海南东北部地区地壳地震各向异性特征初步研究

基于海南省地震台网2000~2013年的区域地震波形数据,用剪切波分裂系统分析方法（SAM）获得了海南琼东北部地区＂九五＂数字台网中2个台站的剪切波分裂参数。结果表明,快剪切波偏振优势方向代表了原地最大主压应力方向。七星岭台NE方向的快剪切波偏振优势方向与区域水平主压应力场方向不一致,与NE走向的断裂一致,体现了局部构造和局部应力场的复杂性;青山岭NNE向的快剪切波偏振优势方向揭示了NNE走向断裂的构造意义。同时,本研究证实,位于活动断裂上或几条活动断裂交汇部位的台站的快剪切波偏振优势方向与对所选用的小地震起控制作用的活动断裂走向一致,而快剪切波偏振优势方向较为离散则反映了该区域复杂的断裂构造和应力分布特征。

基于模糊综合评判法的海南东北部滨海地下水水质评价

滨海地区地下水是重要的水资源,但易受到咸潮及陆源污染物的影响;海南东北部地下水开采量逐年增加,但迄今尚无系统的水质监测与分析。运用模糊数学方法,在分析监测井地下水化学特征的基础上,构造模糊综合评价模型,对海南东北部滨海地下水水质进行评价。水化学特征分析表明:该区地下水化学类型在空间上变化较为单一,所有水样都以碱金属与强酸为主,Na+和Cl-在水中所占比重大,表明受到了咸潮的影响;水化学类型在时间上变化不明显,潮期对水化学类型并无明显影响。模糊综合评价法表明:地下水水质受到潮期影响:测井Z1大小潮时段的水质均属于Ⅱ类水;Z3大小潮时段均属于Ⅳ类;Z4大潮期属于Ⅴ类,小潮期属于Ⅳ类。总体来说,该区域地下水水质已受到海水入侵影响,不适合作为饮用水源。

海南东北部不同林分类型土壤化学性质研究

本文以海南东北部次生林、半红树林、木麻黄与琼崖海棠混交林、木麻黄与大叶相思混交林等4种不同林分类型为研究对象,对样地0~100 cm土壤层的化学性质进行测定与分析。结果表明:4种不同林分类型的土壤化学性质存在差异;土壤pH值为4.08~5.90,均属于酸性土壤;土壤有机质含量为0.23~35.19 g/kg,只有半红树林有机质含量达到中等水平;土壤全氮含量为0.07~1.10 g/kg,半红树林明显高于其他3种森林类型;土壤全磷含量为0.01~0.14 g/kg;土壤全钾含量为0~1.04 g/kg;土壤有效磷含量为0.95~56.97 mg/kg;土壤速效钾含量为0~130.99 mg/kg;土壤硝态氮含量为0~5.91 mg/kg;土壤氨态氮含量为0.01~3.81 mg/kg。

海南岛东北部地下水化学及海水入侵特征分析

运用变异系数、相关系数等指标分析海南东北部地下水化学及海水入侵特征。结果表明:(1)大潮期Na+、Cl-属于弱强度变异,其余离子在大潮期和小潮期均为中等强度变异;大潮期Na+、Mg2+、Ca2+、Cl-及TDS含量高于小潮期,不同时间段离子含量不同。(2)地下水化学成分明显受到海水的影响,海水入侵等级为较严重。

探地雷达(GPR)在海南岛东北部海岸带调查中的应用

对海南岛东北部海岸带调查采用了探地雷达(GPR)研究海岸带沙体的结构、展布和沉积序列,取得了很好的效果。文章通过和有限的露头资料对比以及对反射波形态、结构的研究,确定了海滩脊、海岸沙丘的反射特征以及潜水面的位置。雷达图像显示五龙港古海滩脊由亚水平、不连续、高振幅和透镜状反射波组成;木兰头海岸沙丘已受到人类活动的扰动,短的、陡倾斜反射可能代表未受扰动的海岸风成沙的前积层。研究表明探地雷达是一种可靠、快速和经济的地球物理方法,在砂砾质海岸可产生高质量、高分辨率和连续的反射剖面,值得加以推广。

海南岛东北部土地利用与生态系统服务价值空间自相关格局分析

土地利用/覆被变化是全球环境变化的重要原因,对生态系统服务价值空间分布格局有直接影响。以海南岛东北部为研究对象,基于遥感影像数据,应用空间自相关理论定量探讨了土地利用与生态系统服务价值的空间自相关格局和分布特征,并运用双变量空间自相关分析两者之间的空间响应规律。结果表明:2016年海南岛东北部生态系统服务功能总价值为132.09亿元,其中林地构成生态系统服务功能价值的主体,而湿地的单位生态系统服务价值最高。土地利用类型具有显著的空间自相关性(P<0.05),不同土地利用类型所表现的空间聚集或异常的区域及范围明显不同,以建设用地和林地的空间聚集性最强。研究区生态系统服务价值在空间上呈显著的正相关性(P<0.05),高值区明显聚集于海岸带、东寨港和清澜港红树林一带,低值区集中在海口城区、文昌北部农耕区域;土地利用程度与生态系统服务价值呈空间负相关关系(P<0.05),且具有明显的空间溢出效应。根据研究结论建议继续实施生态修复与保护政策,优化土地利用结构,提升生态核心的服务价值,实现区域可持续发展和维护生态安全。

南海海南岛东北部海区春季水体油类污染现状分析评价

分析评价2019年春季南海海南岛东北部海区(19.50°N-21.50°N,110.50°E-112.50°E)水体油类污染现状。结果显示,调查海区39个站位的水体油类含量均符合第一类海水水质标准(≤0.050 mg/L),就海域油类平均含量高低相对比较而言,近岸海域>远岸海域;以第一类海水水质标准评价,调查海区39个站位的水体油类的单项标准指数均小于1,就海域油类评价单项标准指数高低相对比较而言,近岸海域>远岸海域。

The 3D magnetic structure beneath the continental margin of the northeastern South China Sea

Understanding the continental margin of the Northeastern South China Sea is critical to the study of deep structures, tectonic evolution, and dynamics of the region. One set of important data for this endeavor is the total-field magnetic data. Given the challenges associated with the magnetic data at low latitudes and with remanent magnetism in this area, we combine the equivalent-source technique and magnetic amplitude inversion to recover 3D subsurface magnetic structures. The inversion results show that this area is characterized by a north-south block division and east-west zonation. Magnetic regions strike in EW, NE and NW direction and are consistent with major tectonic trends in the region. The highly magnetic zone recovered from inversion in the continental margin differs visibly from that of the magnetically quiet zones to the south. The magnetic anomaly zone strikes in NE direction, covering an area of about 500 km × 60 km, and extending downward to a depth of 25 km or more. In combination with other geophysical data, we suggest that this strongly magnetic zone was produced by deep underplating of magma associated with plate subduction in Mesozoic period. The magnetically quiet zone in the south is an EW trending unit underlain by broad and gentle magnetic layers of lower crust. Its magnetic structure bears a clear resemblance to oceanic crust, assumed to be related to the presence of ancient oceanic crust there.

Development of Sedimentary Environment in the Northeastern South China Sea Since the Last Glacial Stage

Core D （21°23′02″N, 116°47′13″E, water depth 405 m） was sampled from the upper slope from the northeastern South China Sea （SCS） and applied to analyze the sedimentary environmental change in this sea area since the last glacial stage. The results of grain size analysis, diatom analysis and detrital mineral analysis were well matched. We divided the core D into two layers. The surface sand layer （0 - 2 cm） consisted of residual sediments, which might be originally the sediment in the late Pleistocene and later suffered from being transformed in the post glacial transgression. The lower layer （2 - 130 cm） was quite different from the surface one, which might mainly result from a neritic sedimentary environment in the last glacial stage. Two sedimentary cycles could be detected in the core D： regression during Marine isotope stage （MIS） 4 to transgression during MIS 3 and regression during MIS 2 to transgression during the post glacial.

Vertical structure and evolution of the Luzon Warm Eddy

Eddies are frequently observed in the northeastern South China Sea （SCS）. However, there have been few studies on vertical structure and temporal-spatial evolution of these eddies. We analyzed the seasonal Luzon Warm Eddy （LWE） based on Argo float data and the merged data products of satellite altimeters of Topex/Poseidon, Jason-1 and European Research Satellites. The analysis shows that the LWE extends vertically to more than 500 m water depth, with a higher temperature anomaly of 5℃ and lower salinity anomaly of 0.5 near the thermocline. The current speeds of the LWE are stronger in its uppermost 200 m, with a maximum speed of 0.6 m/s. Sometimes the LWE incorporates mixed waters from the Kuroshio Current and the SCS, and thus has higher thermohaline characteristics than local marine waters. Time series of eddy kinematic parameters show that the radii and shape of the LWE vary during propagation, and its eddy kinetic energy follows a normal distribution. In addition, we used the empirical orthogonal function （EOF） here to analyze seasonal characteristics of the LWE. The results suggest that the LWE generally forms in July, intensifies in August and September, separates from the coast of Luzon in October and propagates westward, and weakens in December and disappears in February. The LWE＇s westward migration is approximately along 19°N latitude from northwest of Luzon to southeast of Hainan, with a mean speed of 6.6 cm/s.

A new method for the estimation of oceanic mixed-layer depth using shipboard X-band radar images

Shipboard X-band radar images acquired on 24 June 2009 are used to study nonlinear internal wave characteristics in the northeastern South China Sea.The studied images show three nonlinear internal waves in a packet.A method based on the Radon Transform technique is introduced to calculate internal wave parameters such as the direction of propagation and internal wave velocity from backscatter images.Assuming that the ocean is a two-layer finite depth system,we can derive the mixed-layer depth by applying the internal wave velocity to the mixed-layer depth formula.Results show reasonably good agreement with in-situ thermistor chain and conductivity-temperature-depth data sets.

Observations of Kuroshio intrusion into the South China Sea

To discuss the intrusion of the Kuroshio into the SCS,we examined the mixing between the North Pacific and South China Sea(SCS) waters based on in-situ CTD data collected in August and September 2008 and the moored ADCP data taken from mid September 2008 to early July 2009.The CTD survey included four meridional sections from 119°E to 122°E around the Luzon Strait,during which pressure,temperature,and salinity were measured.The CTD data show that the isopycnal surface tilted from the SCS to the North Pacific;and it was steeper in the lower layers than in the upper ones.Meanwhile,we found strong vertical mixing taken place in the areas near 121°E.The Kuroshio in high temperature and salinity intruded westward through Luzon Strait.The frequency of buoyancy was one order of magnitude greater than that of the common ones in the ocean,suggesting stronger stratification in the northeastern SCS.On the other hand,the long-term ADCP data show that before late October 2008,the direction of water flow in the SCS was eastward,and from November 2008 to late February 2009,it turned northwestward in the layers shallower than 150 m,while remained unchanged in deep layers from 200 to 450 m.From March to June 2009,the direction shifted with increasing depth from northward to southward,akin to the Ekman spiral.EOF analysis of the current time series revealed dominant empirical modes:the first mode corresponded to the mean current and showed that the Kuroshio intrusion occurred in the upper layers only from late December to early March.The temporal coefficient of the first and the second mode indicated clearly a dominant signal in a quasi-seasonal cycle.

Nonlinear interactions among internal tidal waves in the northeastern South China Sea

We used a set of 75-day long ADCP data from the northeastern South China Sea(SCS) to investigate nonlinear interactions among freely propagating internal tidal waves.The kinetic energy spectra displayed significant peaks at some higher tidal frequencies,such as O1M2(O1+M2),and M4(M2 +M2),where O1 is the lunar diurnal internal tide,M2 is the lunar semidiurnal internal tide,and M4 is the first higher harmonic frequency of M2.These higher tidal harmonic frequency peaks,as well as the fundamental tidal harmonic peaks,show a σ-2.3 spectral falloff rate with frequency.In addition,we explored the possible generation mechanism of higher tidal harmonics.Analysis on the rotary and bicoherence spectra suggests that strong forced non-resonant interaction induced by nonlinear advections was the dominant physical mechanism that induced these higher tidal harmonics.Moreover,the energetic,freely propagating semidiurnal(M2) internal tidal wave played the most crucial role in these interactions.These results indicate that strong nonlinear forced non-resonant interactions among internal tides can be one of the processes responsible for the redistribution of energy in the internal wave spectrum.

A dipole wind curl pattern induced by Taiwan Island and its effect on upper stratification in the northeastern South China Sea

Using hydrographic data sampled during four successive late summer-early autumn cruises in 2004-2007, vertical stratification along transects in the lee of Taiwan Island was analyzed to investigate upper ocean responses to orographically induced dipole wind stress curl (WSC). Results indicate that mixed-layer depth (MLD) and its relationship with thermocline depth varied under different local wind forcings. Average MLD along the transects from the 2004 to 2007 cruises were 18.5,30.7,39.2 and 24.5m, respectively. The MLD along the transects deepened remarkably and resulted in thermocline ventilation in 2005 and 2006, whereas ventilation did not occur in 2004 and 2007. Estimates indicate that frictional wind speed was the major factor in MLD variations. To a large degree, the combined effects of frictional wind speed and Ekman pumping are responsible for the spatial pattern of MLD during the cruises.

Sea surface temperature anomalies in the South China Sea during mature phase of ENSO

Based on the 18-year （1993-2010） National Centers for Environmental Prediction optimum interpolation sea surface temperature （SST） and simple ocean data assimilation datasets, this study investigated the patterns of the SST anomalies （SSTAs） that occurred in the South China Sea （SCS） during the mature phase of the E1 Nifio/Southem Oscillation. The most dominant characteristic was that of the out- of-phase variation between southwestern and northeastern parts of the SCS, which was influenced primarily by the net surface heat flux and by horizontal thermal advection. The negative SSTA in the northeastern SCS was caused mainly by the loss of heat to the atmosphere and because of the cold-water advection from the western Pacific through the Luzon Strait during E1 Nifio episodes. Conversely, it was found that the anomalous large-scale atmospheric circulation and weakened western boundary current during E1 Nifio episodes led to the development of the positive SSTA in the southwestern SCS.

A weakly coupled data assimilation system of a coupled physical–biological model for the northeastern South China Sea

A weakly coupled data assimilation system was established for a coupled physical–biological model for the northeastern South China Sea（NSCS）. The physical model used was the Regional Ocean Modeling System; the biological component was a seven-compartment nitrogen–phytoplankton–zooplankton–detritus ecosystem model; and the data assimilation method was Ensemble Optical Interpolation. To test the performance of the weakly coupled data assimilation system, two numerical experiments（i.e. control and assimilation runs） based on a process-oriented idealized case were conducted, and climatological SST was assimilated in the assimilation run. Only physical variables were adjusted in the weakly coupled data assimilation. The results showed that both the assimilated SST and other unassimilated physical variables had reasonable process responses. Due to the warmer SST observation, the water temperature（salinity） in the assimilation run increased（decreased） in coastal upwelling regions. Both the alongshore and bottom cross-shore currents were reduced, jointly demonstrating the weakening of the upwelling system. Meanwhile, ecosystem variables were also affected to some extent by the SST assimilation through the coupled model. For example, larger phytoplankton（chlorophyll） productivity was found in the upwelling region within the shallow layer due to the warmer waters in the assimilation run. Hence, the application of this data assimilation system could reasonably modify both physical and biological variables for the NSCS by SST assimilation.

Preliminary Study on Seismic Anisotropy in the Crust in the Northeast of Hainan

With SAM shear-wave splitting analysis,shear-wave splitting parameters at two stations of the digital seismic network in the northeast of Hainan are obtained based on the data from the Hainan Digital Seismic Network from 2000 to 2013. The results show that the predominant polarization direction of fast share-wave represents the direction of in-situ maximum principal compressive stress. The predominant polarizations of Qixingling( QXL) seismic station are in the NEE direction,which is different from the direction of principal compressive stress of the Hainan area,but same as the strikes of faults in the NE direction,which means that the local tectonics and stress fields are complicated. The predominant polarization of Qingshanling( QSL) seismic station is in the NNE-NS direction,which indicates the tectonic significance of the strikes of NNE-trending faults.At the same time,the study confirms that the predominant polarizations of the stations located on active faults or at the junctions of several active faults are parallel to the strikes of faults which control the earthquakes used in this analysis, and the predominant polarizations are scattered,which indicates the complicated background of fault structures and stress distribution.

Morphology, sedimentary characteristics, and origin of the Dongsha submarine canyon in the northeastern continental slope of the South China Sea

The Dongsha submarine canyon is a large canyon belonging to a group of canyons on the northeastern South China Sea margin Investigation of the Dongsha canyon is important for understanding the origin of this canyon group as well as the transport mechanism of sediments on the margin, and the evolution of the Taixinan foreland basin and the associated Taiwan orogenic belt. In this study, the morphology, sedimentary characteristics, and origin of the Dongsha canyon were investigated by inte- grating high-resolution multi-channel seismic reflection profiles and high-precision multibeam bathymetric data. This is a slope-confined canyon that originates in the upper slope east of the Dongsha Islands, extends downslope in the SEE direction, and finally merges with the South Taiwan Shoal canyon at a water depth of 3000 m. The total length and average width of the canyon are around 190 and 10 km, respectively. Eleven seismic sequence boundaries within the canyon fills were identified and interpreted as incision surfaces of the canyon. In the canyon fills, four types of seismic facies were defined： parallel onlap fill, chaotic fill, mounded divergent facies, and migrated wavy facies. The parallel onlap fill facies is interpreted as altemating coarser turbidites or other gravity-flow deposits and fine hemipelagic sediments filling the canyon valley. The chaotic fill faci- es is presumed to be debrites and/or basal lag deposits filling the thalwegs. The mounded divergent and migrated wavy seismic facies can be explained as canyon levees consisting mainly of overspilled fine turbidites and sediment waves on the levees or on the canyon-mouth submarine fans. Age correlation between the sequence boundaries and the ODP Site 1144 data suggests that the Dongsha canyon was initiated at approximately 0.9 Ma in the middle Pleistocene. Mapping of the canyon indicates that the canyon originated at the upstream portion of the middle reach of the modem canyon, and has been continuously expanding both upstream and downstream by retrogressive erosion, incision, and deposition of turbidity currents and other gravity transport processes. The ages of the sequence boundaries representing major canyon incision events are in good agreement with those of global sea-level lowstands, indicating that sea-level changes may have played an important role in the canyon＇s development. The Dongsha canyon developed in a region with an active tectonic background characterized by the Taiwan up- lifting and the development of the Taixinan foreland basin. However, no evidence suggests that the canyon formation is directly associated with local or regional faulting and magmatic activities. Turbidity currents and other gravity transport processes （includ- ing submarine slides and slumps） may have had an important influence on the formation and evolution of the canyon.

Light carbon isotope events of foraminifera attributed to methane release from gas hydrates on the continental slope, northeastern South China Sea

In 2013, the China Geological Survey and Guangzhou Marine Geological Survey conducted the second Chinese gas hydrate expedition in the northern South China Sea （SCS） and successfully obtained visible gas hydrate samples. Five of the thirteen drilling sites were cored for further research. In this work, Site GMGS2-08 is selected for the stable isotopic analy- sis of foraminifera present in the boreholes in order to reveal the carbon isotopic characteristics of the foraminifera and their response to methane release in the gas hydrate geological system. Our results show that the methane content at Site GMGS2-08 is extremely high, with headspace methane concentrations up to 39300 μmol L^-1. The hydrocarbon δ^13C values, ranging from -69.4%o to -72.3‰ PDB, distinctly indicate biogenic generation. Based on the δD analytical results （-183‰ to -185‰ SMOW）, headspace methane is further discriminated to be microbial gas, derived from CO2 reduction. By isotopic measurement, five light δ^13C events are found in the boreholes from Site GMGS2-08, with foraminiferal δ^13C values being ap- parently lower than the normal variation range found in the glacial-interglacial cycles of the SCS. The δ^13C values of benthic Uvigerina peregrina are extremely depleted （as low as -15.85‰ PDB）, while those of planktonic Globigerinoides ruber reach -5.68‰ PDB. Scanning electron micrograph （SEM） studies show that foraminiferal tests have experienced post-depositional alteration, infilled with authigenic carbonate, and the diagenetic mineralization is unlikely to be related to the burial depths. The correlation calculation suggests that the anaerobic oxidation of organic matter has only weak influences on the δ^13C com- position of benthic foraminifera. This means that the anomalous δ^13C depletions are predominantly attributed to the overprint- ing of secondary carbonates derived from the anaerobic oxidation of methane （AOM）. Furthermore, the negative δ^13C anoma- lies, coupled with the positive δ^18O anomalies observed at Site GMGS2-08, are most likely the critical pieces of evidence for gas hydrate dissociation in the geological history of the study area.

Dongsha erosive channel on northern South China Sea Shelf and its induced Kuroshio South China Sea Branch

Based on a data base of multi-channel seismic profiles covered over Dongsha plateau of the northern South China Sea margin, we found that the sea bed morphology of northern South China Sea margin had been changed dramatically after Dongsha uplifting, that sedimentary layer since Miocene age had been eroded with maximum eroded thickness more than 1000 m, and that an erosive channel had been formed of 20 km in width and 200 km in length and several hundreds meters in depth on the outer shelf of northern South China Sea. The erosive channel is parallel to the 600 m isobath line, stretching from northeast to the southwest north of Dongsha uplift. The Kuroshio intrudes the South China Sea through Luzon Strait both in winter time and summer time, and in the northern South China Sea margin area, the intruded Kuroshio Branch takes the form of Pacific-Indian Ocean Through Flow (PITH) in winter time, while the Luzon Strait Subsurface Inflow (LSSIF) in summer time, the routes of both PITH and LSSIF coincide well with the distribution of the erosive channel. After climbing from the northern slope up to the northern shelf, and after joined by the southward flow from the middle northern shelf of South China Sea, the Kuroshio Branch is strengthened and thus is able to erode the sea floor, and the shape of the erosive channel is a result of the long-term interaction between the Kuroshio South China Sea Branch and the Dongsha outer shelf sea floor.