An operational model to simulate post-accidental radionuclide transfers in Toulon marine area: preliminary development

As part of its development of post-accident management tools, the French Institute for Radiological Protection and Nuclear Safety is setting up a model to simulate radionuclide dispersion in the Toulon marine area (one of France’s main military ports). The model is based on the MARS 3D code developed by IFREMER. It reproduces hydro-sedimentation phenomena in the Bay of Toulon with a horizontal spatial resolution of 100 m and 30 vertical sigma levels and also factors in radioactive decay and dissolved/particulate distribution of the radionuclides studied. With no tide, the major currents in this area are generated by the wind. The model effectively reproduces the resulting hydrodynamic phenomena, which were measured throughout the summer of 2009 in the channel that links the Little Bay to the Large Bay of Toulon. When the Mistral (wind from the West/Northwest) blows, a surface current quickly appears, which pushes water southwards from the Little Bay, and which is offset by a bottom current (upwellings). When the wind blows from the East, the currents move in the opposite direction, and southeasterly waves, dependent on wind strength and fetch, occur in the Large Bay. Here, we give an example of the simulated dispersion of radionuclides released directly into the surface waters near the Arsenal, demonstrating the constraint relative to dispersion generated by the half-closed configuration of the Little Bay. Sediment in the Little Bay also forms an area where the most highly reactive radionuclides would accumulate, and where the lack of waves has the effect of considerably limiting the phenomena of resuspension.     

Assessing meteotsunami potential of high-frequency air pressure oscillations observed in the middle Adriatic

High-resolution air pressure series collected from a triangle of middle Adriatic microbarograph stations between April 2009 and March 2011 have been analysed to extract the rapid pressure changes normally found during meteotsunamis. Five-minute air pressure tendencies were used to detect an event. Wavelet and cross-wavelet analysis showed that the energies of high-frequency pressure changes that occurred during the warm part of the year were an order of magnitude higher than those that occurred during the cold part of the year. Coherence between stations was normally found at periods longer than 1 h, while air pressure disturbances were dispersive and not coherent at shorter periods. This implies that the disturbances had little to no potential to generate meteotsunamis in the middle Adriatic area, as the eigenoscillations in bays and harbours of the region are over timescales of minutes up to a few tens of minutes.     

Storage conditions of Bezymianny Volcano parental magmas: results of phase equilibria experiments at 100 and 700 MPa

The crystallization sequence of a basaltic andesite from Bezymianny Volcano, Kamchatka, Russia, was simulated experimentally at 100 and 700 MPa at various water activities (aH₂O) to investigate the compositional evolution of residual liquids. The temperature (T) range of the experiments was 950–1,150 °C, aH₂O varied between 0.1 and 1, and the log of oxygen fugacity (fO₂) varied between quartz–fayalite–magnetite (QFM) and QFM + 4.1. The comparison of the experimentally produced liquids and natural samples was used to constrain the pressure (P)–T–aH₂O–fO₂ conditions of the Bezymianny parental magma in the intra-crustal magma plumbing system. The phase equilibria constraints suggest that parental basaltic andesite magmas should contain ~2–2.5 wt% H₂O; they can be stored in upper crustal levels at a depth of ~15 km, and at this depth they start to crystallize at ~1,110 °C. The subsequent chemical evolution of this parental magma most probably proceeded as decompressional crystallization occurred during magma ascent. The final depths at which crystallization products accumulated prior to eruption are not well constrained experimentally but should not be shallower than 3–4 km because amphibole is present in natural magmas (>150 MPa). Thus, the major volume of Bezymianny andesites was produced in a mid-crustal magma chamber as a result of decompressional crystallization of parental basaltic andesites, accompanied by mixing with silicic products from the earlier stages of magma fractionation. In addition, these processes are complicated by the release of volatiles due to magma degassing, which occurs at various stages during magma ascent.     

Observations of Hipparcos short-period red giant stars

Optical UBV(RI) _C and infrared JHK photometry is presented of a small sample of giant stars with short periods in the Hipparcos catalogue. Observations were limited, but were sufficient to rule out most of the Hipparcos periods. Radial velocity measurement were also made for a few stars, over six successive nights. Low-level variability was detected in a few stars. It is argued that in most cases the brightness variations are primarily due to temperature changes. These findings show that high-overtone pulsations in M giant stars occur, if at all, in a far more limited number of stars than proposed in the authors' previous discussion of the Hipparcos data alone.     

星系金属丰度的研究进展(Ⅰ):定标方法

金属丰度是表征星系特征的重要参量,对于理解星系的形成与演化具有重要意义。随着观测设备的不断完善与发展,已经获得越来越多的星系(包括近邻星系、中等红移及高红移星系)金属丰度的观测资料。在光致电离模型方面也取得了很大进展．这些对于理解星系中金属及恒星成分的累积历史有非常重要的作用。有多种方法可以用来估计星系的金属丰度(主要是星际介质中气相的O丰度),介绍和评述了估计星系的O丰度的多种方法,包括电子温度的方法、R23方法以及其他一些“强线”比值的方法,并给出了相应的解析公式,同时介绍了电离星云的物理本质及由光致电离模型估计星系金属丰度的方法,还给出了估计星系的C和N元素丰度的方法。     

Differentiation and crystallization conditions of basalts from the Kerguelen large igneous province: an experimental study

Phase relations of basalts from the Kerguelen large igneous province have been investigated experimentally to understand the effect of temperature, fO₂, and fugacity of volatiles (e.g., H₂O and CO₂) on the differentiation path of LIP basalts. The starting rock samples were a tholeiitic basalt from the Northern Kerguelen Plateau (ODP Leg 183 Site 1140) and mildly alkalic basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet Peninsula), representing different differentiation stages of basalts related to the Kerguelen mantle plume. The influence of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log fO₂ ~ ΔQFM + 4) and reducing conditions (log fO₂ ~ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the fH₂. In all experiments, a significant influence of the fO₂ on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg²⁺/(Mg²⁺ + Fe²⁺)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The pre-eruptive temperature of the alkalic basalt was about 950–1,050°C. The water content of the melt was below 2.5 wt% H₂O and strongly oxidizing conditions (log fO₂ ~ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C, with a water content below 2 wt% H₂O and a log fO₂ ~ ΔQFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich residual melts (e.g., alkali basalt). The enrichment of alkalis in residual melts is enhanced at high fO₂ and low aH₂O.     

The Arctic Ocean—a Canadian perspective from IPY

Canada??s IPY program funded seven marine projects spanning the North American Arctic. Work embraced oceanography, air-sea interactions, storm response, paleo-climate and trace-element chemistry. Notable findings are emerging. Conditions in the Beaufort were unusual in 2007, with very high air pressure bringing strong winds, rapid ice drift, thin winter ice, enhanced shelf-break upwelling and a maximum in freshwater retention in the Beaufort Gyre. A mapping of trace chemicals suggests that Arctic mid-depth circulation may also have reversed. Study of Canadian Arctic through-flow revealed a net annual seawater export of 44,000 cubic kilometres from the Arctic to Baffin Bay. Observations of sea ice, sustained through the IPY, affirmed that ice cover is the key attribute of Arctic seas, with wind as a potent agent in its variation. Surveys have shown that the anthropogenic decline in seawater alkalinity is aggravated in the Arctic by low temperature and low salinity resulting from ice melt. Careful experiments have revealed that Arctic phytoplankton growth is constrained by scarcity of dissolved iron where light levels are low. A manganese fingerprint in sediments has tracked changing sea level during the Ice Age. Sediment-core analysis has revealed the Arctic Oscillation as a dominant cause of long-period climate variations during the Holocene. One project has demonstrated how multi-tasked vessels can maintain a watch on Canada??s Arctic within a reliable affordable logistic framework, while a wave forecast model developed by another for the Beaufort is suitable for operational use.     

Cadmium isotopic composition in the ocean

The oceanic cycle of cadmium is still poorly understood, despite its importance for phytoplankton growth and paleoceanographic applications. As for other elements that are biologically recycled, variations in isotopic composition may bring unique insights. This article presents (i) a protocol for the measurement of cadmium isotopic composition (Cd IC) in seawater and in phytoplankton cells; (ii) the first Cd IC data in seawater, from two full depth stations, in the northwest Pacific and the northwest Mediterranean Sea; (iii) the first Cd IC data in phytoplankton cells, cultured in vitro. The Cd IC variation range in seawater found at these stations is not greater than 1.5 ε_Cd/amu units, only slightly larger than the mean uncertainty of measurement (0.8 ε_Cd/amu). Nevertheless, systematic variations of the Cd IC and concentration in the upper 300 m of the northwest Pacific suggest the occurrence of Cd isotopic fractionation by phytoplankton uptake, with a fractionation factor of 1.6 ± 1.4 ε_Cd/amu units. This result is supported by the culture experiment data suggesting that freshwater phytoplankton (Chlamydomonas reinhardtii and Chlorella sp.) preferentially take up light Cd isotopes, with a fractionation factor of 3.4 ± 1.4 ε_Cd/amu units. Systematic variations of the Cd IC and hydrographic data between 300 and 700 m in the northwest Pacific have been tentatively attributed to the mixing of the mesothermal (temperature maximum) water (ε_Cd/amu = −0.9 ± 0.8) with the North Pacific Intermediate Water (ε_Cd/amu = 0.5 ± 0.8). In contrast, no significant Cd IC variation is found in the northwest Mediterranean Sea. This observation was attributed to the small surface Cd depletion by phytoplankton uptake and the similar Cd IC of the different water masses found at this site. Overall, these data suggest that (i) phytoplankton uptake fractionates Cd isotopic composition to a measurable degree (fractionation factors of 1.6 and 3.4 ε_Cd/amu units, for the in situ and culture experiment data, respectively), (ii) an open ocean profile of Cd IC shows upper water column variations consistent with preferential uptake and regeneration of light Cd isotopes, and (iii) different water masses may have different Cd IC. This isotopic system could therefore provide information on phytoplankton Cd uptake and on water mass trajectories and mixing in some areas of the ocean. However, the very small Cd IC variations found in this study indicate that applications of Cd isotopic composition to reveal aspects of the present or past Cd oceanic cycle will be very challenging and may require further analytical improvements. Better precision could possibly be obtained with larger seawater samples, a better chemical separation of tin and a more accurate mass bias correction through the use of the double spiking technique.