Abstract-- In this study, we used the Navy '..s Master Oceanographic Observation Data Set (MOODS), consisting of 116 019 temperature and 9 617 salinity profiles, during 1968-1984 to inves-tigate the temporal and spatial variabilities of South China Sea.th~ohaline structures and circulation. For temperature, profiles were binned into 204 monthly data sets from 1968 to 1984 (17 years). For salinity, profiles were binned into 12 climatological monthly data sets due to the data paucity. A two-scale optimal interpolation method was used to establish a three-dimens!onal monthly-varying gridded da-ta set from MOODS, covering the area of 5 °- 25°N and 105 °- 125°E and the depth from the surface to 400 m. After the gridded data set had been established, b;;!h oompa;ite analysis and the Empirical Or-thogonal Function (EOF) analysis (for temperature only) were used to identify the major thennohaline fratures including annual mean, monthly anomalies, and interannual thermal variabilities. The inverted monthly circulation pattern using the P- vector methOd is also discussed. Key worm The South China Sea, thermohaline structure, circulation

The seasonal ocean circulation and the seasonal thermal structure in the South China Sea (SCS) were studied numerically using the Princeton Ocean Model (POM) with 20-km horizontal resolution and 23 sigma levels conforming to a realistic bottom topography. A 16-month control run was performed using climatological monthly mean wind stresses, restoring-type surface salt and heat, and observational oceanic inflow/outflow at the open boundaries. The seasonally averaged effects of isolated forcing terms are presented and analyzed from the following experiments: 1) nonlinear dynamic effects removed, 2) wind effects removed, and 3) open boundary inflow/outflow set to zero. This procedure allowed analysis of the contribution of individual parameters to the general hydrology and specific features of the SCS: for example, coastal jets, mesoscale topographic gyres, and countercurrents. The results show that the POM model has the capability of simulating seasonal variations of the SCS circulation and thermohaline structure. The simulated SCS surface circulation is generally anticyclonic (cyclonic) during the summer (winter) monsoon period with a strong western boundary current, a mean maximum speed of 0.5 m s21 (0.95 m s21), a mean volume transport of 5.5 Sv (10.6 Sv) (Sv [ 106 m3 s21), and extending to a depth of around 200 m (500 m). During summer, the western boundary current splits and partially leaves the coast; the bifurcation point is at 148N in May and shifts south to 108N in July. A mesoscale eddy on the