Isotope fractionation of neon during stepheating extraction?: a comment on ‘Re‐interpretation of the existence of a primitive plume under Australia based on neon isotope fractionation during step heating’ by Gautheron and Moreira (2003)

Using a Rayleigh distillation fractionation model, we calculate that the maximum isotope fractionation potentially achievable is less than 5% during the early stages of gas release from a sample. Our calculation corrects the erroneous conclusions of Gautheron and Moreira (2003), who re‐interpreted the plume‐like neon isotopic compositions found in metasomatic apatite from a south‐eastern Australian xenolith (Matsumoto et al., 1997) to be the result of Rayleigh‐type isotope fractionation of originally MORB‐type neon during stepheating gas extraction. We stress that the modelling of neon isotopic fractionation by Gautheron and Moreira (2003) is incorrect, and that the finding of a plume‐like neon isotopic composition in the apatite by Matsumoto et al. (1997) remains a quite valid and robust conclusion.     

Depth distribution of radiolarians from the Chukchi and Beaufort Seas, western Arctic

The depth distributions of the radiolarian fauna in the Chukchi and Beaufort Seas, marginal seas of the western Arctic Ocean, were examined quantitatively in depth-stratified plankton tows from 4 or 5 intervals above 500 m and in surface sediments from various depths between 163 and 2907 m. The radiolarian assemblage from the water column in September 2000 was dominated by Amphimelissa setosa and followed by the Actinomma boreale/leptoderma group, Pseudodictyophimus gracilipes and Spongotrochus glacialis. These species are related to the Arctic Surface Water shallower than 150 m. This assemblage is similar to that in the Greenland Sea relating to the ice edge, but did not contain typical Pacific radiolarians in spite of the flow of water of Pacific origin in this region. The living depth of Ceratocyrtis historicosa was restricted to the relatively warm water between 300 and 500 m corresponding to the upper Arctic Intermediate Water (AIW) originating from the Atlantic Ocean. Radiolarian assemblages in the surface sediments are similar to those in the plankton tows, except for common Cycladophora davisiana in sediment samples below 500 m. C. davisiana is probably a deep-water species adapted to the lower AIW or the Canadian Basin Deep Water ventilated from the shelves.     

振动台试验对砂土地基中桩基础模型的动力反应研究

通过振动台试验,对群桩基础模型和桩筏基础模型在水平荷载作用下的动力反应进行了研究。试验内容包括对单独的地基模型;在地基模型中安装群桩基础模型;在地基模型中安装桩筏基础模型的3种振动试验和砂土的三轴试验。结果显示,如果能选择合理的相似性准则,可以利用振动台试验对桩基础在振动荷载下的动力行为进行分析。     

Estimating the Asian radon flux density and its latitudinal gradient in winter using ground-based radon observations at Sado Island

Terrestrial radon-222 flux density for the Asian continent, integrated over distances of 4500 km, is estimated in two 20° latitudinal bands centred on 48.8°N and 63.2°N. The evaluation is based on three years of wintertime radon measurements at Sado Island, Japan, together with meteorological and trajectory information. A selection of 18% of observations are suitable for evaluation of an analytical expression for the continental surface flux. Various meteorological assumptions are discussed; it is found that there is a substantial effect of increased complexity of the formulation on the flux estimates obtained. The distribution of spatially integrated radon flux over the Asian landmass is reported for the first time. Expressed as geometric means and 1σ-ranges, estimated fluxes are 14.1 mBq m⁻² s⁻¹ (1σ-range: 18 mBq m⁻² s⁻¹) and 8.4 mBq m⁻² s⁻¹ (1σ-range: 10 mBq m⁻² s⁻¹) for the lower and higher latitude bands. These results constitute an annual minimum in flux densities for these regions, and are higher than previously reported. The existence of a latitudinal gradient in the continental radon source function is confirmed; the present estimate for Asia (−0.39 mBq m⁻² s⁻¹ per degree of latitude) is in agreement with the northern hemisphere terrestrial radon flux gradient proposed previously.