The seasonal variation of the thermocline and its formation mechanism in the sea area around Nansha Islands in 2013

Tian Yongqing; Huang Honghui; Gong Xiuyu; Yu Shaomei; Jing Chunsheng; Gao Lu

doi:10.3969/j.issn.0253-4193.2017.12.003

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Tian Yongqing, Huang Honghui, Gong Xiuyu, Yu Shaomei, Jing Chunsheng, Gao Lu. The seasonal variation of the thermocline and its formation mechanism in the sea area around Nansha Islands in 2013[J]. Haiyang Xuebao, 2017, 39(12): 20-31. doi: 10.3969/j.issn.0253-4193.2017.12.003

Citation:

Tian Yongqing, Huang Honghui, Gong Xiuyu, Yu Shaomei, Jing Chunsheng, Gao Lu. The seasonal variation of the thermocline and its formation mechanism in the sea area around Nansha Islands in 2013[J]. Haiyang Xuebao, 2017, 39(12): 20-31. doi: 10.3969/j.issn.0253-4193.2017.12.003

Citation:

Tian Yongqing, Huang Honghui, Gong Xiuyu, Yu Shaomei, Jing Chunsheng, Gao Lu. The seasonal variation of the thermocline and its formation mechanism in the sea area around Nansha Islands in 2013[J]. Haiyang Xuebao, 2017, 39(12): 20-31. doi: 10.3969/j.issn.0253-4193.2017.12.003

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The seasonal variation of the thermocline and its formation mechanism in the sea area around Nansha Islands in 2013

doi: 10.3969/j.issn.0253-4193.2017.12.003

1.
Third Institude of Oceanography, State Oceanic Administration, Xiamen 361005, China;Guangdong Provincial Key Laboratory of Fishery Ecology and Environment/Key Laboratory of Open-sea Fishery Exploitation, Ministry of Agriculture, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China
2.
Guangdong Provincial Key Laboratory of Fishery Ecology and Environment/Key Laboratory of Open-sea Fishery Exploitation, Ministry of Agriculture, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China
3.
Third Institude of Oceanography, State Oceanic Administration, Xiamen 361005, China

Received Date: 2017-02-03
Rev Recd Date: 2017-06-30

Abstract

Abstract

With the survey and remote sensing data, we revealed the seasonal characteristics of the thermocline in the sea area around Nansha Islands sea area in 2013. Specifically, the mean value of the thermocline upper-bounds depth was almost the same in spring, summer and winter, which was around 45 to 47 m, and it was maximum in autumn which was as deep as 60 m. For the thermocline thickness, in the seasons of summer, autumn and winter it demonstrated almost the same mean value ranging from 85 to 87 m, while a slightly smaller value of 78 m was found in spring. The mean value of the thermocline intensity was almost the same throughout the year from spring to winter, which ranged from 0.13 to 0.15℃/m. The formation mechanism of such seasonal characteristics of thermocline upper-bounds depth was also revealed. In spring, it was deep in the west whereas shallow in the east. This is because that the western area was controlled by relatively low net heat fluxes, high wind speeds and the negative wind stress curl, and it is also influenced simultaneously by the mesoscale warm eddy and the anticyclonic circulation from the coastal area off the eastern Indo-China Peninsula; contrarily, the eastern area was controlled by relatively high net heat fluxes, low wind speed as well as the Ekman pumping effect induced by the wind stress curl. In summer, the depth was almost uniform from west to east. It was because that, in the north of 10°N, the wind-induced vortex mixing, though being strong, was undermined by the Ekman pumping, whereas in the south of 10°N the wind-induced vortex mixing, which although was weak, was affected by the negative wind stress curl. In autumn, the mean depth was 15 m deeper than those in the other three seasons. The reason was that the sea area of Nansha Islands was controlled by a warm eddy which induced the anticyclonic circulation that subsequently deepened the thermocline upper-bounds depth through the convergence of upper layer seawater. When it came to winter, the Ekman pumping induced by the positive wind stress curl and the cyclconic circulation caused by the cold eddy worked together, which lifted up the mean value of the thermocline upper-bounds depth by 15 m compared with that in autumn.
- the Nansha Islands sea area,
- thermocline,
- wind stress curl,
- Ekman pumping

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References(26)

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