Impact of Kuroshio on the dissolved oxygen in the East China Sea region

A marine survey was conducted from 18 May to 13 June 2014 in the East China Sea (ECS) and its adjacent Kuroshio Current to examine the spatial distribution and biogeochemical characteristics of dissolved oxygen (DO) in spring. Waters were sampled at 10?25 m intervals within 100 m depth, and at 25?500 m beyond 100 m. The depth, temperature, salinity, and density (sigma- t ) were measured in situ with a conductivity-temperature-depth (CTD) sensor. DO concentrations were determined on board using traditional Winkler titration method. The results show that in the Kuroshio Current, DO content was the highest in the euphotic layer, then decreased sharply with depth to about 1 000 m, and increased with depth gradually thereafter. While in the ECS continental shelf area, DO content had high values in the coastal surface water and low values in the near-bottom water. In addition, a low-DO zone off the Changjiang (Yangtze) River estuary was found in spring 2014, and it was formed under the combined influence of many factors, including water stratification, high primary productivity in the euphotic layers, high accumulation/ sedimentation of organic matter below the euphotic layers, and mixing/transport of oceanic current waters on the shelf. Most notable among these is the Kuroshio intruded water, an oceanic current water which carried rich dissolved oxygen onto the continental shelf and alleviated the oxygen deficit phenomenon in the ECS, could impact the position, range, and intensity, thus the formation/destruction of the ECS Hypoxia Zone.     

The impact of the Changjiang River plume extension on the nanoflagellate community in the East China Sea

Variation in the summer nanoflagellate community on the continental shelf ecosystem of East China Sea (ECS) is closely coupled with environmental variation due to extension of the Changjiang River plume. Spatial patterns of nanoflagellate abundance were studied in June and August 2003, June 2006 and July 2007 over the ECS shelf. The Changjiang River plume was smaller during the August 2003 and July 2007 cruises than during the rest other 2 cruises. Total nanoflagellates densities varied between 1 and 120 × 10² cells ml⁻¹ with the highest abundances occurring within the Changjiang River plume during large plume periods. In the small plume periods, the range of nanoflagellates abundance was 3–33 × 10² cells ml⁻¹ and the highest abundances were observed during these periods either within the Changjiang River plume or the Yellow Sea Coastal Water (YSCW). During large plume periods, nanoflagellate abundance closely related to changes in salinity and during the small period, abundance was most related to water temperature. The pigmented nanoflagellate community (PNF) within Changjiang River plume, especially in the <3 μm size class, appears to increase in response to terrestrial or anthropogenic inorganic nutrient loading in the discharge of fresh water from the Changjiang River. The PNF abundance pronounced increase caused the variation of nanoflagellate community of ECS in summer. We suggest that the discharge of fresh water from Changjiang River has significant ecological impacts on spatial variations in nanoflagellate community in the ECS.     

Long-term changes of dissolved oxygen,hypoxia, and the responses of the ecosystems in the East China Sea from 1975 to 1995

Observation data obtained in the 32°N transect (transect E) in 1975–1995 were used to analyze the long-term changes in dissolved oxygen (DO) concentration and near-bottom hypoxic water in the East China Sea (ECS). A declining trend in annual average DO concentration and the degree of DO saturation was observed. Consequently, the apparent oxygen utilization in the western waters of transect E was on the rise. There was a seasonal hypoxic phenomenon in near-bottom water in the western water of transect E. The width of hypoxic water formed in summer gradually extended eastward along the continental shelf (transect E) at the rate of 3.12 km year⁻¹. Three potential reasons might have caused the formation and maintenance of near-bottom hypoxic water. First, the special hydrological topography and hypoxic deep water of the Taiwan Warm Current provided a backdrop for the hypoxic zone. Second, in summer, the strength of water column stratification restricts water exchange. Third is the occurrence and decay of the phytoplankton bloom. In surface water, nutrient concentrations increased gradually, and chlorophyll (Chl a), primary production, and phytoplankton biomass in summer increased. On the other hand, the community structure of phytoplankton, zooplankton, and zoobenthos became simple. Blooming phytoplankton consumed plenty of nutrients in the surface, but the upwelling of nutritious bottom water was suppressed by the strong thermocline. As a result, sinking of phytoplankton was enhanced because of nutrient deficiency. In recent years, a serious lack of zoobenthos in the study area corresponded to a higher degree of hypoxia. This phenomenon would have a major effect on the evolution of ecological dynamic systems in the ECS.     

东海对台风云娜的海洋响应

Many typhoons pass through the East China Sea(ECS) and the oceanic responses to typhoons on the ECS shelf are very energetic. However, these responses are not well studied because of the complicated background oceanic environment. The sea surface temperature(SST) response to a severe Typhoon Rananim in August 2004 on the ECS shelf was observed by the merged cloud-penetrating microwave and infrared SST data. The observed SST response shows an extensive SST cooling with a maximum cooling of 3°C on the ECS shelf and the SST cooling lags the typhoon by about one day. A numerical model is designed to simulate the oceanic responses to Rananim.The numerical model reasonably simulates the observed SST response and thereby provides a more comprehensive investigation on the oceanic temperature and current responses. The simulation shows that Rananim deepens the ocean mix layer by more than 10 m on the ECS shelf and causes a cooling in the whole mixed layer. Both upwelling and entrainment are responsible for the cooling. Rananim significantly deforms the background Taiwan Warm Current on the ECS shelf and generates strong Ekman current at the surface. After the typhoon disappears, the surface current rotates clockwise and vertically, the current is featured by near inertial oscillation with upward propagating phase.     

东海陆架区中尺度涡运动路径的统计特征分析

基于1993—2017年卫星高度计海面高度异常中尺度涡旋追踪数据集,对东海陆架区及从西北太平洋入侵东海的涡旋进行路径分类、季节变化及特征参量统计分析,并结合再分析流场资料,进行背景流场、涡度场分析。研究结果显示,近25 a,在东海追踪到318个气旋涡和276个反气旋涡。根据涡旋运动路径将其分为:东海陆架浅海生成往深海传播型(148个)、深海生成向东海陆架浅海传播型(35个)、沿等深线运动型(180个)、徘徊型(121个)、外来入侵到达东海陆架型(25个)及外来入侵到达东海深海型(85个)。6类涡旋的数量存在明显的季节分布,各个类型气旋与反气旋涡数量的季节分布也各不相同。其中,沿等深线运动型涡在春、夏季的数量高于秋、冬季。陆架浅海区生成往深海运动型涡的季节分布较为平均,气旋式涡在夏季数量最少,在春季和冬季数量较多。黑潮与涡旋数量的季节分布有关。徘徊型涡的平均生命周期最长,约为44 d;陆架浅海生成往深海运动型及外来入侵到达东海陆架的中尺度涡具有最大的平均振幅,为13.2 cm;外来入侵到达东海陆架型涡具有最大的直径,为122 km;外来入侵到达东海深海型涡在进入东海后的生命周期、振幅、直径在数值上均为最小。     

Spring phytoplankton bloom in the fronts of the East China Sea

Frontal areas between warm and saline waters of the Kuroshio currents and colder and diluted waters of the East China Sea (ECS) influenced by the Changjiang River were identified from the satellite thermal imagery and hydrological data obtained from the Coastal Ocean Process Experiment (COPEX) cruise during the period between March 1^st and 10^th, 1997. High chlorophyll concentrations appeared in the fronts of the East China Seas with the highest chlorophyll-a concentration in the southwestern area of Jeju Island (~2.9 mg/m³) and the eastern area of the Changjiang River Mouth (~2.8 mg/m³). Vertical structures of temperature, salinity and density were similar, showing the fronts between ECS and Kuroshio waters. The water column was well mixed in the shelf waters and was stratified around the fronts. It is inferred that the optimal condition for light utilization and nutrients induced both from the coastal and deep waters enhances the high phytoplankton productivity in the fronts of the ECS. In addition, the high chlorophyll-a in the fronts seems to have been associated with the water column stability as well.     

~(234)U/~(238) as a potential tracer for tracking water masses mixing in the northern East China Sea

The optimum multiparameter(OMP) method was often used to determine the percentages of water masses based on temperature, salinity and other parameters, like nutrient or dissolved oxygen(DO). There are a number of water masses in the East China Sea(ECS), a marginal sea of the western Pacific Ocean. However, it is difficult to clarify the proportion of water masses using traditional parameters, such as temperature, salinity, nutrient or DO because of the occurring of intensive biogeochemical processes in the near shore and shelf areas. Here, we reported the use of ~(234)U/~(238)Uactivity ratio embedded in the OMP method. The results indicate that seawater in the northern ECS mainly consisted of the estuarine water of Changjiang River(CEW), Kuroshio water(KW), and Yellow Sea Coastal Current(YSCC). In March 2017, the CEW only influenced the offshore waters shallower than30 m; the KW affected the east edge and the YSCC contributed more than 75% in the northern ECS.     

234U/238U as a potential tracer for tracking water masses mixing in the northern East China Sea

The optimum multiparameter (OMP) method was often used to determine the percentages of water masses based on temperature, salinity and other parameters, like nutrient or dissolved oxygen (DO). There are a number of water masses in the East China Sea (ECS), a marginal sea of the western Pacific Ocean. However, it is difficult to clarify the proportion of water masses using traditional parameters, such as temperature, salinity, nutrient or DO because of the occurring of intensive biogeochemical processes in the near shore and shelf areas. Here, we reported the use of 234U/238U activity ratio embedded in the OMP method. The results indicate that seawater in the northern ECS mainly consisted of the estuarine water of Changjiang River (CEW), Kuroshio water (KW), and Yellow Sea Coastal Current (YSCC). In March 2017, the CEW only influenced the offshore waters shallower than 30 m; the KW affected the east edge and the YSCC contributed more than 75% in the northern ECS.     

东海沿海季节性海平面异常成因

Based on the analysis of sea level, air temperature, sea surface temperature(SST), air pressure and wind data during 1980–2013, the causes of seasonal sea level anomalies in the coastal region of the East China Sea(ECS) are investigated. The research results show:(1) sea level along the coastal region of the ECS takes on strong seasonal variation. The annual range is 30–45 cm, larger in the north than in the south. From north to south, the phase of sea level changes from 140° to 231°, with a difference of nearly 3 months.(2) Monthly mean sea level(MSL)anomalies often occur from August to next February along the coast region of the ECS. The number of sea level anomalies is at most from January to February and from August to October, showing a growing trend in recent years.(3) Anomalous wind field is an important factor to affect the sea level variation in the coastal region of the ECS. Monthly MSL anomaly is closely related to wind field anomaly and air pressure field anomaly. Wind-driven current is essentially consistent with sea surface height. In August 2012, the sea surface heights at the coastal stations driven by wind field have contributed 50%–80% of MSL anomalies.(4) The annual variations for sea level,SST and air temperature along the coastal region of the ECS are mainly caused by solar radiation with a period of12 months. But the correlation coefficients of sea level anomalies with SST anomalies and air temperature anomalies are all less than 0.1.(5) Seasonal sea level variations contain the long-term trends and all kinds of periodic changes. Sea level oscillations vary in different seasons in the coastal region of the ECS. In winter and spring, the oscillation of 4–7 a related to El Ni?o is stronger and its amplitude exceeds 2 cm. In summer and autumn, the oscillations of 2–3 a and quasi 9 a are most significant, and their amplitudes also exceed 2 cm. The height of sea level is lifted up when the different oscillations superposed. On the other hand, the height of sea level is fallen down.     

东海温度锋的分布特征及其季节变异

根据１９３４－１９８８年东海水文观测资料，重点分析东海温度锋的分布特征及其季节变异，并结合近期中日黑潮合作调查研究成果，初步探讨温度锋季节变异和水团演变的关系，所得主要结论是：（１）东海不仅常年存在浙闽沿岸锋，东海北部陆架锋和黑潮锋，而且、春、夏两季，在东海南部还出现一条东海中部出架锋。（２）江海温度锋季节变化的特点是：冬季，锋的宽度和强度皆是表层最强，夏季，表层温度锋仅出现在浙江近岸小范围海域。     

台湾北部海域黑潮与中尺度涡旋研究进展

The kuroshio,originating from the sea southeast of Taiwan andeast of bashi channel,is the western boundary current of the pacific and has the characterisics of strong flows,high temperature and high salinity.mesoscale eddies have strong kinetie energy with a vertical extent of 100m and a horizontal magnitude of 100km. the submarine topography northeast of Taiwan has complicated strucrures.the continental shelf region shallower than 200m occupies the western and middle part of the east china sea(ecs).in the southeastern ECS lies the deep okinawa trough,in which the main depth can reach more than 1000m.it is the geomorphological separatrix between the continental shelf and the ryukyu islands,. the kuroshio enters the ECS along the east coast of taiwen,flows northeastward along the shelf slope,and hence intrudes across the shelf break.in this paper,our concern is the interaction between the kuroshio in ECS and the taiwan strait waters on the continental shelf. meanwhile the mesoscale eddies in the north of Taiwan is another attention point.     

Seasonal variations in nutrients and chlorophyll-a concentrations in the Northern east China sea

Nutrients, chlorophyll-a, particulate organic carbon (POC), and environmental conditions were extensively investigated in the northern East China Sea (ECS) near Cheju Island during three seasonal cruises from 2003 to 2005. In spring and autumn, relatively high concentrations of nitrate (2.6~12.4 μmol kg^-1) and phosphate (0.17~0.61 μmol kg^-1) were observed in the surface waters in the western part of the study area because of the large supply of nutrients from deep waters by vertical mixing. The surface concentrations of nitrate and phosphate in summer were much lower than those in spring and autumn, which is ascribed to a reduced nutrient supply from the deep waters in summer because of surface layer stratification. While previous studies indicate that upwellings of the Kuroshio Current and the Changjiang (Yangtze River) are main sources of nutrients in the ECS, these two inputs seem not to have contributed significantly to the build-up of nutrients in the northern ECS during the time of this study. The lower nitrate:phosphate (N:P) ratio in the surface waters and the positive correlation between the surface N:P ratio and nitrate concentration indicate that nitrate acts as a main nutrient limiting phytoplankton growth in the northern ECS, contrary to previous reports of phosphate-limited phytoplankton growth in the ECS. This difference arises because most surface water nutrients are supplied by vertical mixing from deep waters with low N:P ratios and are not directly influenced by the Changjiang, which has a high N:P ratio. Surface chlorophyll-a levels showed large seasonal variation, with high concentrations (0.38~4.14 mg m^-3) in spring and autumn and low concentrations (0.22~1.05 mg m^-3) in summer. The surface distribution of chlorophyll-a coincided fairly well with that of nitrate in the northern ECS, implying that nitrate is an important nutrient controlling phytoplankton biomass. The POC:chlorophyll-a ratio was 4~6 times higher in summer than in spring and autumn, presumably because of the high summer phytoplankton death rate caused by nutrient depletion in the surface waters.     

Dimethylsulfide in coastal zone of the East China Sea

Dimethylsulfide (DMS) in seawater were observed four times from February 1993 to August 1994 along a fixed section (PN line) in the East China Sea. The DMS concentrations showed remarkable temporal and spatial variations. The DMS concentrations were generally higher in the upper euphotic layer of the continental shelf zone in summer. The spatial variation, however, was more pronounced even in well mixed winter water, where the concentration of DMS varied widely from 3 to 106 ng-S/l in the continental shelf zone while the salinity was vertically almost uniform. This means that DMS in seawater is rapidly produced and decomposed with a time scale less than one month in the water column. The largest value of 376 ng-S/l was obtained at 5 m depth near the mouth of Changjiang River in August 1994. The mean concentrations in the surface 30 m layer in the continental shelf zone were 21, 54, 126 and 57 ng-S/l in February, October, June and August, respectively, which were about twice as large as those in the Kuroshio region. The mean fluxes of DMS from the East China Sea to the atmosphere are estimated to be 49 g-S/m²/day in winter and 194 g-S/m²/day in summer in the continental shelf zone, and to be 32 and 107 g-S/m²/day in the Kuroshio region.     

北白令海透明胞外聚合颗粒物的含量与来源

透明胞外聚合颗粒物(TEP)是海水中大量存在的黏性颗粒物质,它对于海洋颗粒物的聚集、有机碳的埋藏、食物网物质的传递、痕量金属的清除与迁出等均起着重要作用。本研究开展了夏季北白令海陆架、陆坡和海盆区透明胞外聚合颗粒物含量和分布的研究。结果表明,北白令海TEP含量介于34~628 mg/m3(Xeq)之间,其中陆架、陆坡和海盆区TEP的平均含量分别为240, 145和83 mg/m3(Xeq),整体呈现由陆架向外海降低的趋势。在陆坡和海盆区,TEP含量随着深度的增加而降低,但在陆架近底层水中,观察到TEP高含量的特征,与近底层水高的TSM, POC相对应。TEP与荧光强度、TSM、POC等的关系分析显示,研究海域TEP存在两个来源,其一为海洋上层水体的浮游生物,其主要贡献于陆架上层、陆坡和海盆水体;其二为陆架沉积物的底栖生物,其通过沉积物再悬浮贡献于陆架近底层水。     

威海市天鹅湖海洋牧场底层海水溶解氧浓度时间变化特征

依据威海市天鹅湖海洋牧场2016年7—10月海洋生态环境海底有缆在线观测系统的长期连续观测数据,研究了该牧场底层海水溶解氧浓度的时间变化特征,并探讨了其可能的影响因素。结果表明:观测期间海水溶解氧浓度平均值为6.65mg/L,呈先下降后上升的变化趋势,月平均值最小为6.36mg/L,出现在9月。溶解氧月浓度标准差呈先减小后增大的变化趋势,而溶解氧日浓度标准差总体变化趋势与月浓度标准差相反。底层海水基本上处于不饱和状态,月均溶解氧消耗量在观测期间逐月增大。海水温度是影响溶解氧浓度变化的主要因素。7月1日至8月24日期间,牧场海域存在季节性温跃层。7月1日至17日与8月11日至24日期间,溶解氧浓度下降可能受季节性温跃层和海水温度上升的共同影响;7月18日至8月1日期间,溶解氧浓度变化不受季节性温跃层控制。大风过程会增强表、底层海水交换,使溶解氧浓度上升。月均溶解氧浓度日变化均表现出双峰双谷的特征,与月均水深日变化对比, 7—8月0—13时无显著正相关性, 7—8月1—23时及9—10月相位变化基本一致,涨潮时海水溶解氧浓度升高,而落潮时降低,说明研究区域外海水溶解氧浓度很可能高于近岸,而潮流输运过程使得近岸海水溶解氧浓度随潮汐过程变化。     

东海2012年夏季海-气界面碳交换及其区域碳汇强度变化趋势初探

基于2012年7月对东海的调查,剖析了其水体中各形态碳(pCO2、DIC、DOC、POC)的区域分布特征,估算了海-气界面CO2的交换通量(FCO2),探讨了影响其交换的主要因素,在此基础上,结合历史资料初步分析了近十几年来该海域海-气界面CO2交换通量的变化趋势。结果表明,2012年7月长江口邻近海域相对南部陆架区具有较低的DIC浓度,而DOC与POC的浓度相对较高。调查区域表层水pCO2变化范围为96.28~577.7μatm(1atm为101 325Pa),平均值为297.6μatm,低值区出现在长江冲淡水区(30°~33°N,123°~125°E),高值区主要分布在东海陆架的南部区域。表层水pCO2主要受控于长江冲淡水的输入和混合(盐度)、台湾暖流以及生物生产等。调查海域2012年7月海-气FCO2平均为(-6.410±7.486)mmol/(m2·d),表现东海在夏季是大气CO2的汇区,区域碳汇强度由强到弱依次为:长江冲淡水区(CDW)、黄东海混合水区(YEMW)、陆架咸淡水混合区(SMW)、近岸上升流区(CUW)和台湾暖流区(TWCW),东海夏季每日吸收大气CO2(以C计)约(18.3±19.8)kt。结合历史资料分析发现,近十几年来东海夏季碳汇强度有增强趋势,CDW区的海-气界面CO2通量平均年增速为-0.814mmol/(m2·d),即海水吸收大气二氧化碳每年增加约54.6kt,是夏季东海碳汇增加的最主要贡献者。     

Internal solitary waves in the East China Sea

A European Space Agency＇ s ENVISAT advanced synthetic aperture radar （ASAR） image covering Zhejiang coastal water in the East China Sea （ECS） was acquired on 1 August 2007. This image shows that there are about 20 coherent internal solitary wave （ISW） packets propagating southwestward toward Zhejiang coast. These ISW packets are separated by about 10 kin, suggesting that these ISWs are tide-generated waves. Each ISW packet contains 5-15 wave crests. The wavelengths of the wave crests within the ISW packets are about 300 m. The lengths of the leading wave crests are about 50 km. The ISW amplitude is estimated from solving KdV equation in an ideal two-layer ocean model. It is found that the ISW amplitudes is about 8 m. Further analysis of the ASAR image and ocean stratification profiles show that the observed ISWs are depression waves. Analyzing the tidal current finds that these waves are locally generated. The wavelength and amplitude of the ECS ISW are much smaller than their counter- parts in the South China Sea （SCS）. The propagation speed of the ECS ISW is also an order of magnitude smaller than that of the SCS ISW. The observed ISWs in the ECS happened during a spring tide period.     

Micro- and macronutrients in the southeastern Bering Sea: Insight into iron-replete and iron-depleted regimes

Surface transects and vertical profiles of macronutrients, dissolved iron (D-Fe), and dissolved manganese (D-Mn) were investigated during August 2003 in the southeastern Bering Sea. We observed iron-limited, HNLC surface waters in the deep basin of the Bering Sea (15-20 μmol/kg nitrate, ∼0.07 nmol/kg D-Fe, and ?1.0 nmol/kg D-Mn); nitrate-limited, iron-replete surface waters over the shelf (<0.1 μmol/kg nitrate, 0.5-4 nmol/kg D-Fe, and 2-33 nmol/kg D-Mn); and high biomass at the shelf break (“Green Belt”), where diatoms appeared to have been stressed by low D-Fe concentrations (<0.3 nmol/kg). Sources of nitrate and iron to the Green Belt were investigated. A mixture of Aleutian North Slope Current water (with elevated, but non-sufficient iron concentrations relative to its high nitrate concentrations) and surface waters from the vicinity of the Bering Canyon (with lower nitrate concentrations, but similar dissolved iron concentrations) was carried along the shelf break by the Bering Slope Current. This water mixture provided macro- and micronutrients at the southern end of the shelf break. The oceanic domain supplied additional macronutrients to Green Belt waters, while the bottom layer of the outer shelf domain supplied additional macro- and micronutrients through enhanced vertical mixing at the shelf break. Surface waters near the Pribilof Islands, where the highest surface D-Fe concentrations were observed (∼5-6 nmol/kg), represent a potential source of additional iron to Green Belt waters. During summer, the subsurface water of the middle shelf domain is a potential source of nitrate to the nitrate depleted waters of the shelf. In this subsurface cool pool, we observed evidence of substantial denitrification with lower than expected nitrate concentrations.     

东海陆架表层水温年际变化时空特征分析

结合东海沿岸嵊山(北)和厦门(南)站1960—2001年海表温度(SST)监测数据与东中国海1982—2011年AVHRR水温资料,讨论了台站监测的空间代表范围,分析了东海陆架SST年际变化的时空特征。结果表明,嵊山和厦门站SST变化分别代表内陆架和台湾海峡。东海陆架52年来SST总体呈升温趋势,冬季最为显著;内陆架的升幅远大于台湾海峡。内陆架水温冬季分别在1977年和1995年发生两次跃升,共升温2.34℃;春、夏、秋季均在1994年发生冷暖转折,分别升高1.19℃、1.43℃和1.16℃。台湾海峡水温冬季在1989年跃升0.91℃,夏季在1987年跃升0.38℃,春、秋季则在1996—1997年间分别升温0.80℃和0.58℃。全年水温变化最大处在长江口附近内陆架海区,可能的主导因素是低盐水与外海水混合:随季风、降水、径流变化的沿岸流、长江冲淡水和台湾暖流给该区域带来不同水团,使得热量向下层输运减少,从而导致东海内陆架升温快于其它海区。