贵州遵义牛蹄塘组黑色岩系的硒同位素变化及其环境指示初探

西南早寒武世牛蹄塘组是分布在中国南方扬子地台的一套黑色岩系,区域上发育有典型富集多金属元素的硫化物矿化层.选取遵义松林小竹牛蹄塘组下部富硒、钼、镍等元素的黑色岩系剖面,利用Se同位素初步探讨了该剖面岩石的沉积环境和硒的可能来源.结果表明,小竹牛蹄塘组下部剖面黑色岩系的δ82/76SeSRM3149比值变化较大,下部底层含碳斑脱岩与磷块岩的变化范围在-4.35‰～ 4.11‰之间;中间镍钼层及碳质页岩、碳质碳酸盐岩的δ82/76SeSRM3149变化范围窄,平均值为0.9‰±0.23‰(n=4);上层碳质页岩为-1.24‰.结合已发表的钼同位素数据,认为中间岩石沉积于缺氧/无氧环境,但存在盆地海水与热液或充氧水团的混合;下层的岩石曾一度位于充氧与贫氧环境的边界面,局部岩石曾暴露地表经历了较强的风化和蚀变作用,海水中硒有可能来自底部富硒斑脱岩的氧化淋滤或海底热液.据此推测遵义松林小竹牛蹄塘组下部岩石的沉积环境极可能处在局限盆地靠近陆地的边缘部分,经历了充氧→贫氧→缺氧/无氧→贫氧的演化阶段.     

Basalt from Louisiana continental shelf

A basalt outcrop was discovered on Alderdice Bank on the outer Louisiana continental shelf. The basalt shows an age of 76.8 ± 3.3 × 10⁶ years. Textural, mineralogical, and chemical characteristics indicate that it is an alkali basalt of shallow intrusive origin. It was probably brought to the seafloor by salt tectonics and exposed due to salt dissolution.An accurate account of the Mesozoic geologic history of the Gulf of Mexico must consider the apparent consanguinity of all magmatic rocks of the region, including the Alderdice Bank basalt, and the apparent basinward decrease in age of magmatic activities.     

棉兰老涡旋的数值模拟

用一个水平分辨率比较高的非线性正压模式,对热带西太平洋海域里的海流进行了数值模拟。计算海流与观测结果颇相一致。结果表明:赤道以北、棉兰老岛以东附近海域中,棉兰老冷涡在一年的大部分时间里都得到发展,但是其范围、强度和中心位置在各个月份并不相同,显示出很强的季节变化;在哈马黑拉岛东北海域,6月份突然出现了一个反气旋式的涡旋;这个涡旋8月份发展得最强,一直持续到10月份,在11月份就消亡了。     

Integrating Uncertainty Theories with GIS for Modeling Coastal Hazards of Climate Change

Prediction of coastal hazards due to climate change is fraught with uncertainty that stems from complexity of coastal systems, estimation of sea level rise, and limitation of available data. In-depth research on coastal modeling is hampered by lack of techniques for handling uncertainty, and the available commercial geographical information systems (GIS) packages have only limited capability of handling uncertain information. Therefore, integrating uncertainty theory with GIS is of practical and theoretical significance. This article presents a GIS-based model that integrates an existing predictive model using a differential approach, random simulation, and fuzzy set theory for predicting geomorphic hazards subject to uncertainty. Coastal hazard is modeled as the combined effects of sea-level induced recession and storm erosion, using grid modeling techniques. The method is described with a case study of Fingal Bay Beach, SE Australia, for which predicted responses to an IPCC standard sea-level rise of 0.86 m and superimposed storm erosion averaged 12 m and 90 m, respectively, with analysis of uncertainty yielding maximum of 52 m and 120 m, respectively. Paradoxically, output uncertainty reduces slightly with simulated increase in random error in the digital elevation model (DEM). This trend implies that the magnitude of modeled uncertainty is not necessarily increased with the uncertainties in the input parameters. Built as a generic tool, the model can be used not only to predict different scenarios of coastal hazard under uncertainties for coastal management, but is also applicable to other fields that involve predictive modeling under uncertainty.     

Trace element diagenesis in pyrite-rich sediments of the Achterwasser lagoon, SW Baltic Sea

The early diagenesis of trace elements (V, Cr, Co, Cu, Zn, As, Cd, Ba, U) in anoxic sediments of the Achterwasser, a shallow lagoon in the non-tidal Oder estuary in the Baltic Sea, was investigated in the context of pyrite formation. The dissolved major redox parameters show a two-tier distribution with transient signals in the occasionally re-suspended fluid mud layer (FM) and a permanently established diagenetic sequence in the sediment below. Intense microbial respiration leads to rapid depletion of O₂ within the uppermost mm of the FM. The reduction zones of Mn, Fe and sulfate overlap in the FM and in the permanently anoxic sediment section which appears to be a typical feature of estuarine sediments, under low-sulfate conditions. Degrees of pyritization (DOP) range from 50% in the FM to remarkably high values > 90% at 50 cm depth. Pyrite formation at the sediment surface is attributed to the reaction of Fe-monosulfides with intermediate sulfur species via the polysulfide pathway. By contrast, intense pyritization in the permanently anoxic sediment below is attributed to mineral growth via adsorption of aqueous Fe-sulfide complexes onto pyrite crystals which had originally formed in the surface layer.The studied trace elements show differential behavior patterns which are closely coupled to the diagenetic processes described above: (i) Zn, Cu and Cd are liberated from organic matter in the thin oxic layer of the sediment and diffuse both upwards across the sediment/water boundary and downwards to be trapped as monosulfides, (ii) V, Cr, Co and As are released during reductive dissolution of Mn- and Fe-oxyhydroxides, (iii) U removal from pore water occurs concomitantly to Fe reduction in the FM and is attributed to reduction of U(VI) to U(IV), (iv) the Ba distribution is controlled by reductive dissolution of authigenic barite in the sulfate reduction zone coupled with upward diffusion and re-precipitation. The incorporation of trace elements into pyrite is most intense for Co, Mn and As, intermediate for Cu and Cr and little to negligible for U, Zn, Cd, V and Ba. The observed trend is largely in agreement with previous studies and may be explained with differing rates for ligand exchange. Slow and fast ligand exchange and thus precipitation kinetics are also displayed by downcore increasing (Mn, Cr, Co and As) or constantly low (Zn, Cu, Cd) pore water concentrations. The downward increasing degrees of trace metal pyritization (DTMP) for Co, Cu, Zn and As are, in analogy to pyrite growth, assigned to adsorption of sulfide complexes or As oxyanions onto preexisting pyrite minerals.     

海洋生物-光学算法研究──南黄海叶绿素浓度的估算

根据１９９５年９月中日合作南黄海现场观测资料，对南黄海生物－光学算法进行研究。首先对南黄海现场多光谱反射比数据进行因子分析，解反射比协方差矩阵的特征问题；解出特征值和对应的特征向量，求出主因子，然后建立叶绿素α对主因子的多元线性回归方程，并对算法进行回报和预报检验。计算结果表明，该算法具有较高精度，同时也显示出天气条件对估算精度产生较大影响。     

Source regions for recruitment of Calanus finmarchicus to Georges Bank: evidence from molecular population genetic analysis of mtDNA

Molecular population genetic analysis has provided evidence that the copepod, Calanus finmarchicus, of the Labrador Current, Gulf of St Lawrence, Scotian Shelf, Gulf of Maine, and Georges Bank constitute a single, interbreeding population. The DNA sequence of a 350 base pair portion of the mitochondrial large subunit (16S) ribosomal RNA (rRNA) gene was determined for a total of 72 individuals collected in 1992, and 110 individuals collected in 1993 from these regions. There was significant heterogeneity in haplotype frequencies among the samples collected in 1992, but this heterogeneity did not resolve into regional patterns. The only regional differences seen were between pooled samples of the western N. Atlantic and those of the Norwegian Sea. There were no significant differences in haplotype frequencies among the samples collected in 1993, and fewer haplotypes were observed in these samples. Intraspecific molecular variation was typical of other marine species: there were 29 haplotypes among the 182 individuals sequenced. The frequency distribution of the haplotypes was highly skewed: 128 individuals shared one haplotype and 19 individuals were unique. There were 24 variable sites among the 350 bases sequenced; estimated nucleotide diversity was 0.0042. The genetic character of C. finmarchicus populations in the western N. Atlantic was stable over time in that three of the haplotypes (including the most abundant) occurred in both 1992 and 1993. However, haplotype frequencies differed significantly between the two years. The lack of regional structure in the 1992 samples and the genetic homogeneity of samples collected in 1993 across the domain from the Labrador Current to the Gulf of St Lawrence to Georges Bank and the Gulf of Maine indicated that there is significant gene flow across this region. The persistent genetic pattern suggests that the Gulf of St Lawrence may be an important source region for recruitment of C. finmarchicus to Georges Bank. Determination of zooplankton dispersal patterns within high gene flow species will provide information that may not be determined by conventional oceanographic analyses.     

Interference fringes on GLORIA side-scan sonar images from the Bering Sea and their implications

GLORIA side-scan sonographs from the Bering Sea Basin show a complex pattern of interference fringes sub-parallel to the ship's track. Surveys along the same trackline made in 1986 and 1987 show nearly identical patterns. It is concluded from this that the interference patterns are caused by features in the shallow subsurface rather than in the water column. The fringes are interpreted as a thin-layer interference effect that occurs when some of the sound reaching the seafloor passes through it and is reflected off a subsurface layer. The backscattered sound interferes (constructively or desctructively) with the reflected sound. Constructive/destructive interference occurs when the difference in the length of the two soundpaths is a whole/half multiple of GLORIA's 25 cm wavelength. Thus as range from the ship increases, sound moves in and out of phase causing bands of greater and lesser intensity on the GLORIA sonograph. Fluctuations (or wiggles) of the fringes on the GLORIA sonographs relate to changes in layer thickness. In principle, a simple three dimensional image of the subsurface layer may be obtained using GLORIA and bathymetric data from adjacent (parallel) ship's tracks. These patterns have also been identified in images from two other systems; SeaMARC II (12 kHz) long-range sonar, and TOBI (30 kHz) deep-towed sonar. In these, and other cases world-wide, the fringes do not appear with the same persistence as those seen in the Bering Sea.