Seasonal dynamics of the phytoplankton community in Sendai Bay,northern Japan

Sendai Bay is located on the Pacific coast of northern Japan and suffered serious damage following the 2011 off the Pacific coast of Tohoku earthquake and tsunami in March 2011. To assess the impact on the marine ecosystem, information was needed on the phytoplankton communities and their seasonal variation. However, such information was limited. Therefore, an intensive monitoring of the phytoplankton was carried out from March 2012 to April 2014. Seasonal variation of the phytoplankton community was similar at coastal and offshore stations. Total phytoplankton biomass, based on Chl a concentration, peaked in spring and then decreased to a minimum in summer, before gradually increasing during early winter and peaking again in the following spring. This seasonal pattern was consistent with previous studies conducted before the earthquake and tsunami. Also, size structure of the phytoplankton community and its four main groups was estimated from the size-fractioned samples of Chl a. Our results also showed that the spring bloom consisted of large diatoms, with their growth ceasing due to nitrogen depletion. The bloom was followed by a summer period where cyanobacteria and picoeukaryote became dominant, with high cell densities in spite of low nutrient concentrations. In addition, sporadic environmental changes, such as those following typhoons, were observed. These resulted in large increases/decreases in individual phytoplankton groups.     

A study into the export of saline water from Hervey Bay, Australia

Australia's climate is one of the world's driest and locally characterised by high year-to-year rainfall variability. Due to high evaporation and low river runoff many estuaries and embayments in the region are characterised by inverse conditions with salinity increasing toward the coast and river mouths. Such conditions were also found during the first comprehensive hydrographic survey of Hervey Bay located at the east coast of Australia in early spring 2004. The survey traced a subsurface salinity maximum that was found in earlier studies within the East Australia Current, east of Hervey Bay to the shallow southwest regions of the bay. These are identified as the most likely source region for locally produced saline Hervey Bay Water. Utilising a simple box model, mean evaporation rates and historical river runoff data, it is demonstrated that inverse conditions are likely to dominate throughout the year. The negative circulation is a climatological feature of this estuary that is not limited to the dry season of the year. Due to persistent drought and declining rainfall in coastal eastern Australia, these conditions are likely to persist into the near future and need to be considered in coastal management strategies.     

Evidence for erosion and deposition by the 2011 Tohoku-oki tsunami on the nearshore shelf of Sendai Bay,Japan

Ongoing geological research into processes operating on the nearshore continental shelf and beyond is vital to our understanding of modern tsunami-generated sediment transport and deposition. This paper investigates the southern part of Sendai Bay, Japan, by means of high-resolution seismic surveys, vibracoring, bathymetric data assimilation, and radioisotope analysis of a core. For the first time, it was possible to identify an erosional surface in the shallow subsurface, formed by both seafloor erosion and associated offshore-directed sediment transport caused by the 2011 Tohoku-oki tsunami. The area of erosion and deposition extends at least 1,100 m offshore from the shoreline down to water depths of 16.7 m. The tsunami-generated sedimentological signature reaches up to 1.2 m below the present seafloor, whereas bathymetric changes due to storm-related reworking over a period of 3 years following the tsunami event have been limited to the upper ~0.3 m, despite the fact that the study area is located on an open shelf facing the Pacific Ocean. Tsunami-generated erosion surfaces may thus be preserved for extended periods of time, and may even enter the rock record, because the depth of tsunami erosion can exceed the depth of storm erosion. This finding is also important for interpretation of modern submarine strata, since erosion surfaces in shallow (depths less than ~1 m) seismic records from open coast shelves have generally been interpreted as storm-generated surfaces or transgressive ravinement surfaces.     

Typical fields of wind waves and swells in the Northern Pacific

Using all of the atmospheric patterns classified by Polyakova A.M., we accomplished calculations of the surface wind fields over the North Pacific for wind waves observable 6, 12, 18, and 24 hours after a storm and the swell waves observable 24, 48, and 72 hours after a storm. The considerable extension of the ocean creates quasi-unlimited speeding up of the wind waves during continuous strong winds (over 20 meters per second). This determines the presence of wide areas of highly developed wind waves with a 5% probability that the wave heights will exceed the 10–12 meter estimates. The swell waves decay faster: their height reduces by half in 24 h, while, in 72 h, they achieve the background level of the ocean’s swell waves.     

孟加拉湾海洋划界案初步研究

孟加拉湾划界案是国际海洋法法庭审理的第一起海洋划界案。法庭对盂加拉国与缅甸的领海、专属经济区及大陆架的划界纠纷进行了裁决。分析研究了该案中法庭对这种大陆架案件的管辖权、当事国双方对这一区域的权利主张以及法庭划界采用的法律与划界的方法(等距离/相关情况方法)。     

Seasonal succession in the diatom community of Sendai Bay,northern Japan,following the 2011 off the Pacific coast of Tohoku earthquake

Sendai Bay in northern Japan suffered serious damage from massive tsunamis generated by the 2011 off the Pacific coast of Tohoku earthquake. The physical disturbance caused by a tsunami may affect the coastal ecosystem, including the planktonic diatom community. We investigated seasonal changes in the diatom community structure at a coastal and an offshore station in Sendai Bay, from June 2011 (3 months after the tsunami) to April 2014. Diatom abundance increased at both stations during the spring. Sporadic increases were also recorded at the coastal station during the summer because of silicate input from river discharge. Seasonal succession of the diatom communities was similar at both the coastal and offshore stations. The onset of the spring bloom consisted mainly of Chaetoceros spp. when water temperatures were low. Subsequently, species such as Skeletonema costatum s.l. became dominant as salinity and nutrient concentrations decreased. Cell density decreased from summer into early winter. Leptocylindrus danicus became dominant in the summer, but was replaced by Thalassiosira cf. mala from autumn into winter. Redundancy analysis (RDA) showed that most of the variation in the diatom community could be explained by temperature, salinity, NO₃ ^?, NO₂ ^?, PO₄ ^3?, and SiO₂. In addition, the occurrence of diatom species before the tsunami showed a similar pattern to that after the tsunami, suggesting that the tsunami did not have a serious impact on the diatom community in Sendai Bay.     

基于生态系统服务的海洋健康评估与调控:以莱州湾为例

近岸海域的生态系统管理,要求对海洋健康进行综合的评估以及对人工调控进行科学的指导,进而促进可持续发展。本文构建了定量化方法,用于评估当前的和近期的基于生态系统服务的海洋健康。以莱州湾为例的研究结果表明,当前的海洋健康指数分值为0.7856(总分为1.0);通过对负面压力进行不同强度的人工调控,得到近期海洋健康预计的变化范围为0.5551到0.8041。具体地说,本文评估得到当前的海洋健康主要表现为文化服务和供给服务基本优秀,而支持服务和调节服务不够良好。若不对持续增长的压力采取有效的调控措施,该近岸海域生态系统会在近期丧失部分支持服务和调节服务;若负面压力被完全控制,该近岸海域生态系统服务的分类等级会得到小幅提升。另外,应进一步加强对生态系统服务尤其是文化服务和调节服务的宣传教育。本文的分析过程和量化结果,为进一步指导人工调控提供了灵活的工具,有助于海岸带区域的生态系统管理。     

Intrusion events of the intermediate Oyashio Water into Sagami Bay, Japan

Intermediate intrusion of low salinity water (LSW) into Sagami Bay was investigated on the basis of CTD data taken in Sagami Bay and off the Boso Peninsula in 1993–1994. In October 1993, water of low temperature (<7.0°C), low salinity (<34.20 psu) and high dissolved oxygen concentration (>3.5 ml I⁻¹) intruded along the isopycnal surface of {ie29-1} at depths of 320–500 m from the Oshima East Channel to the center of the bay. On the other hand, the LSW was absent in Sagami Bay in the period of September–November 1994, though it was always found to the south off the Boso Peninsula. Salinity and dissolved oxygen distributions on relevant isopycnal surfaces and water characteristics of LSW cores revealed that the LSW intruded from the south off the Boso Peninsula to Sagami Bay through the Oshima East Channel. The LSW cores were distributed on the continental slope along 500–1000 m isobaths and its onshore-offshore scales were two to three times the internal deformation radius. Initial phosphate concentrations in the LSW revealed its origin in the northern seas. These facts suggest that the observed LSW is the submerged Oyashio Water and it flows southwestward along the continental slope as a density current in the rotating fluid. The variation of the LSW near the center of Sagami Bay is closely related to the Kuroshio flow path. The duration of LSW in Sagami Bay is 0.5 to 1.5 months.     

罗源湾区域入海非点源污染COD排放量估算

根据汇水流向,借助GIS进行罗源湾汇水区的划分;在ENVI软件下利用遥感分析技术提取土地利用类型;结合研究区域内主要溪流的水质监测结果和土地利用现状,利用反推法计算出农田污染单位面积COD负荷.在此基础上,采用排污系数法和单位面积污染负荷法分别计算出各汇水区农村生活污水、畜禽养殖、农田和村镇建设用地降雨径流的COD排放量.结果表明罗源湾入海非点源污染COD总排量为11 446.44t/a,其中农村生活污水的COD排放量最大,约占38.9%,其次是畜禽养殖、农田和村镇建设用地降雨径流污染.最后提出非点源污染控制的建议.     

乐清湾生态系统脆弱性研究

随着海洋经济的开发与发展,海洋生态环境被破坏的问题日益突出,生态系统变得越来越脆弱.从浙江典型海湾乐清湾入手,分析了乐清湾生态系统脆弱性形成的机制,即自然和人为多种复杂动力因素形成的相互耦合作用下导致生态系统出现了脆弱性,其脆弱性可分为固有脆弱性和特殊脆弱性两类.固有脆弱性主要由陆海动力作用形成的,包括径流、气温、降水、波浪、潮流等环境因素.特殊脆弱性由人类开发活动作用形成的,主要包括海岸工程、滩涂围垦、水产养殖、污染等非环境因素.综合以上原因,指出了乐清湾生态系统处于亚健康状态,并已接近不健康边缘,生态系统极其脆弱,虽然生态系统的主要服务功能尚能发挥,但已不能满足海洋功能区划的要求,严重影响到海洋经济的可持续发展.乐清湾生态系统脆弱性具体表现在以下几个方面:(1) 水体受无机氮和活性磷酸盐污染严重,富营养化程度显著,氮磷比失衡,春季全湾水质为劣四类,夏季76%的海域水质为四类或劣四类;(2) 海湾自然水域实际面积缩小近四分之一,纳潮量相应减少了近5.79%;(3) 生物多样性降低,总生物量和物种数逐年下降,海洋食物链已经遭到严重破坏,生物群落结构发生明显改变;(4) 养殖区沉积物质量下降,在水动力作用下易造成"二次污染";(5) 周边的渔业经济下滑,捕捞鱼类个体偏小,且低值鱼类较多.最后对乐清湾生态系统脆弱性修复提出了对策和建议,主要应落实海洋环境目标管理责任制、加强入海污染物控制、运用生态学原理和技术防治海水养殖污染、利用大型海藻修复水域富营养化以及建立海洋生态环境监测预报和执法管理体系,使海洋生态系统重新进入良性循环,为海洋资源可持续利用提供发展空间.     

湄洲湾潮流特性的数值研究

本文运用一个含动边界的二维河口海岸动力模型模拟了湄洲湾潮汐潮流的基本特征,模拟结果与实测数据吻合较好．在此基础上估算了湄洲湾大、小潮过程的纳潮量,并根据湾内保守示踪物的质量（浓度）随涨、落潮流周期性的变化,进一步估算了湄洲湾的水交换周期,其半交换和80％的交换周期分别为5d和15d．同时可以看出,主航道深水区的水交换特性明显强于湾顶浅水区．     

兴化湾大型底栖生物生态研究

兴化湾大型底栖生物已鉴定有314种,平均生物量为36.60g/m2,平均栖息密度为162个/m2.按Bray-Curtis相似性指数和多维排序尺度可划分为4个群落.应用丰度生物量比较法(ABC)和种类个体几何级数显示群落结构相对稳定.     

泉州湾潮流场的数值模拟研究

本文建立了水深平均的二维潮流数学模型,并利用该模型对泉州湾潮流运动进行了数值模拟研究,模拟的潮位过程、流速与流向均与实测值吻合良好。模拟结果演示了湾口至湾顶潮差逐渐增大、潮位滞后、涨落潮历时变化的特性以及湾内的流速、流态分布特征,表明了湾内潮流为正规半日潮,主航道内流速大于周边地区,潮流较强区域位于鞋沙南北潮沟,南槽流速大于北槽,口门内潮流具有明显的往复流特性,口门外潮流具有一定的旋转流性质。     

Fortnightly shifts of intrusion depth of oceanic water into Ise Bay

To clarify the time change in water exchanges between Ise Bay and the adjacent ocean, repeated hydrographic observations were conducted along the longitudinal section in Ise Bay. The results show that the mixing condition at the bay mouth (Irago Strait) changed fortnightly in summer. During the spring tides, the strait water below the pycnocline was well-mixed and nearly homogeneous. By contrast, it was weakly stratified during the neap tide. There is a strong negative correlation between the tidal range and the density difference between the upper and lower layers at the strait. In summer, the intrusion depth of oceanic water into the bay and consequent hydrographic conditions inside the bay changed frequently according to the tidal strength. During the spring tides a prominent bottom front was created at the bay mouth, indicating that the strait water, which is a mixture of oceanic and bay waters, intruded through the middle layer. On the other hand, during the neaps, cold and saline oceanic water intruded through the bottom layer into the bay. The intrusion depth is significantly correlated with the tidal range. It is considered that the wellmixed strait water, which has a density equivalent to the middle layer inside the bay, is lighter than the bottom bay water and thus intrudes through the middle layer during the spring tides, while insufficient mixing makes the bottom water at the strait heavier than the bay water, leading to the bottom intrusion during the neap tides.     

Differences in abundance and distribution of Alexandrium cysts in Sendai Bay,northern Japan,before and after the tsunami caused by the Great East Japan Earthquake

The tsunami caused by the Great East Japan Earthquake on 11 March 2011 greatly influenced the coastal benthic environment on the northern Pacific coast of Japan. We used the direct count method to investigate changes in the abundance and distribution of Alexandrium (Alexandrium tamarense and Alexandrium catenella) cysts before and after the tsunami in Sendai Bay. Densities of Alexandrium cysts in sediments collected in summer 2011 ranged from 0 to 8,190 cysts cm^?3. In the western part of the bay, the density increased greatly after the tsunami, the highest density being approximately 10 times the density recorded in 2005. Molecular identification of single cysts with multiplex polymerase chain reaction (PCR) showed that Alexandrium tamarense dominated the cyst population in the southwestern part of the bay in 2011. Furthermore, accumulation of cysts on the surface sediment after disturbance of the sediment was confirmed by a laboratory experiment. The main factor causing the drastic changes in abundance and distribution of Alexandrium cysts after the earthquake was considered to be vertical and horizontal redistribution of the cysts in sediments after the tsunami.     

Favorable conditions for cold-water intrusion from the Kuroshio intermediate layer into Osaka Bay

From 1980 to 1995, in August, the bottom layer of Osaka Bay was occupied by cold, nutrient-rich water compared with that observed during both previous and subsequent decades. To investigate the mechanisms for the intrusion of bottom-layer cold water into Osaka Bay, the intrusion into Osaka Bay via the Kii Channel is simulated using a finite-volume coastal ocean model with unstructured triangular cell grids. The initial conditions, boundary conditions, and surface temperature given to the model are obtained from daily reanalysis data provided by the Japan Coastal Ocean Predictability Experiment. The model shows that cold water uplifted on the eastern side of the Kii Peninsula is propagated westward at 1.0 m/s as a coastal boundary current; it reaches the Kii Channel mouth when the Kuroshio axis is located around 74 km south of Cape Shionomisaki. However, the modeled cold water mass at the Kii Channel mouth does not intrude further to the north of the Kii Channel; therefore, another mechanism is required to explain the cold-water intrusion into the bottom layer of Osaka Bay. A plausible explanation is the estuarine circulation established by the freshwater supply at the bay head. When the river runoff is included in the model without forced vertical mixing, the temperature in Osaka Bay decreases 6.6 days later than the temperature decreases at the Kii Channel mouth. Furthermore, the shoreward current speed in the bottom layer of the modeled estuarine circulation is 15 cm/s, which provides the mechanism required for the cold water mass to pass the Kii Channel.     

Assessment of nitrogen loading from the Kiso-Sansen Rivers into Ise Bay using stable isotopes

Concentrations of particulate organic nitrogen (PN), dissolved inorganic nitrogen (DIN), and their nitrogen isotope ratios (δ ¹⁵N) in the Kiso-Sansen Rivers were determined from monthly observations over the course of a year to assess variations in the form and sources of riverine nitrogen discharged into Ise Bay. The δ ¹⁵N values of NO₃ ⁻ observed in the Kiso-Sansen Rivers showed a logarithmic decreasing trend from 8 to 0‰, which varied with the river discharge, indicating mixing between point sources with high δ ¹⁵N and non-point sources with low δ ¹⁵N. The influence of isotope fractionation of in situ biogeochemical processes (mainly DIN assimilation by phytoplankton) on δ ¹⁵N of NO₃ ⁻ was negligible, because sufficient concentrations of NH₄ ⁺ for phytoplankton demand would inhibit the assimilation of NO₃ ⁻. A simple relationship between river discharge and δ ¹⁵N of NO₃ ⁻ showed that the fraction of total NO₃ ⁻ flux arising from point sources increased from 4.0–6.3% (1.1–1.8 tN day⁻¹) during higher discharge (>600 m³ s⁻¹) to 30.2–48.3% (2.6–4.1 tN day⁻¹) during lower discharge (<300 m³ s⁻¹). Riverine NO₃ ⁻ discharge from the Kiso-Sansen Rivers can explain 75% of the variations in surface NO₃ ⁻ at the head of Ise Bay over the year.     

Estimation of freshwater runoff into Glacier Bay,Alaska and incorporation into a tidal circulation model

Freshwater discharge is one of the most critical parameters driving water properties within fjord estuarine environments. To date, however, little attention has been paid to the issue of freshwater runoff into Glacier Bay, a recently deglaciated fjord in southeastern Alaska. Estimates of discharge into Glacier Bay and the outlying waters of Icy Strait and Cross Sound are therefore presented. Existing regression equations for southcentral and southeastern coastal Alaska are applied to Glacier Bay to arrive at the estimates. A limited set of acoustic Doppler current profiler (ADCP) measurements generally support the predictions of the regression equations. The results suggest that discharge into the bay ranges from a few hundred to a few thousand m³ s⁻¹ during a typical year. Peak discharges can be much higher, approximately 10,000 m³ s⁻¹ for the 10-year flow event. Estimates of the seasonal variation of discharge are also obtained and reveal a broad peak during the summer months.     

象山港余流特征数值研究

基于Delft3D-Flow模块建立了象山港海域的三维斜压潮流数值模型,结合实测水文资料,研究了象山港的潮(余)流特征,对欧拉余流场的时空分布进行了定量的比较和分析,并与潮流测站计算分析得到的欧拉余流分布对比,很好的模拟了象山港的余流特征。结果表明:由湾外至湾顶,余流呈减小的趋势,湾外余流最大为33 cm/s,湾顶最小,余流平均仅5 cm/s。垂向上,表层余流大于底层余流,表层余流指向湾外,而底层余流则指向湾内。对比斜压、正压两种模式下的欧拉余流分布,可以看出湾顶附近主要受径流控制,两种模式得到的结果基本一致,口门至西沪港区域受径流和潮流的共同影响,斜压模式更准确地模拟出了水体层化和垂向余环流结构。     

三沙湾重矿物研究

三沙湾表层沉积物极细砂中的重矿物不下82种,除少量自生矿物外几乎全是陆源矿物,多数矿物含量变化很大.在岩性和潮流控制下,共形成了12区重矿物组合.