Estimation of the Reflection of Internal Tides on a Slope

Reflection occurs when internal tides impact on a steep continental slope. Separating reflected internal tide signals from incident ones is crucial to develop the parameterization of internal tide-driven turbulent mixing on the continental slopes. In this study, the performances of three different methods for estimating internal tide reflections are examined by using two different cases. The Hilbert transform-based method is found to be more suitable than two other methods for both cases considered in this study. The two other methods are effective for westward-propagating mode-1 internal tides impacting a slope, but inappropriate in the case where internal tides radiate from a Gaussian ridge impact the slope because of their inaccurate estimation of incident internal tides in the latter case. Such inaccurate estimation further influences the extraction of reflected signals and calculation of the reflected and cross term of energy fluxes. In addition, it should be noted that, due to the use of filtering, the method based on Hilbert transform may result in slight bias when assessing the incident and reflected signals near topographic features.     

Seasonal Variability of Internal Tides Northeast of Taiwan

The spatial-temporal characteristics of the barotropic tides and internal tides(ITs) northeast of Taiwan Island are examined, based on a 1-year mooring current observations from May 23, 2017 to May 19, 2018. The results of harmonic tidal analysis show that the barotropic tides are dominated by semidiurnal tides, which is mainly controlled by M_2 tidal components. Moreover, the vertical structures of diurnal and semidiurnal ITs show that the semidiurnal IT shows notable seasonal variation, whereas seasonal variations of the diurnal IT energy is not significant. The semidiurnal IT energy in winter half year is twice that in summer half year. The seasonal variation of semidiurnal IT is mainly modulated by the direction change of the current rather than by the topographic features and stratification. In summer(winter) half year cyclonic(anti-cyclonic) eddies meanly control at this point, so the flow direction is mainly in the southwest(northeast) direction, causing the background flow to flow along(perpendicular to) the isobath. When crossing the isobath, the ITs are generated by the interaction of the barotropic tide and the topography, resulting in the increase of the tidal energy in the winter half year.     

The origin,historical variations,and distribution of heavy metals in the Qiongzhou Strait and nearby marine areas

We analyzed heavy metal concentrations in a number of surface sediments and cores from the Qiongzhou Strait and surrounding marine areas.The areas of high concentrations are primarily outside the eastern mouth of the Qiongzhou Strait and on the west side of the Leizhou Peninsula,whereas the areas of low concentrations are located primarily in the eastern Qiongzhou Strait.The maximum Cd,Pb and Zn concentrations in the samples collected in our study do not exceed the official standards for marine sediments,whereas the concentrations of Cr and Cu slightly exceed the standards.Correlations exist between the concentrations of Cu,Pb,Zn,Cr and Cd,and the concentrations of these metals are positively correlated with the mean particle size(φ value),indicating that the finer sediments have adsorbed greater amounts of heavy metal elements than the coarser sediments.An evaluation of the potential environmental risks demonstrates that certain indices of heavy metal pollution and environmental risks are relatively low and may be assigned low risk levels,thereby indicating that,in terms of heavy metals,the marine sedimentary environment in this region is only mildly impacted.Our analysis of the contaminant origins shows that the heavy metals in this region primarily originate in the Pearl River Estuary and that a small amount of them is derived from local runoff.The elevated heavy metal concentrations from the upper sections of the cores started 130 years ago,which indicats that heavy metals in the surface sediments are primarily due to human activities associated with industrialization.     

重力数据约束的二维地震层析成像在台湾海峡南部的应用

地震-重力联合反演可以降低多解性,针对大勘探范围内岩石波速-密度关系存在较大散布的问题,引入交叉梯度结构约束构建统一的目标函数是一种有效的解决方案。利用台湾海峡南部HX-13测线进行验证:由于火成岩侵入体的存在,部分区域难以拾取可靠的地震初至,常规的走时反演无法准确恢复基底面的形态。搜集研究区的船测重力资料,根据地震地质条件和数据特点设置合适的反演参数,实现基于物性和结构双重约束的重力-地震联合反演。由对反演结果的分析和解释可以看出,该方法可在很大程度上弥补地震数据不完备的缺陷,使反演过程稳定,并提高模型的可靠性。     

建筑用海砂资源开发利用适宜性评价初探:以琼州海峡东口为例

经济的快速发展, 对砂石料的需求巨大, 海砂的开发成为当前的热点。琼州海峡东口海砂资源丰富, 资源潜力概算可达数十亿方。依据前期调查数据, 选取含泥量、含砂量、粒级、海砂厚度、水深和离岸距离6类指标, 采用层次分析法, 构造判断矩阵计算评价因子的权重, 运用ArcGIS空间分析功能进行叠加, 对琼州海峡东口的海砂进行了开发适宜性评价。结果表明: 经计算将研究区分为开发适宜性好、较好、中等、较差、差5个等级, 其中浅滩区域海砂规模大、质量好、水深浅和开采环境影响小, 其开发适宜性最佳。分析了不同的指标对海砂开发适宜性的影响, 在浅滩区, 厚度和含砂量指标贡献较大; 在近岸海湾, 环境影响是主要因子; 在琼州海峡深槽区, 水深条件则成为海砂开发的主要限制条件。根据海砂资源的特点, 建立了以资源自然属性、开发技术条件、生态环境影响和行政管理为主要因子的海砂开发利用适宜性评价体系, 具体工作可选取不同的指标开展评价。研究结果可以为研究区海砂的开发利用和其他区域海砂开发适宜性评价提供参考。      

Seasonal and Interannual Variability of Bering Strait Throughflow from AO-FVCOM and Observation

A high-resolution Arctic Ocean-Finite Volume Community Ocean Model(AO-FVCOM) and observational current data from 14 mooring stations in Bering Strait and surrounding regions between 1990 and 2015 were used to study the seasonal and interannual variability of Bering Strait throughflow(BST). AO-FVCOM represented the BST with a climatological northward flux of 1.06 Sv, which was close to the observational mean of 0.94 ± 0.26 Sv. From the model results, the strongest volume flux was in summer, approximately 45% larger than that in winter. Interannual variability of BST was also indicated in the model results, and the maximum and minimum annual mean transports are in 2007 and 2012, respectively. AO-FVCOM showed larger differences from the observations in 2000, 2002, and 2015 than in other years, which may be related to the limitation of atmospheric forcing for the model. According to the driving mechanisms of BST, sea level difference(SLD) across the strait dominates the northward volume transport, and local wind is also important in forcing the seasonal variability of the BST and SLD patterns to change the BST indirectly.     

Observation of continental shelf wave propagating along the eastern Taiwan Strait during Typhoon Meranti 2016

This study is the first to depict typhoon-induced continental shelf wave(CSW) propagation in the eastern Taiwan Strait(TWS) during the passage of Typhoon Meranti in 2016 using tidal gauge data and along-track satellite altimeter data.The strong amplitude response of sea level oscillations(within the range of 0.30-0.54 m) as a free,barotropic CSW after Meranti,which impacted the TWS,was clearly detected in time and frequency(in bands of 64-81 h) using wavelet and cross-wavelet analyses.The measured group and phase speeds were consistent with the dispersion curves for CSW with the first-mode derived from the cross-shelf sections of the eastern TWS,with the mean speeds reaching 3 and 5.6±0.7 m/s,respectively.Coincidentally,the typhoon-induced sea level anomaly(SLA) was also captured by the satellite altimeter before this CSW entered into the TWS.Using the theoretical cross-shore CSW modes to fit the SLA data,the results indicated that the first three wave modes can interpret this CSW event appeared in the southern TWS very well,with the first mode being the dominant one.     

沿海地区经济结构的变化与近岸海域环境污染

近岸海域环境恶化已成为明显的事实.从污染物的种类和含量上看,这和沿海地区经济结构的变化有很大的关系.本文先用理论的分析方法,从影响近岸海域环境的因素和经济-环境投入产出表及模型的不同角度论证了沿海地区经济结构与近岸海域环境之间存在很大的相关性;然后运用实证的分析方法,从全国沿海县(市、区)和广东省沿海城市不同范围上论证了沿海地区经济结构与近岸海域环境之间也存在很大的相关性.     

海上主航迹带边界统计推断与海西航路警戒区布局优化分析

台湾海峡是东北亚各国与东南亚、印度洋沿岸各国间的海上捷径,其交通主流是通行海峡的南北向航次,然而海峡两岸启动大三通后,穿越海峡的客货运船舶日益增多,导致闽台直航航次与台湾海峡南北干线主交通流交叉现象凸显,台湾海峡西侧水域冲突日益加剧。本文根据船舶轨迹观测数据,抽样出通行海峡南北及横穿海峡的航次样本,应用轨迹栅格化方法建立统计推断模型,以概率形式表达南北干线、两岸直航的海运利用分布,推断出2种交通流的主航迹带,识别南北向交通主流与两岸直航交通支流的显著冲突区,以此调整现有警戒区设置方案。研究结果表明：轨迹统计推断法能定量化分析海西现有交通流模式,易于辨识横越海峡的船舶与通行海峡在航船舶的冲突区中心,为优化警戒区布局提供有效的方法支撑;调整后的海西警戒区中心可与台湾本岛西岸港口外侧的直航船舶通过点对接,形成海峡两岸直航的固定航线,可降低台湾海峡船舶冲突隐患,规范台湾海峡的船舶交通秩序。     

日本地震活动与潮汐相关性统计研究

选取日本及邻区作为研究区域,对其进行子区域的划分。基于日月引起的起潮力,通过Schuster检验计算出每个子区域的p值,在此基础上对满足p<5%的子区域建立Schuster谱,判断该地区的地震活动率是否存在周期性变化,进而对日本的地震活动与潮汐应力的相关性进行研究。结果显示,在划分的75个子区域中,有22个子区域满足p＜5%,且其中2个子区域的Schuster谱显示出明显的0.5 d潮周期,说明这些地区的地震活动在一定程度上受到潮汐触发作用的影响。     

Microbial ecological associations in the surface sediments of Bohai Strait

Microbial communities play key roles in the marine ecosystem. Despite a few studies on marine microbial communities in deep straits, ecological associations among microbial communities in the sediments of shallow straits have not been fully investigated. The Bohai Strait in northern China(average depth less than 20 m) separates the Bohai Sea from the Yellow Sea and has organic-rich sediments. In this study, in the summer of 2014, six stations across the strait were selected to explore the taxonomic composition of microbial communities and their ecological associations. The four most abundant classes were Gammaproteobacteria, Deltaproteobacteria, Bacilli and Flavobacteriia. Temperature, total carbon, depth, nitrate, fishery breeding and cold water masses influenced the microbial communities, as suggested by representational dif ference and composition analyses. Network analysis of microbial associations revealed that key families included Flavobacteriaceae, Pirellulaceae and Piscirickettsiaceae. Our findings suggest that the families with high phylogenetic diversity are key populations in the microbial association network that ensure the stability of microbial ecosystems. Our study contributes to a better understanding of microbial ecology in complex hydrological environments.     

利用sPn震相测定台湾海峡M6.2地震震源深度

采用波形互相关技术获得Pn震相准确到时,然后应用滑动时窗相关法获取sPn与Pn震相的走时差,通过该走时差测定台湾海峡M6.2地震震源深度为14.7 km,并对测定的结果进行分析解释.对比本文计算结果与CAP方法的反演结果得出,本文研究方法更加方便、快捷、精确.     

FLUXES OF SEAWATER AND SOME DISSOLVED CHEMICALS IN THE BASHI STRAIT

An Acoustic Doppler Current Profiler (ADCP) was used in Nov. 1990 measure the seawaterfluxes in a southeast-northwest cross-section in the Bashi Strait to a depth of 400 m. Measuredconcentrations of dissolved oxygen (DO), phosphate (PO_4), nitrate (NO_3), silicate (SiO_2), total alkalinity(TA) and calculated total CO_2, (TCO_2) and the current speed were used to estimate the flux densities(concentration times current speed) of seawater and chemicals.The fluxes of nutrients were near zero near surface and increased with depth. For oxygen andcarbonates, the distributions of flux had structures similar to that of the curmt speed field.     

Beach Morphology and Coastline Evolution in the Southern Bohai Strait

The beach studied in this paper spans a length of 51 km and is one of several long sandy beaches in the southern Bohai Strait. Due to the obstruction of islands in the northeast and the influence of the underwater topography, the wave environment in the offshore area is complex; beach types and sediment transport characteristics vary along different coasts. The coastlines extracted from six aerial photographs in different years were compared to demonstrate the evolving features. Seven typical beach profiles were selected to study the lateral beach variation characteristics. Continuous wind and wave observation data from Beihuangcheng ocean station during 2009 were employed for the hindcast of the local wave environment using a regional spectral wave model. Then the results of the wave hindcast were incorporated into the LITDRIFT model to compute the sediment transport rates and directions along the coasts and analyze the longshore sand movement. The results show that the coastline evolution of sand beaches in the southern Bohai Strait has spatial and temporal variations and the coast can be divided into four typical regions. Region(I), the north coast of Qimudao, is a slightly eroded and dissipative beach with a large sediment transport rate; Region(II), the southwest coast of Gangluan Port, is a slightly deposited and dissipative beach with moderate sediment transport rate; Region(III), in the central area, is a beach that is gradually transformed from a slightly eroded dissipative beach to a moderately or slightly strong eroded bar-trough beach from west to east with a relatively moderate sediment transport rate. Region(IV), on the east coast, is a strongly eroded and reflective beach with a weak sediment transport rate. The wave conditions exhibit an increasing trend from west to east in the offshore area. The distribution of the wave-induced current inside the wave breaking region and the littoral sediment transport in the nearshore region exhibit a gradual weakening tendency from west to east, which is opposite to the trend of the wave conditions outside the breaking region. The presence of submerged shoal(Dengzhou Shoal), deep trough(Dengzhou Channel), islands and irregular topography influnces the wave climate, beach types, wave-induced current features, littoral sediment transport trends and coastline evolution patterns in the southern Bohai Strait. Human activities, such as the sand exploitation of Dengzhou Shoal and other coastal engineering projects, also influence the beach morphology and coastline evolution.     

Characteristics of water exchange in the Luzon Strait during September 2006

The Luzon Strait is the only deep channel that connects the South China Sea(SCS) with the Pacific.The transport through the Luzon Strait is an important process influencing the circulation,heat and water budgets of the SCS.Early observations have suggested that water enters the SCS in winter but water inflow or outflow in summer is quite controversial.On the basis of hydrographic measurements from CTD along 120° E in the Luzon Strait during the period from September 18 to 20 in 2006,the characteristics of t...     

A dynamic box model of bioactive elements in the southern Taiwan Strait

A dynamic box model was applied to study the characteristics of biogeochemical cycling of PO_4-P,NO_3-N,AOU,POC and PON in the southern Taiwan Strait region based on field data of the"Minnan Taiwan Bank Fishing Ground Upwelling Ecosystem Study" during the period of Dec.1987-Nov.1988.According to the unique hydrological and topographical features of the region,six boxesand three layers were considered in the model.The variation rates and fluxes of elements induced by hor-izontal current,upwelling,by diffusion,sinking of particles and biogeochemical processes were estimatedrespectively.Results further confirmed that upwellings had important effects in this region.Thenearshore upwelling areas had net input fluxes of nutrients brought by upwelling water,also had high de-pletion rates of nutrients and production rates of particulate organic matter and dissolved oxygen.Theabnormal net production of nutrients in the middle layer(10-30m) indicated the important role of bacte-ria in this high production region.Th