Temporal And Spatial Variation Characteristics Of The Salinity Field In The South China Sea And The Adjacent Northwest Pacific Ocean From 1871 To 2010

The salinity of seawater is the main parameter to describe the marine climate and environment.Its distribution and variation rule have a profound influence on the research of the marine characteristics and the role of the ocean in the complex system of sea and air.The distribution and long-term changes of the salinity field in the South China Sea and the adjacent Northwest Pacific Ocean have important impacts on the climate and environment in China,and lay a foundation for understanding the impact of China's marginal seas on the climate change in China.At the same time,the Northwest Pacific Ocean is the main formation area and way area that affects the Chinese typhoon.Understanding its characteristics and changes in marine hydrology and climate environment can provide a basis for accurate prediction of typhoons.Based on the SODA₂.2.4 ocean assimilation data developed by the University of Maryland and the global seabed topographical database released by the National Geophysical Data Center?NGDC?in 2009,this paper explores the effects of the latest climate reference year?1981-2010?on the South China Sea and the adjacent Northwest Pacific Ocean The salinity field reflects the climate structure of the study area.Empirical Orthogonal Function Analysis?EOF?and Morlet Wavelet Analysis were used to analyze the spatio-temporal change and period of the salinity data from 1871 to 2010.The main conclusions are as follows:?1?The salinity field in the study area can be obviously divided into two areas,the South China Sea and the Pacific Northwest.The SSS in the South China Sea was significantly lower than that of the SSS in the Northwest Pacific Ocean.The salinity showed a decreasing trend from the northeastern North Pacific to the southwestern South China Sea.The annual amplitude of SSS in the South China Sea varies widely in different sea areas.The maximum amplitude of the SSS appears in the vicinity of the Hong Kong and Macao regions on the continental shelf,reaching as high as 4.66 psu with a minimum value of about 0.5psu in the central South China Sea.The SSS of the Northwest Pacific is relatively small and basically consistent,and the minimum appears in the southwest,which is 0.08 psu.?2?The SSS low value areas in the South China Sea are mainly distributed in Hong Kong,Macao and Beibu Bay on the continental shelf,and 31.5-33 psu in the northern part of the Gulf of Thailand,and have obvious regularity of cyclical changes.Salt will increase in January-April and May-October Salt reduction,salt increase in November-December,and isohaline were banded;in contrast,the salinity of the central South China Sea from January to May remained basically unchanged,and isohaline was banded,salt was added from June to September,and isohaline was group-like distribution,10-12 months of salt,and isohaline gradually restore the ribbon distribution.The distribution of SSS in the northwestern Pacific from low latitude to high latitude is high-low-high,with isohaline distribution in a banded distribution;The area south of 4.75 ° N,the area north of 14.75 ° N is the high salt area?34.2-35psu?,while the area north of 4.75 ° N and the area south of 14.75 ° N is the relatively low salt area?33.95-34.4psu?.?3?The monthly variation of shallow salinity at the depth of 100 m was the most obvious,with a "S" curve changing periodically and with a wide range of variation.100-300 m,the periodic variation of salinity is far less obvious than that of 100 m,and to the middle of 2000 m,the salinity fluctuation in the whole study area is less than 0.3psu.2000 m deep,the salinity value does not change with the change of the month,but different sea salinity values are different,a difference of 0.059 psu.?4?The surface salinity field is mainly affected by precipitation,runoff,sea surface temperature,ocean current and topography.The influence of temperature on the variation of salinity was not obvious.The isotherms showed a zonal distribution.From high latitude to low latitude temperature gradually increased,there are obvious differences in summer and other seasons distribution isotherm.In the aspect of ocean current,the influence of ocean current on salinity variation is significant.The direction of surface ocean current determines the trend of salinity,and the salinity and surface ocean currents flow basically parallel.?5?The EOF spatial analysis of the salinity anomaly field from January to December in the six representative layers shows that most of the 5m layer of the South China Sea is negative anomaly,the western North Pacific has a consistent positive anomaly,and the central and northern regions are positive anomalies In the intense sea area,the sea area anomaly in the study area in November is the opposite.The 97 m South China Sea and the southwestern part of the Southwest Pacific?south of 5.25 ° N?show negative anomaly,while the north-central Pacific Northwest shows a positive anomaly.In March and May,the anomaly of the sea area is opposite.171 m layer of the South China Sea area is a weak negative anomaly,the largest absolute value of the Northwest Pacific anomalies are still in the central and northern waters.The 466 m and 729 m layers of the northwestern Pacific Ocean show two positive-negative-positive or negative-positive-negative anomalies from low latitudes to high latitudes in different months.1626 m layer,the positive and negative anomalies throughout the study area is very weak,between-0.01-0.01.?6?EOF time analysis of the salinity anomaly field from January to December in six representative layers shows that the time coefficient of each representative layer is mainly divided into three stages with the year.Although the trend of individual months is the opposite,the 12-month time coefficient curves are close to "0" with years and the time coefficients after 1960 s are roughly-1-1.?7?The analysis of the salinities anomaly field from January to December in six representative layers shows that the periods of variation of each representative layer are different,and the periods of large and medium scales are more obvious than those of small-scale periods.The 5m layer has a period of 5 years,7-9 years,15-16 years and 27-29 years.The 97 m layer has 4-5 years,7-8 years,11-12 years and 16-18 years of period.The 171 m layer has 7 Year,11-12 year,15-17 year period;466m layer has 4,7-9,12-14,25-29 years period;729m layer has 5 years,9 years,12-14 years,26-29-year cycle;1626-m layer has 9-year cycle.