, but generally weak (5–20 cm s⁻¹), while faster currents are found along shorelines, outcrops, and bathymetric highs. Bathymetric data reveal steep slopes with little to no modern sediment throughout the bay, suggesting lack of deposition due to tidal currents.  相似文献   

Paleoenvironment and the archaeological record at the L'Anse Aux Meadows Site,Newfoundland     

A. M. Davis  J. H. McAndrews  B. L. Wallace 《Geoarchaeology》1988,3(1):53-64

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Biotic consequences of a shift in invertebrate ecosystem engineers: Invasion of New Zealand rocky shores by a zone‐forming ascidian          下载免费PDF全文

Andrew R. Davis  Katherine Walls  Andrew Jeffs 《Marine Ecology》2018,39(3)

The pervasive effects of invasive ecosystem engineers, that is those species that modify their environment, are well documented, but rarely have the broader impacts of one foundation invertebrate species being replaced by another been examined. In New Zealand, green‐lipped mussels, Perna canaliculus, commonly dominate wave‐exposed rocky shores. The recent appearance of an invasive ecosystem engineer, the ascidian Pyura doppelgangera, at the very northern tip of New Zealand now threatens to exclude these bivalves from this habitat. Here, we report major shifts in assemblages associated with the invader and chronicle its continued spread. We examined epibiota associated with clumps of mussels and clumps of Pyura from two rocky shore habitats—pools and emergent substrata at two locations. We detected some differences in species richness in biota associated with the two foundation species, but faunal abundance only differed between the locations. These minor changes were dwarfed by the shift in species composition within clumps of each foundation species. Molluscs, particularly gastropods, and crustaceans dominated the assemblage within mussels. In contrast, tubicolous polychaetes dominated the fauna associated with the ascidian. Sessile epifauna, notably barnacles and calcareous tube‐dwelling polychaetes, were common on mussels, but never encountered on the ascidian. Multivariate analysis revealed marked dissimilarity (>80%) between the characteristic mussel and ascidian faunas with virtually no overlap. This biotic shift overshadowed any differences between habitats and locations. The broader implications of these faunal shifts for local and regional patterns of biodiversity, as well as ecosystem function, remain unclear, but deserve further attention.  相似文献   

Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801     

Christopher R. J. Charles  Pierre-Yves F. Robin  Donald W. Davis  Phil J. A. McCausland 《Meteoritics & planetary science》2018,53(5):935-951

The approximately spherical shapes of chondrules has long been attributed to surface tension acting on ~1 mm melt droplets that formed and cooled in the microgravity field of the solar nebula. However, chondrule shapes commonly depart significantly from spherical. In this study, 109 chondrules in a sample of CR2 chondrite NWA 801 were imaged by X-ray computed tomography and best-fitted to ellipsoids. The analysis confirms that many chondrules are indeed not spherical, and also that the chondrules’ collective shape fabric records a definite 13% compaction in the host meteorite. Dehydration of phyllosilicates within chondrules may account for that strain. However, retro-deforming all chondrules shows that a large majority were already far from spherical prior to accretion. Possible models for these initial shapes include prior deformation of individual chondrules in earlier hosts, and, as suggested by previous authors, rotation of chondrules as they were solidifying, and/or “streaming” of molten chondrules by their differential velocities with their gaseous hosts after melting. More in situ 3-D work such as this study on a variety of unequilibrated chondrites, combined with detailed structural petrography, should help further constrain these models and refine our understanding of chondrite formation.  相似文献   

Pseudo-cryptic species Arenicola defodiens and Arenicola marina (Polychaeta: Arenicolidae) in Wadden Sea,North Sea and Skagerrak: Morphological and molecular variation     

Pieternella C. Luttikhuizen  Rob Dekker 《Journal of Sea Research》2010,63(1):17-23

The polychaete Arenicola defodiens, or black lug, was recently described as a morphologically highly similar species alongside the blow lug Arenicola marina. So far it was only known from the British Isles. A double spawning peak was observed earlier in lugworms of the western Wadden Sea. Here, we test the hypothesis that the two spawning peaks represent the two species in sympatry. This hypothesis is refuted on the basis of both morphological and mitochondrial DNA data; both spawning peaks are attributed to A. marina. In spite of this, we confirm, on the basis of new collections as well as re-examination of museum collections, the presence of A. defodiens in the western Wadden Sea, North Sea and also the Skagerrak; its distribution is restricted to habitats which are either submerged or have short emersion times, have relatively coarse sediments and high and stable salinities. Sympatry is common. The species differ strongly in the mitochondrial DNA fragment examined; the observed 14% uncorrected minimum difference amounts to an estimated 33–63 million years since sequence divergence. The amount of intraspecific molecular variation is larger for A. defodiens than for A. marina. This is evidence to suggest that A. marina may have undergone more recent and/or more severe population size bottlenecks.  相似文献   

Hydrologist: John D. Hewlett (1922–2004)     

C. Rhett Jackson  Wayne T. Swank  Rob Olszewski 《水文研究》2005,19(10):2093-2095

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Europe adapts to climate change: Comparing National Adaptation Strategies     

G. Robbert Biesbroek  Rob J. Swart  Timothy R. Carter  Caroline Cowan  Thomas Henrichs  Hanna Mela  Michael D. Morecroft  Daniela Rey 《Global Environmental Change》2010,20(3):440-450

For the last two decades, European climate policy has focused almost exclusively on mitigation of climate change. It was only well after the turn of the century, with impacts of climate change increasingly being observed, that adaptation was added to the policy agenda and EU Member States started to develop National Adaptation Strategies (NASs). This paper reviews seven National Adaptation Strategies that were either formally adopted or under development by Member States at the end of 2008. The strategies are analysed under the following six themes. Firstly, the factors motivating and facilitating the development of a national adaptation strategy. Secondly, the scientific and technical support needed for the development and implementation of such a strategy. Thirdly, the role of the strategy in information, communication and awareness-raising of the adaptation issue. Fourthly, new or existing forms of multi-level governance to implement the proposed actions. Fifthly, how the strategy addresses integration and coordination with other policy domains. Finally, how the strategy suggests the implementation and how the strategy is evaluated. The paper notes that the role of National Adaptation Strategies in the wider governance of adaptation differs between countries but clearly benchmarks a new political commitment to adaptation at national policy levels. However, we also find that in most cases approaches for implementing and evaluating the strategies are yet to be defined. The paper concludes that even though the strategies show great resemblance in terms of topics, methods and approaches, there are many institutional challenges, including multi-level governance and policy integration issues, which can act as considerable barriers in future policy implementation.  相似文献   

DISCUSSION OF "Statistical Prediction Intervals for the Evaluation of Ground-Water Quality," by Robert D. Gibbons, July-August 1987 issue, v. 25, no. 4, pp. 455–465     

Charles B. Davis  Roger J. McNichols 《Ground water》1988,26(1):90-91

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Statistical Issues and Problems in Ground Water Detection Monitoring at Hazardous Waste Facilities     

Roger J. McNichols  Charles B. Davis 《Ground Water Monitoring & Remediation》1988,8(4):135-150

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Bifurcation of volcanic plumes in a crosswind     

Gerald G. J. Ernst  John P. Davis  R. Stephen J. Sparks 《Bulletin of Volcanology》1994,56(3):159-169

Bent-over buoyant jets distorted by a crosscurrent develop a vortex pair structure and can bifurcate to produce two distinct lobes which diverge from one another downwind. The region downwind of the source between the lobes has relatively low proportions of discharged fluid. Factors invoked by previous workers to cause or enhance bifurcation include buoyancy, release of latent heat at the plume edge by evaporating water droplets, geometry and orientation of the source, and the encounter with a density interface on the rising path of the plume. We suggest that the pressure distribution around the vortex pair of a rising plume may initially trigger bifurcation. We also report new experimental observations confirming that bifurcation becomes stronger for stronger bent-over plumes, identifying that bifurcation can also occur for straight-edged plumes but gradually disappears for stronger plumes which form a gravity current at their final level and spread for a significant distance against the current. Observations from satellites and the ground are reviewed and confirm that volcanic plumes can show bifurcation and a large range of bifurcation angles. Many of the bifurcating plumes spread out at the tropopause level and suggest the tropopause may act on the plumes as a density interface enhancing bifurcation. Even for quite moderate bifurcation angles, the two plume lobes become rapidly separated downwind by distances of tens of kilometers. Such bifurcating plumes drifting apart can only result in bilobate tephra fall deposits. The tephra fall deposit from the 16 km elevation, SE spreading, bifurcating volcanic plume erupted on 15 May 1981 from Mt Pagan was sampled by previous workers and clearly displayed bilobate characteristics. Examples of bilobate tephra fall deposits are reviewed and their origin briefly discussed. Bilobate deposits are common and may result from many causes. Plume bifurcation should be considered one of the possible mechanisms which can account for come examples of bilobate tephra fall deposits.  相似文献