Stratigraphy and internal structure of wind-dominated barrier islands (dune and machair) of the Outer Hebrides,Scotland     

J. Pile  J.A.G. Cooper  D.W.T. Jackson 《地球表面变化过程与地形》2019,44(7):1482-1493

The barrier islands that fringe the western shore of the Outer Hebrides are globally unusual in that they are developed on a planated bedrock (strandflat) surface. They also contain the most extensive area of machair (a distinctive vegetated sandy plain) in the British Isles. This paper presents the first investigation of the internal structure and morphology of these barrier islands and investigates the controls on their structure. The barriers form extensive (300-1000 metres wide) but thin (1.5-2 m) surficial deposits typically resting on bedrock. In areas where depressions exist in the bedrock, and where sediment supply permits, transgressive dunes underlie the machair. A distinctive machair facies of sub-horizontal, undulating reflections, which are laterally continuous over tens of metres is the dominant component of the barriers at each site. This reflects episodic deposition of windblown sand up to the level of the water table. Thereafter any additional sand is transported through the system to accumulate in topographic lows as lake fills, or on topographic highs as ‘high machair’. Eight radar facies were identified, the extent and presence of which vary between the study sites. Bedrock topography and sediment supply are interpreted as the dominant controls on variability in barrier structure. © 2019 John Wiley & Sons, Ltd.  相似文献   

High‐temporal resolution fluvial sediment source fingerprinting with uncertainty: a Bayesian approach          下载免费PDF全文

Richard J. Cooper  Tobias Krueger  Kevin M. Hiscock  Barry G. Rawlins 《地球表面变化过程与地形》2015,40(1):78-92

This contribution addresses two developing areas of sediment fingerprinting research. Specifically, how to improve the temporal resolution of source apportionment estimates whilst minimizing analytical costs and, secondly, how to consistently quantify all perceived uncertainties associated with the sediment mixing model procedure. This first matter is tackled by using direct X‐ray fluorescence spectroscopy (XRFS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses of suspended particulate matter (SPM) covered filter papers in conjunction with automatic water samplers. This method enables SPM geochemistry to be quickly, accurately, inexpensively and non‐destructively monitored at high‐temporal resolution throughout the progression of numerous precipitation events. We then employed a Bayesian mixing model procedure to provide full characterization of spatial geochemical variability, instrument precision and residual error to yield a realistic and coherent assessment of the uncertainties associated with source apportionment estimates. Applying these methods to SPM data from the River Wensum catchment, UK, we have been able to apportion, with uncertainty, sediment contributions from eroding arable topsoils, damaged road verges and combined subsurface channel bank and agricultural field drain sources at 60‐ and 120‐minute resolution for the duration of five precipitation events. The results presented here demonstrate how combining Bayesian mixing models with the direct spectroscopic analysis of SPM‐covered filter papers can produce high‐temporal resolution source apportionment estimates that can assist with the appropriate targeting of sediment pollution mitigation measures at a catchment level. © 2015 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

A gradient‐ratio method for the semi‐automatic interpretation of gravity map data sets     

G.R.J. Cooper 《Geophysical Prospecting》2012,60(5):995-1000

The application of semi‐automatic interpretation techniques to potential field data can be of significant assistance to a geophysicist. This paper generalizes the magnetic vertical contact model tilt‐depth method to gravity data using a vertical cylinder and buried sphere models. The method computes the ratio of the vertical to the total horizontal derivative of data and then identifies circular contours within it. Given the radius of the contour and the contour value itself, the depth to the source can be determined. The method is applied both to synthetic and gravity data from South Africa. The Matlab source code can be obtained from the author upon request.  相似文献   

A comparison of annual and seasonal carbon dioxide effluxes between sub-Arctic Sweden and High-Arctic Svalbard     

Mats P. Björkman  Elke Morgner  Robert G. Björk  Elisabeth J. Cooper  Bo Elberling  & Leif Klemedtsson 《Polar research》2010,29(1):75-84

Recent climate change predictions suggest altered patterns of winter precipitation across the Arctic. It has been suggested that the presence, timing and quantity of snow all affect microbial activity, thus influencing CO₂ production in soil. In this study annual and seasonal emissions of CO₂ were estimated in High-Arctic Adventdalen, Svalbard, and sub-Arctic Latnjajaure, Sweden, using a new trace gas-based method to track real-time diffusion rates through the snow. Summer measurements from snow-free soils were made using a chamber-based method. Measurements were obtained from different snow regimes in order to evaluate the effect of snow depth on winter CO₂ effluxes. Total annual emissions of CO₂ from the sub-Arctic site (0.662–1.487 kg CO₂ m^–2 yr^–1) were found to be more than double the emissions from the High-Arctic site (0.369–0.591 kg CO₂ m^–2 yr^–1). There were no significant differences in winter effluxes between snow regimes or vegetation types, indicating that spatial variability in winter soil CO₂ effluxes are not directly linked to snow cover thickness or soil temperatures. Total winter emissions (0.004–0.248 kg CO₂ m^–2) were found to be in the lower range of those previously described in the literature. Winter emissions varied in their contribution to total annual production between 1 and 18%. Artificial snow drifts shortened the snow-free period by 2 weeks and decreased the annual CO₂ emission by up to 20%. This study suggests that future shifts in vegetation zones may increase soil respiration from Arctic tundra regions.  相似文献   

Water‐worked gravel beds in laboratory flumes – a natural analogue?     

James R. Cooper  Simon J. Tait 《地球表面变化过程与地形》2009,34(3):384-397

An investigation has been conducted to identify the key parameters that are likely to scale laboratory sediment deposits to the field scale. Two types of bed formation were examined: one where sediment is manually placed and screeded and the second where sediment is fed into a running flume. This later technique created deposits through sequential cycles of sediment transport and deposition. Detailed bed surface topography measurements have been made over a screeded bed and three fed beds. In addition, bulk subsurface porosity and hydraulic conductivity have been measured. By comparing the four beds, results revealed that certain physical properties of the screeded bed were clearly different from those of the fed beds. The screeded bed had a random organization of grains on both the surface and within the subsurface. The fed beds exhibited greater surface and subsurface organization and complexity, and had a number of properties that closely resembled those found for water‐worked gravel beds. The surfaces were water‐worked and armoured and there was preferential particle orientation and direction of imbrication in the subsurface. This suggested that fed beds are able to simulate, in a simplified manner, both the surface and subsurface properties of established gravel‐bed river deposits. The near‐bed flow properties were also compared. It revealed that the use of a screeded bed will typically cause an underestimation in the degree of temporal variability in the flow. Furthermore, time‐averaged streamwise velocities were found to be randomly organized over the screeded bed but were organized into long streamwise flow structures over the fed beds. It clearly showed that caution should be taken when comparing velocity measurements over screeded beds with water‐worked beds, and that the formation of fed beds offers an improved way of investigating intragravel flow and sediment–water interface exchange processes in gravel‐bed rivers at a laboratory scale. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Pure compound and sediment elutriate embryo larval assay of winter flounder from the Hudson/Raritan Estuary and Long Island Sound     

T. A. Young  A. M. Daly  K. R. Cooper   《Marine environmental research》2000,50(1-5)

Winter flounder (Pseudopleuronectes americanus), a demersal egg layer, is at risk from dioxins and metals in the sediments of the Hudson/Raritan Estuary (the Estuary). The effects of tetrachlorodibenzo-p-dioxin (TCDD), mercuric chloride and sediment elutriates on the embryos of winter flounder from four sites in the Estuary, and a reference site: Long Island Sound (LI) were examined. Embryos were exposed from 2 days after fertilization until 2 days post hatch. TCDD absorption by embryos/larvae ranged from 13 to 44%, with an average 23.4%. One experiment, with the LI population showed a LD₅₀ of 1.8 pg/larva (2.6 ng/g) and LD₁₀ of 0.9 pg/larva (1.4 ng/g). Major observed lesions included pericardial edema (PE), and spinal lesions (SL). Background lesion occurrence in controls was 0.31 lesions/individual, and 0.27 major lesions/individual. NOELs were observed for PE 0.3–0.5 pg/larva, and SL 1.4–9.0 pg/larva. PE and SL are good indicators of low and high dose effects of TCDD in winter flounder, respectively. With mercuric chloride all populations showed 50% mortality at 100 μg/l, and 50% lesions at 25–50 μg/l. Three of seven sediment elutriates collected from the Estuary were acutely toxic. Site-specific variability in sediment toxicity and breeding stock sensitivity to known contaminants was observed. Future studies should incorporate metamorphosis from larva to juvenile. (USEPA:CR825437, NIEHS:ES07148).  相似文献   

Editor's note     

David Cooper  Rod Hine  Darren Bellerby  Peter Ghiringhelli 《Astrophysics and Space Science》1995,229(1):163-167

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The GIS approach to evaporite-karst geohazards in Great Britain   总被引：2，自引：0，他引：2  

A. H. Cooper 《Environmental Geology》2008,53(5):981-992

Evaporite karst in Great Britain has formed in Permian and Triassic gypsum, and in Triassic salt. Active dissolution of these deposits can occur on a human rather than a geological timescale causing subsidence and building damage. The British Geological Survey has taken two approaches towards understanding and advising on hazards caused by dissolution of these soluble rocks. At a detailed level, a national database and GIS of karstic features is being populated. Information gathered includes dolines, springs, stream sinks, caves and building damage. At a national level, the soluble rocks in Great Britain have been identified and digital-map polygon information relating to them was extracted from the British 1:50,000-scale digital geological map. These areas have been assessed, and in places their margins extended to include some overlying rocks where subsidence features are known to penetrate upwards through the overlying sequence. The national areas have then been assessed using detailed local information to assign a susceptibility rating from A (extremely low) to E (high), depending on the nature and regularity of the subsidence events that occur. This national zonation of the soluble rocks can be used for planning, construction and in the insurance businesses. This has proved useful for assessing the potential stability of linear routes, such as roads and pipelines or for other important structures such as bridges and buildings. The information can also be used to delineate zones of karstic groundwater flow.  相似文献   

Lightning characteristics of derecho producing mesoscale convective systems     

Mace L. Bentley  John R. Franks  Katelyn R. Suranovic  Brent Barbachem  Declan Cannon  Stonie R. Cooper 《Meteorology and Atmospheric Physics》2016,128(3):303-314

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Bowers Swell: Evidence for a zone of compressive deformation concentric with Bowers Ridge, Bering Sea     

Michael S. Marlow  Alan K. Cooper  Shawn V. Dadisman  Eric L. Geist  Paul R. Carlson 《Marine and Petroleum Geology》1990,7(4)

Bowers Swell is a newly discovered bathymetric feature which is up to 90 m high, between 12 and 20 km wide, and which extends arcuately about 400 km along the northern and eastern sides of Bowers Ridge. The swell was first revealed on GLORIA sonographs and subsequently mapped on seismic reflection and 3.5 kHz bathymetric profiles. These geophysical data show that the swell caps an arcuate anticlinal ridge, which is composed of deformed strata in an ancient trench on the northern and eastern sides of Bowers Ridge. The trench fill beneath the swell is actively deforming, as shown by faulting of the sea floor and by thinning of the strata across the crest of the swell. Thinning and faulting of the trench strata preclude an origin for the swell by simple sediment draping over an older basement high. We considered several models for the origin of Bowers Swell, including folding and uplift of the underlying trench sediment during the interaction between the Pacific plate beneath the Aleutian Ridge and a remnant oceanic slab beneath Bowers Ridge. However, such plate motions should generate extensive seismicity beneath Bowers Ridge, which is aseismic, and refraction data do not show any remnant slab beneath Bowers Ridge. Another origin considered for Bowers Swell invokes sediment deformation resulting from differential loading and diapirism in the trench fill. However, diapirism is not evident on seismic reflection profiles across the swell. We favour a model in which sediment deformation and swell formation resulted from a few tens of kilometers of low seismicity motion by intraplate crustal blocks beneath the Aleutian Basin. This motion may result from the translation of blocks in western Alaska to the south-west, forcing the movement of the Bering Sea margin west of Alaska into the abyssal Aleutian Basin.  相似文献