CÁC ĐẶC TRƯNG NHIỆT ĐỘ VÀ ĐỘ MUỐI TẰNG MẶT TẠI VÙNG BIỂN NAM TRUNG BỘ VIỆT NAM

The analyzed results of the characteristics of sea surface temperature and sea surface salinity in South Central Vietnamese waters based on MODIS and VOS data sources have revealed the variation of sea surface temperature and sea surface salinity in high ranges. Study results show that the average value of sea surface salinity ranges from 30 psu to 34 psu and is relatively stable. However, the weather is very harsh: Deviation between the highest and lowest values of sea surface temperature is 13.9°C in the seasons and that in months is 11.14°C. This is a very high amplitude, indicating the large variation of daily, monthly and seasonal temperature. The study results will help scientists and aqua-farmers take rational decisions in the selection of suitable species for aquaculture, biodiversity and environmental protection in South Central Vietnamese waters.Kết quả phân tích các đặc trưng của yếu tố nhiệt độ và độ muối tầng mặt vùng biển Nam Trung Bộ Việt Nam dựa trên nguồn số liệu MODIS và VOS đã cho thấy đây là vùng biển có nhiệt độ và độ muối tầng mặt nằm ở dải rất cao. Độ muối phổ biến dao động trong khoảng từ 30‰ đến 34‰ và khá ổn định. Tuy nhiên, thời tiết ở đây rất khắc nghiệt: Biên độ dao động nhiệt độ (khoảng chênh giữa nhiệt độ cao nhất và thấp nhất) trong mùa là 13,91°C và trong tháng là 11,14°C. Đây là biên độ dao động rất cao, biểu thị sự biến động của nhiệt độ trong ngày, trong tháng và trong mùa rất lớn. Kết quả nghiên cứ trên sẽ hỗ trợ các nhà quản lý và người nuôi trồng thủy sản có những quyết định hợp lý hơn trong việc chọn lựa giống loài thích hợp trong nuôi trồng thủy sản, bảo vệ đa dạng sinh học, bảo vệ môi trường tại vùng biển Nam Trung Bộ

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. 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The Degradation of Methylene Blue by Microcubes Catalyst -Fe2O3 Via Heterogenous Fenton Process

Cubic Fe2O3 was synthesized in a facile approach by annealing molecular organic framework Prussian Blue (PB) at 350oC, 550oC, and 650oC. The final product was characterized by IR, Raman and XRD spectroscopic methods illustrating the presence of pure a-Fe2O3. SEM images of this material revealed a homogeneous morphology of microcube Fe2O3 with a size of about 500 nm. The catalytic activity of cubic Fe2O3 was investigated on the degradation of methylene blue in a heterogeneous Fenton system. It was shown that the thermally oxidative decomposition of PB at 550oC has resulted in porous Fe2O3 which exhibited highest MB degradation efficiency. In the presence of 0.5 M H2O2 and 0.3 g/L Fe2O3 at pH = 3.59, 50 ppm MB in studied solution has been removed at a rate constant of 0.0398 min-1, which is comparable with other analogous catalytic materials