Reanalysis of principal component analysis to resume past vegetation and environment

In the paper 11 pollen types were selected from the original pollen and spore records of 54 samples in Fenzhuang profile of Beijing region, then 54 × 11 matrix was set up. Based on the pollen data of Fenzhuang profile from the Late Pleistocene to the Early Holocene, the paper gives a further analysis to subdivide zone of the pollen assemblages and changes of paleovegetation and paleoenvironment in this area using principal component analysis (PCA). PCA can play an complementary role for subdividing zone, at the same time, it can eliminate the difference to subdivide zone of the pollen assemblages caused by artificial factors. Finally to the biodiversity in plant communities and complex geographical environment in Beijing region, using great dispersal of accumulative percent of total in PCA (for cumulative rate only 57% from the first three factors of PCA), may sufficiently correspond to the environmental characteristic, so as to recover past climate condition much better. Supported by National Natural Science Foundation of China (No. 49571066, 39470132).     

辽宁本溪中三叠世苏铁类密脉中国似查米亚

中国似查米亚属Sinozamites Sze是中国北方中、晚三叠世苏铁植物门Cycadophyta代表成分之一.自该属发现以来,该属在分类上属于苏铁目还是本内苏铁目一直不清楚.本文对产于辽宁本溪中三叠世林家组的密脉中国似查米亚S.myrioneurus表皮构造进行了研究.由于标本未保留角质层,故选择超景深显技术,发现该属气孔器属于单唇型,从而确立了该属植物属于苏铁目.研究过程中,既用盐酸又用硝酸来清除化石表面杂质.另根据已有的标本所显示的裂片和羽轴上下过渡关系,对该种羽片进行了部分重建.在此基础上,系统比较了类似的苏铁植物.     

High concentrations of exopolymeric substances in Arctic winter sea ice: implications for the polar ocean carbon cycle and cryoprotection of diatoms

Exopolymeric substances (EPS) produced by microorganisms play important roles in various aquatic, porous, and extreme environments. Only recently has their occurrence in sea ice been considered. We used macroscopic and microscopic approaches to study the content and possible ecological role of EPS in wintertime fast ice near Barrow, Alaska (71°20′ N, 156°40′ W). Using Alcian blue staining of melted ice samples, we observed high concentrations of EPS in all samples examined, ranging from 0.79 to 7.71 mg xanthan gum equivalents (XGEQV) l⁻¹. Areal conversions to carbon equivalents yielded 1.5−1.9 g C m⁻² ice in March and 3.3−4.0 g C m⁻² in May (when the ice was thicker). Although EPS did not correlate with macronutrient or pigment data, the latter analyses indicated ongoing or recent biological activity in the ice within temperature horizons of −11°C to −9°C and warmer. EPS correlated positively with bacterial abundance (although no functional relationship could be deduced) and with dissolved organic carbon (DOC) concentrations. Ratios of EPS/DOC decreased at colder temperatures within the core, arguing against physical conversion of DOC to EPS during freezing. When sea-ice segments were maintained at representative winter temperatures (−5°C,−15°C and −25°C) for 3−14 months, the total EPS content increased significantly at rates of 5−47 μg XGEQV l⁻¹ d⁻¹, similar to published rates of EPS production by diatoms. Microscopic images of ice-core sections at these very cold temperatures, using a recently developed non-invasive method, revealed diatoms sequestered in spacious brine pockets, intact autofluorescent chloroplasts in 47% of the (pennate) diatoms observed, and indications of mucus in diatom-containing pores. The high concentrations of EPS detected in these winter ice cores represent a previously unrecognized form of organic matter that may contribute significantly to polar ocean carbon cycles, not only within the ice but after springtime release into the water column. The EPS present in very high concentrations in the brine of these microhabitats appear to play important buffering and cryoprotectant roles for microorganisms, especially diatoms, against harsh winter conditions of high salinity and potential ice-crystal damage.     

Constraining the dating of late Quaternary marine sediment records from the Scotia Sea (Southern Ocean)

In Southern Ocean sediments south of the Antarctic Polar Front, the scarcity of calcareous microfossils hampers the development of sediment chronologies based on radiocarbon dating and oxygen isotope stratigraphy established from carbonate. In this study, radiometric dating, magnetic susceptibility (MS), biogenic opal content, diatom abundance fluctuation, and paleomagnetic information were investigated on a north–south transect of central Scotia Sea sediment cores to verify their reliability as stratigraphic tools in the study area. Radiocarbon dating on organic carbon humic acid fraction can be used to establish the stratigraphy of upper core sections, but regional comparison and correlation are needed to verify a possible bias by fossil carbon contamination. For the long-term stratigraphy, MS, which can be correlated to the Antarctic ice core dust/climate signal, represents the most valuable parameter. Fine-grained single domain magnetite, probably of biogenic origin, makes a significant contribution to the interglacial MS signal, while major contributions from detrital material affect the glacial MS record. The core from the southern Scotia Sea contains significant proportions of biogenic magnetite also in glacial sediments, suggesting depositional environments different from those of the northern Scotia Sea. Our data suggest low contributions of high-coercive minerals to the overall magnetic intensity of glacial and interglacial Scotia Sea sediments, which excludes dust as a main source of the magnetic signal. Opal content can be used to distinguish between cold and warm intervals for the past 300 thousand years. Abundance fluctuation patterns of diatom species Fragilariopsis kerguelensis and Eucampia antarctica are useful stratigraphic tools for periods back to Marine Isotope Stage (MIS) 6. The Mono Lake geomagnetic excursion is identified in Scotia Sea sediments for the first time. Possible correlations of ash layers are suggested between Scotia Sea sediments and East Antarctic ice cores. They have potential to serve as additional age markers for further studies in this area.     

华北板块北缘中二叠统于家北沟组植物化石及其大地构造意义

通过对内蒙古赤峰市广兴源乡于家北沟组模式剖面植物化石和安山质晶屑岩屑凝灰岩锆石U-Pb同位素年代学的研究,结合动物化石的分析,确认于家北沟组地质时代为中二叠世。于家北沟组植物化石以Gigantonoclea hallei Asama、Fascipteris sinensis Stockm. et Math.、Pecopteris taiyuanensis Halle、Pterophyllum daihoense Kaw.等众多华夏植物群典型分子为特征,属于典型的华夏植物群。目前,在中二叠世植物群中,从未发现有华夏和安加拉两大植物群的混生现象,这一事实进一步表明,中二叠世横亘于华北板块和佳蒙地块之间的古亚洲洋尚未闭合,在植物地理分布上起着重要的阻隔作用。     

Sedimentary diatoms along a temporal and spatial gradient of metal contamination

We examined changes at the community and population level of sedimentary diatoms over a wide temporal and spatial gradient of metal pollution encountered in cores from three lakes in the Abitibi mining region (Québec, Canada). Diatom communities on the whole appeared to be very tolerant of metal contamination, as shown by diatom cell accumulation rates decreasing only under the most severe conditions of contamination, which were found from the 1930s to the 1980s in Lac Dufault (cadmium, up to 94 μg/g dry sediment; Cu, up to 8600 μg/g; Zn, up to 9000 μg/g). Under the moderate conditions of contamination observed in the other two lakes and in the most recent sediment of Lac Dufault, diatom cell accumulation rates tended to increase over values typical of the pre-mining period. However, there were increasing rearrangements of the community composition along the contamination gradient. Under moderate metal enrichment, the diatom community of Lac Vaudray experienced only subtle changes, with Cyclotella stelligera, albeit decreasing, remaining the dominant taxon. In the intermediately contaminated Lac Caron, several benthic taxa, noticeably Cymbella silesiaca and several Fragilaria species, rose in taxonomic importance. The most extreme contamination observed in Lac Dufault led to a severely impoverished community almost entirely represented by Achnanthes minutissima and Brachysira vitrea. With increasing levels of contamination, there was a shift from planktonic to benthic taxa and morphotypes and a consistent decrease in the siliceous stomatocysts/diatom frustules ratio. These trends suggest that littoral zones may represent an important refugium under conditions of high contamination. Responses to metal stress were in general more evident at the population than at the community level. Cyclotella stelligera and B. vitrea had a consistent negative and positive response, respectively, along the gradient and are the most promising indicators of metal pollution for this region.     

中国吉林大拉子组的时代探讨

大拉子组是我国东北地区早白垩世的典型层位,但该组的具体地质年代一直存在不同的看法。根据最近发现的植物化石材料,通过对大拉子组被子植物优势属的地质分布以及与国内外被子植物群的对比研究,发现大拉子组与北美Potomac带B中部的被子植物群较为相似,结合孢粉、昆虫、叶肢介、介形虫及鱼化石等其他生物化石证据,认为吉林大拉子组的地质时代很可能为阿尔必中期或晚期。     

内蒙古短花针茅草原种子植物区系研究

对短花针茅草原种子植物科、属、种的区系特征进行了统计分析,结果表明：①研究区共统计种子植物31科,96属,161种,并集中分布在几个大科,区系的优势现象明显;②属种比为1∶1.68,较内蒙古自治区、全国及全世界均低,物种分化程度低;③植物区系组成具有明显的温带性质,但与热带植物区系也存在一定的亲缘关系,具有过渡性;④植物区系组成以年轻成分为主,兼有古老性;⑤植物生活型特征表明本区多年生草本植物占绝对优势,表现出草原植物群落种类组成的特征,但由于该区土壤覆沙或沙质化明显,因此,灌木和半灌木种类也较多;⑥植物水分生态类群以旱生为主,非旱生也占有很大比例,具有明显的过渡性;⑦该生态系统比较脆弱,应加强保护,合理利用,实现可持续性发展。     

Temporal variation in community–environment relationships and stream classifications in benthic diatoms: Implications for bioassessment

Diatom based biomonitoring tools are proven to be a practical way to indicate stream conditions, but only little is known how stable diatom inferred stream classifications are in time. We studied annual variation in diatom community–environment relationships, community structure and diatom indices (Index of Pollution Sensitivity, IPS and Trophic Diatom Index, TDI) during three consecutive years (2010–2012) in four drainage basins distributed in Finland. We also used a cluster analysis to examine if stream classifications resulted in distinct and temporally stable community types. We found only subtle temporal variation in community–environment relationships, nutrient concentrations (N, P) and conductivity consistently being the main factors structuring communities. According to Mantel tests, diatom communities resembled each other significantly at different years, and the values of IPS and TDI indices remained relatively stable in the basins through time. The stream classification based on diatoms also resulted in temporally stable and statistically distinct community types. We thus suggest that sampling of diatoms, e.g., in every three years seems to be a reliable procedure to assess biological water quality. Generally, to choose the correct metrics to assess water quality is essential, and both biological and physicochemical factors should be considered.     

山东五图含煤岩系孢粉组合及其地层意义

对五图组含煤岩系进行研究 ,所揭示的孢粉植物群中 ,被子植物榆粉 (Dlmipollenites)和栎粉 (Quercoidites)有很高的含量 ,此外有山核桃粉 (Caryapollenites)、朴粉 (Celtipollenites)、枫杨粉 (Pterocaryapollenites)、胡桃粉(Juglanspollenites)、桦粉 (Betulaepollenites)、苗榆粉 (Ostryoipollenites)、枥粉 (Carpinipites)和小栗粉 (Cupuliferoipollenites)等 ,其中热带、亚热带分子占很大的比重 ,且有很高的分异度 ;裸子植物含量不高 ,主要为松粉(Pinuspollenites)和云杉粉 (Piceaepollenites) ,其次为杉粉 (Taxodiaceaepollenites)和麻黄粉 (Ephedripites) ;蕨类孢子一般含量较少 ,仅在部分样品中三角孢 (Deltoidospora)含量很高。在参考沉积、古气候、海平面变化以及其他门类化石资料的基础上 ,对孢粉化石群的时代归属及我国东部区域相关问题作了讨论 ,得出五图组孢粉组合特征与其他古生物资料所得的时代意见一致 ,属早始新世晚期到中始新世早期 ,其古气候特征也与全球海洋气候特征相符合。