Transport and accumulation of actinide elements in the near-shore environment: field and modelling studies   总被引：2，自引：0，他引：2  

OLIVIA J. MARSDEN†  LIAM ABRAHAMSEN†  NICHOLAS D. BRYAN†  J. PHILIP DAY†  L. KEITH FIFIELD‡  CLARISSA GENT†  PHILLIP S. GOODALL§  KATHERINE MORRIS¶  FRANCIS R. LIVENS 《Sedimentology》2006,53(1):237-248

Nuclear facilities in coastal locations often discharge low‐level liquid wastes into the sea and the radioisotopes in these discharges are of interest both in assessing possible environmental impacts and as tracers for coastal processes. The distributions of a range of artificial radionuclides, derived from the authorized discharges from British Nuclear Fuels (BNFL) Sellafield, have been determined in the sediments of an intertidal salt marsh in the Esk Estuary, Cumbria, UK. Where published discharge histories exist (for ¹³⁷Cs, ²³⁸Pu, ^239,240Pu and ²⁴¹Am), the sediment core‐profile distributions of these radionuclides have been compared with the releases from Sellafield, and consistent values of the accumulation rate (0·226 ± 0·007 g cm^?2 yr^?1) are obtained. A quantitative model has been developed, describing association of radionuclides with suspended particulate material, which is then accumulated and mixed in an offshore mud patch before resuspension and deposition in the salt marsh. The model has been used to describe radionuclide distributions observed in both the mud patch and the salt marsh, and to identify isotopes for which post‐depositional remobilization or solution transport from the discharge point are important. The behaviour of the commonly studied isotopes (¹³⁷Cs, ²³⁸Pu, ^239,240Pu and ²⁴¹Am) is similar to that observed at this and other nearby locations. The activation product isotope ²³⁶U is enhanced in these sediments over the natural baseline by four to eight orders of magnitude, and the results suggest that Sellafield‐derived uranium is comparably mobile to ¹³⁷Cs in these sediments although the processes governing the behaviour of these two elements may be different. In situ production of ²⁴¹Am by decay of its ²⁴¹Pu parent has generated only 17% of the current sediment inventory of this isotope, insufficient to account for the increase over the last 20–25 years, and suggesting that the input material for these sediments is preferentially enriched in Am relative to Pu during transport from the offshore mud patch. The discharge history of ²⁴⁴Cm, which is unknown, has also been reconstructed from the sediment profile and the model.  相似文献   

Biogenic particles in the surface microlayer and overlaying atmosphere in the central Arctic Ocean during summer     

CAROLINE LECK  E. KEITH BIGG † 《Tellus. Series B, Chemical and physical meteorology》2005,57(4):305-316

  相似文献   

THE 'LITTLE ICE AGE': RE-EVALUATION OF AN EVOLVING CONCEPT   总被引：4，自引：0，他引：4  

JOHN A. MATTHEWS  KEITH R. BRIFFA 《Geografiska Annaler: Series A, Physical Geography》2005,87(1):17-36

ABSTRACT. This review focuses on the development of the ‘Little Ice Age’ as a glaciological and climatic concept, and evaluates its current usefulness in the light of new data on the glacier and climatic variations of the last millennium and of the Holocene. ‘Little Ice Age’ glacierization occurred over about 650 years and can be defined most precisely in the European Alps (c. AD 1300–1950) when extended glaciers were larger than before or since. ‘Little Ice Age’ climate is defined as a shorter time interval of about 330 years (c. AD 1570–1900) when Northern Hemisphere summer temperatures (land areas north of 20°N) fell significantly below the AD 1961–1990 mean. This climatic definition overlaps the times when the Alpine glaciers attained their latest two highstands (AD 1650 and 1850). It is emphasized, however, that ‘Little Ice Age’ glacierization was highly dependent on winter precipitation and that ‘Little Ice Age’ climate was not simply a matter of summer temperatures. Both the glacier‐centred and the climate‐centred concepts necessarily encompass considerable spatial and temporal variability, which are investigated using maps of mean summer temperature variations over the Northern Hemisphere at 30‐year intervals from AD 1571 to 1900. ‘Little Ice Age’‐type events occurred earlier in the Holocene as exemplified by at least seven glacier expansion episodes that have been identified in southern Norway. Such events provide a broader context and renewed relevance for the ‘Little Ice Age’, which may be viewed as a ‘modern analogue’ for the earlier events; and the likelihood that similar events will occur in the future has implications for climatic change in the twenty‐first century. It is concluded that the concept of a ‘Little Ice Age’ will remain useful only by (1) continuing to incorporate the temporal and spatial complexities of glacier and climatic variations as they become better known, and (2) by reflecting improved understanding of the Earth‐atmosphere‐ocean system and its forcing factors through the interaction of palaeoclimatic reconstruction with climate modelling.  相似文献   

Sudden changes in arctic atmospheric aerosol concentrations during summer and autumn     

E. KEITH BIGG  CAROLINE LECK  E. DOUGLAS NILSSON 《Tellus. Series B, Chemical and physical meteorology》1996,48(2):254-271

  相似文献   

The spatial distribution of coarse surface grains and the stability of gravel river beds     

MIGULE M. PIEDRA  HEATHER HAYNES  TREVOR B. HOEY 《Sedimentology》2012,59(3):1014-1029

  相似文献   

Analysing laser‐scanned digital terrain models of gravel bed surfaces: linking morphology to sediment transport processes and hydraulics     

REBECCA HODGE  JAMES BRASINGTON  KEITH RICHARDS 《Sedimentology》2009,56(7):2024-2043

The grain‐scale topography of a sediment surface is a key component of a fluvial system, affecting aspects including sediment transport, flow resistance and ecology. However, its effect is hard to quantify because of the need for grain‐scale elevation data from in situ fluvial gravel surfaces which are difficult to collect. The sediment surface properties are, therefore, commonly estimated as a function of the sediment grain‐size distribution; however, because of additional factors, such as grain packing and shape, there is not necessarily a unique relationship between the two. A new methodology has been developed that uses terrestrial laser scanning to collect grain‐scale topographic data from in situ fluvial gravel surfaces, from which digital terrain models are created. This paper investigates methods of analysing such digital terrain models, and possible sedimentological interpretations that can be drawn from the analysis. Eleven digital terrain models from exposed gravel surfaces in two contrasting rivers (the River Feshie and Bury Green Brook) were analysed by calculating: the distribution of surface elevations, semivariograms, surface inclinations, surface slopes and aspects and grain orientation. The distribution of surface elevations and surface slope and aspect analysis were found to be most informative. In the River Feshie, grain‐size was interpreted as being a dominant control on sediment surface structure and gravel imbrication was identified. In Bury Green Brook, the location of the digital terrain models within the riffle–pool sequence was the dominant control on surface structure and grain orientation. Such digital terrain models therefore provide a new approach to measuring and quantifying the topography of fluvial sediment surfaces.  相似文献   

Using magnetic resonance imaging for experimental analysis of fine‐sediment infiltration into gravel beds     

HEATHER HAYNES  ELISA VIGNAGA  WILLIAM M. HOLMES 《Sedimentology》2009,56(7):1961-1975

Sedimentologists recognize that development of a fine‐resolution, truly three‐dimensional analytical tool is essential if the internal structure of an opaque material is to be examined. This paper therefore seeks to: (i) test the viability of magnetic resonance imaging for sedimentological research; and (ii) investigate fine‐sediment infiltration into gravel beds. The results of six experiments are analysed quantitatively using Image J post‐processing software. Data indicate that magnetic resonance imaging‐based measurements of particle axes and volumes are comparable with standard laboratory techniques. Furthermore, the technique permits visualization and analysis of differences in the pattern of fine‐sediment infiltration (median particle diameter, d) into a framework of gravel (median particle diameter, D). Data clearly illustrate a siltation process for samples of D/d = 34 and a sealing process for samples of D/d = 7 where the seal is restricted to a depth equal to 2D. This pore‐scale visualization is valuable to the understanding of hydraulic–sediment–habitat interactions.  相似文献   

The methodological basis for fine‐resolution,multi‐proxy reconstructions of ombrotrophic peat bog surface wetness     

MATTHEW J. AMESBURY  KEITH E. BARBER  PAUL D. M. HUGHES 《Boreas: An International Journal of Quaternary Research》2011,40(1):161-174

Amesbury, M. J., Barber, K. E. & Hughes, P. D. M. 2010: The methodological basis for fine‐resolution, multi‐proxy reconstructions of ombrotrophic peat bog surface wetness. Boreas, 10.1111/j.1502‐3885.2010.00152.x. ISSN 0300‐9483. The need for Holocene peat‐based palaeoclimatic records of increased temporal resolution has been widely identified in recent research. The often rapid growth rates of ombrotrophic bogs, when combined with fine‐resolution (i.e. millimetre‐scale) sampling, provide an as yet largely unexploited potential to derive sub‐decadal palaeoclimatic data from this proxy‐archive. However, multi‐proxy, fine‐resolution analyses require changes to standard methodologies, and the application of sampling techniques that are new to peat‐based palaeoclimate research. A peat sampler was custom‐built to allow precise and replicable millimetre‐scale subsampling. Subsequent methodological testing revealed that, irrespective of sample thickness (i.e. resolution), halving the standard sample volume used for plant macrofossil (from 4 cm³ to 2 cm³) and testate amoebae (from 2 cm³ to 1 cm³) analyses and the sample weight used for peat humification analysis (from 0.2 g to 0.1 g dried peat) did not affect the interpretation of the results. A contiguous 1‐mm sampling resolution for plant macrofossil analysis was also tested, but it was found that contiguous 5‐mm samples provided a more reliable background record to fine‐resolution testate amoebae and peat humification analyses. Based on these findings, a standardized and systematic methodological approach was developed, using the custom‐built peat slicer to take millimetre‐scale samples that provide enough sample material for both testate amoebae and peat humification analyses to be performed at 1‐mm resolution. This approach will facilitate the testing of the palaeoclimatic reliability of multi‐proxy, fine‐resolution peat‐based records.  相似文献   

Last Glacial Maximum equilibrium-line altitude trends and precipitation patterns in the Sangre de Cristo Mountains, southern Colorado, USA     

KURT A. REFSNIDER  KEITH A. BRUGGER  ERIC M. LEONARD  JAMES P. McCALPIN  PHILIP P. ARMSTRONG 《Boreas: An International Journal of Quaternary Research》2009,38(4):663-678

Precipitation patterns during the Last Glacial Maximum (LGM) in the Rocky Mountains varied due to the influence of the continental ice sheets and pluvial lakes. However, no constraints have been placed on potential changes of southeasterly Gulf of Mexico-derived moisture that today contributes considerable precipitation to the easternmost ranges of the southern and middle Rocky Mountains. The Sangre de Cristo Mountains of southern Colorado are ideally situated to assess the relative importance of westerly and southeasterly-derived moisture during the LGM. Based on reconstructions of 30 palaeoglaciers in the Sangre de Cristo Mountains, we find that LGM equilibrium-line altitudes (ELAs) on the east side of the range were systematically 100–200 m lower than ELAs on the west side. The observed ELA pattern is strikingly similar to modern precipitation patterns in the study area, suggesting that southeasterly-derived precipitation had a significant influence on the mass balances of LGM glaciers.  相似文献   

Laboratory observations and simple models of slow oscillations in cooled salt-stratified bodies     

J. A. WHITEHEAD  LIANKE TE RAA  TOMOKI TOZUKA  JOSEPH B. KELLER  KEITH BRADLEY 《地球，A辑:动力气象学与海洋学》2005,57(5):798-809

  相似文献