978 resultados para EAST CHINA SEA
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The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon isotope records of mixed layer dweller a ruber and thermocline dweller N. dutertrei in piston core CSH1 and core DGKS9603 collected separately from the Tsushima warm current and the Kuroshio dominated area. The result showed that the Tsushima warm current vanished in the lowstand period during 40-24 cal ka BP, while the Kuroshio still flowed across the Okinawa Trough, arousing strong upwelling in the northern Trough. Meanwhile, the influence of freshwater greatly increased in the northern Okinawa Trough, as the broad East China Sea continental shelf emerged. The freshwater reached its maximum during the last glacial maximum (LGM), when the upwelling obviously weakened for the lowest sea-level and the depression of the Kuroshio. The modern Tsushima warm current began its development since 16 cal ka BP, and the impact of the Kuroshio increased in the middle and northern Okinawa Trough synchronously during the deglaciation and gradually evolved as the main water source of the Tsushima current. The modern Tsushima current finally formed at about 8.5 cal ka BP, since then the circulation structure has been relatively stable. The water of the modern Tsushima current primarily came from the Kuroshio axis. A short-term wiggle of the current occurred at about 3 cal ka BP, probably for the influences from the enhancement of the winter monsoon and the depression of the Kuroshio. The cold water masses greatly strengthened during the wiggle.
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Well-dated, high-resolution records of planktonic foraminifera and oxygen isotopes from two sediment cores, A7 and E017, in the middle Okinawa Trough reveal strong and rapid millennial-scale climate changes since similar to 18 to 17 thousand years before present (kyr B.P.). Sedimentation rate shows a sudden drop at similar to 11.2 cal. kyr B.P. due to a rapid rise of sea level after the Younger Dryas (YD) and consequently submergence of the large continental shelf on the East China Sea (ECS) and the retreat of the estuary providing sediment to the basin. During the last deglaciation, the relative abundance of warm and cold species of planktonic foraminifera fluctuates strongly, consistent with the timing of sea surface temperature (SST) variations determined from Mg/Ca measurements of planktonic foraminifera from one of the two cores. These fluctuations are coeval with climate variation recorded in the Greenland ice cores and North Atlantic sediments, namely Heinrich event 1 (H1), Bolling-Allerod (B/A) and YD events. At about 9.4 kyr B.P., a sudden change in the relative abundance of shallow to deep planktonic species probably indicates a sudden strengthening of the Kuroshio Current in the Okinawa Trough, which was synchronous with a rapid sea-level rise at 9.5-9.2 kyr B.P. in the ECS, Yellow Sea (YS) and South China Sea (SCS). The abundance of planktonic foraminiferal species, together with Mg/Ca based SST, exhibits millennial-scale oscillations during the Holocene, with 7 cold events (at about 1.7, 2.3-4.6, 6.2, 7.3, 8.2, 9.6, 10.6 cal. kyr BP) superimposed on a Holocene warming trend. This Holocene trend, together with centennial-scale SST variations superimposed on the last deglacial trend, suggests that both high and low latitude influences affected the climatology of the Okinawa Trough. (c) 2006 Elsevier B.V. All rights reserved.
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Locating the quantitized natural sediment fingerprints is an important work for marine sediment dynamics study. The total of 146 sediment samples were collected from the Shelf of the East China Sea and five rivers, including Huanghe (Yellow), Changjiang (Yangtze), Qiantang, Ou and Min River. The sediment grain size and the contents of rare earth elements (REEs) were measured with laser particle size analyzer and ICP-MS technology. The results show that absolute REE content (Sigma REE) and the concentration ratio of light REEs to heavy REEs (L/HREE) are different in the sediments among those rivers. There are higher REE contents in being less than 2 m and 2-31 mu m fractions in the Changjiang Estuary surface sediments. The REE contents of bulk sediment are dominated by the corresponding values of those leading size-fractions. Sigma REE of sediment is higher close to the estuaries and declines seaward on the inner shelf of the East China Sea (ECS). The L/HREE ratio has a tendency of increase southward from 28 degrees N. Hydrodynamic conditions plays a predominate role on spacial distributions of the surficial sediment's REE parameters. In some situations, the currents tend to remove the coarser light grains from initial populations, as well as the deposit of the finer heavy mineral grains. In other situations, the currents will change the ratio of sediment constituents, such as ratio between silts and clays in the sediments. As a result, the various values of Sigma REE or L/HREE ratio in different bulk sediments are more affected by the change of size-fractions than source location. Under the long-term stable hydrodynamic environment, i.e., the East China Sea Shelf, new sediment transport model based on the size and density gradation concept may help to understand the spatial distribution patterns of REE parameters.
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To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea (ECS) shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector (BSR) occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural "anomalies" are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation: to help gather enough methane into a small area and to modulate the thermal regime.
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Gridded sound speed data were calculated using Del Grosso's formulation from the temperature and salinity data at the PN section in the East China Sea covering 92 cruises between February 1978 and October 2000. The vertical gradients of sound speed are mainly related to the seasonal variations, and the strong horizontal gradients are mainly related to the Kuroshio and the upwelling. The standard deviations show that great variations of sound speed exist in the upper layer and in the slope zone. Empirical orthogonal function analysis shows that contributions of surface heating and the Kuroshio to sound speed variance are almost equivalent.
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Based on the Estuarine, Coastal and Ocean Modeling System with Sediments (ECOMSED) model, a 3-D hydrodynamic-transport numerical model was established for the offshore area near the Yangtze Estuary in the East China Sea. The hydrodynamic module was driven by tide and wind. Sediment module included sediment resuspension, transport and deposition of cohesive and non-cohesive sediment. The settling of cohesive sediment in the water column was modeled as a function of aggregation (flocculation) and deposition. The numerical results were compared with observation data for August, 2006. It shows that the sediment concentration reduces gradually from the seashore to the offshore area. Numerical results of concentration time series in the observation stations show two peaks and two valleys, according with the observation data. It is mainly affected by tidal current. The suspended sediment concentration is related to the tidal current during a tidal cycle, and the maximum concentration appears 1 h-4 h after the current maximum velocity has reached.
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该文对中国黄海和东海的蓝细菌在春、秋两季的生态分布特点进行了研究和比较,对黄海蓝细胞从10月至次年6月的生态分布进行了研究.1.东黄海海区:在秋季(2000年10月19日至11月29日)和春季(2001年3月26日至4月24日)两个季节中蓝细菌丰度在0.19~7.84×10<'4>cell/ml之间,生物量在0.56~13.74μgC/L之间,整体水平上春季比秋季高(蓝细菌的丰充与生物量平均值春季分析为4.83×10<'4>cell/ml和7.25μgC/L;秋季分别为1.72×10<'4>cell/ml和5.07μgC/L),东海比黄海高(蓝细菌生物量平均值春季黄海和东海分别为4.42μgC/L和5.52μgC/L;秋季黄海和东海分别为7.02μgC/L和7.45μgC/L).2.黄海海区:黄海蓝细菌丰度与生物量随时间变化趋势为10月至12月降低(蓝细菌丰度分别为15×10<'4>cell/ml和1.19×10<'4>cell/ml,生物量分别为4.41μgC/L和3.49×10<'4>cell/ml),4月(蓝细菌丰度与生物量分别为4.68×10<'4>cell/ml和7.02μgC/L)与12月相比有明显增高,蓝细菌丰度4月是12月的3.93倍,生物量4月是12月的2.01倍,4月至6月蓝细菌生物量大致稳定,略有增加(5月和6月蓝细菌丰度分别为5.23×10<'4>cell/ml和5.25×10<'4>cell/ml,生物量分别为7.85μgC/L和7.88μgC/L).研究发现蓝细菌在水体中的垂直分布与温度变化比较一致.
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本论文通过对冲绳海槽南部的MD05-2908孔、北黄海的B-U35、B-U41、B-L44孔和北黄海的299份表层样中的孢粉组成、堆积速率、有机碳氮同位素的综合研究,分析了北黄海的孢粉来源、传播动力和途径,并与其它古气候记录对比,重建了末次冰消期以来东亚季风的演化。 MD05-2908孔孢粉组合特征显示6800-3800a BP间气候温暖干燥,其间存在着两次明显的温度降低、湿度增加阶段,即6800-6600a BP和5800-4850a BP;3800a BP以后,气候变得比较寒冷湿润,中世纪暖期和小冰期分别位于990-480a BP和480-230a BP。 北黄海表层孢粉百分含量等值线图显示北黄海不同海域孢粉来源不同,北黄 海东部海域(123.5°E以东的陆架区域)孢粉主要来源于鸭绿江;北黄海中部海域(123.5°E-122.6°E的陆架区域)孢粉来源比较复杂,既有来自辽东半岛、沿海岛屿、山东半岛,还有由黄海暖流携带而来的;北黄海西部海域(122.6°E以西的陆架区域)孢粉以黄海沿岸流携带而来的黄河来源的为主。 北黄海表层孢粉百分含量等值线图还显示,北黄海东部海域孢粉分布主要受 鸭绿江冲淡水影响,波浪和潮汐的作用较弱;北黄海中部海域孢粉分布受黄海暖流和辽东沿岸流的分支共同影响;黄海暖流与黄海沿岸流在山东半岛东北部相遇,形成一逆时针方向的涡旋,该涡旋控制着北黄海西部海域孢粉的分布。 B-U35孔、B-U41和B-L44孔孢粉组合特征显示,12830-12350a BP时气候 寒冷干燥,植被以旱生草本植物为主,时间上可能对应YD事件;12350-10100a BP时植被以针叶林为主,林下生长着大量蕨类植物,气候寒冷湿润,可能对应着YD事件;10100-6600a BP时植被以落叶阔叶林为主,伴生大量旱生草本植物,气候温暖干燥;6600-5000a BP时植被以针叶-落叶阔叶混交林为主,旱生草本植物含量下降,相对上一阶段温度有所降低,但气候更湿润,可能对应全新世最佳期;5000-4000a BP时针叶林所占比例扩大,温度再次降低,湿度变化不明显;4000-500a BP旱生草本植物含量增加,气候寒冷干燥;500a BP-至今,受人类活动影响,植被遭到严重破坏。 B-U35孔和B-U41孔淡水水生植物花粉百分含量曲线显示11750a BP以来黄河河口地区沼泽湿地面积几经变化。10100-6600a BP时沼泽湿地范围在上一阶段的基础上进一步扩大;6600-2850a BP间沼泽湿地大面积缩小,水生植物属种式微;2850a BP之后黄河河口地区沼泽湿地面积再次扩大,水生植物重新繁盛。 MD05-2908孔蕨类孢子百分含量被用来作为中国东南部季风演化的代用指标。结果显示6800-3800a BP时夏季风较强,其间有两次夏季风减弱阶段,分别位于6800-6600a BP和5800-4850a BP,3800a BP以来,夏季风明显减弱,此期的夏季风减弱除受太阳辐射量的减少影响外,可能还与El Nino的频繁爆发有关。 B-U35孔和B-U41孔蒿属、藜科、麻黄科百分含量被用来作为中国中北部夏季风演化的代用指标。研究表明,11750a BP以来东亚夏季风强度在10100-6600a BP时,显著加强,6600a BP左右,夏季风开始减弱,4000a BP以后夏季风显著减弱。 将MD05-2908孔、B-U35孔和B-U41孔夏季风代用指标进行对比发现,中晚全新世以来中国南-北湿度变化特征正好相反,东亚夏季风强度变化以及由此引起的雨锋的南进北撤可能是导致中国不同区域中晚全新世以来降雨量不同的主要原因。
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该文论述了春秋季黄东海大型底栖动物的生态学特点,并结合历史资料,对底栖动物的季节变化及年际变化作了初步探讨.论文所需资料由2000年10~11月与2001年3~4月在黄东海进行的春秋季调查获得,在121~127<'0>E.26~26<'0>N之间海域共设49个大型底栖动物取样站.除少数种类待鉴定外,两次调查共发现四大类群底栖动物543种,其中多毛类39科147种,软件动物56科182种,甲壳类41科144种,棘皮动物21科70种.该文对黄东海大型栖动物种类分布特点、生物量及栖息密度的分布与季节变化进行研究,并计算生物多样性指数,作生物多样性分析.
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在海洋渔业资源不断衰退的今天,渔业资源管理正经历着由单种和多种资源管理向生态系统水平管理的转变。开展在各种干扰因素影响下鱼类群落演替方向的研究是引入基于生态系统渔业管理策略的必要环节,本文以东海北部海域鱼类群落为研究对象,对其近十几年来结构和功能的变化趋势进行分析,以期今后为渔业资源的科学管理提供理论基础。 捕捞是引起鱼类群落结构变化的最为重要的因素,本研究首先就捕捞对鱼类群落影响的国内外研究方法进行了综述与归纳。在研究捕捞对鱼类群落的影响时,所选用的群落参数指标应符合预期性、可测性、敏感性和排他性标准,业已利用的研究方法大致可为生物多样性、聚合特征指标、群落功能性指标、多元分析以及生态系统模型五大类。各研究方法单独使用均无法全面反映群落的结构变化状况,建议在实际研究过程中同时使用多种研究方法进行鱼类群落结构的变化分析,以期全面掌握捕捞活动影响下鱼类群落结构的变动状况,更好地为渔业资源的科学管理提供理论支撑。 根据1991年1月和2004~2006年1月东海北部水域渔业资源底拖网调查资料,从物种和同功能种团两个层面分析了东海北部鱼类群落多样性及其结构组成特征的变化。同功能种团是生态系统中起着相似生态作用、并占据相近或相似生态位的若干物种集合体,本文结合各鱼种的摄食习性和活动能力差异,将该水域内的鱼类划分为8个同功能种团,分别为浮游动物食性种团、浮游/底栖动物食性种团、底栖动物食性种团、底栖/游泳动物食性种团、杂食性种团、活动能力强的游泳动物食性种团、软骨鱼类种团、活动能力弱的游泳动物食性种团。研究结果显示:东海北部冬季鱼类群落的物种多样性和同功能种团多样性呈显著线性正相关。经过十余年后,尽管该群落的物种多样性和同功能种团多样性均未发生显著变化,但各同功能种团内的物种数发生了明显变化,物种多样性与同功能种团多样性之间的关系曲线斜率由0.547增加到0.627,群落的生态冗余性有所降低。相似性分析检验表明,两时段群落间的物种和同功能种团结构组成均发生了显著变化,带鱼、龙头鱼、小黄鱼、黄鲫、灰鲳等物种和软骨鱼类种团、浮游/底栖动物食性种团相对量的变化是造成鱼类群落结构变化的主要因素。鱼类群落结构已显现出向以浮游动物食性和活动能力强的游泳动物食性鱼种为主体的方向发展的趋势。 最后本研究对实施伏季休渔以后近十年来东海北部鱼类群落的动态进行了分析。研究表明:实施伏休以后部分物种得到一定程度的恢复,而另些物种在伏休结束后强大的捕捞压力下仍然不断衰退,群落的物种生物量组成正朝一定的方向进行变化,但是这种变化并没有给鱼类群落带来稳定性和功能性方面的好转,群落仍处于中度干扰状态,物种多样性没有得到显著提高;群落的生产力水平以及营养传递效率没有恢复的迹象。每年伏休结束后强大的捕捞压力使伏季休渔没有达到预期的效果。为更有效的保护渔业资源、恢复东海北部生态系统,建议继续加大管理力度,进一步降低该海域的捕捞强度。
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在东海进行了浮游动物(桡足类)群体的摄食研究。桡足类群体按体长被分为大、中、小三级用荧光法测定了肠道色素含量,同时对浮游动物的昼夜摄食节律及垂直移动进行了观察。结果表明,浮游动物的肠道色素平均含量随体形的增大而增大;大型浮游动物在摄食中占了主要地位;大型和中型浮游动物均有明显的摄食节律。在两个连续站,每天只有少于10%的初级生产被桡足类群体所摄食(分别为4.86%和6.75%)。因此,浮游桡足类群体的摄食不会限制浮游植物种群的增长。
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近十年,国内外学者从不同的角度对浪流相互作用进行了研究,但由于问题本身的复杂性,仍然存在很大的探讨空间。特别是在我国,这一领域的研究并不多见,且现有的研究成果多是单向耦合。本文从风应力、底摩擦应力、波致辐射应力三方面入手尝试研究浪流相互作用。利用海浪模式SWAN和海流模式POM构建的浪-流耦合模式,对1994年8月上中旬渤海、黄海、东海区域两次台风过程下的部分海洋要素进行了对比模拟实验。经过初步的研究,得到了一些有价值的认识。结果表明: (1)在台风中心外围的大风区,Donelan公式的计算结果要高于POM原有的计算结果,最大增幅可达30%,拖曳系数高值区的范围也明显增大。 (2)Signell方案给出的底摩擦系数计算结果随时间有明显变化的区域集中在水深50米以浅的海域。 (3)三项应力共同给浪流耦合模式带来的水位变化与三项应力中的任意两项组合带来的水位变化有相似的空间分布型。福州沿岸最大增幅0.25m以上,温州沿岸最大增幅0.3m,长江入海口处最大增幅0.25m左右,仁川沿岸最大增幅则达到0.4m。 (4)耦合后的结果与岸边站点实测水位的对比结果显示,基隆、坎门站的水位在台风经过前后时段更接近于观测值,特别是极值水位处。 (5)流的存在显著的影响有效波高的计算结果。在黄渤海区域,潮流对有效波高的增减在极值处可达0.2m。在台湾岛东北海域黑潮流系附近,流对有效波高的增加最大可达1.8m。 上述结果对近岸风暴潮和海浪的预报具有指示意义。
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本文在整个东海范围内对颗粒有机碳、颗粒有机氮、ATP进行了测定,并通过ATP对颗粒有机碳中的生命与非生命部分进行了定量区分。春季表层颗粒有机碳的分布以东海陆架区中部为中心向周围递减,与ATP的分布特点相似,说明主要受生物活动影响,秋季表层颗粒有机碳的最高值出现在长江口,并且从江口向外海递减,这种分布特点主要是由长江径流和颗粒物的再悬浮造成的。发现春季颗粒有机碳与ATP在外陆架区的真光层中存在着良好的线性相关关系,秋季则未发现两者间的任何相关关系。但是,无论春秋,ATP与叶绿素a在真光层中均存在较好的线性相关关系,真光层以下各层则未发现这种关系。
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为研究鄂霍次克海天然气水合物区沉积物古菌、甲烷厌氧氧化古菌和硫酸盐还原细菌的多样性分布,我们以PCR技术为基础构建mcrA、dsrAB和古菌16S rRNA 基因文库。对所获得的序列进行系统进化和统计学分析发现:鄂霍次克海古菌类群主要为Marine Benthic Group D (MBG-D)、Marine Benthic Group B (MBG-B)、Marine Crenarchaeotic Group I(MG- I),另外少量古菌16S rRNA基因序列为Anaerobic Methanotrophs 2c(ANME-2c),主要分布在LV39-25H岩心的表层沉积物中。LV39-40H岩心表层的古菌群落结构与其他六个层位古菌群落结构相比有着显著的差异。mcrA基因序列主要为催化甲烷厌氧氧化的古菌ANME-2(c和d簇),在所研究的各个层位的沉积物中均广泛分布。少量的ANME-1(a簇)发现于LV39-40H岩心表层以下的沉积物中。产甲烷古菌数目不多,集中分布在LV39-25H岩心200cm和LV39-40H岩心180cm的沉积物中。dsrAB基因文库分析表明硫酸盐还原细菌种类丰富,表层沉积物中硫酸盐还原细菌多样性最高。在两个岩心所有层位的沉积物中都有一定数量的克隆属于DSS簇,它们可能与ANME共生催化甲烷的厌氧氧化作用。总之,所有数据表明在鄂霍次克海天然气水合物区存在着较活跃的甲烷厌氧氧化作用,揭示了参与甲烷厌氧氧化作用的微生物群落结构和多样性。 为研究东海内陆架闽浙沿岸泥质区不同深度沉积物中古菌群落垂向分布特征,通过古菌16S rRNA 基因文库共得到473个有效克隆50个OTUs (Operational Taxonomic Units)。16S rRNA基因序列系统进化和统计分析发现古菌分别归属于泉古生菌(Crenarchaeota)和广古生菌(Euryarchaeota),其中以Miscellaneous Crenarchaeotic Group(MCG)为主,仅含少量的MBG-B、South African Gold Mine Euryarchaeotic Group(SAGMEG)、 ANME-3、MG- I和MBG-D。该泥质区沉积物可能存在由ANME-3催化的甲烷厌氧氧化作用,同源序列分析表明其古菌群落分布与周边环境有较大联系。UniFrac与沉积物环境因子分析表明该泥质区古菌群落垂向分布与沉积物有机质含量和粒度变化密切相关。 通过对比发现,鄂霍次克海天然气水合物区甲烷厌氧氧化古菌主要为ANME-2和少量的ANME-1,而东海内陆架泥质区甲烷厌氧氧化古菌仅为极少量的ANME-3;鄂霍次克海天然气水合物区广古生菌和泉古生菌数量各占一半,主要为MBG-D、MBG-B、MG-I。东海内陆架泥质区沉积物古菌序列主要为泉古生菌(MCG)。海域类型的不同以及有机碳含量等环境因子的差异可能是这两个海域古菌群落结构差异的主要原因.
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利用表面荧光显微镜计数法调查我国黄、东海浮游细菌(包括异养细菌和蓝细菌)生态分布状况,对其在春秋两个季节不同水文状况下与浮游植物叶绿素、无机盐等之间的关系进行了研究。同时,利用流式细胞仪分选功能分离纯化了6株海洋聚球蓝细菌,并对其遗传多样性及捕光色素组成成分进行了分析。 春秋两季黄东海异养细菌丰度大致相当,异养细菌丰度在105-106 Cell ml-1左右。春季异养细菌丰度总体表现为随离岸越远先逐渐降低后略微增高的趋势,秋季异养细菌丰度有离岸越远逐渐增高的趋势。 春季黄东海异养细菌转化率和水体异养细菌生产力与温度呈正相关;异养细菌生物量与海水温度呈负相关。秋季的水文状况较春季较复杂,不同区域的水团对异养细菌有显著影响。 春、秋季,聚球蓝细菌生物量占浮游植物总生物量的百分比分别在4-98%(平均值42%)和在4-93%(平均值30%)之间。 胶州湾浮游细菌的年季变化研究表明,海洋浮游细菌在一年的变化有明显规律。浮游细菌丰度随温度变化呈正相关。 系统进化分析表明,在黄海海域分离到的3株聚球蓝细菌都属Marine Cluster I,它们都含有捕光色素藻红蛋白PE。在东海分离到的3株聚球蓝细菌中,ECS01和ECS02含有捕光色素藻蓝蛋白PC, ECS01和ECS02与Synechococcus sp6301近缘关系很近。ECS03含PE,并且与在日本海分离到的MBIC10089独立成枝。