Diatom assemblages and water depth in Lake 239 (Experimental Lakes Area,Ontario): implications for paleoclimatic studies

Diatom assemblages in surface sediments were sampled along three transects in Lake 239, from the Experimental Lakes Area (NW Ontario), and analyzed in order to explore the relationship between modern species distributions and water depth. Approximately 170 diatom species were identified in surficial sediments at lake depths from 2 to 30 m. The species composition varied with sample depth but remained highly similar across all three transects. The main patterns of variation in the diatom assemblages across transects, derived from a detrended correspondence analysis (DCA), showed that assemblages were highly correlated (r = 0.97 to 0.98). At depths > 8 m the pattern of predominantly benthic composition changed to a planktonic assemblage dominated by Cyclotella stelligera. This depth currently corresponds to the depth of 1% light penetration as assessed from extinction coefficient measurements. Diatom species diversity increases with the switch to the near-shore benthic taxa in all three transects. Additionally, there is a large decrease in the ratio of chrysophyte scales to diatoms at depths < 8 m. Light transmission data from wet and dry periods over the last 35 years suggests that during dry periods the extent of the littoral zone should change by over 2 m. We suggest that cores along a transect from 8 to 14 m should provide a highly sensitive location for detailed paleoclimatic study.     

Factors influencing seed germination of Cyperus capitatus, inhabiting the moving sand dunes in southern Europe

Cyperus capitatus Vandelli (Cyperaceae) is distributed in coastal sandy habitats and mobile dunes of south Europe. Its seed germination ecology is not known, despite its potential to be used in re-vegetation projects. Laboratory experiments were conduced to assess the effects of salinity, light regime, cold stratification and burial on seed germination of this species. Overall, increasing salinity delayed germination, increased seed dormancy and mean time to germination (MTG), and reduced final germination percentage, inhibiting it completely above 1% of salinity; although it did not affect seed viability. C. capitatus seeds exhibited their greatest germination at levels between 0 and 1% in non-stratified seeds, and between 0 and 0.5% for stratified seeds. Thus, the effect of salt was greater for stratified seeds at 5 °C. Germination in light/darkness conditions was similar to that in full darkness. Finally, burial in sand of C. capitatus seeds appeared to have a significant effect on cumulative percentage of germination. Seeds buried at depths greater than 2 and 3 cm showed a lower germination success than those on sand surface or buried at shallower depths. Burial also affected the beginning and speed of seed germination.     

俯冲洋壳的折返及其相关问题讨论

大洋俯冲带中高压(HP)和超高压(UHP)岩石的折返机制一直以来都是俯冲工厂中最不为人知的问题之一.本文根据搜集全球折返到地表的洋壳榴辉岩基础数据(包括岩石学特征、峰期温压条件和折返P-T轨迹),初步探讨了洋壳榴辉岩的折返机制.根据峰期矿物组合、温压条件和对应的地温梯度,典型大洋俯冲带中的榴辉岩可以分为三类:含柯石英的UHP硬柱石榴辉岩(2.7～ 3.2GPa,470 ～ 610℃,5～7℃/km)、HP硬柱石榴辉岩(1.7～2.6GPa,360～ 620℃,5～8℃/km)和HP绿帘石榴辉岩(1.5 ～2.3 GPa,540 ～ 630℃,7～12℃/km).与大陆俯冲碰撞造山带中的HP-UHP榴辉岩相比,洋壳榴辉岩具有较低的峰期温压条件和较高的低密度含水矿物的含量,但是普遍缺失高密度的蓝晶石.已有的俯冲洋壳的折返模式都基于一个假设:洋壳榴辉岩密度比周围地幔大.因此,洋壳榴辉岩的折返必须借助于低密度的蛇纹岩或者变沉积岩.MORB体系的热力学模拟研究表明,俯冲洋壳的矿物组合、矿物含量和密度主要受低密度含水矿物(如硬柱石、绿泥石、蓝闪石和滑石等)的稳定性控制,并且在同等深度条件下,冷俯冲洋壳的密度低于热俯冲洋壳的密度.经历冷俯冲(～6℃/km)洋壳的密度在＜ 110～ 120km(P ＜3.3 ～ 3.6GPa)的深度仍小于周围地幔,但是经历热俯冲(～ 1O℃/km)洋壳的密度在＞60km(P＞1.8GPa)的深度就已经超过周围地幔.结合高温高压实验资料和地球物理观察数据,我们认为在＞120km的深度,俯冲基性洋壳本身密度大于周围地幔,不存在低密度的地幔楔蛇纹岩(蛇纹石已发生分解),并且大洋板块的俯冲角度突然增大可能阻碍了更深部的低密度变沉积岩的折返.以上这三个方面的原因可能导致现今折返到地表的洋壳榴辉岩和变沉积岩的形成深度普遍小于120km.折返过程中硬柱石脱水分解会导致洋壳密度增大,退变形成的蓝晶石榴辉岩的密度大于周围地幔,无法折返,这可能是全球洋壳榴辉岩中普遍缺失蓝晶石的主要原因.     

偏最小二乘（PLS）—极谱络合吸附催化波同时测定轻稀土La,Ce,Pr,Nd,Sm,Eu

运用２７３Ａ电化学系统确定了偏最小二乘计极 法同时测定Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ分量的最佳体系为：０．０８ｍＬ的ＸＯ、ＰＨ＝４．０的ＨＡＣ－ＮａＡＣ缓冲溶液６ｍＬ。６种轻稀土在１．０＊１０＾－７－８．０＊１０＾－６ｍｏｌ＝／Ｌ的浓度范围内有良好的线性关系,每种稀土元素的检出限为１．４＊１０＾－８ｍｏｌ／Ｌ。６种轻稀土的相对标准偏差为６．７％－１２．８％。     

桑沟湾水域浮游植物的光量子产值

于1989－1990年对山东半岛的桑沟湾水域进行了综合调查,利用对自然水域现场测量的方法,对浮游植物兀合色素对光的吸收及其光量子产值进行了4个季度月的测量和计算,目的是研究这种浅海养殖生态系统初级生产过程中的能量流动状况。结果表明,该海区光量子产值的范围为0.189×10-2molC／E－6．019×10-2molC／E;浮游植物吸收的光能占海面总吸收光能的0.9％－5.5％;浮游植物的光利用率为0.026％－0.101％,与其他海区相比,较为偏低。     

光照强度对番红砗磲外套膜颜色变化的影响

以蓝色、棕黄色和绿色三种不同外套膜颜色的番红砗磲(Tridacna crocea)为实验对象,设置5000 lx、10000 lx和15000 lx三组光照强度,探究了番红砗磲外套膜颜色变化与光照强度的相关性.结果表明:(1)在不同光照强度下,蓝色个体外套膜颜色加深,棕黄色个体颜色变化不大,而绿色个体外套膜颜色变浅.(...     

海藻多糖分子量及其分布测定Ⅱ——GPC/LALLS联机测定四种海藻多糖分子量分布

采用凝胶渗透色谱与激光小角光散射仪联机(GPC/LALLS)测定了青岛海洋大学海洋药物与食品研究所新研制的四种海藻多糖的分子量分布。分别得到四种海藻多糖的微分、积分分子量分布曲线图、分布宽度指数(D)和数量平均、重量平均和Z均分子量。     

温度、盐度和光照条件对翡翠贻贝滤水率的影响

在实验室的条件下,研究照度、温度、盐度对翡翠贻贝（Ｐｅｒｎａ ｖｉｒｉｄｉｓ）滤水率的影响。结果表明,在一定温度（１６￣３１℃）和盐度（１６￣３２）范围内,滤水率与温度、盐度呈正相关关系。但温度和盐度的交互作用不明显。开始时翡翠贻贝的滤水率随温度的上升而增加,当温度达到２６℃以上时,滤水率的变化趋缓或不再增加。翡翠贻贝的滤水率随盐度的长高而增大,特别是在低温的条件下,滤水率随盐度的变化更为明显。此