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.

Survey of reefs based on Landsat 8 operational land imager(OLI)images in the Nansha Islands, South China Sea

A detailed survey of the reefs in the Nansha Islands＇ sea that are of strategic importance is conducive to their future development. In this study, a total of 50 Landsat 8 operational land imager（OLI） images were used to analyze the geological features and spectral characteristics of the Nansha reefs. The exposed islands/sandbanks,reef flats and sub-tidal reefs were identified with the near-infrared band, the red and green bands, and the blue band, respectively. Based on the relationships among various characteristics and bands illustrated in the OLI images, the maximum between-cluster variance threshold algorithm（OTSU method） and the mathematical morphology were employed to extract characteristic parameters of the spatial geometry of the reefs from top to bottom, which were subsequently operated by a series of post-processing methods such as vectorization,simplification and topological analysis. Among the 132 standalone reefs and 16 atolls that are identified in the study, four reefs have yet to be named in the Standard Names of Various Islands in the South China Sea and the website Nansha Islands Online（http：//www.nansha.org/）. Another 24 ones are exposed to the atmosphere even during high tides. Taiping Island with an area of 0.57 km^2 represents the largest exposed geological feature. This study demonstrated the applicability of medium-resolution satellite images to derive the coral reef information effectively and thus provided information for the related departments that are responsible to manage the coast.An improved resolution of multispectral bands with the panchromatic band in higher spatial resolution（15 m for OLI image） is expected to provide an optimum satellite based approach to map marine habitats.

A quantitative approach to monitoring new sand cay migration in Nansha Islands

Sand cay is a special kind of islet formed by coral detritus and bioclast, which is common in Nansha Islands of China. Some sand cays play an important role in ocean strategy and economy, but surprisingly we know little about them, especially those recently formed sand cays. In this research, we monitor migration of a new sand cay in Nanxun Jiao（Gaven Reef） using a series of Quick Bird and World View-2 satellite images between June 2006 and August 2013. We conduct a regression between migration distance and wind observational data to examine the migration patterns of the new sand cay. The migration distance is calculated based on the sand cay locations extracted based on Normalized Difference Water Index（NDWI）. The wind observational data downloaded from NOAA are reformed into four wind direction vectors. Based on the results of regression, we concluded that the migration of the new sand cay on Nanxun Jiao was significantly associated with the east, west and north wind.East wind was the main influence factor of the migration; its impact strength was almost twice as the west and north wind. The south wind has little effect on the migration of the sand cay, which is partly blocked by the artificial structure in the south.

Remote sensing composite information's trend surface analysis of Nansha Islands coral islets and reefs' top

Based on the remote sensing information feature of Nansha coral islets and reefs that controlled by the Nansha Islands local area's goological structure and growth law, by means of mathematical model and PC, the Nansha Islands coral islets and reefs' top geological data' spatial distribution and local change trend are simulated by using the trend surface system on the remote sensing composite information, and an scientific interpretation and local comparison of Nansha coral islands and islets' spatial distribution feature are made.

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.

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.

THE PHYSICAL CONDITIONS AND DEVELOPMENT OF THE NANSHA ISLANDS

Qwing to the unique environments,rich marine resources, monsoon climate and ocean current, the Chinese fishennen from Hainan and Guangdong came to the Nansha Islands 2000 years ago. They have kept engnging in the developmen of production since then. The rich historical records and a lot of cultural relics have proved this.

Oceanographic Survey of Nansha Islands Completed

A research project on the Nansha Islands and adja-cent seas was checked andaccepted by a panel organized by theMinistry of Science and Technology(MOST) in Beijing January 18. Nansha Islands, the southern-

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.

The research on the remote sensing＇s information tree model of the Nansha coral islets and reef＇s spatial structure

Based on the Nansha coral islets and reef's time-space attributes,and the intension and extension of the remote sensing information, the concept model and concept system of coral islets and reef are proposed.Then twin-tree remote sensing information model for different kinds of reef is constructed by using abstracted islets and reef's primitive, and the structure recognition system for coral islets and reef type is developed.

The remote sensing composite information entropy and types of Nansha coral reef atolls

In the viempint that the coral reef atolls' growth index of the Nansha Islands is influenced by many factors, the measured remote sensing comopite information including some mutually related factors is divided into 10 geographic events as N1, N2 ..., N10, and the analysis of the atolls' information entropy is made. From the value of theentropy, the closed related factors with the index of the emerged atolls are shown. In proper order, the factors are reeftop's area(0. 319), lagoon's area(0. 324), open-degree of atoll(0. 336), trend of atoll(0. 551 ). On the basis of thiswork, a new description function of the emerged atoll growth index is proposed. This function can be used to identifythe open my of Nansha atoll growth.

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).