| Currently, the research of temporal-spatial variation characteristics of chlorophyll-a concentration commonly based on the combination of in-situ data and SeaWiFS remote sensing data. However, the SeaWiFS has already exceeded its service life of 5 years, and there is an uncertainty that whether SeaWiFS could still be used in ocean color remote sensing in the future. So, we adopted the MODIS image data which was considered as a suitable replacement. In the beginning, we verified inversion ability of MODIS chlorophyll-a data product in the northern South China Sea, and results showed that the data gained form MODIS reflected the actual measured chlorophyll-a distribution qualitatively, and it also met the data requirement in temporal-spatial research.The temporal-spatial variation characteristics of chlorophyll-a concentration obtained by MODIS satellite sensor in the northern South China Sea (SCS) during 2004-2006 were analyzed combining with the in-situ data, as well as the response from part of environmental impact factors were analyzed. In this paper, the spatial pattern of chlorophyll-a concentrations was studied both on horizontal and vertical distributions. Four sets of profiles were used in horizontal characteristic analysis——longitude profile consists of 3-sites in 120oE, latitude profile consists of 2-sites in 18oN, oblique profile consists of 2-sites between the Taiwan Strait and Luzon Strait, as well as profile consists of 3-sites from the Pearl estuary to open water. The first 3 profiles were researched comprehensively to find out the correlation of chlorophyll-a concentration horizontal characteristic with salinity and temperature of ocean, as well as the impacts of South China Sea water and the Kuroshio in the Luzon Strait and upwelling in the Taiwan Strait on chlorophyll-a concentration horizontal distribution. At the same time, we analyzed the chlorophyll-a concentration horizontal characteristic on the fourth profile, and impact of upwelling. By mapping spatial distribution map of average chlorophyll-a, contour map of ocean temperature and ocean salinity in September 2004, the comparison investigation was conducted to find out the correlation between chlorophyll-a distribution and salinity and temperature of ocean.The results showed the chlorophyll-a concentration horizontal distribution characteristic as follows: the coastal area was generally significantly higher than the open waters, and downward trend was seen from inshore to offshore; The highest chlorophyll-a concentration was located near the Pearl estuary and the Taiwan Strait; The wide range of high chlorophyll-a concentration belt were found almost parallel to sea shoreline in Guangdong coastal; The widespread low chlorophyll-a concentration distribution was showed in vast central waters of the Luzon Strait Northwest. The regional differences of chlorophyll-a concentration in whole northern South China Sea was significant and regional differences decreased in winter, and increased in spring. The vertical distribution of chlorophyll-a concentration was marked by the highest value which was appeared under surface layer of all stations. In the northern South China Sea (SCS), chlorophyll-a concentration showed a significant seasonal cycling phenomenon which high value distribution presented in winter, and reached the highest level in January, as well as low value distribution in spring and the lowest level around May every year. The chlorophyll-a concentration increased gradually during summer, and decreased initially but increased afterward during fall.Besides, sea temperature influenced the vertical distribution of chlorophyll-a concentration,and horizontal distribution of chlorophyll-a concentration was affected by salinity. The spatial distribution of chlorophyll-a concentration also affected by the South China Sea water and the Kuroshio in the Luzon Strait, as well as upwelling in the Taiwan Strait and Pearl River plume. |
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