四环藻属(Tetracyclus Ralfs) 中的新化石种和变种 (硅藻门 Bacillariophyta)

描述的四环藻属中的3个新种和3个新变种:辐射四环藻Tetracyclus radiatus, 小四环藻T.minutus,近不连结四环藻椭圆形变种 T.subdivisium ellipticus, 岩生四环藻近盾形变种T.rupestris var.subclypeatus, 塞拉托木四环藻T.celatom var. minor constrictus 和短尖头四环藻T.mucronatus.这些新化石种根据形状、初生肋、次生肋和三生肋的数量,中央胸骨的长度及轴区的形态特征加以区别.新化石种的确立有可能是中国中新世硅藻植物群中的特有种.     

An in situ iron-enrichment experiment in the western subarctic Pacific (SEEDS): Introduction and summary

To test the iron hypothesis in the subarctic Pacific Ocean, an in situ iron-enrichment experiment (SEEDS) was performed in the western subarctic gyre in July–August 2001. About 350 kg of iron (as acidic iron sulfate) and 0.48 mol of the inert chemical tracer sulfur hexafluoride were introduced into a 10-m deep surface mixed layer over an 80 km² area. This single iron infusion raised dissolved iron levels to 2.9 nM initially. Dissolved iron concentrations rapidly decreased after the infusion, but levels remained close to 0.15 nM even at the end of the 14-day experimental period. During SEEDS there were iron-mediated increases in chlorophyll a concentrations (up to 20 μg l⁻¹), primary production rates, biomass and photosynthetic energy conversion efficiency relative to waters outside the iron-enriched patch. The rapid and very high accumulation of phytoplankton biomass in response to the iron addition appeared to be partly attributable to shallow mixed-layer depth and moderate water temperature in the western subarctic Pacific. However, the main reason was a floristic shift to fast-growing centric diatom Chaetoceros debilis, unlike the previous iron-enrichment experiments in the equatorial Pacific and the Southern Ocean, in both of which iron stimulated the growth of pennate diatoms. The iron-mediated blooming of diatoms resulted in a marked consumption of macronutrients and drawdown of pCO₂. Biological and physiological measurements indicate that phytoplankton growth in the patch became both light- and iron-limited, making phytoplankton biomass relatively constant after day 9. The increase in microzooplankton grazing rate after day 9 also influenced the net growth rate of phytoplankton. There was no significant increase in the export flux of carbon to depth during the 14-day occupation of the experimental site. The export flux between day 4 and day 13 was estimated to be only 13% of the integrated primary production in the iron-enriched patch. The major part of the carbon fixed by the diatom bloom remained in the surface mixed layer as biogenic particulate matter. Our findings support the hypothesis that iron limits phytoplankton growth and biomass in a ‘bottom up’ manner in this area, but the fate of algal carbon remains unknown.     

南海晚第四纪的硅藻遗体及其地质意义：Ⅰ.硅藻种类及其生态环境

南海北部和中部三个晚第四纪柱样沉积物中，鉴定出硅藻５６属１９３种和变种。其中，相对含量大于１０％的硅藻种有１５种，相对含量５％－１０％的种有９种，相对含量１％－５％的种有４１种，依据硅藻的地理分布，确定了其中１８种常见硅藻的生态环境。     

Phytoplankton assemblages in the CoOP-WEST coastal upwelling area

Elevated levels of phytoplankton were observed at the Northern California coastal upwelling ecosystem studied as part of the CoOP-WEST project during monthly summer surveys in 2000, 2001 and 2002. The high concentrations of chlorophyll were made up mostly of larger cells; the phytoplankton communities that resulted were dominated by centric diatoms. The highest chlorophyll a concentrations were observed when large diatoms or small colony-forming species dominated the assemblages. In contrast, when smaller nano-flagellates and picoplankton were dominant, total chlorophyll a concentrations were over four or five-fold lower than when diatoms were prevalent, illustrating the importance of large diatoms to total phytoplankton biomass. Each year, when chlorophyll concentrations were greatest, Chaetoceros species created a Chaetoceros-dominated system. A few other genera contributed to the upwelling diatom community, mostly the centric diatoms Asterionella, Thalassiosira, Rhizosolenia (including Guinardia and Proboscia), and the pennate Nitzschia. These diatoms have been described in other coastal upwelling ecosystems, and at this study site form a functional group that are apparently well adapted to the high-nutrient, turbulent conditions that are typical of these coastal regions.     

南海晚第四纪的硅藻遗体及其地质意义──Ⅲ.南海北部深海平原边部KL29剖面的硅藻组合

南海北部深海平原边部KL29柱样中共鉴定出硅藻169种和变种，隶属于53属。依据硅藻种类的含量变化，自下而上划分为三个硅藻带。其中，Ⅰ带划分出5个亚带，Ⅱ带划分出8个亚带。文中讨论了各硅藻带的古温度和古地理条件，并依据结节圆筛藻壳体大小的比值变化，确定出该柱样的地质年代：Ⅲ带属于全新世沉积，Ⅱ、Ⅰ带均属于晚更新世的沉积。     

Influence of microfossils and pyrites on the behaviour of oceanbed sediments

An attempt has been made to investigate the microfabric and mineralogical features of marine sediments collected from the north-east coastal region of Singapore. A limited laboratory studies on shear strength, consolidation and chemical analysis were carried out to examine the geotechnical characteristics of marine sediments. Emphasis has been focussed on the microfabric aspects of microfossils (diatom) and pyrite, and their influence on the soil properties. Test results indicated the predominant presence of microfossils (diatom) and pyrite, and their impact on the marine sediments behaviour has been discussed briefly. The abundant presence of microfossils results in an increase in strength, compressibility and hydraulic conductivity due to the presence of large voids between the skeleton structures.     

Responses of the chaetognath, Sagitta elegans, and larval Pacific hake, Merluccius productus, to spring diatom and copepod blooms in a temperate fjord (Dabob Bay, Washington)

As part of a broader field study examining the potentially deleterious effects of diatoms on planktonic food webs, we examined the abundance, stage composition, diet, and feeding success of the chaetognath, Sagitta elegans, and the abundance and morphometric condition of larval Pacific hake, Merluccius productus. Our objective was to look for a relationship between spring phytoplankton blooms and planktonic predators, as mediated by their copepod prey, with special reference to possible deleterious effects of diatoms. Zooplankton were collected weekly during February–May and in mid-summer of 2002 and 2003 in Dabob Bay, Washington State, USA. S. elegans abundance was high in summer of both years and was higher in spring 2003 than spring 2002. Larval chaetognaths dominated the population in early spring and remained present throughout sampling. S. elegans consumed mostly copepods. The abundance of larval S. elegans was correlated with the abundance of copepodites, although no relationship between chaetognath feeding success and prey abundance was found. Larval Pacific hake abundance was high (1200 larvae per square meter) in late February and early March of 2002 and 2003 and decreased rapidly in late spring. The morphometric condition of M. productus was not significantly related to copepod abundance. These results indicate that any deleterious effects of diatoms on copepod abundance, at the scale seen during spring 2002 and 2003 in Dabob Bay, did not greatly affect the next higher trophic level.     

Paleohydrology of Lake Nhaucati (southern Mozambique), ∼400 AD to present

This paper investigates the correlations between lake level change, rainfall variability and general atmospheric forcing in southern Africa. The analysis of fossil diatom assemblages in a sediment sequence from the small, rain-fed Lake Nhaucati, southern Mozambique, is presented and discussed in relation to regional palaeoclimate data. The accumulation of organic sediments in Lake Nhaucati began 1,600 years ago when the lake level was rising. Lithology and pollen suggest a low stand at 800 AD, which correlates with other climate proxies from the summer rainfall region of southern Africa. The diatom assemblage suggests that lake levels were high between 900 and 1300 AD, with shorter low stands at c.1100 and 1200 AD. The period after 1400 AD was marked by a slow rate of accumulation and consequently a low temporal resolution. The correlation with other climate proxies in the summer rainfall region, written sources, and pollen data suggests repeated droughts corresponding to the Little Ice Age, though the driest periods may have caused complete desiccation of the lake. Higher lake levels are suggested after 1800 AD, though written sources suggest droughts in the beginning of the twentieth century. The analysis shows a good correlation with palaeoclimate data from the summer rainfall region and confirms the presence of an anti-phase relationship between the summer rainfall region of southern Africa and the bi-modal rainfall region of east tropical Africa. It also supports the general hypothesis that variation in the intensity of the Inter Tropical Convergence Zone is the main agent modulating rainfall over southern and eastern Africa on centennial timescales.     

Impact of multispecies diatom bloom on plankton community structure in Sundarban mangrove wetland,India

A multispecies bloom caused by the centric diatoms, viz. Coscinodiscus radiatus, Chaetoceros lorenzianus and the pennate diatom Thalassiothrix frauenfeldii was investigated in the context of its impact on phytoplankton and microzooplankton (the loricate ciliate tintinnids) in the coastal regions of Sagar Island, the western part of Sundarban mangrove wetland, India. Both number (15–18 species) and cell densities (12.3 × 10³ cells l⁻¹ to 11.4 × 10⁵ cells l⁻¹) of phytoplankton species increased during peak bloom phase, exhibiting moderately high species diversity (H′ = 2.86), richness (R′ = 6.38) and evenness (E′ = 0.80). The diatom bloom, which existed for a week, had a negative impact on the tintinnid community in terms of drastic changes in species diversity index (1.09–0.004) and population density (582.5 × 10³ to 50 × 10³ ind m⁻³). The bloom is suggested to have been driven by the aquaculture activities and river effluents resulting high nutrient concentrations in this region. An attempt has been made to correlate the satellite remote sensing-derived information to the bloom conditions. MODIS-Aqua derived chlorophyll maps have been interpreted.     

Separating wheat from chaff: Diatom taxon selection usingan artificial neural network pruning algorithm

This study addresses the question of what diatom taxa to includein a modern calibration set based on their relative contribution in apalaeolimnological calibration model. Using a pruning algorithm for ArtificialNeural Networks (ANNs) which determines the functionality of individual taxa interms of model performance, we pruned the Surface Water Acidification Project(SWAP) pH-diatom data-set until the predictive performance of thepruned set (as assessed by a jackknifing procedure) was statistically differentfrom the initial full-set. Our results, based on the validation at each5% data-set reduction, show that (i) 85% of the taxa canbe removed without any effect on the pH model calibration performance, and (ii)that the complexity and the dimensionality reduction of the model by theremoval of these non-essential or redundant taxa greatly improve therobustness of the calibration. A comparison between the commonly usedmarginal criteria for inclusion (species tolerance andHill's N2) and our functionality criterion shows that the importance ofeach taxon in an ANN palaeolimnological model calibration does not appear todepend on these marginal characteristics.