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Abstract
This study examined satellite chlorophyll-a (chl-a) concentration and in situ observations in Sanya Bay (SYB). In situ observation of chl-a was conducted four times per year at 12 sampling stations in SYB from January 2004 to October 2008. Monthly satellite chl-a was derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) during 2000–2012. This study compared satellite chl-a values to in situ measurements in SYB. The two data sets match well in the whole region except for two estuaries. Results show that the average in situ chl-a was 1.49 mg m−3 in SYB. Chl-a was relatively higher (>2 mg m−3) and more variable in coastal areas, with a tendency to decrease offshore (<0.4 mg m−3). The chl-a level in summer displayed obviously vertical stratification, with higher values at the bottom and lower values at the surface. Analysis of monthly mean chl-a showed that the highest level (>2 mg m−3) appeared in December, with the lowest in March (<1 mg m−3). The gradients are ranked winter, autumn, summer and spring. There was higher chl-a in autumn and winter, which may be associated with the stronger wind monsoon then. Annual mean chl-a from 2000 to 2012 varied from 1.17 to 2.05 mg m−3, with the minimum in 2001 and the maximum in 2005. The chl-a level presented a roughly increasing tendency from 2000 to 2012, which may be related to the increasing nutrients associated with the development of tourism and fishery.
Acknowledgements
In situ chl-a was measured by the Tropical Marine Biological Research Station, Chinese Academy of Sciences, in Hainan.
Funding
The present research was supported by the National Natural Science Foundation of China [grant numbers: 41376125 and 41006070], Educational Commission of Guangdong Province, China [2012KJCX0065], and Scientific Research Foundation for the Talents by Guangdong Ocean University.