SPOT5数据东沙环礁珊瑚礁遥感能力分析

对于大面积的大比例尺珊瑚礁遥感制图而言,SPOT5数据是一种高性价比卫星遥感资料.以Quickbird2数据对东沙环礁珊瑚礁的分类、解译的矢量结果作为该区域实际的珊瑚礁分布,以此为基础分析SPOT5数据的珊瑚礁遥感制图能力.SPOT5只有两个水体穿透信道,从基于光谱数据的分类角度看,以XS1通道为准的珊瑚礁信息提取易将高反射的沙底质归为珊瑚礁;以XS2通道为准的珊瑚礁分布制图存在提取不足问题.由于空间分辨率提高,对潟湖淤泥质中的珊瑚礁提取能力较强,要优于ETM数据.结合ETM数据及PCA融合后的SPOT5的遥感解译结果,能提高SPOT5数据的制图能力.     

Evaluation of sea water ingress into an Indian atoll

Groundwater is the prime source of fresh water in most part of world. The groundwater floats in the form of thin lens which is vulnerable to various stresses such as tide, cyclone, draught, abstraction, etc. The problem of getting this meager resource of fresh groundwater sustained for longer time, becomes more difficult task on tiny atoll with large population depending on it. In order to develop sustainable management scheme and identify vulnerable part of aquifer, systematic assessment of groundwater quality on such island have become imperative. Detailed hydrochemical study has been carried out to identify potential fresh groundwater resources on Andrott Island, UT of Lakshadweep, India. The analysis has given an early signal of deterioration in groundwater quality in some parts of the island during non-monsoon period, whereas the quality becomes slightly better during monsoon period. The study suggests immediate measures for arresting the deterioration in groundwater quality as well as augmentation for restoration of aquifer in some parts of the island.     

南海宣德环礁东南海域地质灾害特征

宣德环礁作为我国南海诸岛礁开发利用程度最高的岛礁之一, 其周围海域地质灾害对岛礁基础工程建设及人类活动具有重大危害。为适应南海岛礁可持续发展的需要, 文章采用广州海洋地质调查局2018年采集的单道地震数据, 对宣德环礁东部斜坡带海域灾害地质因素进行综合解释和分析。结果表明, 研究区主要发育有海底滑坡、海底陡坎和断层3类地质灾害。海底滑坡是研究区主要灾害地质因素, 规模大小不一, 海底陡坎和断层为次要地质灾害。海底陡坎根据成因可分为礁体陡坎和滑坡陡坎, 礁体陡坎为礁盘形成过程中受海平面上升控制形成, 滑坡陡坎为海底滑坡导致。通过分析认为陡峭的地形和峡谷水道的侵蚀搬运作用是研究区地质灾害发育的主控因素。这些地质灾害对海洋工程建设及管线铺设均有不利的影响, 应尽量避开。     

南沙群岛永暑礁小潟湖岩心有孔虫动物群及其沉积环境

根据永暑礁小潟湖"南永3"井高分辨率的岩心材料,结合其高精度TIMS U系测年,系统研究了1 682 a B.P.以来环礁潟湖沉积柱样的有孔虫分类?类型与属种的组成,揭示了其垂直变化?有孔虫共48属62种,都是全新世-现代种,其中底栖有孔虫55种?其组成表征了印度洋-太平洋有孔虫区系和热带珊瑚礁相环境?即使由温凉水种浮游有孔虫偏多的时段所反映的表层水温也相对偏低,推测其变化幅度很小?底栖有孔虫茸刺距轮虫δ18O含量的变化曲线呈4峰4谷交替,反映了永暑礁海区近1 682 a以来的气候有4个凉期和4个暖期,同2 000a以来的全球气候变化周期一致?有孔虫种类的垂向变化也反映了海平面有些小变动?     

Bikini Atoll coral biodiversity resilience five decades after nuclear testing

Five decades after a series of nuclear tests began, we provide evidence that 70% of the Bikini Atoll zooxanthellate coral assemblage is resilient to large-scale anthropogenic disturbance. Species composition in 2002 was assessed and compared to that seen prior to nuclear testing. A total of 183 scleractinian coral species was recorded, compared to 126 species recorded in the previous study (excluding synonomies, 148 including synonomies). We found that 42 coral species may be locally extinct at Bikini. Fourteen of these losses may be pseudo-losses due to inconsistent taxonomy between the two studies or insufficient sampling in the second study, however 28 species appear to represent genuine losses. Of these losses, 16 species are obligate lagoonal specialists and 12 have wider habitat compatibility. Twelve species are recorded from Bikini for the first time. We suggest the highly diverse Rongelap Atoll to the east of Bikini may have contributed larval propagules to facilitate the partial resilience of coral biodiversity in the absence of additional anthropogenic threats.     

南沙群岛永暑礁泻湖岩心的氨基酸与沉积环境

南沙群岛永暑礁小泻湖南永3井的高分辨率岩心系统揭示了环礁泻湖近1682aBP来的沉积柱样的氨基酸组成和含量，其垂直变化同该岩心的有机孔虫丰度、微型腹足类丰度和δ^18O含量的垂直变化基本一致，反映了沉积环境及其变化。南沙群岛珊瑚礁区与中国及全球的历史气候变迁是同步的。     

Long term remeasurements of micro-erosion meter rates,Aldabra Atoll,Indian Ocean

Micro-erosion meter sites, installed on Aldabra Atoll, Indian Ocean in 1969 to measure erosion rates in coastal and subaerial sites, were remeasured in 1971 and again in 1982. The orders of magnitude of calculated erosion rates are comparable but the precise figures and patterns differ. For subaerial sites the short term (1969–71) range of 0·11–0·58 mm a^?1 compares with a long term (1971–82) range of 0·06–0·75 mm a^?1; for coastal sites short term ranges of 0·002–7·5 mm a^?1 compare with long term rates of 0·09–2·7 mm a^?1. Interpretation and extrapolation of short term data should only be made with caution.     

南海九章环礁中牛轭礁和西门礁新生沙洲沉积特征与动态

南沙群岛的珊瑚礁以环礁形式存在, 拥有各具特色的地貌形态。九章环礁中的牛轭礁和西门礁是两座发育有新生沙洲的环礁, 代表灰沙岛形成前一个重要的过渡性地貌演化阶段。这两处新生沙洲表层沉积物样品的粒度分析表明: 沉积物主要组分为珊瑚碎屑, 长轴中值粒径在14~45mm之间, 属于砾石级别; 样品分选系数在4.5~31之间, 分选性很差; 球度值为0.52~0.68, 球度差。粒度特征值中, 中值粒径具有随着到水边线距离的增大而升高的趋势, 而分选性和球度与距水边线距离关系不大。整体上中值粒径与分选系数呈正相关关系, 而与球度呈负相关关系。历史文献记载和卫星图像表明, 牛轭礁和西门礁上的新生沙洲都是近年来才形成的, 与风暴过程及冬季风有关。牛轭礁上沙洲向北迁移, 同时其长轴向东南方向延伸; 西门礁上沙洲整体向东南方向迁移, 并形成回弯形沙嘴形态。新生沙洲的出现与珊瑚碎屑物质供给变化或风暴浪作用变化的关系还需进一步探讨。     

Airborne Gravity Surveys Over Taiwan Island and Strait,Kuroshio Current and South China Sea: Comparison of GPS and Gravity Accuracies at Different Flight Altitudes

We compare the accuracies of GPS and gravity observations obtained from three airborne gravity surveys over Taiwan Island at altitude 5000 m and over Kuroshio Current, Taiwan Strait, and Dongsha Atoll at altitude 1500 m. A kinematic network adjustment was used to determine the positions of the aircrafts. GPS positioning errors are at the decimeter-level, which are not entirely propagated to velocity and acceleration errors due to cancellation of long wavelength errors. Outliers are downweighted in the Gaussian filtering to improve the gravity accuracy, especially at altitude 1500 m. Compared with the upward-continued gravity, the gravity anomalies from the 1500-m surveys show a consistent accuracy of about 3 mgal; the accuracy from the 5000-m survey is degraded, especially over high mountains. The RMS crossover differences at 1500 m and 5000 m are all below 3 mgal, suggesting flight altitudes do not affect the crossover difference. Coherence analysis suggests that the spatial resolvable wavelengths of the airborne gravity range from 4 km (altitude 1500 m) to 6 km (altitude 5000 m).     

Calcareous Sands from a Coral Atoll-Should It Be Mined or Not?

Many lagoons of coral atolls contain huge reserves of very pure calcareous sands in an easily exploitable form that can be used in a number of industries. It is well known that the geomorphic situation in these coral islands is very delicate. With reference to the calcareous sand deposits in the coral atolls of Lakshadweep, a diversity of opinion exists on the aspect of exploitation, though the reserves were proved more than 20 years ago. Elsewhere calcareous sands have been used for several purposes. No raw materials other than coral sands and corals are available in these islands for developmental work such as construction of building and jetties. Several recommendations have been made to keep the system undisturbed to maintain the ecosystem. It is suggested that an attempt should be made to determine an optimum depth of exploitation of these sands without affecting the reef growth and balance of the ecosystem. This will improve the island economy and better quality of life for the islanders. The strategy will help development elsewhere also.