地史重大转折期的环境变化学术讨论会综述

概述了地史重大转折期的环境变化学术讨论会４个方面的主要科学内容：古生代与中生代之交的全球环境变化,泥贫纪弗拉期与法门期之交的全球环境变化,元古宙与显生宙之交扔全球环境变化和地史重大转折期环境变化的研究方法。围绕上述内容,评述了发言人和专题发言人的主要科学资料和科学思想以及本次会议形成的共识。     

华北地台中寒武统张夏组上部高频层序研究

根据华北地台东部寒武系露头层序地层研究,将张夏组划分为两个正层序,其中上部正层序（５３０－５２５ＭａＢ．Ｐ．,三叶虫带Ａｍｐｈｏｔｏｎ－Ｔａｉｔｚｕｉａ带至Ｄａｍｅｓｅｌａ带）由４个亚层序和１７－２３个小层序组成,其中正层序和亚层序具有高分辨率区域地层对比意义。每一级层序均表现为向上变浅和变粗进积型序列,底部常以间断－加深面或洪泛面为界。该时期的海平面变化具有高频振荡特点,构成一个三级复合海平面变化旋回。由不同级别层序所反映的海平面变化旋回可以分别与天文周期的奥特周期（２—５Ｍａ）、米兰科维奇长周期（０．１—０．４Ｍａ）和米兰科维奇短周期（０．０２—０．０４Ｍａ）相对比。据层序地层和相序及相模式的研究,识别出６种类型的小层序,陆棚盆地至上缓坡显示出由Ａ—Ｆ类型的规律性变化。     

新疆玛纳斯湖沉积物氧同位素记录的古气候信息探讨──与青海湖和色林错比较

内陆封闭湖泊自生碳酸盐氧同位素组成与大气降水同位素组成、空气相对湿度和地面气温这三个参数相关。我国季风带的青海湖与色林错的δ~(18)O曲线非常相似,说明古气候变化受相同因素驱动。在10500～9500aB．P．的末次冰期向全新世的过渡期,这两个湖泊的δ~(18)O值大幅度下降,这是夏季风雨水的低δ~(18)O值的缘故。属于西风带的玛纳斯湖和季风带的青海湖的δ~(18)O曲线基本上是对称的。大约9500～4000aB．P,图形由对称转变为相似,据此推论当时夏季风的影响范围可能达到新疆北部。     

Velocities of elastic waves andv P/v S ratios in dry and water-saturated rock samples at high pressure

Elastic wave velocities and the ratiov _P/v _S were studied for dry and initially saturated samples of carbonate and crystalline rocks at pressures to 2 kbar. In initially saturated samplesv _P increases in crystalline rock, whereas in sedimentary rock it may either increase or decrease with increasing pressure. Under the same conditionsv _S remains approximately constant in crystalline rocks and decreases in sedimentary samples. The ratiov _P/v _S as a function of pressure increases in dry rocks and decreases in saturated ones. Saturated samples always have higherv _P/v _S ratios than dry ones. It appears that the geometry of the pore space influences the acoustic properties of saturated crystalline rocks.     

Longshore variations in nearshore wave processes at magilligan point,northern ireland

Magilligan Point is a recurved cuspate foreland at the mouth of Lough Foyle. Two wave regimes intersect in the estuary mouth and the manner of their interplay controls shoreline changes. Ocean swell waves from the N and NE are refracted around the recurve, losing both height and energy longshore. Width of the surf zone decreases and waves tend to steepen, although both these changes and wave refraction owe something to nearshore geometry. Angle of wave approach becomes more acute and a westerly flowing longshore current moves sand S and SW along the beach. Estuary waves from the S and SW are wind-driven with high-frequencies and steepnesses. They generate a northeasterly current which returns material N, but dies out as the waves become obliterated by nearshore attenuation and breaking of swell. It is possible to identify a time-averaged null-point where shoreline wave power is balanced, although this tends to shift over short periods causing rapid morphological changes. The existence of two independent, but counteractive cells ensures the long-term maintenance of the foreland, without requiring major or continuous supplies of fresh sediment.     

A Three-year Study of Nonmethane Hydrocarbons in Surface Air over Saxony (Germany)

Measurements of the nonmethane hydrocarbon (NMHC) mixing ratio over a period of 42 months were carried out for the first time in the air of a research station situated in the former East Germany during the SANA project. Apart from four species, all other species analysed showed a statistically significant downward trend at the 95% significance level. The decrease of the hydrocarbon concentrations was superimposed by seasonal variations. A drop of about 40% of the annual mean values from 1993 to 1995 was observed. This development reflects the dramatic changes in traffic, industry, power economy, and agriculture in Saxony after the reunification of Germany. The remove of two-stroke engined cars is reflected in NMHC mixing ratio changes, as is the removal of obsolete chemical plants. Generally it was not possible to relate causes and effects of a single event, but in some cases major changes in concentrations and NMHC ratios occurred coincidentally with the disappearance of a specific emission source.     

陕西省人工神经元网络降水年,季度预报系统

利用Ｂ－Ｐ人工神经元网络进行了陕西省年度,季度降水预报试验,提出了利用０－１模型解决多等级预报问题的方法,并建立了年度,季度等级预报模型,经过试验,表明该方法预报效果良好,最后对模式在应用中的一些问题及目前其它预报模型的差异等进行了讨论。     

中国地区大气气溶胶辐射强迫及区域气候效应的数值模拟

利用太阳直接辐射日总量和日照时数等多年观测资料,反演了中国地区大气气溶胶0.75 μm光学厚度的年、月平均值,分析了我国大气气溶胶状况的时空分布特征。据此,在中国区域气候模式中考虑气溶胶的辐射影响,模拟中国地区气溶胶直接辐射强迫的大小及气候响应的季节变化特征。计算结果表明: 我国大气气溶胶光学厚度多年平均分布状况是以四川盆地为大值中心向四周减少;长江中下游武汉附近和南疆盆地为另两个大值中心;青藏高原为气溶胶低值区;我国绝大部分地区春季气溶胶光学厚度值最大,各地气溶胶光学厚度最小值出现的季节则有所不同。气溶胶辐射强迫介于-5.3～-13 W/m2之间;辐射强迫具有春、夏季大,秋、冬季小,冬季南方偏大,夏季北方偏大的特征。气溶胶辐射强迫的分布与其光学厚度的分布基本一致。由于气溶胶的影响,中国大陆地区地面气温均有所下降,四川盆地到长江中下游地区以及青藏高原北侧到河套地区降温最为明显,分别可达-0.4℃和-0.5℃。气候响应具有明显的季节特征。地面气温的变化除与辐射强迫的大小有关外,还受大气环流的影响。