Atmospheric Response To Spatial Variations In Concentration And Size Of Polynyas In The Southern Ocean Sea-Ice Zone     

R. A. Dare  B. W. Atkinson 《Boundary-Layer Meteorology》2000,94(1):65-88

Although it is well known that sea-ice regions are important components of the Earth's climate system, the exchanges of energy between ocean, ice and atmosphere are not well understood. The majority of past observational and modelling studies of atmosphere-surface interactions over sea-ice regions were primarily concerned with airflow over a single, isolated area of open water. The more realistic situations of multiple polynyas within a sea-ice field and different areal concentrations of sea ice were studied here. Spatial structure of the atmospheric boundary layer in response to this surface was simulated using a high-resolution numerical model. A sea-ice concentration of 80%, typical of the Southern Ocean sea-ice zone, was maintained within a 100-km wide domain. The effects of three polynya characteristics were assessed: their horizontal extent; local concentration of sea ice (LCI); and their arrangement with ice floes. Over polynyas of all sizes distinct plumes of upward heat flux, their width and height closely linked to polynya width, resulted in mixed layers 600 to 1000 m deep over and downwind of the polynyas, their depth increasing with polynya width. Mean surface heat flux (MSHF) increased with size in polynyas less than 30 km wide. The air-to-ice MSHF over the first 10 km of sea-ice downwind of each polynya and the domain-average surface heat flux increased linearly with polynya width. Turbulent kinetic energy plumes occurred over all polynyas, their heights and widths increasing with polynya widths. Downward flux of high momentum air in the plumes caused increased wind speeds over polynyas in the layer from about 300–1000 m above the surface, the depth varying directly with polynya width. MSHFs decreased as LCIs increased. The arrangement of polynyas had relatively little effect on the overall depth of the modified layer but did influence the magnitude and spatial structure of vertical heat transfer. In the two-polynya case the MSHF over the polynyas was larger when they were closer together. Although the MSHF over the sea ice between the polynyas decreased in magnitude as their separation increased, the percentage of the polynya-to-air heat recaptured by this ice floe increased fivefold.  相似文献   

Population biology of the Norway lobster, Nephrops norvegicus (L.) in the Firth of Clyde, Scotland II: fecundity and size at onset of sexual maturity     

Tuck  I. D.; Atkinson  R. J. A.; Chapman  C. J. 《ICES Journal of Marine Science》2000,57(4):1227-1239

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The origin and persistence of alpine vernal ponds in mineral soils     

Violet Harrison-Day  Joe Atkinson  Jamie B. Kirkpatrick 《地球表面变化过程与地形》2019,44(11):2202-2210

Little is known of the processes that create and maintain vernal ponds in mineral soils in alpine environments. On the Central Plateau, Tasmania, we tested the hypotheses that vernal pond complexes on mineral soils formed in response to the underlying topography of a glacio-fluvial plain; relate to present day topography; resulted from past damming by organic accumulation; are moulded by wind. The underlying topography did not relate to the surface ponds, nor were they on steeper slopes than adjacent areas without ponds. The morphology of the ponds and the morphological and edaphic characteristics of the pond complexes and adjacent areas are consistent with an origin by organic material damming. The strongest winds orientate most ponds, rather than the aspect of the slope. Sediments were preferentially caught on sticky traps to the northeast of the ponds, away from fierce prevailing southwesterly winds. Temperature measurements and fortnightly observation showed non-concordant patterns of variation in water levels in the ponds. We deduce that the complexes of vernal ponds may have formed in previous moister conditions more favourable to organic matter accumulation, possibly in the early Holocene, and are maintained by a faster rate of accumulation of mineral and organic particles in the tussock grassland adjacent to the ponds than in the ponds themselves. © 2019 John Wiley & Sons, Ltd.  相似文献   

Magnitude Estimation for the 2011 Tohoku-Oki Earthquake Based on Ground Motion Prediction Equations     

Attieh Eshaghi  Kristy F. Tiampo  Hadi Ghofrani  Gail M. Atkinson 《Pure and Applied Geophysics》2015,172(8):2139-2155

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Rate of Glacial Valley Deepening During the Late Quaternary in Assynt,Scotland     

N. J. Hebdon  T. C. Atkinson  T. J. Lawson  I. R. Young 《地球表面变化过程与地形》1997,22(3):307-315

A dated landscape history of the Allt nan Uamh valley in the Assynt area is constructed, spanning the last 300 ka, using geomorphological analysis, U-series speleothem dating, and existing cave surveys. The mean rate of valley deepening is estimated to lie between 47 and 68 m per glacial/interglacial cycle of 100 ka. This, combined with an estimated duration of glaciation, implies glacial erosion rates of about 2 mm a⁻¹, in agreement with modern process measurements. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Radiometric dating of the Middle Palaeolithic tool industry and associated fauna of Pin Hole Cave,Creswell Crags,England     

Roger M. Jacobi  Peter J. Rowe  Mabs A. Gilmour  Rainer Grün  Timothy C. Atkinson 《第四纪科学杂志》1998,13(1):29-42

Uranium-series dating of derived speleothem suggests that the sediments enclosing a Middle Palaeolithic stone artefact assemblage in Pin Hole Cave probably accumulated after about 64 ka, and ¹⁴C dates indicate a likely age of > 40 ka for the large mammal fauna associated with it. Electron spin resonance data from the fauna conform with these age constraints and are consistent with accumulation between 38 and 50 ka. This evidence supports the view that Britain was recolonised by hominids during Oxygen Isotope Stage 3. Stratigraphically higher stone tool industries demonstrate the local presence of both early Upper and late Upper Palaeolithic cultures. © 1998 John Wiley & Sons, Ltd.  相似文献   

Modelling the distribution of hard seabed using calibrated multibeam acoustic backscatter data in a tropical,macrotidal embayment: Darwin Harbour,Australia     

P. Justy W. Siwabessy  Maggie Tran  Kim Picard  Brendan P. Brooke  Zhi Huang  Neil Smit  David K. Williams  William A. Nicholas  Scott L. Nichol  Ian Atkinson 《Marine Geophysical Researches》2018,39(1-2):249-269

Spatial information on the distribution of seabed substrate types in high use coastal areas is essential to support their effective management and environmental monitoring. For Darwin Harbour, a rapidly developing port in northern Australia, the distribution of hard substrate is poorly documented but known to influence the location and composition of important benthic biological communities (corals, sponges). In this study, we use angular backscatter response curves to model the distribution of hard seabed in the subtidal areas of Darwin Harbour. The angular backscatter response curve data were extracted from multibeam sonar data and analysed against backscatter intensity for sites observed from seabed video to be representative of “hard” seabed. Data from these sites were consolidated into an “average curve”, which became a reference curve that was in turn compared to all other angular backscatter response curves using the Kolmogorov–Smirnov goodness-of-fit. The output was used to generate interpolated spatial predictions of the probability of hard seabed (p-hard) and derived hard seabed parameters for the mapped area of Darwin Harbour. The results agree well with the ground truth data with an overall classification accuracy of 75% and an area under curve measure of 0.79, and with modelled bed shear stress for the Harbour. Limitations of this technique are discussed with attention to discrepancies between the video and acoustic results, such as in areas where sediment forms a veneer over hard substrate.  相似文献   

On the risk of hydraulic fracturing in CO2 geological storage          下载免费PDF全文

Panos Papanastasiou  Euripides Papamichos  Colin Atkinson 《国际地质力学数值与分析法杂志》2016,40(10):1472-1484

We present a contribution on the risk of hydraulic fracturing in CO₂ geological storage using an analytical model of hydraulic fracturing in weak formations. The work is based on a Mohr–Coulomb dislocation model that is extended to account for material with fracture toughness. The complete slip process that is distributed around the crack tip is replaced by superdislocations that are placed in the effective centers. The analytical model enables the identification of a dominant parameter, which defines the regimes of brittle to ductile propagation and the limit at which a mode‐1 fracture cannot advance. We examine also how the corrosive effect of CO₂ on rock strength may affect hydraulic fracture propagation. We found that a hydraulically induced vertical fracture from CO₂ injection is more likely to propagate horizontally than vertically, remaining contained in the storage zone. The horizontal fracture propagation will have a positive effect on the injectivity and storage capacity of the formation. The containment in the vertical direction will mitigate the risk of fracturing and migration of CO₂ to upper layers and back to the atmosphere. Although the corrosive effect of CO₂ is expected to decrease the rock toughness and the resistance to fracturing, the overall decrease of rock strength promotes ductile behavior with the energy dissipated in plastic deformation and hence mitigates the mode‐1 fracture propagation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

A multi‐tracer approach to quantifying groundwater inflows to an upland river; assessing the influence of variable groundwater chemistry          下载免费PDF全文

A. P. Atkinson  I. Cartwright  B. S. Gilfedder  H. Hofmann  N. P. Unland  D. I. Cendón  R. Chisari 《水文研究》2015,29(1):1-12

Understanding the behaviour and variability of environmental tracers is important for their use in estimating groundwater discharge to rivers. This study utilizes a multi‐tracer approach to quantify groundwater discharge into a 27 km upland reach of the Gellibrand River in southwest Victoria, Australia. Ten sampling campaigns were conducted between March 2011 and June 2012, and the distribution of ²²²Rn activities, Cl and ³H concentrations imply the river receives substantial groundwater inflows. Mass balances based on ²²²Rn, Cl and ³H yield estimates of groundwater inflows that agree to within ± 12%, with cumulative inflows in individual campaigns ranging from 24 346 to 88 467 m³/day along the studied river section. Groundwater discharge accounts for between 10 and 50% of river flow dependent on the time of year, with a high proportion (>40 %) of groundwater sustaining summer flows. Groundwater inflow is largely governed by regional groundwater flowpaths; between 50 and 90% of total groundwater inflows occur along a narrow 5–10 km section where the river intersects the Eastern View Formation, a major regional aquifer. Groundwater ²²²Rn activities over the 16 month period were spatially heterogeneous across the catchment, ranging between 2000 Bq/m³ and 16 175 Bq/m³. Although groundwater ²²²Rn activities display temporal variation, spatial variation in groundwater ²²²Rn is a key control on ²²²Rn mass balances in river catchments where groundwater and river ²²²Rn activities are within an order of magnitude of each other. Calculated groundwater discharges vary from 8.4 to 15 m³/m/day when groundwater ²²²Rn activities are varied by ± 1 σ. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Reconstructing the confluence zone between Laurentide and Cordilleran ice sheets along the Rocky Mountain Foothills,south‐west Alberta          下载免费PDF全文

Daniel J. Utting  Nigel Atkinson  Steven Pawley  Stephen J. Livingstone 《第四纪科学杂志》2016,31(7):769-787

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