海洋硅藻稳定同位素研究进展

对海洋初级生产力贡献约40%的硅藻,在全球气候与碳循环中扮演着重要的角色。硅藻稳定同位素(δ30Si和δ18O,δ13C和δ15N)测试对象分别为从海洋沉积物中提取的纯硅藻壳体的生物硅和氧及其内嵌有机质的碳和氮。联合运用各种物理分离(去有机质、碳酸盐,筛分,差异沉降,重液浮选以及微池分流重力场流分离技术)和化学纯化技术从沉积物中提纯出硅藻是其稳定同位素古海洋学应用的前提。确定硅藻δ15N两种制样过程(燃烧和湿式消解)中是否分别存在大气N2和非NO3-组分的污染;δ30Si分析中氟化剂使用的避免、制样方法的改进以及MC-ICP-MS对硅同位素分辨能力的提高;δ18O分析中硅藻壳体外层不稳定氧的完全有效去除,是其同位素古海洋学应用范围扩大和精度提高的关键。硅藻δ13C能评估大气PCO2和海洋初级生产力变化;δ15N和δ30Si可定量示踪海洋硝酸盐和硅酸等营养物利用程度;δ18O则记录了海表温度和海水氧同位素组成。硅藻稳定同位素信号单一,受后期改造作用弱,生命效应低,解译针对性强,在两极和赤道少(或缺)有孔虫海区应用广泛。在此基础上,对目前该领域中存在的问题及未来的研究方向进行了阐述。     

硅藻与色素在古环境演化研究中的意义——以固城湖为例

根据固圾湖ＧＳ１孔沉积物中硅藻的丰度与组合、色素的含量与有关参数,并结合孢粉、有机碳等分析数据,较详细地讨论了从晚冰期到全新世中期（１５．３￣６．０ｋａＢ．Ｐ．）固城湖地区古气候古环境演化的过程。同时尝试把硅藻与色素的结合作为度量湖泊古初始生产力的有效性,以及识别沉积记录有关人类活动的可能性。文中还专门论述了全新世纪初期海相硅藻出现的层位特点与背景,并与太湖作了比较,这一现象对重新认识长江三角洲地     

从藻类化石的垂直分布探讨杭州西湖的演变历程

于１９９４年春在杭州西湖东北面,西面及湖中心小瀛洲３个钻孔共取了７０号岩芯样,经浮选,筛选,以显微镜检鉴定化石藻种,并分析其垂直分布,从而探讨西湖的形成历史,西湖自晚更新世以来的６个化石藻带由下而上依次为：轮藻带,微藻带,微红金颗藻－近缘针杆藻－条纹小环藻带,圆筛藻带,圆筛藻－近缘针杆藻－微红金颗藻桥穹藻－异极藻－短缝藻带和水花束丝藻带,从而反映了西湖的６个发育时期,淡水古湖沼期,淡咸水过渡期,海     

Ultrastructure study of the diatom——Ⅱ. Synedra, Cyclophora, Plagiogramma, Opephora, Fragilaria and Pseudostaurosira

Ｕｌｔｒａｓｔｒｕｃｔｕｒｅｓｔｕｄｙｏｆｔｈｅｄｉａｔｏｍ──Ⅱ．Ｓｙｎｅｄｒａ，Ｃｙｃｌｏｐｈｏｒａ，Ｐｌａｇｉｏｇｒａｍｍａ，Ｏｐｅｐｈｏｒａ，ＦｒａｇｉｌａｒｉａａｎｄＰｓｅｕｄｏｓｔａｕｒｏｓｉｒａ￥ＬｉｕＳｈｉｃｈｅｎｇ（Ｒｅｃｅｉｖｅｄ...     

西沙海洋硅藻研究：Ⅳ.胸隔藻属不等组微细结构

用光镜，透射电镜和扫描电镜记录了属于胸隔藻属不等组的９种硅藻的内外壳面的结构。其中有５种做了ＴＥＭ和ＳＥＭ的观察。     

Marine diatom uptake of iron bound with natural colloids of different origins

Natural colloids are abundant in seawater and are an intermediary in the fate, transport and bioavailability of many trace elements. Knowledge of the pathways and mechanisms of the biological uptake of colloidal Fe and other Fe species is of paramount importance in understanding Fe limitation on marine phytoplankton and thus carbon sequestration in the ocean. Whether the natural colloids serve as a source for the biological Fe requirements of marine phytoplankton, or just as a sink for particle-reactive metals in the oceans remains largely unknown. This study examined the bioavailability of Fe bound with colloids from different regions to a coastal diatom (Thalassiosira pseudonana). Natural colloids were isolated by cross-flow ultrafiltration and radiolabeled with ⁵⁹Fe before being exposed to phytoplankton. Control experiments were conducted to ensure that ⁵⁹Fe radiolabeled onto the colloids remained mostly in the colloidal phase. Both the natural oceanic and coastal colloidal organic matter complexed Fe (1 nm–0.2 μm) can be biologically available to the marine diatom even though its uptake was lower than the low molecular weight counterparts. By comparing the measured Fe internalization fluxes and the calculated maximum diffusive uptake fluxes, it is evident that ligand exchange kinetics on the cell surface may control the internalization of macromolecular Fe. The calculated concentration factors under dark and light conditions were generally comparable. Colloidal Fe, as an important intermediary phase, can be actively involved in the planktonic food web transfer through biological uptake and regeneration processes. The bioavailable fraction of Fe may be substantially underestimated by only considering the truly dissolved Fe or overestimated when using the external fluxes, such as aerosol Fe, as the bioavailable fraction.     

Temporal variations in the abundance and sinking flux of diatoms under fast ice in summer near Syowa Station, East Antarctica

To investigate the fate of ice algae released from sea ice, we investigated the abundance, species composition, and sinking flux of diatoms in the water column under fast ice near Syowa Station, Antarctica during the summer of 2005/2006. The diatom assemblage in the water column consisted of chain-forming planktonic species, in contrast to the under-ice assemblage dominated by pennate species reported from this site in the past; this dissimilarity suggests the presence of an unconsolidated platelet ice layer under the congelation ice, within which planktonic species can bloom. Among the dominant diatoms, Porosira pseudodenticulata and Pseudo-nitzschia cf. turgiduloides were dominant in the water column, and their water column stocks were higher than their mass sedimentation. These species apparently maintain their populations in the surface layer, as their production remains in the water column. In contrast, Fragilariopsis kerguelensis and Thalassiosira australis were scarce in the water column but rich in the flux, indicating active sinking and export of their production to the benthic ecosystem. This distinction in buoyancy control and sinking characteristics of the dominant diatoms on release from the fast ice influences the diatom species composition and carbon flow under the ice.     

Diatom response to mid-Holocene climate change in Lago di Massaciuccoli (Tuscany,Italy)

A sedimentary sequence from the Mediterranean coastal basin of Lago di Massaciuccoli (Tuscany, Italy) was analyzed for diatoms, covering two periods over the past ca. 7,000 years. The site was selected because it is situated in a sensitive position at the limit between Mediterranean and Central European climates and biomes. Our focus is on the impact of accelerated human activity during the recent past (water uptake in the catchment, sand extraction, wastewater discharge) and on a phase of evident change between 6,600 and 5,400 cal. BP. The diatom record suggests fresh-water conditions and rather high lake levels until ca. 6,000 years ago. The subsequent shift towards brackish conditions peaked at around 5,500 cal. BP. We relate this shift to a pervasive change towards a drier climate that has been observed elsewhere in the Mediterranean and Northern African regions, and stands in contrast to the shift towards a cooler and more humid climate in the nearby Alps (200–350 km distant) and in central Europe. Pollen and charcoal records from a previous study on the same sedimentary sequence were used to gain additional insights about the causes of the changes in the diatom assemblages and apply numerical methods to search for common trends and correlations.     

The hot spring and geyser sinters of El Tatio, Northern Chile

The siliceous sinter deposits of El Tatio geothermal field in northern Chile have been examined petrographically and mineralogically. These sinters consist of amorphous silica (opal-A) deposited around hot springs and geysers from nearly neutral, silica-saturated, sodium chloride waters. Water cooling and evaporation to dryness are the main processes that control the opal-A deposition in both subaqueous and subaerial settings, in close spatial relation to microbial communities. All fingerprints of organisms observed in the studied sinter samples represent microbes and suggest that the microbial community is moderately diverse (cyanobacteria, green bacteria, and diatoms). The most important ecological parameter is the temperature gradient, which is closely related to the observed depositional settings: 1) Geyser setting: water temperature = 70–86 °C (boiling point at El Tatio: 4200 m a.s.l.); coarse laminated sinter macrostructure with rapid local variations; biota comprises non-photosynthetic hyperthermophilic bacteria. 2) Splash areas around geysers: water temperature = 60–75 °C; laminated spicule and column macrostructure, locally forming cupolas (< 30 cm); predominant Synechococcus-like cyanobacteria. 3) Hot spring setting: water temperature = 40–60 °C; laminated spicules and columns and subspherical oncoids characterize the sinter macrostructure; filamentous cyanobacteria Phormidium and diatoms (e.g., Synedra sp.) are the most characteristic microbes. 4) Discharge environments: water temperature = 20–40 °C; sinter composed of laminated spicules and oncoids of varied shape; cyanobacterial mats of Phormidium and Calothrix and diatoms (e.g., Synedra sp.) are abundant. El Tatio is a natural laboratory of great interest because the sedimentary macrostructures and microtextures reflect the geological and biological processes involved in the primary deposition and early diagenesis of siliceous sinters.     

一种淡水水华硅藻——链状弯壳藻(Achnanthidium catenatum)

作为区域重要饮用水源的浙江绍兴汤浦水库于2010年5月期间暴发以硅藻和蓝藻为主的藻类水华.对库尾、库中和坝前3处浮游植物样品进行采集和分析,结果表明,汤浦水库浮游植物密度在1.13×108～1.56×108cells/L之间,水华优势种之一为我国大陆地区首次报道的羽纹纲硅藻———链状弯壳藻(Achnanthidium catenatum),另一种为丝状蓝藻———湖泊假鱼腥藻(Pseudanabaena limnetica),两者的平均相对丰度分别为65.6%和28.2%;链状弯壳藻是弯壳藻属中唯一适应浮游生长的种类,具有独特的带面观,能以壳面相连形成2～3个细胞的短链状群体;对国内外3次链状弯壳藻为优势种的水华案例进行分析,发现该藻为广温性种类,适应低光强和低磷浓度生长;水华生消机理则需进一步研究.