Accumulation,solid partitioning and remobilisation of 99Tc in subtidal and intertidal sediments in the Irish Sea

Recent studies have shown that accumulation of ⁹⁹Tc in seabed sediments labelled by authorised radioactive liquid discharges into the NE Irish Sea from the Sellafield reprocessing complex is greater than previously thought. In this paper, new data on ⁹⁹Tc concentration profiles in subtidal and intertidal sediments from the eastern and western Irish Sea are provided with a view to elucidating the processes responsible for the incorporation and retention of ⁹⁹Tc in the seabed. The data show that substantial amounts of ⁹⁹Tc have accumulated in the fine-grained subtidal sediments off the Cumbrian coast, particularly after increased releases from Sellafield following the commissioning of the Enhanced Actinide Removal Plant (EARP) in 1994. In all the cores taken in this area, ⁹⁹Tc has been found to be present to depths in excess of 30 cm. Analysis of ¹³⁷Cs and ²⁴¹Am profiles, together with other supporting geochemical data, show a high degree of homogenisation of the sediments down to these depths as a result of physical and biological processes, and confirm that incorporation of ⁹⁹Tc into the sediment compartment is actually the result of mixing and reworking, rather than active sediment accumulation. In contrast, active deposition of material transported from this mixed pool of sediment appears to be the dominant mechanism controlling ⁹⁹Tc profiles in intertidal areas close to the Sellafield discharge outfall.Data obtained from the analysis of subtidal sediment cores from the western Irish Sea mud basin suggest that similar mixing processes to those occurring in the subtidal sediments of the eastern Irish Sea are also active in this area. Time-series data on ⁹⁹Tc concentrations in surficial sediments from this basin, gathered in the period 1988–2004, inclusive, show a clear increase in concentrations, by a factor of ～2, between samples collected pre-EARP and post-EARP. The constancy of ⁹⁹Tc concentrations in surface sediments throughout the 1980s and the early-1990s suggests that little redissolution and export of ⁹⁹Tc occurred over this extended period. A similar observation applies to the post-EARP period, when concentrations remained relatively constant despite the reported steady decrease in ⁹⁹Tc concentrations in the overlying waters.This apparent lack of remobilisation is consistent with data from sequential extraction analyses, which indicate that the bulk of the ⁹⁹Tc is strongly bound to non-labile geochemical phases, with only a small proportion associated with exchangeable and acido-soluble phases. Further, these analyses show that ⁹⁹Tc is not associated with oxygen-sensitive and highly-reactive acid-volatile sulphides (AVS) to any significant extent.     

Mössbauer study of Meridiani Planum,the first iron‐nickel meteorite found on the surface of Mars by the MER Opportunity

Abstract— –Meridiani Planum is the first iron meteorite found on Mars. It was discovered in 2005 by the Mars Exploration Rover Opportunity (MER‐B). Mössbauer spectra (MS) of the unbrushed and brushed meteorite species were acquired in 10 degrees temperature windows in the range of 210–260 K. Earlier examinations of these MS have led to the conclusion that the meteorite, which contains ～～7 wt% Ni, belongs to the IAB meteorite group. Here, making use of a recently developed calibration/folding procedure for MER MS, we report the results of the MS analyses for the single temperature windows m5 (210–220 K), m6 (220–230 K), m7 (230–240 K), and m89 (240–260 K). All spectra consist of a sextet and a ferric doublet. The hyperfine field of the sextet, extrapolated to room temperature, is ～～34.5 T, which is, based on Mössbauer studies of meteorites found on Earth, indeed consistent with the presence of kamacite. The fractional spectral area of the sextet is ～～0.96 of the total spectrum. The ferric doublet has an average quadrupole splitting of 0.70 mm/s and is not diagnostic of any specific Fe mineral.     

P–T–t evolution and textural evidence for decompression of Pan-African high-pressure granulites, Lurio Belt, north-eastern Mozambique

Pan‐African high‐pressure granulites occur as boudins and layers in the Lurio Belt in north‐eastern Mozambique, eastern Africa. Mafic granulites contain the mineral assemblage garnet + clinopyroxene + plagioclase + quartz ± magnesiohastingsite. Garnet porphyroblasts are zoned with increasing almandine and spessartine contents and decreasing grossular and pyrope contents from core (Alm₄₆Prp₃₂Grs₂₁Sps₂) to rim (Alm₅₂Prp₂₆Grs₁₉Sps₃). This pattern is interpreted as a retrograde diffusion zoning with the preserved core chemistry representing the peak metamorphic composition. Mineral reaction textures occur in the form of monomineralic and composite plagioclase ± orthopyroxene ± amphibole ± biotite ± magnetite coronas around garnet porphyroblasts. Thermobarometry indicates peak metamorphic conditions of up to 1.57 ± 0.14 GPa and 949 ± 92 °C (stage I), corresponding to crustal depths of ～55 km. Zircon yielded an U–Pb age of 557 ± 16 Ma, inferred to date crystallization of zircon during peak or immediately post‐peak metamorphism. Formation of plagioclase + orthopyroxene‐bearing coronas surrounding garnet indicates a near‐isothermal decompression of the high‐pressure granulites to lower pressure granulite facies conditions (stage II). Development of plagioclase + amphibole‐coronas enclosing the same garnet porphyroblasts shows subsequent cooling into amphibolite facies conditions (stage III). Symplectitic textures of the corona assemblages indicate rapid decompression. The high‐pressure granulite facies metamorphism of the Lurio Belt, followed by near‐isothermal decompression and subsequent cooling, is in accordance with a long‐lived tectonic history accompanied by high magmatic activity in the Lurio Belt during the late Neoproterozoic–early Palaeozoic East‐African–Antarctic orogeny.     

孟加拉湾超级风暴费林对西藏强降水的影响分析

利用NCEP/NCAR(2.5°×2.5°)再分析资料和常规、非常规观测资料,通过环境场和中尺度特征较全面细致地分析了孟加拉湾风暴费林（Phailin）对西藏特大暴雪的影响。研究表明：“费林”对强降水的影响主要是登陆减弱为低压后,低压云系分两个阶段形成三个中尺度对流云团,对流云团在南支槽的作用下上高原。而强降水的发生和南风风速的大小有直接的对应关系,西南低空急流建立后西藏南部才出现强降水,而低空急流的建立是靠南支槽的贡献。南风风速和强降水的这一重要关系为此类天气提供了预报着眼点。     

Spatio-temporal variability of currents over a mobile dune field in the Dover Strait

A one month field campaign featuring two spring–neap tide cycles and three strong storms has been performed in a mobile dune area located in the central part of the Dover Strait. These dunes are known to move in a complex manner as their migration direction varies in space and time (Le Bot et al., 2000, Le Bot, 2001, Le Bot and Trentesaux, 2004). In order to gain some insights into the dune motion processes we present an analysis of the spatio-temporal variability of currents in the area emphasizing the relative influence of tides and storms. A total of eight different hydro-meteorological regimes have been distinguished during the experiment duration. The analysis of the currents measurements at five locations in the area shows that the eight hydro-meteorological regimes induce very different current responses at the bottom. The residual tidal currents exhibit a significant spatial variability both in direction and in intensity. A numerical model of tidal currents over the Dover Strait confirms the strong spatio-temporal variability of the residual tidal currents featuring three singular points. Amongst them, a saddle point is located just south of the I-dune at the convergence of opposite direction residual tidal currents. The wind-induced currents are almost uniform in space, their intensity and direction however strongly depends on the wind regime and thus on time. The mean total current feature a spatial pattern which can be tidal of wind-induced currents dominated, or either in balance, depending on the regime considered. At the PERMOD campaign time scale, the total current is dominated by the residual tidal current. These results proved to give valuable insights to explain the complex dynamics of dune motion observed in this area by Le Bot et al., 2000, Le Bot, 2001, Le Bot and Trentesaux, 2004 at short and long time scales.     

Glacial-interglacial mean sea level pressure change due to sea level, ice sheet and atmospheric mass changes

The change in the global mean atmospheric pressure between glacial and interglacial periods is evaluated at sea level. This change originates in a modification of topography and in a possible variation in the atmospheric mass. In this calculation the atmosphere is at hydrostatic equilibrium, and the parameters describing the glacial period are varied in a plausible range. The result, with constant atmospheric mass, is a mean sea level pressure decrease of 9–15 hPa linked with the deglaciation. The corresponding pressure change at the reference level corresponding to the present day sea level does not exceed one hPa. When considering only the change in the atmospheric mass, an increase which does not exceed 2 hPa is found, linked with the deglaciation.     

A Critical Appraisal of the Global Warming Debate

Major changes are occurring in the global warming debate. Popular alarmist views are giving way to more balanced assessments of the situation. There is now greater emphasis on the lack of consensus among climatologists on fundamental scientific issues related to climate change.     

Evolution and Morphodynamics of a Prograded Beach‐Ridge Foreland,Northern Baffin Island,Canadian Arctic Archipelago

Landward retreat (marine transgression) is a common response of coastal systems to rising relative sea level. However, given sufficient sediment supply, the coast may advance seaward. The latter response of gravel barriers has been recorded in parts of southeastern and northwestern Canada, where seaward‐rising sets of beach ridges are observed in areas of Holocene RSL rise. Cape Charles Yorke, northern Baffin Island, is a 5 km long gravel foreland characterized by seaward‐rising beach‐ridge crest elevations. The prograded morphology of the Cape Charles Yorke foreland is a prime example of coastal response to a combination of rising RSL and abundant sediment supply, an unusual and little‐documented pattern in the Canadian Arctic. The main gravel supply to Cape Charles Yorke is likely from eroding bedrock and raised marine deposits southwest of the foreland. Although not the dominant sediment source, the Cape Charles Yorke delta contributed to the formation of the foreland by sheltering it from easterly storm waves and providing an anchor point for the prograding ridges. The truncation of relict ridges by the modern shoreline suggests a recent regime shift from continuous deposition to predominant erosion. The cause and timing of this shift are unknown but could result from a recent dwindling in sediment supply, increased accommodation space, increased wave energy, and/or an accelerated rise of relative sea level.