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This study analyzes monthly variability of thermocline and its mechanism in the South China Sea (SCS). The study is based on 51-year (1960–2010) monthly seawater temperature and surface wind stress data from Simple Ocean Data Assimilation (SODA), together with heat flux, precipitation and evaporation data from the National Centers for Environmental Prediction (NCEP), the National Oceanic and Atmospheric Administration (NOAA) and the Woods Hole Oceanographic Institution, respectively. The results reveal that the upper boundary depth (Zup), lower boundary depth (Zlow), thickness (ΔZ) and intensity (Tz) of thermocline in the SCS show remarkable monthly variability. Being averaged for the deep basin of SCS, Zupdeepens gradually from May to the following January and then shoals from February to May, while Zlowvaries little throughout the whole year. Further diagnostics indicates that the monthly variability of Zupis mainly caused by the buoyancy flux and wind stress curl. Using a linear method, the impacts of the buoyancy flux and wind stress curl on Zupcan be quantitatively distinguished. The results suggest that Zuptends to deepen about 4.6 m when the buoyancy flux increases by 1×10-5kg/(m∙s3), while it shoals about 2.5 m when the wind stress curl strengthens by 1×10-7N/m³.

This paper investigates the response of the thermocline depth (TD) in the South China Sea (SCS) to the El Niño-Southern Oscillation (ENSO) events using 51-year (from 1960 to 2010) monthly seawater temperature and surface wind stress data acquired from the Simple Ocean Data Assimilation (SODA), together with heat flux data from the National Centers for Environmental Prediction (NCEP), precipitation data from the National Oceanic and Atmospheric Administration (NOAA) and evaporation data from the Woods Hole Oceanographic Institution (WHOI). It is indicated that the response of the SCS TD to the El Niño or La Niña events is in opposite phase. On one hand, the spatial-averaged TDs in the SCS (deeper than 200 m) appear as negative and positive anomalies during the mature phase of the El Niño and La Niña events, respectively. On the other hand, from June of the El Niño year to the subsequent April, the spatial patterns of TD in the north and south of 12°N appear as negative and positive anomalies, respectively, but present positive and negative anomalies for the La Niña case. However, positive and negative TD anomalies occur almost in the entire SCS in May of the subsequent year of the El Niño and La Niña events, respectively. It is suggested that the response of the TD in the SCS to the ENSO events is mainly caused by the sea surface buoyancy flux and the wind stress curl.