Spatial differentiation of sea surface salinity in the South China Sea and the adjacent Northwest Pacific based on big data analysis

Abstract

Based on the monthly average salinity data of SODA-2.2.4, this article analyzed the climatic distribution, spatial differentiation, monthly variation characteristics and divided the climate zones of the sea surface salinity (SSS) in the South China Sea (SCS) and the adjacent Northwest Pacific (NWP) during the climate reference period of 1981-2010, and explored the impact factors, which would provide a basis for further research on climate change. The results show that the average SSS at the study area is 33.99 psu; generally, the SSS in SCS is lower than NWP about 0-3.3 psu. The distribution pattern of SSS in SCS, showed a decreasing from northeast to southwest during November to next March. The high salt tongue formed northeastern South China Sea (NE-SCS) and the low salinity area located at the southwestern South China Sea (SW-SCS) with the large precipitation and near the estuaries where fresh water was flowed into the sea, especially from April to November. In NWP, a high-salt area is located at the north, where is the extension of the high-salt zone formed by the subtropical high pressure area index of northern hemisphere (SHPAINH) to the study area, and its SSS is highest in April and lowest in September. A sub-high salinity zone is located at the south, where is an extension of the high salinity zone formed by the subtropical high pressure area index of southern hemisphere (SHPAISH), and the SSS is highest in April and lowest in August. The low SSS zone between the two is formed by the low pressure and rainy of the intertropical convergence zone (ITCZ) located north of the equator, and its axis is located near 7°N; in the interior of the low SSS zone, its closed low-salt center is leaning to the west side of Mindanao from December to next July; the low-salt range expands from August to November, and its closed center is leaning toward the Central Eastern Pacific (CEP). In the Sulu Sea and the Sulawesi Sea between SCS and NWP, although they are close to each other in location, the SSS of Sulu Sea is highest in April and lowest in October, with a large annual change, as where located near the low-pressure and rainy area of ITCZ at north of the equator; but the SSS of Sulawesi Sea is highest in December and lowest in June, with a small annual change, as it located close to the northern edge of SHPAISH.