青藏高原各拉丹冬冰芯记录的季节气温变化     

张拥军  康世昌  秦大河  任贾文  张玉兰  Bjorn GRIGHOLM  Paul MAYEWSKI 《地理学报》2007,62(5):501-509

2005 年10-11 月中美联合考察队在各拉丹冬峰北部果曲冰川平坦的粒雪盆 (33^o34'37.8"N, 91^o10'35.3"E, 5720 m a.s.l.) 钻取了一支冰芯, 通过对该冰芯进行多参数定年, 恢复了青藏高原中部各拉丹冬地区近70 年来降水中δ¹⁸O 的变化历史。根据冰芯中季风期和非季风期δ¹⁸O 值与临近气象台站气温的正相关性, 重建了该地区70 年来的春季和夏季的气温变化。结果表明, 各拉丹冬冰芯中δ¹⁸O 记录的春季和夏季升温趋势非常明显; 根据回归分析, 冰芯中非季风期的δ¹⁸O 每增大(或减小) 1‰相当于春季气温升高(或降低) 1.3 ^oC; 季风 期的δ¹⁸O 每增大(或减小) 1‰相当于夏季气温升高(或降低) 0.4 ^oC; 各拉丹冬冰芯中δ¹⁸O 记录恢复的春季和夏季气温与北半球春季和夏季的气温变化具有一致的趋势, 但各拉丹冬地区的增温幅度比北半球要大, 同时春季的增温幅度也高于夏季。  相似文献   

Spatial variation in hatch date distributions and origin of pelagic juvenile cod in Icelandic waters   总被引：5，自引：3，他引：2  

Marteinsdottir  Gudrun; Gunnarsson  Bjorn; Suthers  Iain M 《ICES Journal of Marine Science》2000,57(4):1182-1195

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Effects of hypoxia on benthic macrofauna and bioturbation in the Estuary and Gulf of St. Lawrence,Canada     

Rénald Belley  Philippe Archambault  Bjorn Sundby  Franck Gilbert  Jean-Marc Gagnon 《Continental Shelf Research》2010

The bottom water in the >300 m deep Lower St. Lawrence Estuary (LSLE) is persistently hypoxic in contrast to the normoxic bottom waters in the Gulf of St. Lawrence (GSL). We photographed the seabed at 11 stations in the Estuary and Gulf of St. Lawrence (EGSL) during the summers 2006 and 2007 and analysed the images to identify bioturbation traces (lebensspuren) and benthic macrofauna. The objective was to identify the environmental variables that influence the density and diversity of benthic macrofauna and bioturbation traces, and the differences that exist among regions with high, medium and low oxygen levels in the bottom water. The bottom water oxygen concentration is the variable that best explains the densities of total-traces as well as surface-traces. However, the density of these traces was higher in hypoxic regions than in well-oxygenated regions. The higher density of traces in the hypoxic region of the LSLE is mainly due to the activities of the surface deposit feeder Ophiura sp., which occurs in large numbers in this region. Possible explanations explored are stress behaviour of the organisms in response to hypoxia and different benthic macrofauna community structures between the hypoxic regions of the LSLE and the normoxic regions of the GSL. In the former, surface deposit feeders and low-oxygen tolerant species dominate over suspension feeders and low-oxygen intolerant species.  相似文献   

Suitability of fish scales as archives of temporal variations in ambient mercury levels in estuaries     

Christine Desjardins  Charles Gobeil  Bjørn Sundby 《Estuaries and Coasts》2006,29(5):855-859

To examine the suitability of fish scales as a historical archive, of environmental mercury (Hg) contamination, we analyzed a collection of scales taken from striped bass (Morone saxatilis) captured in the St. Lawrence Estuary between 1994 and 1962. The total mass of Hg in individual scales increases linearly with the weight of the scale, suggesting that Hg is well preserved in the scale tissue. Age, length, and sex of specimens captured during the same year did not significantly influence the concentration of Hg in the scales. The average Hg concentrations in scales of specimens captured in 1956 (53.2 ±9.1 ng g⁻¹) and 1962 (58.6±7.7 ng g⁻¹) are nearly twice as high as in scales from 1951 (30.2±3.0 ng g⁻¹). These results follow the trend revealed in sediment cores from the St. Lawrence Estuary. A high level of Hg in scales from 1945 (68.7±18.4 ng g⁻¹) could have been caused by an episode of Hg contamination around 1945 not recorded in the sediment or by a diet-related change in Hg exposure.  相似文献   

Dual speciation of nitrogen in silicate melts at high pressure and temperature: An experimental study     

Mathieu Roskosz  Bjorn O. Mysen  George D. Cody 《Geochimica et cosmochimica acta》2006,70(11):2902-2918

Solubility and speciation of nitrogen in silicate melts have been investigated between 1400 and 1700 °C and at pressures ranging from 10 to 30 kbar for six different binary alkali and alkaline-earth silicate liquids and a Ca-Mg-alumino silicate. Experiments were performed in a piston-cylinder apparatus. The nitrogen source is silver azide, which breaks down to Ag and molecular N₂ below 300 °C. At high pressure and temperature, the nitrogen content may be as high as 0.7 wt% depending on the melt composition, pressure, and temperature. It increases with T, P and the polymerization state of the liquid. Characterization by Raman spectroscopy and ¹⁵N solid state MAS NMR indicates that nitrogen is not only physically dissolved as N₂ within the melt structure like noble gases, but a fraction of nitrogen interacts strongly with the silicate network. The most likely nitrogen-bearing species that can account for Raman and NMR results is nitrosyl group. Solubility data follow an apparent Henry’s law behavior and are in good agreement with previous studies when the nitrosyl content is low. On the other hand, a significant departure from a Henry’s law behavior is observed for highly depolymerized melts, which contain more nitrosyl than polymerized melts. Possible solubility mechanisms are also discussed. Finally, a multi-variant empirical relation is given to predict the relative content of nitrosyl and molecular nitrogen as a function of P, T, and melt composition and structure. This complex speciation of nitrogen in melts under high pressure may have significant implication concerning crystal-melt partitioning of nitrogen as well as for potential elemental and isotopic fractionation of nitrogen in the deep Earth.  相似文献   

Structural similarity of glasses and melts relevant to petrological processes     

Friedrich A. Seifert  Bjorn O. Mysen  David Virgo 《Geochimica et cosmochimica acta》1981,45(10):1879-1884

High-temperature Ramun spectroscopic investigations of melts in the systems GeO₂. Na₂O-SiO₂ and Na₂O-Al₂O₃-SiO₂ demonstrate the close structural relationships between melts and glasses. No coordination changes with temperature and no new anionic species have been observed in the melt relative to those in the glass. The relative concentration of different anionic units changes only slightly in the temperature range 100–1350 C. With increasing temperature, compositions with three-dimensionally connected structural units exhibit an intensity increase of a band characteristic of a defect in the network structure, but the network still remains essentially intact.  相似文献   

Assessment of different metrics for physical climate feedbacks     

Daniel Klocke  Johannes Quaas  Bjorn Stevens 《Climate Dynamics》2013,41(5-6):1173-1185

We quantify the feedbacks from the physical climate system on the radiative forcing for idealized climate simulations using four different methods. The results differ between the methods and differences are largest for the cloud feedback. The spatial and temporal variability of each feedback is used to estimate the averaging scale necessary to satisfy the feedback concept of one constant global mean value. We find that the year-to-year variability, combined with the methodological differences, in estimates of the feedback strength from a single model is comparable to the model-to-model spread in feedback strength of the CMIP3 ensemble. The strongest spatial and temporal variability is in the short-wave component of the cloud feedback. In our simulations, where many sources of natural variability are neglected, long-term averages are necessary to get reliable feedback estimates. Considering the large natural variability and relatively small forcing present in the real world, as compared to the forcing imposed by doubling CO₂ concentrations in the simulations, implies that using observations to constrain feedbacks is a challenging task and requires reliable long-term measurements.  相似文献   

Redox equilibria of iron and silicate melt structure: Implications for olivine/melt element partitioning     

Bjorn O. Mysen 《Geochimica et cosmochimica acta》2006,70(12):3121-3138

Olivine/melt partitioning of ΣFe, Fe²⁺, Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺, and Ni²⁺ has been determined in the systems CaO-MgO-FeO-Fe₂O₃-SiO₂ (FD) and CaO-MgO-FeO-Fe₂O₃-Al₂O₃-SiO₂ (FDA3) as a function of oxygen fugacity (f_O2) at 0.1 MPa pressure. Total iron oxide content of the starting materials was ∼20 wt%. The f_O2 was to used to control the Fe³⁺/ΣFe (ΣFe: total iron) of the melts. The Fe³⁺/ΣFe and structural roles of Fe²⁺ and Fe³⁺ were determined with ⁵⁷Fe resonant absorption Mössbauer spectroscopy. Changes in melt polymerization, NBO/T, as a function of f_O2 was estimated from the Mössbauer data and existing melt structure information. It varies by ∼100% in melts coexisting with olivine in the FDA3 system and by about 300% in the FD system in the Fe³⁺/ΣFe range of the experiments (0.805-0.092). The partition coefficients ( in olivine/wt% in melt) are systematic functions of f_O2 and, therefore, NBO/T of the melt. There is a -minimum in the FDA3 system at NBO/T-values corresponding to intermediate Fe³⁺/ΣFe (0.34-0.44). In the Al-free system, FD, where the NBO/T values of melts range between ∼1 and ∼2.9, the partition coefficients are positively correlated with NBO/T (decreasing Fe³⁺/ΣFe). These relationships are explained by consideration of solution behavior in the melts governed by Qⁿ-unit distribution and structural changes of the divalent cations in the melts (coordination number, complexing with Fe³⁺, and distortion of the polyhedra).  相似文献   

A GCSS Boundary-Layer Cloud Model Intercomparison Study Of The First Astex Lagrangian Experiment     

Christopher S. Bretherton  Steven K. Krueger  Matthew C. Wyant  Peter Bechtold  Erik Van Meijgaard  Bjorn Stevens  Joao Teixeira 《Boundary-Layer Meteorology》1999,93(3):341-380

Three single-column models (all with an explicit liquid water budget and compara-tively high vertical resolution) and three two-dimensional eddy-resolving models (including one with bin-resolved microphysics) are compared with observations from the first ASTEX Lagrangian experiment. This intercomparison was a part of the second GCSS boundary-layer cloud modelling workshop in August 1995.In the air column tracked during the first ASTEX Lagrangian experiment, a shallow subtropical drizzling stratocumulus-capped marine boundary layer deepens after two days into a cumulus capped boundary layer with patchy stratocumulus. The models are forced with time varying boundary conditions at the sea-surface and the capping inversion to simulate the changing environment of the air column.The models all predict the observed deepening and decoupling of the boundary layer quite well, with cumulus cloud evolution and thinning of the overlying stratocumulus. Thus these models all appear capable of predicting transitions between cloud and boundary-layer types with some skill. The models also produce realistic drizzle rates, but there are substantial quantitative differences in the cloud cover and liquid water path between models. The differences between the eddy-resolving model results are nearly as large as between the single column model results. The eddy resolving models give a more detailed picture of the boundary-layer evolution than the single-column models, but are still sensitive to the choice of microphysical and radiative parameterizations, sub-grid-scale turbulence models, and probably model resolution and dimensionality. One important example of the differences seen in these parameterizations is the absorption of solar radiation in a specified cloud layer, which varied by a factor of four between the model radiation parameterizations.  相似文献   

Tracking herring schools with a high resolution sonar. Variations in horizontal area and relative echo intensity   总被引：3，自引：2，他引：1  

Misund  Ole Arve; Ferno  Anders; Pitcher  Tony; Totland  Bjorn 《ICES Journal of Marine Science》1998,55(1):58-66

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