南海表层沉积物中放射虫的组合特征与海洋环境

南海拥有较齐全的边缘海地理地貌与生态环境, 沉积物中保存的放射虫种类繁多, 个体丰富.本文采用数理统计与聚类分析方法, 对表层沉积物中放射虫的组合特征进行了较为详细的定量分析, 以期获得可靠的放射虫组合与分布的特征.聚类分析结果显示, 放射虫组合在南海表层沉积物中的分布大致可区分为5种类型: 陆架浅水区型、陆坡珊瑚礁区型、中央海盆区型、南部富营养区型和夏季上升流区型, 它们分别对应于特有的海洋环境, 并由含有某些优势种类的放射虫群落所组成.进一步分析还表明, 南海的北部、中部和南部分别表现为3个不同生态环境的海区: 北部海区受陆源影响较为明显; 中部海区被中央水团、海底火山活动和夏季上升流活动所控制; 南部海区总体上属于典型的珊瑚礁海洋环境, 生态与沉积环境明显优越于北部海区.南海表层沉积物中放射虫的组合分布特征较好地响应和反映了所在海区的生态环境与沉积条件, 是探讨古海洋环境的重要依据.      

Improved regional scale processes reflected in projected hydrological changes over large European catchments

For the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC), the recent version of the coupled atmosphere/ocean general circulation model (GCM) of the Max Planck Institute for Meteorology has been used to conduct an ensemble of transient climate simulations These simulations comprise three control simulations for the past century covering the period 1860–2000, and nine simulations for the future climate (2001–2100) using greenhouse gas (GHG) and aerosol concentrations according to the three IPCC scenarios B1, A1B and A2. For each scenario three simulations were performed. The global simulations were dynamically downscaled over Europe using the regional climate model (RCM) REMO at 0.44° horizontal resolution (about 50 km), whereas the physics packages of the GCM and RCM largely agree. The regional simulations comprise the three control simulations (1950–2000), the three A1B simulations and one simulation for B1 as well as for A2 (2001–2100). In our study we concentrate on the climate change signals in the hydrological cycle and the 2 m temperature by comparing the mean projected climate at the end of the twenty-first century (2071–2100) to a control period representing current climate (1961–1990). The robustness of the climate change signal projected by the GCM and RCM is analysed focussing on the large European catchments of Baltic Sea (land only), Danube and Rhine. In this respect, a robust climate change signal designates a projected change that sticks out of the noise of natural climate variability. Catchments and seasons are identified where the climate change signal in the components of the hydrological cycle is robust, and where this signal has a larger uncertainty. Notable differences in the robustness of the climate change signals between the GCM and RCM simulations are related to a stronger warming projected by the GCM in the winter over the Baltic Sea catchment and in the summer over the Danube and Rhine catchments. Our results indicate that the main explanation for these differences is that the finer resolution of the RCM leads to a better representation of local scale processes at the surface that feed back to the atmosphere, i.e. an improved representation of the land sea contrast and related moisture transport processes over the Baltic Sea catchment, and an improved representation of soil moisture feedbacks to the atmosphere over the Danube and Rhine catchments.     

Parameterization of snow-free land surface albedo as a function of vegetation phenology based on MODIS data and applied in climate modelling

The aim of this study was to develop an advanced parameterization of the snow-free land surface albedo for climate modelling describing the temporal variation of surface albedo as a function of vegetation phenology on a monthly time scale. To estimate the effect of vegetation phenology on snow-free land surface albedo, remotely sensed data products from the Moderate-Resolution Imaging Spectroradiometer (MODIS) on board the NASA Terra platform measured during 2001 to 2004 are used. The snow-free surface albedo variability is determined by the optical contrast between the vegetation canopy and the underlying soil surface. The MODIS products of the white-sky albedo for total shortwave broad bands and the fraction of absorbed photosynthetically active radiation (FPAR) are analysed to separate the vegetation canopy albedo from the underlying soil albedo. Global maps of pure soil albedo and pure vegetation albedo are derived on a 0.5° regular latitude/longitude grid, re-sampling the high-resolution information from remote sensing-measured pixel level to the model grid scale and filling up gaps from the satellite data. These global maps show that in the northern and mid-latitudes soils are mostly darker than vegetation, whereas in the lower latitudes, especially in semi-deserts, soil albedo is mostly higher than vegetation albedo. The separated soil and vegetation albedo can be applied to compute the annual surface albedo cycle from monthly varying leaf area index. This parameterization is especially designed for the land surface scheme of the regional climate model REMO and the global climate model ECHAM5, but can easily be integrated into the land surface schemes of other regional and global climate models.     

The partitioning of seawater cations during the transformation of gypsum to anhydrite

The coprecipitation of Sr, Mg, Na and K with anhydrite during the dehydration of gypsum was studied in laboratory experiments. The partition coefficients of Mg and Sr between anhydrite and solution decrease with increasing temperature. The partition coefficients of the alkali-ions do not depend upon temperature, but are affected by the brine composition.The mechanism of the phase transformation gypsum → anhydrite occurs via dissolution and precipitation, when the coprecipitated-ions are repartitioned between the new phase and the solution. The partition coefficients established in this study are applicable also for primary anhydrite.During the dehydration of gypsum at elevated temperatures metastable bassanite may form as an intermediate stage. The amount of cations coprecipitated with bassanite is much larger than the amount coprecipitated with anhydrite or gypsum. This phenomenon may have an influence on the partitioning of cations during the dehydration of gypsum, particularly on Sr.The partition coefficients of seawater cations between anhydrite and the brine are similar to those between gypsum and the brine. For this reason the coprecipitated-ions are not expected to be good indicators to distinguish between primary and secondary calcium sulfate minerals.The temperature effect on the coprecipitation of Mg and Sr with anhydrite makes these ions possible indicators for the temperature at which the phase transformation occurred. This temperature corresponds to the depth of burial of the gypsum at the stage of dehydration.The coprecipitation of seawater cations with anhydrite in the natural environment was studied in two systems: A small Pleistocene evaporite lens from the Sinai Peninsula and the Triassic anhydrite of the Mohilla Formation, Israel. The coprecipitated-ion composition of these samples was used to derive the conditions under which the anhydrite was formed.     

南海西北陆缘多金属结核地球化学特征及成因

对取自南海西北陆缘海域的大型多金属结核进行了电子探针、X射线粉晶衍射(XRD)、等离子质谱仪(ICP-MS) 和等离子光谱仪(ICP-AES) 等方面的分析.结核核心部位的主要矿物组成为石英、伊利石、钠长石和绿泥石, 壳层的主要矿物为δMnO₂等.铁、锰组分呈现Fe含量高、Mn含量低和Mn/Fe低的特征.Si含量高, Cu、Co、Ni含量低; 稀土元素(REE) 含量高, 平均为1472.30×10-6, 轻稀土与重稀土的比值(LREE/HREE) 达19.54, 并且存在较强的Ce正异常.元素含量的变化显示: 从结核内壳层到外壳层, Fe、Mn、Cu、Co等元素含量呈不规律变化, 具有典型的边缘海特征, 该特征反映结核在形成过程中受到边缘海沉积环境波动变化的影响, 陆源物质供应量的增加对Fe、REE、Si等元素的富集起到了促进作用, 而对Mn、Ca等元素的富集则产生明显的稀释作用.多金属结核Mn/Fe比及Mn-Fe- (Cu+Ni) ×10三组分图解显示, 南海北部陆缘多金属结核为水成成因, 该成因与结核所赋存的边缘海环境密切相关, 反映了结核成长发育的过程中, 南海典型的边缘海沉积条件和多变的古海洋环境因素对其产生了重要影响.      

New Reference Materials,Analytical Procedures and Data Reduction Strategies for Sr Isotope Measurements in Geological Materials by LA-MC-ICP-MS

Laser ablation multi-collector mass spectrometry (LA-MC-ICP-MS) has emerged as the technique of choice for in situ measurements of Sr isotopes in geological minerals. However, the method poses analytical challenges and there is no widely adopted standardised approach to collecting these data or correcting the numerous potential isobaric inferences. Here, we outline practical analytical procedures and data reduction strategies to help establish a consistent framework for collecting and correcting Sr isotope measurements in geological materials by LA-MC-ICP-MS. We characterise a new set of plagioclase reference materials, which are available for distribution to the community, and present a new data reduction scheme for the Iolite software package to correct isobaric interferences for different materials and analytical conditions. Our tests show that a combination of Kr-baseline subtraction, Rb-peak-stripping using βRb derived from a bracketing glass reference material, and a CaCa or CaAr correction for plagioclase and CaCa or CaAr + REE²⁺ correction for rock glasses, yields the most accurate and precise ⁸⁷Sr/⁸⁶Sr measurements for these materials. Using the analytical and correction procedures outlined herein, spot analyses using a beam diameter of 100 μm or rastering with a 50–65 μm diameter beam can readily achieve < 100 ppm 2SE repeatability ("internal") precision for ⁸⁷Sr/⁸⁶Sr measurements for materials with < 1000 μg g^-1 Sr.