Summary of IAEA-MEL's investigation of Kara Sea radioactivity and radiological assessment     

P. P. Povinec  I. Osvath  M. S. Baxter  S. Ballestra  J. Carroll  J. Gastaud  I. Harms  L. Huynh-Ngoc  L. Liong Wee Kwong  H. Pettersson 《Marine pollution bulletin》1997,35(7-12):235-241

IAEA-MEL participated in five expeditions to the Kara Sea with the aim of assessing the radiological consequences of dumped radioactive wastes in the Novaya Zemlya Bays and Trough. The programme included sampling, in-situ underwater investigations, laboratory analyses of water, sediment and biota samples, the development of a marine radioactivity database, modelling and radiological assessment, the organization of intercomparison exercises and the evaluation of distribution coefficients. Radiometric investigations have shown that no radiologically significant environmental contamination has occurred. Leakages which have led to locally increased levels of radionuclides in sediment have only been observed in Stepovoy and Abrosimov Bays. Computer modelling results suggest that only radiological effects on local and regional scales may be of importance. The global radiological impact of the disposals in the Arctic Seas will be negligible.  相似文献   

Predicting seasonal ocean variability around New Zealand using a coupled ocean-atmosphere model     

Catherine O. de Burgh-Day  Claire M. Spillman  Craig Stevens  Oscar Alves  Graham Rickard 《新西兰海洋与淡水研究杂志》2019,53(2):201-221

We present a first assessment of the Sea Surface Temperature (SST) and 300m Heat Content (HC) ensemble mean skill of the Australian Community Climate and Earth-System Simulator-Seasonal v1.0 (ACCESS-S1) around New Zealand on seasonal timescales, using a set of retrospective ensemble forecasts for 1990-2012. This was verified against Reynolds AVHRR analysis and Bluelink ReANalysis 3.5 (BRAN3.5). For inshore areas with depth <300m, the model shows skill forecasting for summer at a lead time of 0 months, with 66% and 65% of model grid cells having correlation coefficients exceeding 0.6 for SST and 300m HC respectively. Regions of lower skill seem to be associated with the model representation of the complex and variable frontal systems around New Zealand, and an overly-strong response to the El Niño Southern-Oscillation (ENSO). Nevertheless, the skill of ACCESS-S1 around New Zealand suggests there is potential for the development of useful seasonal forecast products for the region.  相似文献   

Directional measurements of wave growth in a short and narrow fetch geometry     

H. Pettersson  K. K. Kahma 《Journal of Atmospheric & Ocean Science》2005,10(1):15-29

The growth of young waves along a narrow bay and their directional spectra were studied. The fetch geometry was found to affect the shape of the spectrum already when the waves were young. When compared to the growth from a straight shoreline, the dimensionless energy was reduced, but the change in dimensionless peak frequency was smaller. The behaviour of the young waves was similar to that of the mature waves but the differences between narrow and broad fetch geometries were smaller, which suggests that due to a stronger nonlinear transfer the young waves are less sensitive to the fetch geometry. The directional spectrum of the young waves in the narrow fetch geometry was narrower at all energy containing frequencies than the spectra from broad fetch geometry, which further supports the conclusion that the shape of the spectrum is not independent of the fetch geometry.  相似文献   

ASPERA-3 on Mars Express     

Stas Barabash  Rickard Lundin 《Icarus》2006,182(2):301-307

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Development of a regional ocean model for New Zealand     

G. J. Rickard  M. G. Hadfield  M. J. Roberts 《新西兰海洋与淡水研究杂志》2013,47(5):1171-1191

A regional ocean model with a horizontal resolution of 1/6° encompassing the New Zealand Exclusive Economic Zone is described. The regional model successfully downscaled solutions from a high resolution, global, coupled model HadCEM. Transport estimates from the global and regional models were compared with observations, and both models supported largely consistent, climatological mean solutions. The regional model used monthly mean forcing at the surface. Nevertheless, the regional model eddy kinetic energy (EKE) spatial patterns compared favourably with long‐term mean satellite altimetric estimates, although the modelled background EKE amplitudes were much lower than observed. A series of permanent eddies associated with the western boundary current system around the top of the North Island of New Zealand were reproduced, and an eddy adjacent to Norfolk Ridge was identified in both the global and regional models. The western boundary current system around the North Island of New Zealand and the associated eddies were the most sensitive components of the model solutions, being influenced by initial conditions, wind forcing, and the model domain size.  相似文献   

Time-resolved,defect-hosted,trace element mobility in deformed Witwatersrand pyrite     

Denis Fougerouse  Steven M. Reddy  Christopher L. Kirkland  David W. Saxey  William D. Rickard  Robert M. Hough 《地学前缘(英文版)》2019,10(1):55-63

The Pb isotopic composition of rocks is widely used to constrain the sources and mobility of melts and hydrothermal fluids in the Earth's crust. In many cases, the Pb isotopic composition appears to represent mixing of multiple Pb reservoirs. However, the nature, scale and mechanisms responsible for isotopic mixing are not well known. Additionally, the trace element composition of sulphide minerals are routinely used in ore deposit research, mineral exploration and environmental studies, though little is known about element mobility in sulphides during metamorphism and deformation. To investigate the mechanisms of trace element mobility in a deformed Witwatersrand pyrite(FeS_2), we have combined electron backscatter diffraction(EBSD) and atom probe microscopy(APM). The results indicate that the pyrite microstructural features record widely different Pb isotopic compositions, covering the entire range of previously published sulphide Pb compositions from the Witwatersrand basin. We show that entangled dislocations record enhanced Pb, Sb, Ni, Tl and Cu composition likely due to entrapment and short-circuit diffusion in dislocation cores. These dislocations preserve the Pb isotopic composition of the pyrite at the time of growth(~3 Ga) and show that dislocation intersections, likely to be common in deforming minerals, limit trace element mobility. In contrast, Pb, As, Ni, Co, Sb and Bi decorate a highangle grain boundary which formed soon after crystallisation by sub-grain rotation recrystallization.Pb isotopic composition within this boundary indicates the addition of externally-derived Pb and trace elements during greenschist metamorphism at ~2 Ga. Our results show that discrete Pb reservoirs are nanometric in scale, and illustrate that grain boundaries may remain open systems for trace element mobility over 1 billion years after their formation.  相似文献   

Microstructural constraints on the mechanisms of the transformation to reidite in naturally shocked zircon     

Timmons?M.?EricksonEmail author  Mark?A.?Pearce  Steven?M.?Reddy  Nicholas?E.?Timms  Aaron?J.?Cavosie  Julien?Bourdet  William?D.?A.?Rickard  Alexander?A.?Nemchin 《Contributions to Mineralogy and Petrology》2017,172(1):6

Zircon (ZrSiO₄) is used to study impact structures because it responds to shock loading and unloading in unique, crystallographically controlled manners. One such phenomenon is the transformation of zircon to the high-pressure polymorph, reidite. This study quantifies the geometric and crystallographic orientation relationships between these two phases using naturally shocked zircon grains. Reidite has been characterized in 32 shocked zircon grains (shocked to stages II and III) using a combination of electron backscatter diffraction (EBSD) and focused ion beam cross-sectional imaging techniques. The zircon-bearing clasts were obtained from within suevite breccia from the Nördlingen 1973 borehole, close to the center of the 14.4 Ma Ries impact crater, in Bavaria, Germany. We have determined that multiple sets (up to 4) of reidite lamellae can form in a variety of non-rational habit planes within the parent zircon. However, EBSD mapping demonstrates that all occurrences of lamellar reidite have a consistent interphase misorientation relationship with the host zircon that is characterized by an approximate alignment of a {100}_zircon with a {112}_reidite and alignment of a {112}_zircon with a conjugate {112}_reidite. Given the tetragonal symmetry of zircon and reidite, we predict that there are eight possible variants of this interphase relationship for reidite transformation within a single zircon grain. Furthermore, laser Raman mapping of one reidite-bearing grain shows that moderate metamictization can inhibit reidite formation, thereby highlighting that the transformation is controlled by zircon crystallinity. In addition to lamellar reidite, submicrometer-scale granules of reidite were observed in one zircon. The majority of reidite granules have a topotaxial alignment that is similar to the lamellar reidite, with some additional orientation dispersion. We confirm that lamellar reidite likely forms via a deviatoric transformation mechanism in highly crystalline zircon, whereas granular reidite forms via a reconstructive transformation from low-crystallinity ZrSiO₄ within the reidite stability field. The results of this study further refine the formation mechanisms and conditions of reidite transformation in naturally shocked zircon.  相似文献   

Energy Release Sites in Magnetic Fields Containing Single Or Multiple Nulls     

Galsgaard  K.  Reddy  R. V.  Rickard  G. J. 《Solar physics》1997,176(2):299-325

An ongoing debate is how magnetic energy is released in solar flares, which type of magnetic instabilities are responsible for triggering the energy release, and which magnetic topologies are most likely to host the instabilities. In this connection magnetic reconnection has been a general ingredient, with most of the previous work focussing on 2D reconnection. A natural extension to this is to investigate reconnection in 3D topologies, in particular the behaviour of magnetic nulls and the magnetic topology associated with them. This paper investigates the difference in dynamical behaviour of a numerical domain that either contains a double null-point pair connected by a separator or only a fraction of the separator defined by the null-points. The experiments show that nulls can either accumulate current individually, or act together to produce a singular current collapse along the separator. The implication of these results for the interpretation of coronal data is discussed.  相似文献   

Larval connectivity of harbours via ocean currents: A New Zealand study     

Stephen M. Chiswell  Graham J. Rickard 《Continental Shelf Research》2011,31(10):1057-1074

Non-indigenous marine species (NIMS) are likely to be introduced into harbours by ballast water discharge or hull fouling, and then spread by natural means in the nearshore/shelf circulation. Reanalysis currents from the Australian Bluelink modelling project are used with particle-tracking to estimate the potential dispersal kernels for major New Zealand ports. A random walk term is added to the particle-tracking algorithm to account for missing variability in the numerical model currents. With few data to validate the model, the choice of added diffusivity is made by comparing simulated dispersal with observed dispersal of Global Program drifters. Histograms of the dispersal times between the ports are computed, along with estimates of the 10⁻¹ and first percentile dispersal times, which are taken as proxies for the minimum dispersal time between the ports. The 10⁻¹ percentile times range from 1 day (e.g., Bay of Islands to Whangarei) to several months (Tauranga to Chatham Islands). We identify eight geographical regions, based on the coastal currents and present kernels for a representative port in each region, along with tables of the 10⁻¹ and first percentile dispersal times for all ports. The regions are: (1) northeast coast of the North Island (influenced by the East Auckland Current), (2) east coast of the North Island (East Cape Current), (3) west coast of the North Island (West Auckland Current/Taranaki Bight circulation), (4) Cook St (circulation in Cook St), (5) east coast of the South Island (Southland Current), (6) west coast of the South Island (Westland Current), (7) Fiordland (Subtropical Front/Southland Current), and (8) the Chatham Islands.  相似文献   

Comparison of Measured Ozone Production Efficiencies in the Marine Boundary Layer at Two European Coastal Sites under Different Pollution Regimes     

A. R. Rickard  G. Salisbury  P. S. Monks  A. C. Lewis  S. Baugitte  B. J. Bandy  K. C. Clemitshaw  S. A. Penkett 《Journal of Atmospheric Chemistry》2002,43(2):107-134

Ozone production efficiencies (E_N), which can be defined as the netnumber of ozone molecules produced per molecule of NO_xoxidised, have been calculated from measurements taken during three intensive field campaigns (one in the spring, EASE 96, and two in the summer, EASE 97 and TIGER 95), at two European coastal sites (Mace Head, Ireland (EASE) and Weybourne, Norfolk (TIGER)) impacted by polluted air masses originating from both the U.K. and continental Europe, as well as relatively clean oceanic air masses from the Arctic and Atlantic. From a detailed wind sector analysis of the EASE 96 and 97 data it is clear that two general types of pollution regime were encountered at Mace Head. The calculated ozone production efficiency in clean oceanic air masses was approximately 65, which contrasted to more polluted air, from the U.K. and the continental European plume, where the efficiency decreased to between 4 and 6. The latter values of E_Nagree well with literature measurements conducted downwind of various urban centres in the U.S. and Europe, which are summarised in a wide-ranging review table. The E_N value calculated for clean oceanic air is effectivelyan upper limit, owing to the relatively rapid deposition of HNO₃ tothe ocean. Consideration of the variation of E_N with NO_x forthe three campaigns suggests that ozone production efficiency is relatively insensitive to both geographical location and season. The measuredE_N values are also compared with values derived from steady-state expressions. An observed anti-correlation between E_N and measured ozone tendencyis briefly discussed.  相似文献