Biomarker reconstruction of phytoplankton productivity and community structure changes in the middle Okinawa Trough during the last 15 ka

Biomarkers have been widely used to reconstruct phytoplankton productivity and community structure changes, and this method has been applied for the first time in the middle Okinawa Trough during the transition from the last deglaciation to the Holocene. The total content of all marine phytoplankton biomarkers, used as a total productivity indicator, reveals higher productivity during the deglaciation. The ratios of the biomarkers are used as community structure indicators which show that, compared with the Holocene, the contribution from haptophytes decreased while the contributions from diatoms and dinoflagellates increased during the deglaciation. The increased productivity during the deglaciation was likely caused by the stronger winter monsoon. Also increased nutrient supply from terrestrial sources contributes to the higher productivity due to lower sea-level, which is consistent with higher terrestrial biomarker （long-chain n-alkanols） content. These changes in the nutrient supply also con- tributed to the community structure changes in the Okinawa Trough.     

Using quantile regression to analyze the stressor–response relationships between nutrient levels and algal biomass in three shallow lakes of the Lake Taihu Basin,China

Understanding the stressor–response relationship between nutrient levels and algal biomass is a prerequisite for the management of eutrophication in lakes. In this study, a quantile regression(QR) approach was used to interpret the stressor–response relationships between nutrient(e.g., phosphorus, nitrogen) concentrations and algal biomass as measured by chlorophyll-a(Chl-a) levels. QR results indicated that Lake Dianshan and Lake Changdang,which are both heavily eutrophicated, were P-limited only.In contrast, Lake Kuilei, which has significantly lower nutrient levels and algal biomass than the other two lakes,was P- and N-limited. Moreover, in Lake Kuilei, N and P levels had significant interaction effects on the algal biomass at the upper quantiles(s [ 0.68). The degree to which the lakes were P-limited increased with rises in the mean total P concentration in the lakes. QR has many advantages over ordinary least squares regression for discriminating limiting factors and, in particular, allows us to estimate changes near the upper extremes of distributions associated with limiting factors. QR is adapted to more specialized risk management problems, such as early warnings of the risk of algal blooms.The probable value-at-risk of harmful algal blooms for Lake Kuilei, Lake Dianshan and Lake Changdang is s = 0.76(Chl-a = 9 mg/m3), s = 0.87(Chl-a = 24 mg/m3) and s = 0.72(Chl-a = 35 mg/m3), respectively. Given the results of the stressor–response relationship analysis, we conclude that reductions in P input represent the most feasible and least costly approach for managing eutrophication in the shallow lakes of the Lake Taihu Basin. To control the magnitude and duration of algal blooms in shallow lakes,reductions in P and N inputs are required. The 95 % CI bounds of slopes indicated that the interactions of nonnutrient factors with nutrients had strong impacts on the algal biomass in lightly eutrophicated Lake Kuilei. It is suggested that, in addition to reductions in nutrient loads,several ecological measures, such as an increase in the biomass of submerged macrophytes and the reduction of hydraulic retention time by flushing, could represent important components of an integrated approach to eutrophication management in the Lake Taihu Basin.     

Seasonal variation of size-fractionated phytoplankton in the Pearl River estuary

To investigate the dynamics of phytoplankton size structure in the Pearl River estuary, concentrations of size-fractionated chlorophyll a (Chl a) were determined during four cruises carried out in 2008 and 2010. The distribution of Chl a in this geographical location showed a high degree of temporal variation. Chl a concentrations were highest in autumn, approximately three times higher than those in summer and winter. Microphytoplankton was the dominant contributor, accounting for 66.9% of the Chl a concentration in autumn 2008. In summer and spring 2008, nano-sized cells dominated the phytoplankton population throughout the study region. During the winter cruise, two different areas of water were found, characterized by (1) low salinity and high nutrient content and (2) high salinity and low nutrient content; nano- and picophytoplankton co-dominated the first area, while microphytoplankton dominated the second. It is arguable that grazing could have played a role in determining phytoplankton community size structure in winter. Nutrient concentrations were assumed not to limit phytoplankton growth during the investigation period. Size-differential capacity in competing for the resources available under different hydrodynamic conditions seemed to be the major factor in determining seasonal variation in the structure of the phytoplankton communities. High N:P ratios in the Pearl River estuary had major implications for nutrient pollution control. Our results indicated that studies of phytoplankton size structure provide greater insight into phytoplankton dynamics and are necessary to better manage water quality in the Pearl River estuary.     

The biogeochemical behavior of dissolved aluminum in the southern Yellow Sea: Influence of the spring phytoplankton bloom

Many recent studies have investigated the nutrient-type profiles of dissolved aluminum(Al) in the ocean.Significant scavenging of dissolved Al can occur during phytoplankton blooms,but the mechanism remains unclear.The distribution of dissolved Al in the southern Yellow Sea(SYS) was investigated in winter and spring 2009.Following measurements at grid stations during the spring sampling cruise,two drifting anchor surveys of more than 100 h were conducted to trace the variation of dissolved Al concentration during the spring phytoplankton bloom(SPB).The concentration of dissolved Al in the SYS decreased from 40 nmol/L in February to 30 nmol/L in March and 10-20 nmol/L in April,while the concentration of Chl a increased from < 2 μg/L in March to > 4 μg/L in April.The concentration of dissolved Al in the SYS decreased significantly with the development of the phytoplankton bloom,which indicated biological scavenging of dissolved Al from water column.The proportion of dissolved Al scavenged from water column by different phytoplankton species differed at the two drifting stations,with greater removal efficiency demonstrated by diatoms than dinoflagellates.Phytoplankton samples collected from the Chl a maximum layer were washed with trace metal clean reagent(oxalate-EDTA-citrate,abbreviate as oxalate solution,Tovar-Sanchez et al.,2003) to enable the surface-scavenged(extracellular) and intracellular Al pools associated with phytoplankton to be differentiated.Thirty-nine to ninetysix percent of the total Al was found to be existed in the interior pools,which indicated that biological absorption was the important way to scavenge dissolved Al during phytoplankton blooms in the SYS.     

Dynamic control on grain-size distribution of terrigenous sediments in the western South China Sea: Implication for East Asian monsoon evolution

High-resolution oxygen isotope stratigraphy of Core MD05-2901, which is located off eastern Vietnam in the western South China Sea （SCS）, was established and indicated that the core spans a time period of the past 450 ka. Based on the bulk density, fractional porosity and lithogenic content of the sediments, terrigenous mass accumulation rate （TMAR） was obtained, which is 4.9-6.0 g cm^-2 ka^-1 on average during interglacial stages, higher than that during glacial stages, i.e. 1.9-5.0 g cm^-2 ka^-1, which is different from northern and southern SCS which show higher TMAR in glacial stages. By principle component analysis of grain size distribution of all the samples, two main control factors （F1 and F2） were obtained, which are responsible for about 80% variance of granularity. The contents of grain size population 1.26-2.66 μm% and 10.8-14.3 μm% which are sensible to F1 show high-frequency fluctuation, and correlate well with the summer insolation at 15^o N. They exhibit a distinct cyclicity with frequencies near 23 ka and 13 ka, in contrast to a strong frequency peak near 100 ka obtained in proxies 4.24-7.42 μm% and 30.1-43.7 μm% controlled mainly by F2. The sedimentary character of this part of the SCS was controlled by variations of input flux from two main source areas, namely the southwest and north SCS, which were transported by different circulations of surface current forced by East Asian summer monsoon and winter monsoon respectively. We believe that the East Asian summer monsoon has fluctuated with high frequency and been forced by changes in solar insolation in low latitude associated with precession and half precession, while ice-volume forcing is probably a primary factor in determining the strength and timing of the East Asian winter monsoon but with less important insolation forcing.     

Dynamic of Grassland Biomass in Different Degenerative Stages

The dynamics of plant community and above- and belowground biomass of the different degenerative stages was researched of Kobresia hurnlis meadows of Nakchu prefecture in Tibet Autonomous Region. The results indicated that the aggravation of the degree of deterioration of alpine meadow is, the lower the vegetation coverage, percentage of excellent forage, and biodiversity are. The total aboveground biomass is highest in the lightly degraded stages while it is lowest in the extremely degraded stages. With the aggravation of degradation, the aboveground biomass of forbs increases while that of Cyperaceae decreases. We found that the belowground biomass was mostly distributed in the 0-10 cm soil depth in the alpine meadow with a ＂T＂-shape distribution feature, and with the acceleration of deterioration, the numbers of roots becomes less and less. Meanwhile, the above- and belowground biomass of the different degraded communities was significantly correlated（r= 0. 963）. There is an obvious positive correlation with the above- and belowground biomass in different degenerative stages, and their ratio increased with the aggravation of degradation.     

Spectral absorption coefficient of phytoplankton and its relation to chlorophyll a and remote sensing reflectance in coastal waters of southern China

The spectral absorption coefficient of phytoplankton in coastal waters of southern China is investigated. Large variations in the absorption coefficient of phytoplankton are found. The absorption coefficient of phytoplankton at 443 nm ranged from 0. 006 m- 1 to 0. 484 m - 1, with an average value of 0. 067 m - 1. The chlorophyll-specific absorption coefficient of phytoplankton is also a bio-optical varito pigment composition of phytoplankton and package effect. The chlorophyll-specific absorption coefficient of phytoplankton decreases with the increasing of chlorophyll a concentration. This relationship can be described by a power law function, with the parameters and the coefficient of determination r2 as functions of wavelength, but the parameters describing the relationships in present study differed from that in Case 1 waters, thus the regional adjustment of model parameters was of particular significance for improving the accuracy of bio-optical algorithms for estimation of Chl-a concentration and primary production from remotely sensed data. Regression analysis of reflectance (R rs) ratio and absorption coefficient of phytoplankton (a ph) indicates a close correlation between them, which means that it is possible to retrieve absorption coefficient of phytoplankton using ocean color remote sensing data in optically complex coastal waters.     

Evolution of the South China Sea and monsoon history revealed in deep-sea records

As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropale-ontology, pollen and other analyses, was adopted for reconstructing the evolutionary history of the East Asian monsoon, which was characterized by a series of paleo-climate events especially at 8, 3.2, 2.2 and 0.4 Ma. The new record indicates similar stages in the development of the East and South Asian monsoons, with an enhanced winter monsoon over East Asia being the major difference. The rich spectrums of monsoon variability from the southern SCS also reveal other characteristic features of the low latitude ocean. Evidence for the evolution of the SCS includes the hemipelagic Oligocene sediments, implying the existence of deep water environments during the early seafloor spreading stage of the SCS basin. The four major unconformities and some remarkabl ediagenetic features in upper Oligocene deposits indicate the strongest tectonic events in the region. From a careful comparison of lithologies and sedimentation rates, we conclude that the prominent differences in sedimentary environments between the southern and northern SCS were established only by ～3 Ma.     

Simulation or meridional overturning in the upper layer of the South China Sea with an idealized bottom topography

The large-scale upper circulations and meridional overturning in the upper layer of the South China Sea (SCS) with idealized bottom topography in winter and summer are investigated. Simulations with the GFDL general circulation model are carried out under the conditions of open or enclosed boundary regarding transport in the Luzon Strait. The intrusion area of Kuroshio, its impact on the meridional overturning in the upper layer of the SCS and seasonal characteristic of this impact are explored, respectively. The model is forced by climatological wind stress and relaxed to monthly mean climatological temperature and salinity. The resultant meridional overturning is non-enclosed, wit htransporting from north to south in the surface and returning to north at the depth of about 500 m in winter, about 200 m in summer, with amplitudes of 10^5 m^3/s. It shows the transporting path of intermediate water of the SCS and offers an idealized reference for further study on dynamics of wind-driven and thermohaline circulation of the SCS.     

The coral grayness in northern South China Sea and its description of interdecadal variation of precipitation in south China

The interdecadal variation of coral grayness in northern South China Sea （SCS） is studied using the annual mean coral grayness in northern SCS from 1789 to 1992 and annual precipitation at Guangzhou from 1908 to 1992 by Singular Spectrum Analysis （SSA）, correlation analysis, Mann-Kendalrs abrupt change analysis and composite analysis. The interdecadal variation of south China precipitation as reflected by the series of Guangzhou precipitation rebuilt with the coral grayness is discussed. The results show that the variation of coral grayness in SCS has significant terms of tendency, much-weighted interdecadal variation and weak interannual variation. There was a century-scale abrupt change of coral grayness at the end of the 1880s that changed from positive anomalies to negative anomalies. The global field of SST difference corresponding to the point of abrupt change was negative anomalies over the SCS and neighboring northern Indian Ocean, most of central and western Pacific Ocean and coastal areas of the northern Atlantic Ocean. The large-scale distribution of SST anomalies is concomitant with the century-scale abrupt change of coral grayness in SCS. Negative correlation exists between the coral grayness in SCS and precipitation in Guangzhou on the interdecadal scale and the interdecadal precipitation in Guangzhou as reflected by the interdecadal data of SCS coral grayness shows that the interdecadal variation of south China precipitation changes significantly from phase to phase. The current study aims at contributing in the effort of identifying alternative indexes for climate change in south China on the interdecadal scale and beyond.     

A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization

Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the 'iron hypothesis'. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction.     

夏季东海陆架浮游植物类群结构对不同风场条件的响应分析

为探讨东海的主要物理过程对浮游植物生物量和类群结构的时空分布影响,采用高效液相色谱法分析2006年和2011年夏季东海陆架条件下的浮游植物光合色素的组成及含量,并通过CHEMTAX对浮游植物群落的结构进行分析。结果表明,不同风场条件下东海浮游植物生物量和类群结构均有显著差异。在2006年夏季航次,受弱西北风的控制,长江冲淡水向外延伸面积较大,东海陆架叶绿素a的平均浓度为1 228.6ng/L,主要特征光合色素多甲藻素(Peri)、19-己酰基氧化岩藻黄素(19-hex)、19-丁酰基氧化岩藻黄素(19-but)、玉米黄素(Zea)和二乙烯基叶绿素a(DV-Chl.a)相对较高,浮游植物以硅藻(41%)和甲藻(16%)为主要优势类群;2011年夏季航次,受强东南风影响,底层低温高盐水涌升现象明显,东海陆架叶绿素a(Chl.a)的平均浓度(2 677.9ng/L)比2006年高一倍,叶绿素b(Chlb.)、青绿藻素(Prasino)、新黄素(Neo)和别藻黄素(Allo)等光合色素浓度相对较高,硅藻(60%)在浮游植物群落中占主要优势。     

淀山湖浮游植物群落时空分布动态初步研究

为了解淀山湖浮游植物群落时空变化特点,于2008年10月至2009年9月对淀山湖浮游植物进行四季调查.调查发现浮游植物8门126属384种,群落组成以绿藻、隐藻、蓝藻和硅藻为主,尖尾蓝隐藻(Chroomonas acuta Uterm)和小球藻(Chlorella vulgaris Beij)为淀山湖全年主要优势种,微囊藻属(Microcystis)藻类为夏季主要优势种之一.浮游植物平均密度为4.01×10~6cells·L~(-1),且夏季春季冬季秋季.浮游植物Shannon-Wiener,Margalef和Pielou指数分别在0.31～1.59,2.22～7.98和0.17～0.82之间波动,指示淀山湖浮游植物多样性和均匀度较好.通过聚类分析法将淀山湖浮游植物分为4个主要类群:类群Ⅰ位于中部及西南部(S3,S6,S7)区域,类群Ⅱ为湖东-东南(S1,S2)区域,类群Ⅲ为湖北-湖西(S4,S5)区域,类群Ⅳ为S,类群间差异与种群密度及优势种不同有关.根据历史调查资料,分析了淀山湖浮游植物群落结构长期变化情况,为淀山湖富营养化防治提供依据.     

上海城区小型河道生物组成特征及食物链结构分析

2007年11月-2008年10月对上海市城区4条小型河道(曹杨环浜、午潮港、横港和朝阳河)中的生物组成进行了调查分析.结果共鉴得浮游植物268种,浮游动物157种,大型底栖动物21种,高等植物10种,鱼类13种.浮游植物包括绿、裸、硅、蓝、黄、隐、甲和金藻8个类群,其中以绿、裸、硅和蓝藻数量最多;浮游动物中原生动物、轮虫、枝角类和桡足类分别为94种(不含植鞭毛虫)、44种、13种和6种;底栖动物中软体动物14种,环节动物3种,甲壳动物和水生昆虫幼体各2种;鱼类包括7科,分别为鲤科、鳉科、塘鳢科、斗鱼科、(?)虎鱼科、鳢科和合鳃鱼科,其中鲤科最为丰富,占全部鱼种的53.8%;高等植物包括沉水植物4种、挺水植物4种及浮叶植物2种.曹杨环浜的浮游植物、浮游动物、底栖动物、鱼类和高等植物的种类均最为丰富,且浮游植物和鱼类的组成较均一,无明显优势种,高等植被密度大,以沉水植物为主;横港浮游生物种类最少,脊椎动物仅见外来小型鱼类食蚊鱼,高等植物则以挺水植物为主,分布区域较为集中;午潮港和朝阳河的浮游植物以蓝绿藻为优势种,高等植物分别仅1和2种,且密度小、覆盖率低.4条河道的生物食物链结构都趋于简单化,且能量输出方式较为单一.鉴于上述情况,建议在今后的生态修复中要因河道而异,适当改善底栖动物、鱼类和水生高等植物的组成结构,增加物种丰富度,促进食物链结构复杂化.     

茅尾海富营养化程度及其对浮游植物生物量的影响

于2003～2010年每年的枯水季(1～3月)、丰水季(6～8月)和平水季(10～11月)对茅尾海每年3期共22次表层海水取样,调查无机氮、磷酸盐、化学需氧量及浮游植物叶绿素a的变化,用富营养化指数评价该海域的富营养化程度,并分析营养化程度对浮游植物生物量的影响.结果发现,茅尾海无机氮、磷酸盐和化学需氧量均显上升的趋势...     

High bacterivory by the smallest phytoplankton in the North Atlantic Ocean

Planktonic algae <5 m in size are major fixers of inorganic carbon in the ocean. They dominate phytoplankton biomass in post-bloom, stratified oceanic temperate waters. Traditionally, large and small algae are viewed as having a critical growth dependence on inorganic nutrients, which the latter can better acquire at lower ambient concentrations owing to their higher surface area to volume ratios. Nonetheless, recent phosphate tracer experiments in the oligotrophic ocean have suggested that small algae obtain inorganic phosphate indirectly, possibly through feeding on bacterioplankton. There have been numerous microscopy-based studies of algae feeding mixotrophically in the laboratory and field as well as mathematical modelling of the ecological importance of mixotrophy. However, because of methodological limitations there has not been a direct comparison of obligate heterotrophic and mixotrophic bacterivory. Here we present direct evidence that small algae carry out 40-95% of the bacterivory in the euphotic layer of the temperate North Atlantic Ocean in summer. A similar range of 37-70% was determined in the surface waters of the tropical North-East Atlantic Ocean, suggesting the global significance of mixotrophy. This finding reveals that even the smallest algae have less dependence on dissolved inorganic nutrients than previously thought, obtaining a quarter of their biomass from bacterivory. This has important implications for how we perceive nutrient acquisition and limitation of carbon-fixing protists as well as control of bacterioplankton in the ocean.     

Climate-driven trends in contemporary ocean productivity

Contributing roughly half of the biosphere's net primary production (NPP), photosynthesis by oceanic phytoplankton is a vital link in the cycling of carbon between living and inorganic stocks. Each day, more than a hundred million tons of carbon in the form of CO2 are fixed into organic material by these ubiquitous, microscopic plants of the upper ocean, and each day a similar amount of organic carbon is transferred into marine ecosystems by sinking and grazing. The distribution of phytoplankton biomass and NPP is defined by the availability of light and nutrients (nitrogen, phosphate, iron). These growth-limiting factors are in turn regulated by physical processes of ocean circulation, mixed-layer dynamics, upwelling, atmospheric dust deposition, and the solar cycle. Satellite measurements of ocean colour provide a means of quantifying ocean productivity on a global scale and linking its variability to environmental factors. Here we describe global ocean NPP changes detected from space over the past decade. The period is dominated by an initial increase in NPP of 1,930 teragrams of carbon a year (Tg C yr(-1)), followed by a prolonged decrease averaging 190 Tg C yr(-1). These trends are driven by changes occurring in the expansive stratified low-latitude oceans and are tightly coupled to coincident climate variability. This link between the physical environment and ocean biology functions through changes in upper-ocean temperature and stratification, which influence the availability of nutrients for phytoplankton growth. The observed reductions in ocean productivity during the recent post-1999 warming period provide insight on how future climate change can alter marine food webs.     

香溪河库湾春季水华纵向分布对水层结构的响应

为研究三峡水库支流库湾春季水华暴发空间差异及成因,本研究于2010年4月18日对三峡水库干流和香溪河库湾的水动力、营养盐、浮游植物等因子进行了现场监测.结果显示：三峡水库支流春季水华浮游植物生物量及群落结构空间差异较大,库湾中上游暴发了严重的硅藻水华,而下游及三峡水库干流没有水华;库湾中复杂的分层异重流对水温结构产生显著影响,使其呈独特的垂向分层;水温分层纵向差异导致的光混比（Zeu/Zmix）纵向分布差异是引起水华情势和浮游植物群落结构纵向差异的主要原因.研究结果将为三峡水库支流水华机理和防控措施研究提供支撑.