Drivers,Trends,and Patterns of Changing Vegetation-greenness in Nansha Islands,China from 2016 to 2022

Changes in vegetation status generally also represents changes in the ecological health of islands and reefs(IRs).However,studies are limited of drivers and trends of vegetation change of Nansha Islands,China and how they relate to climate change and human activities.To resolve this limitation,we studied changes to the Normalized Difference Vegetation Index(NDVI)vegetation-greenness index for 22 IRs of Nansha Islands during normal and extreme conditions.Trends of vegetation greenness were analyzed using Sen's slope and Mann-Kendall test at two spatial scales(pixel and island),and driving factor analyses were performed by time-lagged partial correlation analyses.These were related to impacts from human activities and climatic factors under normal(temperature,precipitation,radiation,and Normalized Difference Built-up Index(NDBI))and extreme conditions(wind speed and latitude of IRs)from 2016 to 2022.Results showed:1)among the 22 IRs,NDVI increased/decreased significantly in 15/4 IRs,respectively.Huayang Reef had the highest NDVI change-rate(0.48%/mon),and Zhongye Island had the lowest(–0.29%/mon).Local spatial patterns were in one of two forms:dotted-form,and degradation in banded-form.2)Under normal conditions,human activities(characterized by NDBI)had higher impacts on vegetation-greenness than other factors.3)Under extreme conditions,wind speed(R^(2)=0.2337,P<0.05)and latitude(R^(2)=0.2769,P<0.05)provided limited explanation for changes from typhoon events.Our results provide scientific support for the sustainable development of Nansha Islands and the United Nations‘Ocean Decade’initiative.

Dynamics of picoplankton in the Nansha Islands area of the South China Sea

Dynamics of major picoplankton groups, Synechococcus (Syn), Prochlorococcus (Pro), picoeukaryotes (Euk) and heterotrophic bacteria (Bact) was investigated by flow cytometry for the first time in the Nansha Islands area in the South China Sea. Averaged over the whole investigation area, depth-weighted integrated cell abundance (DWA) of Syn, Pro, Euk and Bact was 1.6 (0.4-5.7)×103, 5.4 (0.1-7.3)×104, 0.7 (0.2-2.2)×103, and 2.3 (1.4-3.2)×105 cells/mL respectively. Picoautotrophic cell abundance was low in the northwest part of the Nansha Islands where surface water temperature was low and the upper mixed layer was shallow. Concurrently, a surface maximum vertical distribution pattern was observed in this area. While in the southeast and east zones where temperatures were relatively higher and nitraclines were deeper, picoplankton is abundant and a subsurface maximum around 50-75 m is observed. Coupling of horizontal and vertical distribution patterns of picoplankton abundance and hydrological status was found, suggesting a strong influence of currents and water column structure on picoplankton distribution in the investigation area. Contrary to that in the shelf water in the East China Sea, the relationship between Pro and Bact in the Nansha Islands area in the South China Sea was not significantly negative but weakly positive. Moreover, a similar distribution pattern of Syn and Pro was observed. Possible reasons for these differences in the two marine regimes were discussed.

The influence of earthquakes on Zhubi Reef in the Nansha Islands of the South China Sea

It is exceedingly important to estimate the stability of coral reefs. In recent years, growing construction projects have been carried out on the reef flat in the South China Sea. As a special marine geotechnical medium, it is made of the reef debris underwent overwhelmingly long geological age. Reefs grow thickly on the carbonate platform after the Late Oligocene and have five to six main sedimentary facies. It can be used as a recorder to measure the occurrence time of recent earthquake. A model of reef body is presented to study the influence of earthquakes according to the geological structure characteristic of reefs in the Nansha Islands. Furthermore, Geo Studio is used to simulate stress and deformation situations within it under various earthquake intensities. A safety factor is calculated by the limit equilibrium method, and the possible scenarios of earthquake-induced landslides and sliding scale are defined with a Newmark sliding block method, as well as stress distribution and deformation behaviors. Therefore, the numerical results suggest that the connections between the coral reef and the earthquake are as follows：（1） the reef body has a good stability under self-gravity state;（2） after the earthquake, it may cause slope＇s instability and bring out slumping when the safety factor is smaller than 1（FS〈1）;（3） the safety factor decreases with the increasing earthquake intensity, and fluctuates around a particular value after a while;and（4） as a new developed part of the reef, the smaller shallow landslide will be easily subject to collapse caused by the earthquake. It is concluded that it is feasible to provide a reference for evaluating the stability of coral reef using a geotechnical engineering simulation method. This can help the engineering constructions in the South China Sea.

Distribution of Organic Matter,Iron,Mangenese in Surface Sediments in the Nansha Islands Sea Area,South China Sea

Concentrations of organic matter, iron and manganese in the deep sea surface sediments in the Nansha Islands sea area, South China Sea are measured. Horizontal and vertical distributions of iron and manganese are discussed. The vertical distribution of iron and manganese in the sediments results from reduction, diffusion, and redeposition of manganese (or iron) oxide and hydroxide in the sediment. There are the maxima of iron and manganese in solid phase in the top of the sediment, which is caused by the penetration of O2 and the upward flux of Mn2+ ( or Fe2+ ). Manganese bacteria play a very important role in the cycle of solid-phase iron and manganese in the ocean environment. Manganese bacteria oxidize Mn2+ ( or Fe2+ ) in dissolved state to Mn4+ ( or Fe3+ ) in oxidized state under the aerobic condition, whereas they reduce iron and manganese in anaerobic conditions.

Characteristics of K_d (490) around Nansha Islands in the South China Sea

The diffusion attenuation coefficient for downwelling irradiance, Kd (490), is an important optical parameter of seawater. The optical property, Kd (490), around Nansha Islands in the South China Sea was analyzed based on optical data profiles measured with SPMR ( SeaWiFS Profiling Multichannel Radiometer ) and SMSR ( SeaWiFS Multichannel Surface Reference ) instrument in April and May, 1999. The results show that Kd (490) is closely correlated with chlorophyll-a concentration, Cchl.a, and that the vertical distribution of Kd (490) shows the strong stratification of the water column in this area. Kd (490) has a similar vertical co-variation as KL (490), the diffusive attenuation coefficient for upwelling radiance. Both coefficients increase with depth in the upper layer, where KL (490) is greater than Kd (490); and after a depth, approximatively at the chlorophyll maximum, they decrease with depth, with the former being smaller than the latter.

THE GEOGRAPHICAL DISCOVERY OF THE NANSHA ISLANDS

Ths paper proves that it is the Chinese people that are the eariiest to discover the Nansha Islands in history, according to the irrefdsble facts from historical records, mpaphical discovenes, the opening of sailing lines and the nandng of places.

A reduced thermodynamic model on the formation of the Nansha warm water

A reduced vertically integrated upper mixed layer model is set up to numerically study the thermodynamic process of the formation of the 'Nansha warm water'(NWW) in the Nansha Islands sea areas in spring. According to the numerical experiments, it is shown that, in spring, the formation of the NWW is mainly due to the sea surface net heat flux and the local weak current strength; the contribution from temperature advection transport and warm water exchange with the outer seas (Sulu Sea or south of Sunda shelf) is very little. In the sea areas where the current is strong, the advection may also play an important role in the temperature field.

Two new species of the genus Nassarius(Gastropoda:Nassariidae) from the South China Sea

Two species of Nassarius Duméril, 1805 from the South China Sea are described and illustrated. The specimens are in the Nassariidae collection of the Marine Biological Museum of Chinese Academy of Sciences, Qingdao.Nassarius concavus sp. nov., from the sandy bottom at a depth of 180 m, resembles Nassarius glabrus Zhang and Zhang, 2014 in general shell morphology, but differs from the latter in having a smaller, more slender adult shell without axial ribs on the upper teleoconch whorls. Nassarius nanshaensis sp. nov., from the Nansha Islands at a depth of 56–147 m, is similar to Nassarius maxiutongi Zhang, Zhang and Li, 2019 in the shell sculpture, but differs in having a more slender shell with a higher spire, and fewer cusps on the rachidian tooth(9–11 vs. 13–17).

Tropical Hainan——China’s Hawaii

BEFORE moving to China,my favorite hideaway was Hawaii,so I was delighted to learn China has its own Hawaii–southernmost Hainan Province.A Han Dynasty(206 BC-AD 220)emperor established a military garrison on Hainan Island,the largest island of Hainan Province,in 110 BC.Sun Yatsen recommended the establishment of a province in the region in 1906,but this did not happen until 1988,the year we moved to China.

Modern microbialites and their environmental signifi-cance,Meiji reef atoll,Nansha (Spratly) Islands,South China Sea

Meiji (Mischief) coral atoll, in Nansha (Spratly) Islands, South China Sea, consists of an annular reef rim surrounding a central lagoon. On the atoll rim there are either protuberant 'motu' (small coral patch reefs on the rim of atoll) islets or lower sandy cays that contain modern microbialite deposits on the corals in pinnacles and surrounding bottoms of the atoll. Microbialites, including villiform, hairy, and thin spine growth forms, as well as gelatinous masses, mats and encrustation, developed on coral colonies and atoll rim sediments between 0 and 15 m deep-water settings. The microbialites were produced by natural populations of filamentous cyanobacteria and grew on (1) bulbous corals together with Acropora sp., (2) on massive colonies of Galaxea fascicularis, (3) on dead Montipora digitata, and (4) on dead Acropora teres, some hairy microbialite growing around broken coral branches. This study demonstrates that microbial carbonates are developed in coral reefs of South China Sea and indicates that microbial processes may be important in the construction of modern reef systems. The results have significance in the determination of nature and composition in microorganisms implied in the formation ancient microbialites, and permit evaluation of the importance of microbial deposits in mo-dern coral reefs and of 'microbialites' in biogeochemical cycles of modern coral reef systems. The re-sults also provide evidence of modern analogues for ancient microbialites in shallow-water settings, and combine with sedimentological studies of ancient microbialites to understand their controls.

Assessment of coral bleaching using symbiotic zooxanthellae density and satellite remote sensing data in the Nansha Islands,South China Sea

Coral bleaching,characterized by a significant loss of symbiotic zooxanthellae,is the primary cause of mass coral mortality and reef degradation throughout the world.The characteristics,processes,and resistance of corals to bleaching varies significantly and is dependent on environmental conditions.We documented a mass coral bleaching event in June 2007 at the Meiji and Zhubi Reefs,Nansha Islands (NS),South China Sea using ecological surveys and measurement of coral zooxanthellae density and sea surface temperatures (SST).More than 35 species of corals (between 0-20 m in depth) were bleached.These bleached corals accounted for 15.6% of total corals in the investigated quadrats.The branching corals Pocillopora and Acropora were the most vulnerable species whereas the massive corals Porites and Favia were more tolerant of the high SSTs.Surprisingly,we found no evidence of bleaching in Agariciidae corals suggesting that this family is resistant to thermal stresses.The bleached corals had lost 72%-90% of their symbiotic zooxanthellae.Furthermore,corals that had no visual signs of bleaching had also lost 31%-53% of their zooxanthellae suggesting that most corals were experiencing the early stage of bleaching.The monthly mean SST during June 2007 was 30.8°C,the highest since 1998.Based on measurements of SST and the Hotspots and DHW data (NOAA),we conclude that it the extremely high SSTs triggered this coral bleaching event.Our results suggest that the previously accepted temperature thresholds used to predict coral bleaching based on satellite data are likely to underestimate the extent and intensity of coral bleaching,at least in the NS.

The geographical characteristics of Nansha Islands in the South China Sea

As is well-known, Nansha Islands in the South China Sea(SCS) are of important strategic position and invaluable ecological value. Therefore, many attentions are paid to either the political and legal aspects of exposed features that matter in the maritime delimitation, or the physical and geographical characteristics of coral reefs that are the predominant structures of these islands. However, it seems that they consistently lose the connection of sciences and humanities in the research of Nansha Islands in the SCS. In this study, we carry out a combinative research, based on remote sensing data using satellite imagery analysis together with historical materials using literature investigation, so as to reconsider to the geographical characteristics of Nansha Islands from a standpoint of the United Nations Convention on the Law of the Sea(UNCLOS). After thoroughly appraising the statuses of these newly formed sand cays, several high tide features of Nansha Islands are identified. By means of the comparison of satellite images coupled with reference to nautical charting and sailing directions during different time periods, we can conclude that the statuses of these high tide features formed on reef platforms are relatively stable due to the growth of reef-building organisms although their migration patterns are subject to external disturbances, and hence the cursory judgment pursuant to the relevant provisions of the UNCLOS about whether a coral reef belongs to a low tide elevation only based on outdated references or ex parte evidences is not reliable. Moreover, it is accordingly justified to improve further development and perfection of the maritime legislation by eliminating such ambiguities with the growth of coral reefs and the evolution of sand cays being both taken into account.

南沙群岛海域长腹剑水蚤(Oithona spp.)的种类组成、数量分布及其与环境因子的关系

中小型桡足类是海洋食物网中重要的中间环节,在碳循环里细菌碳和藻类碳向高营养级转化的过程中扮演重要角色。本文通过分析2013年3—4月、6—7月、9—10月和11—12月南沙群岛海域(111°30′E—112°30′E,4°30′N—11°30′N)的生态环境调查数据,对长腹剑水蚤属(Oithona)的种类组成、数量分布及其与环境因子的关系进行了研究。结果表明:(1)南沙群岛海域共出现长腹剑水蚤15种(包括1个未定种),其中线长腹水蚤(Oithona linearis)、粗长腹剑水蚤(O.robusta)和长刺长腹剑水蚤(O.longispina)为南沙群岛海域首次记录,长腹剑水蚤属种类组成沿水深变化的现象较为明显,该属虽然在南沙群岛海域广泛分布,但单种的出现频率较低,其种类出现的季节性较强;(2)南沙群岛海域的长腹剑水蚤可以划分为常见广布组群Ⅰ和低频组群Ⅱ;(3)长腹剑水蚤年均栖息密度为30ind./m3,季节变化呈单峰型,秋季最高、冬季最低,高数量区主要出现在受南沙西部沿岸流和东部沿岸流影响的近岸海域;(4)在0—750m水深范围内,长腹剑水蚤数量沿水深梯度的垂直变化明显,呈现由浅至深数量明显减少的趋势,长腹剑水蚤主要集中分布在0—75m的水层中,75—500m数量急剧降低至最低后,在500—750m基本维持不变;(5)GAM分析表明,纬度、海水温度、盐度和叶绿素a浓度对长腹剑水蚤数量均有影响,以纬度的影响最为显著,其中长腹剑水蚤属最适温度为28.6—29.2℃,最适盐度为32.6—33.2,最适叶绿素a浓度为5—10μg/L;(6)长腹剑水蚤属更适栖息于低温和低盐,且受沿岸流影响的环境中。因此,其数量分布的季节变化与季风驱动的沿岸流势力强弱密切相关。

20世纪70年代中国香港报刊对西沙事态的反应——以《明报月刊》为考察中心

1974年1月,西沙海战爆发后,中国香港报刊积极报道与战事相关的内容,对中国香港社会的维权动态以及南海诸岛史地知识亦多有着墨,但很少深入探讨中国南海主权。相对而言,《明报月刊》则刊登了一系列由中国香港、中国台湾学者和海外华人学者所撰写的学术维权文章,为中国南海诸岛主权的论证提供了历史和法理依据。

1947年澳大利亚筹备对日和约时南沙群岛的档案搜集与立场

1947年初澳大利亚为维护国家利益提议尽早缔结对日和约,并组建太平洋和约筹备委员会具体负责拟定对日和约草案。在对日领土处置时为了厘清战时为日所占之南沙群岛的归属情况,澳大利亚初步搜集了1939~1946年有关南沙群岛“争议”各方主张、日本占领南沙时的声明与英法反应、战时日本对南沙的开发利用和战后中国政府收复南沙群岛史实等6份核心档案,在此基础上,综合研判后形成南沙群岛归属上中国已实控、法方态度不明及其军事战略价值有限的认知。为此1947年7月9日筹备委员会拟定的对日和约草案只规定了日本放弃南沙群岛,未写明其归属。不过,7月15日澳大利亚驻南京公使馆发给澳外交部的第341号函电旗帜鲜明地指出,除却中国对南沙群岛提出最早主张外,因为岛上居民主要是中国渔民这一事实,别无任何可靠的权威依据,同时排除了法国对南沙群岛提出“主权诉求”的可能。尽管澳大利亚的上述立场最终未写入新一轮的对日和约草案,但其内部函电字里行间流露出的对中国拥有南沙群岛主权的认可,无疑是不可否认的。

20世纪上半叶日本在南沙群岛扩张的历史考察

20世纪上半叶,日本在对外扩张过程中密切关注中国南沙群岛,并将实现对其的控制和占领作为主要目的。日本政府对南沙群岛进行了多次非法调查,编造依据,企图“合法”侵占中国南沙群岛。日本不仅掠夺南沙群岛资源,而且在太平岛建设军事设施,为进军东南亚做准备。日本谋划、侵占中国南沙群岛是其推南进政策的重要一环。在此过程中,日本关注的重点是南沙群岛的战略地位,而非经济资源。日本的侵占导致南沙群岛成为二战后国际社会需要处理的问题之一。

中国知识精英对日本侵占南沙的因应——以民国报刊为中心的考察

1939年3月底,日本侵占南沙群岛是抗日战争进入相持阶段后日本在“南进政策”上迈出的重大一步。当时国内知识精英通过报刊密集发表社论和文章,提出我国对日本侵占南沙的因应之策:坚持南沙群岛主权属我;厘定斯巴特莱群岛为我团沙群岛;研判日本侵占南沙是剑指法、英、美、荷南洋殖民地而与对华战事无涉。这不仅提升了抗战相持阶段后国人进一步的抗日爱国热情、加快了反法西斯统一战线的形成,还为抗战胜利后中国政府正式收复南海诸岛、更改“团沙群岛”为“南沙群岛”和绘制《南海诸岛位置图》等一系列有效管辖南海诸岛的行动,奠定了强大的舆论和思想基础。

克洛玛非法“探险”南沙与中国台湾、菲律宾马尼拉交涉

1956年3月到5月,菲律宾克洛玛等人非法“探险”南沙群岛,引发了台湾地区当局和菲律宾围绕南沙归属问题的交涉。台湾地区当局在交涉之初所具有的优势地位,因海军即将巡弋南沙得到加强,然而受冷战思维的影响,它一开始就采取了妥协态度,这也预示着交涉的最终结果。另外,国内外媒体尤其是中国香港报纸对该事件的报道,在一定程度上有助于还原当时交涉的若干场景。

南海北部陆缘反“S”型构造带的提出及其在新生代晚期地质演化中的作用

通过地震剖面、地形－地貌、断裂构造、地壳结构、中新生代沉积盆地、第四纪地质特征等分析，认为南海北部陆缘存在滨岸岛键、陆坡北缘和陆坡南缘三条反“S”型构造带。它们形成于晚第三纪，较“新华夏系”和“南海系”晚。反“S”型构造带新生代晚期的活动方式，对南海北部陆缘的地质演化影响显著，同时控制了这一区域的灾害性地质因素的活动方式和分布。

1950年菲律宾对西沙、南沙群岛的觊觎与中国的应对--以中国香港报纸为考察中心

中国人民解放军在1950年解放海南岛之后开始经略西沙和南沙群岛,巩固我国的主权防卫工程。然而,菲政府某些政要、媒体担心中国经略两群岛后会“威胁”其地缘政治安全,于是开始编造所谓法理依据(托管地、地理邻近说),为其觊觎行为寻找借口。由于中国政府的警告、中国台湾当局“驻菲大使馆”的反对,以及自身意见不统一、海军实力薄弱等原因,菲律宾暂时放弃了占领南沙群岛的野心。此时南海地缘形势的变化深刻地打上了冷战格局的烙印。中国政府采取维权与建设并举之策,并借助苏联力量进行榆林港海军基地和永兴岛气象设施的建设。