山东半岛硅热流值与区域地质条件的关系

据地下水中ＳｉＯ２含量计算山东半岛硅热流值。以此为基础初步探讨本区的地热场特征及其与区域地质条件的关系。指出：１．山东半岛平均热流值与全球平均热流值接近，但比一般古老地块略高。２．划分出三个地热异常区，在大地构造上，两较高热异常区分别对应于胶北和文登隆起；较低热异常区与胶莱盆地相应。３．地热场总特征及其区域热异常的形态主要与近地表的地层岩性、构造形态和断裂发育程度等地质条件有关，而与中生代的岩浆活动无关，但第四纪岩浆活动对胶北隆起局部（蓬莱一带）热异常有重要作用     

Possible effects of climate change on estuarine nutrient fluxes: a case study in the highly nutrified Schelde estuary (Belgium, The Netherlands)

Global change models predict effects of climate change on hydrological regimes at the continental scale in Europe. The aim of this study was to gain a better understanding of the possible effect of changing external forcing conditions on the functioning of estuarine ecosystems. In densely populated areas, anthropogenic nutrient enrichment and consequent alteration of nutrient biogeochemical cycles have already had a big impact on these ecosystems. The average yearly discharge of the upper Schelde estuary increased nearly threefold over the period 1996–2000, from 28 m³ s⁻¹ in 1996 to 73 m³ s⁻¹ in 2000. The continuously rising discharge conditions over the five-year period were used as a reference situation for possible future effects of climate on ecological functioning through increase of discharge. At high discharges, nutrient (NH₄⁺, NO₃⁻, dissolved silica and PO₄³⁻) concentrations in the tidal fresh- and brackish water showed a decrease of up to 50% while total discharged nutrient loadings increased up to 100%. Opposite effects of increasing discharge on NH₄⁺, NO₃⁻ and dissolved silica concentrations in summer and winter, resulted in the flattening out of seasonal cycles for these nutrients. Under high discharge conditions, silica uptake by diatom communities was lowered. Dissolved silica loadings to the coastal area increased concurrently with total silica loadings upstream. Salt intrusion to the marine parts of the estuary decreased. This resulted in a downstream shift of the salinity gradient, with lower salinity observed near the mouth. As a result, TDIN, NO₃⁻ and dissolved silica concentrations doubled at the mouth of the estuary.     

Dissolved silica concentrations and reactions in pore waters from continental slope sediments offshore from Cape Hatteras, North Carolina, USA

The pore water concentrations of dissolved silica in sediment cores from the continental slope offshore from Cape Hatteras, North Carolina, varied from 150 to almost 700 μ,M with depth in the top 40 cm of sediment. Sediment cores from 630 to 2010 m depth had very similar profiles of dissolved silica in their pore waters, even though these cores came from regions greatly different in slope, topography, sedimentation rate, and abundance of benthic macrofauna. Cores from 474 to 525 m were more variable, both with respect to pore water dissolved silica profiles, and with respect to sediment texture. Experiments indicate that both the rate of dissolution of silica and the saturation concentration decrease as sediment depth below the sediment-seawater interface increases. These data are consistent with depletion of a reactive silica phase in surface sediment, which may be radiolarian tests, or the alteration of biogenic silica to a less reactive form over time. Experimental results suggest that the pore water dissolved silica concentration in sediments below the top few centimeters may be higher than the sediments could now achieve. The flux of dissolved silica out of these sediments is estimated to be 15 μmoles cm⁻² yr⁻¹.     

Opal and chalcedony speleothems on quartz sandstones in the Sydney region,southeastern Australia

Speleothems of silica are far rarer than those of calcite but occur in a range of types including stalactites, stalagmites and flowstones. This study has found a wider range and far greater number of silica speleothems on the quartz sandstones of the Sydney region than the small number of previous accounts had suggested. Speleothems on the Sydney region sandstones are composed of multiple layers of amorphous opal‐A and cryptocrystalline chalcedony. Silica slowly dissolved from detrital and diagenetic quartz and kaolinite clays of the host arenites is redeposited as opal‐A at the sandstone surface when groundwater evaporates. This amorphous silica converts over time by Ostwald‐type paragenesis to the cryptocrystalline form, but the expected intermediate opal‐CT phase has not been detected. The crystallisation of chalcedony at earth‐surface temperatures is generally believed to take an extremely long time and its presence makes these speleothems very significant, especially as it is reported in only a small number of silica speleothems elsewhere. Furthermore, a similar paragenetic silica‐‘ripening’ mechanism may also be involved in the low‐temperature earth‐surface formation of other crystalline silica deposits such as silcrete duricrusts and pedogenic quartz. Additional closely coupled laboratory and field investigations into the processes that control silica paragenesis under earth‐surface conditions are sorely needed.     

Run‐off formation in a humid,temperate headwater catchment using a combined hydrological,hydrochemical and isotopic approach (Jizera Mountains,Czech Republic)

The formation of baseflow and stormflow was examined in the 1.18 km² part of the headwater catchment Uhlí?ská, Jizera Mountains, Czech Republic, over the period 2007–2011, by means of run‐off data and environmental tracers ¹⁸O and SiO₂. The baseflow, computed using the digital filter approach BFLOW, contributes 67% to total streamflow and has a mean residence time of 12.3 months. It is formed by groundwater discharge from the valley deluviofluvial granitic sediments, in combination with soil water in weathered layers on hillslopes during rainfall and snowmelt periods. The prevailing source of the groundwater is the infiltration of snowmelt water. Analysis of 20 run‐off events and their hysteretic patterns demonstrated that the stormflow water has a residence time of about 4 months and is generated by preferential flow on hillslopes combined by soil matrix drainage. Because of slower flow in the soil matrix, the enrichment of pore water in SiO₂ is more pronounced. The stormflow and snowmelt water flowing via preferential pathways of upslope minerals soils pushes the pre‐event groundwater through the pathways in wetlands to the stream, and the wetland can be therefore considered as groundwater supplied. This mechanism has been found to be typical for the groundwater‐supplied headwater catchments of the Jizera Mountains and can be also assumed in other mountainous headwaters of the granitic massif in Central Europe. The main methodological contribution of this study are the residence time calculations stratified by baseflow and event flow, identifying run‐off components of different travel times to streams and linking them with geochemical run‐off sources. This achievement was possible because of a comprehensive dataset on hydrology, stable isotopes and silica hydrochemistry in all relevant run‐off generation components. This concept indicates that a possible long‐term change in snowmelt may affect the run‐off regime of headwater catchments to climate or land‐use changes. Copyright © 2013 John Wiley & Sons, Ltd.     

全球海洋硅循环及研究中面临的主要挑战

海洋硅循环是海洋生物地球化学循环的关键过程之一,对调控全球二氧化碳浓度、海洋酸碱度和多种元素(氮、磷、铁、铝等)的循环具有重要作用。在当今气候变化和人类活动影响日益增强的背景下,硅循环与“生物泵”及碳循环的紧密联系,是其成为地球科学领域研究热点的主要原因。海洋中硅的外部来源主要为河流、地下水、大气沉降、海底玄武岩风化作用和海底热液输送5个途径,在全球气温变暖趋势的影响下,极地冰川融化成为高纬度海域不可忽视的硅源。生物硅在沉积物中的埋藏、硅质海绵和生物硅的反风化作用是重要的海洋硅移除过程。海洋硅循环过程复杂,受生物(生物吸收、降解)、物理(吸附、溶解)和化学(矿化分解和反风化作用)多重因素的影响,针对海洋硅循环关键过程的研究有助于综合评估海洋硅的“源-汇”和收支。本文总结了海洋硅循环的主要过程及海洋硅的收支,根据国际和国内研究现状讨论了当前海洋硅循环研究中面临的主要问题和挑战。现有研究成果显示,海洋硅的外源输入和输出通量比以往的评估分别增加了2.4和2.2倍。在短时间尺度内(<8 ka),全球海洋中硅的收支大致平衡,海洋硅循环基本处于稳定状态。气候变化和人类活动导致河流输送至陆架边缘海的硅通量发生变化,可能影响硅藻等海洋浮游植物种群结构,是未来海洋硅循环研究需要关注的问题之一。陆架边缘海较高沉积速率和强烈的反风化作用提高了该区域生物硅的埋藏效率,准确评估该区域生物硅的埋藏通量仍是亟须解决的难题。目前的研究评估了全球海洋浮游硅藻、硅质海绵以及放射虫生产力,而海洋底栖硅藻生产力的贡献受到忽视,未来需要关注底栖硅藻对生物硅的贡献及其在海洋硅的生物地球化学过程中的作用。     

辽-蒙交界地区晚侏罗世高硅花岗岩:岩石成因与地质意义

高硅(SiO_2 70%)花岗岩不仅是指示大陆地壳成熟度的重要标志,而且蕴含大陆地壳分异机制和稀有金属元素运移行为的关键信息。跨越辽宁-内蒙古两地分布的白音花岩基是沿华北克拉通与中亚造山带边界断裂带侵位的重要的中生代高硅花岗岩,但其形成时代和岩石地球化学特征一直缺乏系统刻画。本次离子探针(SIMS)锆石U-Pb测年指示该花岗岩岩基于晚侏罗世(162～161Ma)侵位。岩体SiO_2含量介于75.7%～77.3%;钙碱性、贫铁镁、弱过铝;富集Th与U,亏损Ba与Sr;稀土元素总量较低(∑REE=40.2×10-6～117×10~(-6)),Eu负异常明显; Zr/Hf和Nb/Ta分异显著;这些特征契合高分异I型花岗岩的典型元素地球化学行为。同时,白音花花岗岩具有低负的ε_(Nd)(t)值(-3.5～-2.6)以及低正的锆石ε_(Hf)(t)值(+0.1～+5.9)。元素与同位素地球化学示踪指示白音花花岗岩可能源自由中亚造山带型新生安山质地壳与少量古老地壳组成的复合源区,其部分熔融生成的原始酸性岩浆经历结晶分异形成高硅花岗岩。作为记录华北克拉通/中亚造山带边界断裂带晚侏罗世走滑/伸展活动的非造山型钉合岩体,白音花高硅花岗岩见证了蒙古-华北板块有别于早白垩世大规模上地壳伸展构造的中晚侏罗世区域弥散状中下地壳伸展行为。中晚侏罗世和早白垩世两段式地壳伸展轨迹不仅契合蒙古-鄂霍茨克构造域造山后重力垮塌过程,而且是促使新晋蒙古-华北板块大陆地壳垂向分异-成熟的高效途径。     

西北太平洋楚科奇海沉积物-水界面营养盐输送通量估算

陆架区沉积物间隙水的营养盐再生是水体营养盐补充的重要途径之一。楚科奇海陆架区中部沉积物间隙水中的营养盐分布,是物理和生物扰动较弱状态下的沉积物-水界面的典型分布。本文对中国第4次北极科学考察采集的4个多管短柱沉积物样品及多管样站位的上层水样进行分析,得到沉积物间隙水、上覆水以及水柱中营养盐数据。结果表明,沉积物间隙水各营养盐浓度均先随沉积深度增加而呈指数快速升高,记为Ⅰ层;然后进入沉积物再矿化作用与营养盐移出速率相互抵消的稳定变化层,营养盐浓度在该阶段基本不变,记为Ⅱ层;最后是营养盐缓慢递减层,记为Ⅲ层,由于该层有机质降解作用耗尽氧气,NO-3和PO3-4被还原细菌利用而失去氧离子。通过双层模式和Fick第一扩散定律,计算得出楚科奇海沉积物-水界面硅酸盐、磷酸盐和硝酸盐的扩散通量分别为1.660mmol/(m2·d)(以Si计量)、0.008mmol/(m2·d)(以P计量)、0.117mmol/(m2·d)(以N计量)(以R06站为例)。四个调查站位沉积物中硅酸盐的扩散通量分别为3.101mmol/(m2·d)(以Si计量,CC1站)、1.660mmol/(m2·d)(以Si计量,R06站)、1.307mmol/(m2·d)(以Si计量,C07站)、0.243mmol/(m2·d)(以Si计量,S23站),含量呈现明显的纬度分布特征。沉积物间隙水N*的分布表明,楚科奇海沉积环境具有很强的反硝化过程,沉积物脱氮作用是硝酸盐一个重要的汇。     

长江口几种优势桡足类对微型浮游动物的摄食研究

利用现场海水培养实验,结合浮游动物网样数据,研究长江口邻近海域几种优势桡足类(中华哲水蚤、背针胸刺水蚤、太平洋纺锤水蚤和精致真刺水蚤)对微型浮游动物的摄食影响。结果表明,精致真刺水蚤虽然属于肉食性种类,但几乎不摄食微型浮游动物;其余三种杂食性桡足类中华哲水蚤、背针胸刺水蚤和太平洋纺锤水蚤对微型浮游动物(纤毛虫+异养甲藻)的摄食率分别为0.66、0.09和0.59μg C/(ind·d),分别占其日总摄食量的29%、24%和37%。其中,异养甲藻在初始生物量和对桡足类饵料贡献上分别占整个微型浮游动物的30%和28%,是微型浮游动物中一个重要的组成类群。中华哲水蚤对微型浮游动物的摄食率与初始食物浓度有显著的正相关关系,并且对体长20μm纤毛虫的清滤率要明显高于对体长20μm的纤毛虫(P0.01)的清滤率,表明其偏好摄食较大个体的食物。通过Chesson选择性指数显示,尽管微型浮游动物在生物量上远小于浮游植物,但桡足类能优先选择摄食微型浮游动物;进一步结合网采浮游动物数据,获得各站三种优势桡足类丰度平均占桡足类总丰度的77%,但它们对微型浮游动物现存生物量的摄食压力仅为0.8%,表明桡足类对微型浮游动物群落的下行控制作用并不明显,仍有大部分微型浮游动物生物量未通过摄食途径进入到桡足类群落中。     

2009-2013年普里兹湾表层水体中生物硅的变化及其与气候事件的关系*

提要：利用中国南极科学考察期间获得的颗粒物样品,对南大洋普里兹湾海域水体中生物硅的含量分布及年际变化情况进行了分析。研究结果显示：在2013年夏季普里兹湾表层水体中生物硅含量在0.38-8.62μmol/ dm₃之间变化,平均为1.55±1.86μmol/ dm₃。生物硅在表层水体中的空间分布趋势是在67°S以南湾内区域表层水体中的含量明显高于67°S以北的湾外区域,最大值出现在普里兹湾陆架区,生物因子是表层水体生物硅含量分布的主控因子。根据不同年份即25、26、27、28、29次南极科学考察期间获取的数据研究显示,普里兹湾表层水体中生物硅含量存在明显的年际差异。结合历史数据分析表明,气候事件对普里兹湾海冰变化有明显的影响,因而对相应年份该海域浮游植物数量种群结构也会产生一定的而影响,从而导致了表层水体中生物硅含量的年际差异。