Methane in the East China Sea water

Methane in the East China Sea water was determined four times at a fixed vertical section along PN line consisting of 11–14 stations, in February 1993, October 1993, June 1994 and August 1994. The mean concentration of methane in the surface water was not significantly higher than that in the open ocean. The methane concentration below the pycnocline increased during the stratified period in summer to autumn and reached to 15 nmoles/l at most in October. The concentration of methane was fairly well correlated with AOU in the layer below the pycnocline in the stratified season. This means that methane in the bottom water has only a single source, which is expected to be anoxic sediments near the coast, and that the oxidation rate of methane in the water is extremely slow in the oxic water. The high methane observed in October completely disappeared in February, indicating that the methane was escaped to the atmosphere or transported to the pelagic ocean by the Kuroshio current. The East China Sea, therefore, is not a large direct and stationary source for the atmospheric methane, but may have some role as a source by supplying it sporadically to the atmosphere in early winter or indirectly from the surface of the pelagic ocean.     

Estimation of the transports through the Strait of Gibraltar

An acoustic doppler current profiler (ADCP) is used to measure the currents and estimate the transports over the Camarinal Sill at the Strait of Gibraltar. The deepest measurements of the ADCP compare well with an underlying conventional current meter. The exchange interface between the Atlantic and the Mediterranean water is defined as the depth of the maximum vertical shear. The mean depth of the shear interface is 147 m. The time series of the depth of the interface and the currents are used to estimate the transports across the Strait. The resulting values are 0.78 Sv for the Atlantic inflow and −0.67 Sv for the Mediterranean outflow. The time series of the shear interface include fortnightly oscillations of 19 m. The time series of the transports are compared with the pressure and sea level difference records across the Strait. Linear multiple regression is used to estimate the (statistical) contribution of each parameter on the variation of transports. The cross strait sea level difference is well correlated with the Atlantic inflow and accounts for 57% of the variability of the transport records which improves to 78% when the fortnightly and monthly cycles are included in the linear regression. The Mediterranean outflow is best correlated with the along strait sea level difference which accounts for only 10% of the variability of the transport record. Again the addition of the M_sf and the MM cycles improves the percentage of the variance accounted for to 37%. The local, along strait wind component is significantly correlated with, both the Atlantic inflow and the across strait sea level difference.     

Volume and heat transports and material fluxes in the East China Sea during April 1994

INTRODUCTIONTherehavebeenmanystudiesandcomputationsonVToftheKuroshiointheEastChinaThisprojectwassupportedbytheNationalNaturalScienceFoundationofChinaundercontractNo.49476278.Asanditsvacation.Forexample,(1)basedonhydrographicobservationsatactionG(PN)f...     

南海与周边海域表层塑料颗粒交换的拉格朗日示踪研究

塑料污染已成为国际海洋界关注的海洋环境问题之一。文章探讨海洋环流对南海及其周边海域表层塑料颗粒交换的影响。在南海周边多个海域, 分别在4个季节投放塑料颗粒。一年后, 用拉格朗日颗粒示踪方法考察投放颗粒的运动轨迹和最终停留位置。结果表明, 在秋、冬季, 大部分塑料颗粒会进入南海和爪哇海, 极少部分颗粒北输送到太平洋; 在春、夏季, 仅有部分颗粒进入南海和爪哇海, 而多数颗粒流到太平洋。南海洋流具有季节特征, 塑料颗粒轨迹特征与之较为符合。     

Characteristics of outer shelf water in the East China Sea

Water mass properties along cross-sections of the Kuroshio in the East China Sea (ECS) are investigated in detail. We used temperature, salinity and dissolved oxygen data from 2000 and 2002, together with historical temperature and salinity data from 1987 to 2004. Water properties were divided into two groups: high and low salinities or oxygen at temperatures warmer than 15 and 12 °C, respectively. We found the existence of outer shelf water W2, as defined by clear modes in frequency distributions of salinity and oxygen within various temperature segments. The outer shelf water was different from both Kuroshio Tropical Water (KTW) and coastal water. We mapped horizontal and vertical distributions of W2, along with W1 and KTW. The outer shelf water was distributed with density σ _t = 22.5–25.5 over a relatively broad area, from the outer continental shelf to the continental slope, particularly in autumn. Vertical distribution of the water suggests that W2 spread from the outer shelf to just the shelf side of the Kuroshio Current velocity maximum. Seasonal variations are examined with historical data along PN section over 17 years, and suggest that the appearance of W2 is distinct in summer and autumn. By comparing temperature–salinity (T–S) diagrams from Taiwan Strait and east of Taiwan, the outer shelf water (W2) originates from South China Sea Tropical Water (SCSTW), as suggested by Chen, J Geophys Res 110:C05012 (2005). The present study of the ECS clearly shows that SCSTW is transported along the east coast of Taiwan or through the Taiwan Strait into the ECS. It then spreads over a relatively wide area from the outer shelf to just the shelf side of the Kuroshio axis, and there is some horizontal mixing between SCSTW and KTW around the shelf break.     

东海海水中的溶存甲烷

基于1994年秋季航次在东海的调查资料,较详细地分析了溶存甲烷在水体中的分布规律、成因和来源.表层水中溶存甲烷呈过饱和状态,饱和度127%～254%,温跃层以上水体中,甲烷的断面分布不同于营养盐的分布,各站测值相近,没有显示出受长江冲淡水的影响,而呈现的舌状分布,在陆架底层水中有明显的高浓度甲烷水体,表明甲烷从沉积物中迅速扩散进入底层水.黑潮次表层水的涌升过程稀释了陆架边缘底层水中的甲烷.在陆架和大洋区测站上,甲烷的垂直分布不同,前者主要受物理混合过程所控制;后者呈大洋区分布特征,在温跃层附近出现甲烷的次表层最大,这可能是陆架底层高浓度甲烷沿等密度面的输送所致.

     

水团相互作用与东海高密水环流的演变

本文利用水文和海流观测资料，从水团相互作用去研究东海高密水及其环流的演变。获得如下一些结果：东海高密水冬季形成于东海中部陆架混合水中，入春以后水团挤压，高密水显得更为突出，入秋后高密水变性，东海中部陆架混合水重新形成；东海高密水核心区可形成气旋环流，从冬到秋经历了一个弱—强—弱的演变过程。海流观测结果证实这个环流是存在的；在东海高密水南侧存在较明显的密度锋，从冬到秋它也经历了一个弱—强—弱的演变过程；水团分析发现，各种与主体分离的混合水从春到夏可在高密水核心周围组合成一个环，从而进一步印证了这个高密水环流的存在     

The statistic inversion algorithms of water constituents for the Huanghai Sea and the East China Sea

A group of statistical algorithms are proposed for the inversion of the three major components of Case-Ⅱ waters in the coastal area of the Huanghai Sea and the East China Sea. The algorithms are based on the in situ data collected in the spring of 2003 with strict quality assurance according to NASA ocean bio-optic protocols. These algorithms are the first ones with quantitative confidence that can be applied for the area. The average relative error of the inversed and in situ measured components‘ concentrations are: Chl-a about 37%, total suspended matter (TSM) about 25%, respectively. This preliminary result is quite satisfactory for Case-Ⅱ waters, although some aspects in the model need further study. The sensitivity of the input error of 5% to remote sensing reflectance (Rrs) is also analyzed and it shows the algorithms are quite stable. The algorithms show a large difference with Tassan‘s local SeaWiFS algorithms for different waters, except for the Chl-a algorithm.     

The formation and evolution of the East China Sea winter dense water

On the basis of the historical profile observations and the recent Kuroshio observations,the yearly formation,development and decay of the high density water found between 50 to 100 m isobath over the middle and southern East China Sea continental shelf are anyalysed. The formation of this high density water occurs between November and March of the following year. A possible reason for it is that as the mixed water between the coastal water and the outer sea water transports northward by the Taiwan Warm Current, its density increases by surface cooling. It also mixes with the neighbouring lower density water masses. The transportation and decay of the high density water through April to July are also descussed. They can be ascribed to the seasonal surface layer warming and the fast development of Taiwan Warm Current. The high density water disappears in August.     

Intrusion of Kuroshio water onto the continental shelf of the East China Sea

As a fundamental study to evaluate the contribution of the Kuroshio to primary production in the East China Sea (ECS), we investigated the seasonal pattern of the intrusion from the Kuroshio onto the continental shelf of the ECS and the behavior of the intruded Kuroshio water, using the RIAM Ocean Model (RIAMOM). The total intruded volume transport across the 200m isobath line was evaluated as 2.74 Sv in winter and 2.47 Sv in summer, while the intruded transport below 80m was estimated to be 1.32 Sv in winter and 1.64 Sv in summer. Passive tracer experiments revealed that the main intrusion from the Kuroshio to the shelf area of the ECS, shallower than 80m, takes place through the lower layer northeast of Taiwan in summer, with a volume transport of 0.19 Sv. Comparative studies show several components affecting the intrusion of the Kuroshio across the 200 m isobath line. The Kuroshio water intruded less onto the shelf compared with a case without consideration of tide-induced bottom friction, especially northeast of Taiwan. The variations of the transport from the Taiwan Strait and the east of Taiwan have considerable effects on the intrusion of the Kuroshio onto the shelf.     

Study on interaction between the coastal water, shelf water and Kuroshio water in the Huanghai Sea and East China Sea

The main processes of interaction between the coastal water, shelf water and Kuroshiowater in the Huanghai Sea (HS) and East China Sea (ECS) are analyzed based on the observation and study results in recent years. These processes include the intrusion of the Kuroshio water into the shelf area of the ECS, the entrainment of the shelf water into the Kuroshio, the seasonal process in the southern shelf area of the ECS controlled alternatively by the Taiwan Strait water and the Kuroshio water intruding into the shelf area, the interaction between the Kuroshio branch water, shelf mixed water and modified coastal water in the northeastern ECS, the water-exchange between the HS and ECS and the spread of the Changjiang diluted water.     

西南黄海近岸低盐水体的来源与输送机制

In the southwestern Yellow Sea there is a low-salinity and turbid coastal water,the Subei Coastal Water(SCW).The origins of freshwater contents and thus the dissolved terrigenous nutrients in the SCW have been debated for decades.In this study,we used a well-validated numerical model to quantify the contributions of multiple rivers,i.e.,the Changjiang River in the south and the multiple Subei local rivers(SLRs) in the north,in forming this yearround low-salinity coastal water.It is found that the freshwater contents in the SCW is dominated by the Changjiang River south of 33.5°N,by the SLRs north of 34.5°N,and by both sources in 33.5°–34.5°N.Overall,the Changjiang River contributes ~70% in the dry season and ~80% in the wet season of the total freshwater contents in the SCW,respectively.Dynamics driving the Changjiang River Plume to flow northward is the tidal residual current,which can even overwhelm the wind effects in winter seasons.The residual currents turn offshore near the Old Yellow River Delta(OYRD) by the collision of the two tidal wave systems,which transport the freshwater from both sources into the interior Yellow Sea.Water age experiments show that it takes 50–150 d for the Changjiang River Plume to reach the SCW in the spring and summer seasons,thus there is a 2-month lag between the maximum freshwater content in SCW and the peak Changjiang River discharge.In the winter and autumn seasons,the low salinity in inner SCW is the remnant Changjiang River diluted water arrived in the previous seasons.     

潮汐对东海陆架边缘处水交换的影响

为探讨潮汐对东海陆架边缘处水交换通量的影响,本文基于ROMS海洋数值模式,对渤海、黄海、东海的潮汐、环流进行了模拟研究。研究结果显示,在水平方向上,潮汐效应主要影响我国台湾岛东北及日本九州西南的水交换,其中在台湾岛东北区域,潮汐效应通过增加黑潮分支流(KBC)的向岸及离岸速度来加强黑潮水的跨陆架交换。潮汐效应对200 m等深线处跨等深线流速的影响量值约为3～5 cm/s。从垂直方向上来看,潮汐效应能够影响到深度200m处水层的深层交换。进一步研究其作用机制,发现潮汐效应主要通过平流输送项来影响水体交换,而其对水体的水平及垂直扩散项的影响较小。     

东海水体中POC的分布特征

本文研究１９９４年春、秋季东海陆架海区水体ＰＯＣ的分布特征。０和１０ｍ层的水平分布图呈现：近岸海区水体的ＰＯＣ含量最高，并片外海递减，黑潮区域是ＰＯＣ的低值区。在离岸远的深水海区受长江径流影响削弱，ＰＯＣ分布比较均匀。秋季ＰＯＣ等值线呈现与岸平行并片外海递减，这是受陆地径流、海区生物活动所控制。春季ＰＯＣ的分布呈现受水团推移的迹象，在ＰＮ线上的４０６－４０８－４１１站位附近海区出现ＰＯＣ高值区，与     

Sediments in the East China Sea

This paper describes measurements of sediments during the 2000-2001 Asian Seas International Acoustic Experiment in the East China Sea. A number of techniques were used to infer properties of these sediments, including gravity and piston cores, subbottom profiling using a water gun, long-range sediment tomography, and in situ measurement of conductivity. Historical data from echosounder records and cores showed two regions of surficial sediments in the experimental area: a silty area to the west and a sandy area to the east. The tomography, cores, and water-gun measurements confirm the two surficial sediment regions seen in the historical data and also indicate that the subbottom structure at the experimental site consists of a thin (0-3 m thick) layer of sandy sediment directly beneath the sea floor. Below this layer, there is an extensive package of sediment with relatively uniform acoustic attributes. Core analysis shows that the surface sediment layer varies in compressional wave speed from a low near 1600 m/s in the west side of the experiment area to 1660 m/s in the east side of the experiment area. Long-range sediment tomography inversions show a similar spatial variation in the surface layer properties. In addition, the layer thickness as determined from tomography is consistent with the estimates from subbottom profiling.     

Trichodesmium in the East China Sea

A study is made on the surface distribution ofTrichodesmium thiebautii Gomont in the East China Sea during the years 1961–1967.

1. This alga is very scarce or absent in the period from January to March, and begins to increase in May and June, reaching the maximum population density from July to September, and again decreases in October and November.
2. In summerT. thiebautii is predominantly distributed in the area along the Kuroshio current with high densities of 10²–10³ filaments/l, occasionally exceeding 10³ filaments/l. This alga is estimated to occupy the major part or almost all the parts of chlorophylla in situ contained in the surface water of this season.
3. The occurrence ofT. thiebautii off the southern coasts of Central Japan seems to be caused rather by the multiplication in its own habitat than by the transportation by the Kuroshio current from the East China Sea.

     

Mechanism of currents through the straits of the Japan Sea: Mean state and seasonal variation

The mechanism governing the mean state and the seasonal variation of the transports through the straits of the Japan Sea is studied using a newly presented, simple analytical model and a basin scale general circulation model (GCM). The GCM reproduces the transports through the straits of the Japan Sea realistically owing to its fine horizontal resolution of about 20 km and realistic topography. A series of experiments conducted by changing surface forcing shows that the annual mean wind-driven circulation in the North Pacific Ocean is most responsible for the formation of the mean transports. It is also found that the seasonal variation of the alongshore component of monsoonal wind stress over the North Pacific basin, especially that over the Okhotsk Sea, is responsible for the seasonal variation of the transports. The simple analytical model can explain these simulated features very well. The physical concept of this model is based on the formation of the around-island circulation through the adjustment of coastally trapped waves and Rossby waves and geostrophic control at the narrow straits. It solves the sea surface heights (SSHs) at the edge of each strait and the transport through it. The value of the line integral of the SSH along the island is determined by the baroclinic Rossby waves approaching the island from the east and the alongshore wind stress around the island. The basin scale seasonal variation of SSH along the coast induced by the variation of the alongshore monsoonal wind stress can also be incorporated into this model by giving the SSH anomaly at the northeastern point of the Soya Strait. Thus, it is suggested that both the mean state and the seasonal variation are caused mainly by wind stress forcing. Minor modification by the seasonal heat flux forcing brings the amplitude and the phase of the seasonal variation closer to the observed values.     

An oil slick spectral experiment of nearshore sea water in the East China Sea

Along with the rapid advance in global industrialization, oil spill events caused by offshore operations, trans- portation and accidents are increasing. Compared with ship surveys, monitoring oil spills through remote sensing has real-time, comprehensive, low-cost advantages, which can effectively guide cleaning and evalu- ation, and reduce the marine ecological destruction resulting from oil spills. Therefore, studying the remote sensing mechanism used to monitor marine oil spills is of great significance for ecological environmen- tal protection. This paper describes an experiment and corresponding analysis based on the above-water method, using the East China Sea coastal turbid water. The analysis shows that ＂upward short-wave＂ in ultraviolet and blue-purple bands and its displacement, along with the changing thickness, are important characteristics for distinguishing between the oil slick and the sea water, and also to differentiate oil slicks of different thicknesses. From blue to near-infrared bands, the spectrum of lube oil is flatter than that of diesel, and the diesel spectrum rises faster than the lube spectrum on the right side of the trough at 400 nm. These two features form an important basis for differentiating diesel from lube oil. These analyses will further the development of oil spill remote sensing in the East China Sea.     

Spatial and temporal variation of water mass mixing characteristic in the East China Sea

On the basis of the observation data of Kuroshio since 1984 and relative historical data in the East China Sea, spatial and temporal variation of water mass mixing characteristic in the observation area is analysed. The main results are as follows.