Structural features of geostrophic circulation in open region of the South China Sea

On the basis of observation data of water temperature and salinity the mean seasonal geostrophic circulation in open region of the South China Sea (SCS) was computed by the dynamic method relative to the 800 decibar reference surface. The results of computation let go to following notices: In both main monsoons (winter and summer) there are two main geostrophic eddies: the anticlockwise eddy in the northern and northwestern part, and the clockwise eddy in the southern part of the SCS with corresponding divergent and convergent zones. The main frontal zones go along the middle latitudes of the sea from the southern continental shelf of Vietnam to the area west of Luzon Island. The strength and stability of the current in winter are higher than in summer. The Kuroshio has an enough strong branch intruding into the SCS through Bashi Strait in winter creating in the sea the water structure similar to that of the Northwest Pacific subtropical and tropical regions. In summer the Kuroshio water can intrude directly only into the area southwest of Taiwan

HIỆN TRẠNG VÀ BIẾN ĐỘNG DIỆN TÍCH CÁC HỆ SINH THÁI BIỂN TIÊU BIỂU TRONG VỊNH NHA TRANG

Assessments of status and temporal changes in distribution of marine habitats in Nha Trang bay were conducted by using interpretation of remote sensing (Orbview 3, SPOT5, ALOS-AVNIR2 and Landsat 8-LCM) and aerial images in combination with ground truthing at 50 key sites representing coral reefs (25 sites), seagrass beds (10 sites), mangroves (5 sites), rocks (5 sites) and sand (5 sites) in 2015. A total of 812 ha of key marine habitats was recorded in 2015 including 754.1 ha of coral reefs, 52.4 ha of seagrass beds and 5.4 ha of mangroves. There was a notable decline in areas of the above marine habitats in the period of 2002 - 2015, in which 64 ha of seagrass beds (equivalent to 45%; mainly at Bai Tien, Phu Quy, Mui Nam and Vung Me, Đam Gia, Song Lo) and 117.4 ha of coral reefs (equivalent to 13.5%; mainly at Dam Gia, Duong De, Song Lo, Bai Tien and Eo Co) have been lost with an exception of increase of 3.1 ha of mangroves by new transplantation project conducted by Nha Trang MPA authority in Dam Bay during the last few years. The decline in the areas of coral reefs and seagrass beds has been caused by expansion and reclaimation of infrastructure for community and tourism development in recent years.Đánh giá hiện trạng phân bố các hệ sinh thái biển tiêu biểu (rừng ngập mặn, thảm cỏ biển và rạn san hô) trong vịnh Nha Trang được thực hiện bằng việc giải đoán ảnh viễn thám Landsat 8-LCM đa phổ, ảnh Google Earth kết hợp với kiểm định thực địa tại 50 điểm chìa khóa (san hô: 25 điểm, cỏ biển: 10 điểm, cây ngập mặn: 5 điểm, đá: 5 điểm và cát: 5 điểm) trong năm 2015. Việc đánh giá sự biến động phân bố các hệ sinh thái nói trên được thực hiện bằng phương pháp phân tích hồi cố dựa trên kết quả giải đoán ảnh viễn thám và ảnh máy bay theo các đợt đánh giá tổng thể đa dạng sinh học tiến hành trong năm 2002 (Orbview 3 và ảnh máy bay), 2005 (SPOT5) và 2007 (ALOS-AVNIR2). Kết quả nghiên cứu xác định có trên 812 ha diện tích các hệ sinh thái tiêu biểu (gồm 754,1 ha rạn san hô, 52,4 ha thảm cỏ biển và 5,4 ha rừng ngập mặn) phân bố trong vịnh Nha Trang vào năm 2015. Nhìn chung, có sự biến động khá lớn diện tích các hệ sinh thái tiêu biểu trong giai đoạn 2002 - 2015, trong đó thảm cỏ biển bị mất 64 ha (tương đương 45%; chủ yếu ở khu vực Bãi Tiên, Phú Quý, Mũi Nam và Vũng Me, Đầm Già, Sông Lô) và rạn san hô bị mất 117,4 ha (tương đương 13,5%, Đầm Già, Đường Đệ, Sông Lô, Bãi Tiên, Eo Cỏ); riêng rừng ngập mặn tăng 3,1 ha do trồng mới ở khu vực Đầm Báy trong giai đoạn nói trên. Nguyên nhân làm mất diện tích các hệ sinh thái là do việc phát triển cơ sở hạ tầng ven bờ và ven đảo để phát triển khu dân cư và cơ sở du lịch trong thời gian qua

MỘT SỐ NHẬN ĐỊNH BAN ĐẦU VỀ HIỆN TƯỢNG SÓNG NỘI XẢY RA Ở VÙNG BIỂN MIỀN TRUNG VIỆT NAM

Internal waves often occur in the East Vietnam Sea and have been determined mainly based on RADAR images. By means of dataset of VNREDSAT-1 satellite images and other imagery sources, for the first time, internal waves in the East Vietnam Sea have been identified by multispectral images; Also the formation mechanism of internal wave in the nearshore waters of Central Vietnam has been found. The analytical results show that the phenomenon of internal wave occurs in the nearshore waters of Central Vietnam mainly in the Southwest monsoon season (from June to September every year) and is located along the edge of the continental shelf. Internal waves formed along the waters of Central Vietnam mainly include the signals that have been generated at the shelf by large waves, through the basin from Luzon Strait. The study results have discovered a new applied aspect of VNREDSAT-1 satellite images in oceanographic research in general and detailed studies on internal waves in particular.Sóng nội thường xuyên xuất hiện ở Biển Đông và đã được các học giả nước ngoài xác định chủ yếu dựa trên tư liệu ảnh RADAR. Bằng sử dụng nguồn ảnh viễn thám đa phổ, đa nguồn, đa thời gian bao gồm cả các ảnh viễn thám đa phổ VNREDSAT-1 (do Việt Nam bay chụp) thu thập trong thời gian gần đây, lần đầu tiên đã nhận dạng hiện tượng sóng nội ở Biển Đông bằng tư liệu ảnh đa phổ cũng như phát hiện ra quy luật hình thành sóng nội ở vùng biển miền Trung Việt Nam. Kết quả phân tích cho thấy, hiện tượng sóng nội xuất hiện ở vùng biển miền Trung Việt Nam, chủ yếu xuất hiện vào mùa gió Tây Nam (từ tháng 6 đến tháng 9 hàng năm) và nằm ở ven rìa của thềm lục địa. Sóng nội hình thành dọc theo vùng biển miền Trung Việt Nam chủ yếu là các tín hiệu được sinh ra tại vùng thềm bởi các sóng lớn, xuyên qua lưu vực từ eo biển Luzon. Kết quả nghiên cứu đã phát hiện ra một khía cạnh ứng dụng khác của ảnh viễn thám VNREDSAT-1 trong lĩnh vực hải dương học nói chung và nghiên cứu chi tiết sóng nội nói riêng

ỨNG DỤNG CÔNG NGHỆ VIỄN THÁM VÀ GIS NGHIÊN CỨU QUÁ TRÌNH DỊCH CHUYỂN ĐƯỜNG BỜ VÀ ĐÓNG/MỞ CỬA ĐẦM Ô LOAN (PHÚ YÊN) GIAI ĐOẠN 1965 - 2014

Application of remote sensing and GIS (Geographic Information System) technologies found that: Fluctuation process of shoreline in O Loan lagoon became evident, through which a general picture of the shoreline development in a long time from 1965 - 2014 has been launched. The process of erosion - accretion evolutions occurred time by time. In which, the period from 1965 - 1995 was the process of erosion - accretion and gradual northward movement of O Loan lagoon inlet, with erosion area greater than deposition area. The period after 1995 was the process of erosion and An Hai inlet opening during rainy season, coincident with northeast monsoon and typhoon activity; and the process of accretion and An Hai inlet closing during dry season, coincident with southwest monsoon.Trên cơ sở ứng dụng công nghệ viễn thám và GIS (hệ thông tin địa lý) cho thấy: Quá trình biến động của đường bờ biển khu vực đầm Ô Loan được thể hiện rõ rệt, qua đó đã đưa ra bức tranh tổng quát về quá trình phát triển của đường bờ, trong một thời gian dài từ năm 1965 - 2014. Các quá trình xói lở - bồi tụ diễn biến theo thời gian. Trong đó, thời kỳ từ năm 1965 - 1995 là các quá trình xói lở - bồi tụ và dịch chuyển cửa biển đầm Ô Loan dần lên phía bắc, với diện tích bị xói lở lớn hơn diện tích được bồi tụ. Thời kỳ từ sau năm 1995 đến nay là quá trình xói lở và mở cửa biển An Hải chủ yếu xảy ra vào mùa mưa, trùng với thời kỳ gió mùa Đông Bắc và bão hoạt động, còn bồi lấp cửa biển xảy ra vào mùa khô, trùng với thời kỳ gió mùa Tây Nam

Spatial and temporal variations of Biological Production in the Asia-Pacific Marginal Seas

This research project consists several main activities which are considered to be able to improve research capability in the Asia-Pacific region, especially in the collaborating countries. In terms of research, the project focused on discerning spatial and temporal variations of marine biological production in the Asia-Pacific marginal seas (the East China Sea, the South China Sea, the Strait of Malacca, and the Gulf of Thailand) utilizing multisensor satellite observations and coupled hydrodynamic-biogeochemical model. As part of the research achievements, one paper was accepted (in press) for publication in Remote Sensing. Other three or four papers are now under preparation for submission to high impact journals. To achieve research objectives, four (4) young scientists from collaborating countries were also involved in the project, that at once allowing them to improve their research capability and to enter international scientific community. In order to expand international networking and/or research collaboration in the near future, international mini-workshop on the western Pacific Ocean and marginal seas biogeochemical variability was also held in Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in February 2014. As feedback of this research project and research continuation, it has been discussed and planned to propose Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellowships for foreign researchers.Project Reference Number: ARCP2012-21NSY-Siswanto, Final Report submitted to APN ; The original publication is available at APN via http://www.apn-gcr.org/resources/items/show/176

Abnormal features of oceanographic characteristics in upwelling Vietnam waters under impact of El Niño events

The summer upwelling that occurs in coastal waters of South Central Vietnam is one of the major hydrographic features in the South China Sea. A weakening of the upwelling after major El Niño events was observed in the literature for previous El Nino events and was verified here from the analysis of new satellite image data sets of sea surface temperature (SST) and surface wind. The analysis of empirical orthogonal function (EOF) from of monthly SST as well as of temporal and spatial variations of SST and wind force allow us to identify abnormal characteristics in ocean surface water that happened after El Niño episode, in agreement with previous studies. Those abnormal characteristics in Vietnam upwelling waters appeared mainly during the summers of 1998, 2003, 2010 and 2016 years for the El Niño decline phase. The upwelling weakening during El Niño decline episodes is associated with the following signals: (1) Wind force and Ekman pump are very weak; (2) the cold  and high chlorophyll-a  tongue is shifted northward but not extended eastward; (3) for years when El Nino occurs, SST strongly increases and reaches a peak in May or early June of next year, during the declining phase of El Niño episode; (4) upwelling phenomenon typically occurs during August and not July. Using a reanalysis dataset derived from the HYCOM/NCODA system coupled with a local Finite Element Model (FEM) allow us to complete our knowledge about the abnormal oceanographic characteristics of deeper water layers after El Niño episodes. The analysis of spatial variations of oceanography fields derived from HYCOM/NCODA/FEM system along zonal and meridional sections and vertical profiles as well as the results obtained from water mass analysis allow us to identify in details the abnormal oceanic characteristics of deeper water layers during the declining  El Niño phase. Those are; (5) Sea water in both surface and deeper water layers were transported dominantly northward  but not eastward; (6) The thermo-halocline layer in South Vietnam upwelling center was deeper (about 90 -100m), compared with previous El Nino and normal years (50-60 m and 35-40 m, respectively); (7) Extreme global warming in recent years (2012-2016) pressed the thermo-halocline layer in upwelling center deeper (90-100 m) during summer. Under the influence of the ocean global warming, this process should progress continuously, the depth of thermo-halocline layer should become therefore deeper and deeper in next years.References Barthel, K., R. Rosland, and N. C. Thai, 2009. Modelling the circulation on the continental shelf of the province Khanh Hoa in Vietnam, J. Mar. Syst., 77(1-2), 89-113. Bui Hong Long, Tran Van Chung, 2009. Calculations of currents in the upwelling region along south-central Vietnamese coast, using three dimensions (3-D) nonlinear model”, Journal of Marine Science and Technology - VAST, 9(2), 01-25 (in Vietnamese). Bui Hong Long, Tran Van Chung, 2017. Preliminary studies on the impact of climate change on the upwelling region south Central Vietnam in summer.  Journal of Marine Science and Technology - VAST , 17(1), 01-19 (in Vietnamese). Colling, A., 2001. Ocean Circulation, Open University Course Team. Second Edition. ISBN 978-0-7506-5278-0. Dippner, J. W., and N. Loick-Wilde, 2011. A redefinition of water masses in the Vietnamese upwelling area, J. Mar. Syst., 84(1-2), 42-47. Hale, W.G, Margham, J.P,  and Sauder, V.A, 2005. Collins Dictionary of  Biology 3rd . London: Collin. Huang, Q.-Z.,W.-Z. Wang, Y. S. Li, and C. W. Li, 1994. Current characteristics of the South China Sea, in Oceanology of China Sea, edited by D. Zhou, Y.-B. Liang, and C. K. Tsebgm, 39-47, Kluwer Acad., Norwell, Mass. H.E. Hurlburt, E.P. Chassignet, J.A. Cummings, A.B. Kara, E.J. Metzger, J.F. Shriver, O.M. Smedstad, A.J. Wallcraft, and C.N. Barron, 2008. Eddy-resolving Global Ocean Prediction, in M. Hecht and H. Hasumi, eds., Ocean Modeling in an Eddying Regime, Geophysical Monograph 177 (American Geophysical Union, Washington, DC ). Knauss, J.A., 2005. Introduction to Physical Oceanography, Waveland Press. Second Edition. ISBN 978-1-57766-429-1. Kuo. N. J, Zheng. Q, Ho C. R, 2004.  Response of Vietnam coastal upwelling to the 1997-1998 ENSO event observed by multisensor data, Remote sensing of Environment, 15 January, 89(1), 106-115. Le Phuoc Trinh, Nguyen Tien Dung, Nguyen Van Minh, Le Minh Tan, Nguyen Kim Vinh, 1981. A proposal of studies on the upwelling of Southeastern coast of Vietnam, Collection of Marine Research Works, 2(2), 13-31 (in Vietnamese). Nguyen Van Long and Vo. Si  Tuan, 2010. Status of coral reefs in Vietnam following the 2010 coral bleaching event. In: Kimura T, Tun K (eds) Status of Coral Reefs in East Asian Seas Region: Ministry of the Environment, Japan, 29-49. NOAA National Centers for Environmental Information, State of the Climate: Global Analysis for Annual 2010, published online January 2011, retrieved on March 25, 2017 from http://www.ncdc.noaa.gov/sotc/global/201013. Ose, T., Y. Song, and A. Kitoh, 1997. Sea surface temperature in the South China Sea: An index for the Asian monsoon and ENSO system, J. Meteorol. Soc. Japan., 75, 1091-1107. Pohlmann, T., 1987. A three dimensional circulation model of the South China Sea., 245-268. In Three-Dimensional Models of Marine and Estuarine Dynamics, ed. by J. J. Nihoul and B. M. Jamart, Elsevier, New York. Qu, T,  Kim, Y.Y, Yaremchuk, M., Tozuka. T, Ishida, A, Yamagata, T., 2004. Can Luzon strait transport play a role in conveying the impact of ENSO to the South China Sea J. Clim. 17, 3644-3657 Shaw, P. T., and S. Y. Chao, 1994.  Surface Circulation in the South China Sea, Deep-Sea Res., I(41), 1663-1683. Siswanto, E., H. Ye, D. Yamazaki, and D.L. Tang 2017. Detailed spatiotemporal impacts of El Niño on phytoplankton biomass in the South China Sea, J. Geophys. Res. Oceans, 122, doi:10.1002/2016JC012276. Sverdrup, H.U., M.W. Johnson and Fleming, R.H., 1942. The Oceans: their physics, chemistry and general biology. Prentice Hall, New York, 1087p. Tang D. L., H. Kawamura, H. Doan Nhu, and W. Takahashi, 2004. Remote sensing oceanography of a harmful algal bloom off the coast of southeastern Vietnam, J. Geophys. Res., 109, C03014, doi:10.1029/ 2003JC002045. Thai Minh Quang, 2016. Studies on influence of  2016.  El Niño event to coral bleaching phenomena in coastal waters in Ninh Hai - Ninh Thuan province. Technical report of  basic research pro­ject funded by Institute of Oceanography - the Vietnam Academy of Science and Technology (in Vietnamese). Tong Phuoc Hoang Son, Vo Van Lanh and Lau Va Khin, 2005. Application of empirical orthogonal function (EOF) for studying thermal structure in sea surface water in South China Sea. The 26th Asian Remote sensing Conference, 7-11 November 2005 in Hanoi. Tran Van Chung, Bui Hong Long, 2016. Effect of temperature field and anomalies of sea water level in East Vietnam Sea in relationship to global climate change - Journal of Marine Science and Technology - VAST, 16(3), 255-266 (in Vietnamese). Vo Van Lanh, 1995. The environmental characteristics of strongly upwelling waters in south of Vietnam and its ecological impacts. Technical report of National project KT03.05. Institute of Oceanography, 480p (in Vietnamese). Vo Si Tuan, 2000. The corals at Con Dao archipelago (South Vietnam): before, during and after the bleaching event in 1998. In: Proceeding of 9th International Coral Reef Symposium, Bali, Indonesia, 23rd-27th October, 895-899. Wang B., An S., 2005. A method for detecting season-dependent modes of climate variability: S-EOF analysis. Geophys. Res. Lett., 32, L15710. Wyrtki K., 1961. Physical oceanography of the Southeast Asian waters, Naga Rep. 2, 195p, Scripps Inst. of Oceanogr., La Jolla, Calif. Xie S.-P., Q. Xie, D. Wang and W. T. Liu, 2003. Summer upwelling in the South China Sea and its role in regional climate variations, J. Geophys. Res., 108(C8), 3261, doi:10.1029/2003JC001867. Xie S.-P., C.-H. Chang, Q. Xie and D. Wang, 2007. Intraseasonal variability in the summer South China Sea: Wind jet, cold filament, and recirculations, J. Geophys. Res., 112, C10008, doi:10.1029/2007JC004238

Application Earth Observation Data for Monitoring Coastal Marine Ecosystes in Vietnam

<p>Poster presented at the "Oceans and Society: Blue Planet"  Symposium in São Paulo, Brazil in November 2012.</p> <p><strong>Abstract</strong></p> <p>The data on spatial distribution, qualitative and quantitative characteristics of coastal habitats can be considered as fundamental and essential information for the planning, policy making on sustainable developing and utilizing these coastal marine ecosystems under impacts of economic development and natural disaster pressures. Coastal wetland habitats of Huong Phong Commune belongs to Huong Tra District, in the central province of ThuaThien Hue, Vietnam was selected as a pilot site for this study. Through analysis of survey and earth observation data, seagrass meadows, mangroves and agriculture ecosystems were mapped.</p

High-resolution benthic habitat mapping from machine learning on PlanetScope imagery and ICESat-2 data

This study proposed a comprehensive approach that utilized PlanetScope imagery for classifying tropical-marine benthic habitats after retrieving bathymetry from ICESat-2 data and water-column correction for areas around Lyson Islands, Vietnam. Exact bathymetry derivation and water column correction were applied to the PlanetScope imagery, making it an effective method for mapping marine benthic habitats. Water column correction was achieved by applying Depth Invariant Index (DII) and Bottom Reflectance Index (BRI). Moreover, two conventional machine learning algorithms, including Random Forest and Support Vector Machine, and a current deep Convolutional Neural Network (CNN) was employed to classify the benthic features. The overall accuracy of these classifiers are 80.74%, 84.19%, and 89.80% with the BRI, 80.17%, 82.75%, and 87.85% with the DII compared to 37.64%, 42.5%, and 47.2% of without corrected water columns respectively. The CNN model demonstrated that the approach significantly maximizes the improvement in benthic classification results in coastal region