2008年夏季西北冰洋表层水浮游植物群落结构的色素表征及其对不同水团的响应

本文依托2008年夏季中国第三次北极科学考察航次,对西北冰洋海盆区和楚科奇海陆架营养盐及光合色素进行了测定和分析。根据海水理化性质将研究海区分为5个区,并使用CHEMTAX软件（Mackery et al.,1996）讨论了西北冰洋不同海区浮游植物群落组成结构及其与环境因子之间的关系。结果显示在楚科奇海陆架区,太平洋入流显著影响浮游植物生物量和群落结构。高营养盐Anadyr水团以及白令陆架水控制海域,表现出高Chl a且浮游植物以硅藻为主,相反,低营养盐如阿拉斯加沿岸流控制海域,Chl a生物量低且以微型,微微型浮游植物为主。在外陆架海区,海冰覆盖情况影响着水团的物理特征及营养盐浓度水平,相应地显著影响浮游植物群落结构。在海冰覆盖区域,硅藻生物量站到总Chl a生物量的75%以上;在靠近门捷列夫深海平原海区,受相对高盐的冰融水影响（MW-HS）,营养盐浓度和Chl a浓度相对海冰覆盖区略高,浮游植物结构中微型、微微型藻类比重增加,硅藻比例则降至33%;南加拿大海盆无冰海区（IfB）,表层水盐度最淡,营养盐浓度最低,相应地显示出低Chl a生物量,表明海冰消退,开阔大洋持续时间延长,将导致低生物量及激发更小型浮游植物的生长,并不有利于有机碳向深海的有效输出。     

南极普里兹湾浮游植物现存量与初级生产力粒级结构和新生产力研究

报道1998～1999年夏季在南极普里兹湾及其毗邻海域对细胞丰度、优势种类组成、生物量和初级生产力的粒级结构、新生产力及其环境制约机制的研究.结果表明,调查海区具有显著的空间区域化特征.普里兹湾及其毗邻陆架区浮游植物现存生物量和生产力均较高,大陆坡和深海区明显降低;营养盐浓度由于浮游植物的消耗则有相反的分布趋势.浮游植物生物量和生产力受水体的垂直稳定度、浮游动物摄食、水温和光照等环境条件的控制.粒度分级测定结果表明,对调查海区叶绿素a的贡献,小型浮游生物为52.2%,微型为29.4%,微微型为18.4%;对初级生产力的贡献,小型为52.4%,微型为28.7%,微微型为18.9%.研究海区的平均新生产力和f比分别为230.6mg/(m2·d)和0.43.     

黑潮源区及其邻近海域叶绿素a浓度的季节分布

2001年冬季、2002年春季和秋季在琉球群岛、台湾岛和吕宋岛以东的西北太平洋黑潮源区及其邻近海域观测叶绿素a浓度季节分布及其粒级结构。结果表明,冬季表层平均叶绿素a浓度高于春季和秋季,台湾岛及以北岛链东南部的北部测区叶绿素a浓度高于巴士海峡及吕宋岛以东的南部海区。叶绿素a垂直分布呈真光层内随垂直深度增加而浓度增大,真光层下至水深200m随垂直深度增加而浓度降低的分布趋势。春季和秋季叶绿素a浓度粒级结构表明,微微型光合浮游生物(Pico级份)对总叶绿素a的贡献占优势,微型(Nano级份)次之,小型(Micro级份)所占比例最小。表层水光合浮游植物细胞丰度在(1.3~13.5)×103cells/dm3,以小粒径的硅藻占优势。呈现出微微型光合浮游生物在观测海区的重要性。     

利用特征色素研究长江口海域浮游植物对营养盐加富的响应

于2009年5月和11月,在长江口邻近海域通过现场营养盐加富实验,研究了浮游植物对营养盐添加的响应。应用高效液相色谱技术分析培养样品中的特征色素组成,通过CHEMTAX软件估算了硅藻、甲藻、隐藻、定鞭藻、金藻、绿藻、青绿藻和蓝藻8个浮游植物类群对叶绿素a生物量的贡献(μg/L)。加富实验结果显示:不同海区或同一海区不同季节的浮游植物生长对营养盐响应不尽相同,这与培养实验水样采集时浮游植物所处的N、P限制状态有着密切的关系。营养盐的加富不仅能够促进浮游植物生物量的增加,也可能引起浮游植物的群落结构的变化。不同浮游植物类群对营养盐添加的敏感性不同,培养实验开始后营养盐的输入使得硅藻在竞争中取得了优势,硅藻所占比重明显上升;但随着培养的进行,营养盐逐渐消耗,一些在低营养条件下竞争能力强的浮游植物类群比如甲藻、蓝藻、隐藻等对生物量的贡献逐渐上升;同时,培养海水中初始浮游植物群落组成对营养盐加富后群落结构的变化有着重要的影响。     

广东沿岸不同海洋功能区秋季浮游植物群落结构比较研究

2003年10月对广东沿岸浮游植物群落结构及相关环境因子进行了调查。设调查站位39个,根据营养盐数据分析表明,珠江对于陆源营养物质输入南海起着重要作用,其营养盐浓度明显高于广东沿岸其它海区。海域浮游植物隶属于62属118种(含变种和变型),其中硅藻门38属83种、甲藻门16属25种、蓝藻门3属4种、绿藻门2属2种、金藻门2属2种及针胞藻纲1属2种,硅藻在种类和生物量上均占主导地位。叶绿素a含量变化较大,测值范围为0.157～18.761mg/m3,最大值出现在珠江口水域GD089站。浮游植物的粒级结构存在明显的地域特点,珠江口及其毗邻海域以微型浮游植物为主,其他海域基本以小型浮游植物为主。     

亚热带和热带环境下夜光藻的摄食压力

2015年以广西三娘湾海域为亚热带海区,三亚海域为热带海区,利用稀释法开展了现场培养实验,测定热带和亚热带海区夜光藻对浮游植物、微型浮游动物对浮游植物的摄食压力,研究了夜光藻对不同粒径的浮游生物的摄食作用.结果表明:两个海区都有比较高的生长率和摄食率,其中细菌有最高的生长率和摄食死亡率;夜光藻的摄食率,从总浮游植物、微微型浮游植物到聚球藻、细菌逐渐增高.亚热带海区与热带海区相比,微型浮游动物的摄食压力更小,表明低温影响了浮游动物的摄食活性;而营养盐是引起亚热带海区高生长率的主要因素.     

南海北部东沙天然气水合物区浮游植物生物量和生产力粒级结构特征及其环境影响分析

本文讨论了2013年5月南海东沙天然气水合物区浮游植物生物量和生产力粒级结构特征及其环境影响因素。结果表明,研究海域表现出典型的低营养盐、低叶绿素a、低生产力特征,浮游植物叶绿素a和初级生产力具有明显的次表层最大值现象。东沙海域生物量和初级生产力粒级结构差异性显著,从生物量和生产力贡献度来看,表现为微微型浮游植物> 微型浮游植物> 小型浮游植物。生物量的垂直分布结果表明,春季不同粒级类群浮游植物在真光层内的分布存在明显不同,比如小型浮游植物在真光层内分布较均匀;微型浮游植物则主要分布于近表层或真光层中部,而微微型浮游植物则主要分布于真光层中部和底部。微微型浮游植物在纬度较低的热带贫营养海区之所以能够占主导优势,最主要的原因是其极小的细胞体积和较大的表面积使其有利于营养竞争。相关性分析表明,南海东沙浮游植物各粒级生物量与温度、pH显著正相关,与硅酸盐、磷酸盐显著负相关;浮游植物各粒级生产力与温度显著正相关,与盐度、磷酸盐显著负相关。磷酸盐含量是影响东沙海域浮游植物粒级结构差异的重要因素之一,同时,光辐照度和水体的真光层深度对东沙天然气水合物区不同粒径浮游植物的垂直分布起着更为重要的调控作用。     

加拿大海盆北部营养盐限制作用研究

利用2008年夏季中国第三次北极科学考察获得的营养盐、叶绿素a、温度和盐度等数据资料,结合现场营养盐添加实验的结果讨论西北冰洋加拿大海盆北部营养盐对浮游植物生长的限制作用。结果表明:由于融冰水稀释作用,加拿大海盆B80站约20m深度存在较强的盐跃层,阻碍了水体上下混合。较低浓度的溶解无机氮(DIN)和硅酸盐(分别为0.31μmol/L和0.94μmol/L)以及严重偏离Redfield比值的N/P、N/Si比值(分别为0.42和0.32)表明加拿大海盆表层水体存在N和Si限制。根据现场营养盐加富实验各培养组叶绿素a浓度变化、营养盐吸收总量差异和浮游植物种群结构,进一步表明氮是北冰洋海盆首要限制营养盐,而Si则抑制了硅质生物的生长。同时,较小的硝酸盐半饱和常数(Ks)证明即使在营养盐充足的情况下北冰洋海盆浮游植物生长速率也处于较低水平。计算得到各培养组营养盐吸收比例(N/P比值)均大于Redfield比值,可能是培养实验过程中以微型、微微型浮游植物为主,硅藻等小型浮游植物为辅造成的。     

基于CMIP6模式分析北极典型海区浮游植物藻华模拟误差

在海冰覆盖的极地海区,浮游植物季节性藻华变化呈现典型的单峰特征。由于藻华过程受控于海冰、光照、混合层深度和营养盐供给等多个因素,其发生时间和强度在地球系统模式模拟结果中存在较大的不确定性。本研究选取11种CMIP6地球系统模式结果,以多种类型的观测资料和产品作为判断参考值,评估各模式结果能否准确模拟北极典型海区（巴伦支海、楚科奇海及白令海）浮游植物藻华动态的变化规律。通过计算能表征光照和营养盐限制的多个指标,分析表层叶绿素a浓度模拟结果的误差来源。结果表明,依据冰下光照时长、混合层变化速率、表层硝酸盐指标将11种模式分为3组,与参考值指标差异较小组别中的模式在藻华模拟方面明显占优,而其余模式在表层硝酸盐或混合层变化的模拟上存在较大误差,导致表层叶绿素a浓度峰值的发生时间延后且峰值浓度误差大。总体而言,地球系统模式配置中除要考虑光照和营养盐这两种基础限制条件外,也需关注由温盐控制的上混合层深度,从而准确模拟出表层叶绿素a浓度的季节性变化规律,上述研究为地球系统模式中相关参数化方案的改进提供了参考。     

春季季风间期巽他陆架和马六甲海峡表层海水浮游植物群落结构研究

于2013年3-5月通过走航取样分别对巽他陆架和马六甲海峡表层海水浮游植物叶绿素a生物量和群落结构进行了观测和研究。结果表明:巽他陆架生物量较低,叶绿素a浓度平均值为(0.083±0.043)μg/L,爪哇海的SS4站位生物量最低,仅为0.014μg/L,浮游植物粒级组成上主要以Pico-级为优势,占80%以上;马六甲海峡自西北至东南存在明显的盐度梯度,在盐度最低的SM5站,叶绿素a生物量最高,达到1.080μg/L;马六甲海峡站位叶绿素a浓度平均值为(0.433±0.315)μg/L,同时浮游植物群落结构变动较大。在海峡西北的SM1-SM4站与巽他海峡类似,主要以聚球藻为优势类群,Pico-级浮游植物占60%~80%;在生物量最高的SM5站,同样以聚球藻为优势类群,而在海峡东南段的SM6和SM7站,虽然叶绿素a浓度相对于SM5略有降低,但仍明显高于其他马六甲海峡站位和巽他陆架站位,此两个站位硅藻比例明显升高,均可达20%以上。从优势类群生物量与环境因子和营养浓度的相关性可以看出,研究海区叶绿素a生物量与水体盐度呈现显著负相关(p0.050),说明陆源输入对研究海区生物量具有明显的影响。另外,硅藻生物量也与磷酸盐浓度(p0.050)和硅酸盐(p0.010)浓度均呈现显著正相关;聚球藻在浮游植物群落中的优势度会受到陆源营养盐输入的影响而降低,但仍然是整个研究区域最优势的浮游植物类群。     

Chlorophyll a Biomass of Netplankton in Surface Waters in the Pacific Sector of the Southern Ocean in Austral Summer

Chlorophyll a of total and particles retained on 30 μm mesh plankton net were both determined in surface waters along two cruise tracks ranging from the Subtropical water to the marginal ice zone in the Pacific sector of the Southern Ocean in austral summer. Total surface chlorophyll a in the study area was mostly less than 1 μg chl a 1⁻¹, and showed distributions with no obvious trend associated with different waters masses of the Antarctic and the Subantarctic, although total chlorophyll a concentrations changed greatly within each water mass. Particularly low concentrations of chlorophyll a were detected in the marginal ice zone. Chlorophyll a contained in 30 μm netplankton made up 5∼60% of total chlorophyll a: large near the marginal ice zone and becoming small with travel towards the north. High percentage shares of netplankton chlorophyll a were confirmed even in low total chlorophyll a concentrations in summer in the Southern Ocean. A positive relation was observed between the percentage of 30 μm netplankton and the “average total chlorophyll a”, although there was great scatter. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mesoscale features and phytoplankton biomass at the GoodHope line in the Southern Ocean during austral summer

Two sets of high-resolution subsurface hydrographic and underway surface chlorophyll a (Chl a) measurements are used, in conjunction with satellite remotely sensed data, to investigate the upper layer oceanography (mesoscale features and mixed layer depth variability) and phytoplankton biomass at the GoodHope line south of Africa, during the 2010–2011 austral summer. The link between physical parameters of the upper ocean, specifically frontal activity, to the spatially varying in situ and satellite measurements of Chl a concentrations is investigated. The observations provide evidence to show that the fronts act to both enhance phytoplankton biomass as well as to delimit regions of similar chlorophyll concentrations, although the front–chlorophyll relationships become obscure towards the end of the growing season due to bloom advection and ‘patchy’ Chl a behaviour. Satellite ocean colour measurements are compared to in situ chlorophyll measurements to assess the disparity between the two sampling techniques. The scientific value of the time-series of oceanographic observations collected at the GoodHope line between 2004 to present is being realised. Continued efforts in this programme are essential to better understand both the physical and biogeochemical dynamics of the upper ocean in the Atlantic sector of the Southern Ocean.     

Evaluation of the performance of HPLC–CHEMTAX analysis for determining phytoplankton biomass and composition in a turbid estuary (Schelde, Belgium)

In the upper Schelde estuary in 2002, phytoplankton biomass and community composition were studied using microscopic and pigment analyses. Chlorophyll a concentration was a good predictor of phytoplankton biomass estimated from cell counts and biovolume measurements. The phytoplankton carbon to chlorophyll a ratio, however, was often unrealistically low (<10). CHEMTAX was used to estimate the contribution of the major algal groups to total chlorophyll a. The dominant algal groups were diatoms and chlorophytes. While diatom equivalents in chlorophyll a predicted diatom biomass relatively well, chlorophyte equivalents in chlorophyll a were only weakly related to chlorophyte biomass. The pigment-based approach to study phytoplankton overestimated phytoplankton biomass in general and chlorophyte biomass in particular in late autumn and winter, when phytoplankton biomass was low. A possible explanation for this overestimation may be the presence of large amounts of vascular plant detritus in the upper Schelde estuary. Residual chlorophyll a, chlorophyll b and lutein in this detritus may result in an overestimation of total phytoplankton and chlorophyte biomass when the contribution of phytoplankton to total particulate organic matter is low.     

Community Structure and Dynamics of Phytoplankton in the Western Subarctic Pacific Ocean: A Synthesis

The phytoplankton community in the western subarctic Pacific (WSP) is composed mostly of pico- and nanophytoplankton. Chlorophyll a (Chl a) in the <2 μm size fraction accounted for more than half of the total Chl a in all seasons, with higher contributions of up to 75% of the total Chl a in summer and fall. The exception is the western boundary along the Kamchatka Peninsula and Kuril Islands and the Oyashio region where diatoms make up the majority of total Chl a during the spring bloom. Among the picophytoplankton, picoeukaryotes and Synechococcus are approximately equally abundant, but the former is more important in term of carbon biomass. Despite the lack of a clear seasonal variation in Chl a concentration, primary productivity showed a large seasonal variation, and was lowest in winter and highest in spring. Seasonal succession in the phytoplankton community is also evident with the abundance of diatoms peaking in May, followed by picoeukaryotes and Synechococcus in summer. The growth of phytoplankton (especially >10 μm cell size) in the western subarctic Pacific is often limited by iron bioavailability, and microzooplankton grazing keeps the standing stock of pico- and nano-phytoplankton low. Compared to the other HNLC regions (the eastern equatorial Pacific, the Southern Ocean, and the eastern subarctic Pacific), iron limitation in the Western Subarctic Gyre (WSG) may be less severe probably due to higher iron concentrations. The Oyashio region has similar physical condition, macronutrient supply and phytoplankton species compositions to the WSG, but much higher phytoplankton biomass and primary productivity. The difference between the Oyashio region and the WSG is also believed to be the results of difference in iron bioavailability in both regions. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-West and Low-East Distribution Patterns of Chlorophyll a, Primary Productivity and Diatoms in the Subarctic North Pacific Surface Waters, Midwinter 1996

We have determined chlorophyll a (Chla) concentration, primary productivity, cell density and species composition of diatoms, and the number of microzooplankton at the surface in the subarctic North Pacific in January 1996. The wet weight of copepods obtained by vertical tows from 150 m to the surface was also measured during the cruise. Chla concentration and primary productivity tended to be higher in the region west of 180°, the western subarctic North Pacific (WSNP), than east of 180°, the eastern subarctic North Pacific (ESNP). The same results were observed for the total diatom cell densities and for the genera Thalassiosira and Denticulopsis. Significant linear relationships were observed between the Thalassiosira cell density and Chla concentration and primary productivity, indicating that Thalassiosira contributes to the high-WSNP and low-ESNP distribution patterns of Chla concentration and primary productivity. Moreover, naked ciliate abundance tended to be lower in the WSNP than in the ESNP, whereas copepod biomass showed an inverse trend. Significantly negative Spearman rank correlations were found between the Thalassiosira cell density and the number of naked ciliates and between the number of naked ciliates and the wet weight of copepods. These results indicate that copepod grazing indirectly controls Thalassiosira cell density via predation on the naked ciliates. We conclude that the high copepod biomass in the WSNP is a factor controlling the high-WSNP and low-ESNP Thalassiosira abundance and hence Chla concentration and primary productivity patterns.     

Depth distribution of radiolarians from the Chukchi and Beaufort Seas, western Arctic

The depth distributions of the radiolarian fauna in the Chukchi and Beaufort Seas, marginal seas of the western Arctic Ocean, were examined quantitatively in depth-stratified plankton tows from 4 or 5 intervals above 500 m and in surface sediments from various depths between 163 and 2907 m. The radiolarian assemblage from the water column in September 2000 was dominated by Amphimelissa setosa and followed by the Actinomma boreale/leptoderma group, Pseudodictyophimus gracilipes and Spongotrochus glacialis. These species are related to the Arctic Surface Water shallower than 150 m. This assemblage is similar to that in the Greenland Sea relating to the ice edge, but did not contain typical Pacific radiolarians in spite of the flow of water of Pacific origin in this region. The living depth of Ceratocyrtis historicosa was restricted to the relatively warm water between 300 and 500 m corresponding to the upper Arctic Intermediate Water (AIW) originating from the Atlantic Ocean. Radiolarian assemblages in the surface sediments are similar to those in the plankton tows, except for common Cycladophora davisiana in sediment samples below 500 m. C. davisiana is probably a deep-water species adapted to the lower AIW or the Canadian Basin Deep Water ventilated from the shelves.     

Stable carbon isotope ratios of plankton carbon and sinking organic matter from the Atlantic sector of the Southern Ocean

The stable carbon isotope composition of particulate organic carbon (POC) from plankton, sediment trap material and surface sediments from the Atlantic sector of the Southern Ocean were determined. Despite low and constant water temperatures, large variations in the δ¹³C values of plankton were measured. ¹³C enrichments of up to 10‰ coincided with a change in the diatom assemblage and a two-fold increase in primary production. Increased CO₂ consumption as a result of rapid carbon fixation may result in diffusion limitation reducing the magnitude of the isotope fractionation. The δ¹³C values of plankton from sea-ice cores display a relationship with the chlorophyll a content. High ‘ice-algae’ biomass, in combination with a limited exchange with the surrounding seawater, results in values of about − 18 to − 20‰. It is assumed that these values are related to a reduced CO₂ availability in the sea-ice system. In comparison with plankton, sinking krill faeces sampled by traps can be enriched by 2–5‰ in ¹³C (e.g. central Bransfield Strait). In contrast, the transport of particles in other faeces, diatom aggregates or chains results in minor isotope changes (e.g. Drake Passage, Powell Basin, NW Weddell Sea). A comparison between the δ¹³C values of sinking matter and those of surface sediments reveals that ¹³C enrichments of up to 3–4‰ may occur at the sediment-water boundary layer. These isotopic changes are attributed to high benthic respiration rates.     

Diatoms in the desert: Plankton community response to a mesoscale eddy in the subtropical North Pacific

As part of the E-Flux project, we documented spatial variability and temporal changes in plankton community structure in a cold-core cyclonic eddy in the lee of the Hawaiian Islands. Cyclone Opal spanned 200 km in diameter, with sharply uplifted isopycnals (80–100 m relative to surrounding waters) and a strongly expressed deep chlorophyll a maximum (DCM) in its central core region of 40 km diameter. Microscopic and flow cytometric analyses of samples from across the eddy revealed dramatic transitions in phytoplankton community structure, reflecting Opal's well-developed physical structure. Upper mixed-layer populations in the eddy resembled those outside the eddy and were dominated by picophytoplankton. In contrast, the DCM was composed of large chain-forming diatoms dominated by Chaetoceros and Rhizosolenia spp. Diatoms attained unprecedented levels of biomass (nearly 90 μg C l⁻¹) in the center of the eddy, accounting for 85% of photosynthetic biomass. Protozoan grazers displayed two- to three-fold higher biomass levels in the eddy center as well. We also found a distinct and persistent layer of senescent diatom cells overlying healthy populations, often separated by less than 10 m, indicating that we were sampling a bloom in a state of decline. Time-series sampling over 8 days showed a successional shift in community structure within the central diatom bloom, from the unexpected large chain-forming species to smaller forms more typical of the subtropical North Pacific. The diatom bloom of Cyclone Opal was a unique, and possibly extreme, example of biological response to physical forcing in the North Pacific subtropical gyre, and its detailed study may therefore help to improve our predictive understanding of environmental controls on plankton community structure.