A New Assessment of Mesoscale Eddies in the South China Sea: Surface Features, Three‐Dimensional Structures, and Thermohaline Transports

Abstract

By analyzing 22 years (1993By analyzing 22 years ( -2015 of daily eddy data, statistics of surface eddy properties were refreshed in the South China Sea. More than 7,000 of historical Argo profiles were collocated into eddy-centered coordinates to reveal the composite mean three-dimensional structure of eddies. The results indicate that eddies of both polarities have long conical shape, with a maximum (minimum) density anomaly of 0.55 kg/m 3 (À0.51 kg/m 3 ) at 60 m (90 m) in the composite cyclonic (anticyclonic) eddy. Temperature and salinity anomalies also peak at eddy cores, with values of À1.5°C and 0.15 psu in the cyclonic eddy and 1.4°C and À0.16 psu in the anticyclonic eddy. The temperature and density anomalies extend vertically to 400-500 m, while the salinity anomalies are apparent only in the upper 150 m. The temperature anomalies contribute about 90% of the density anomalies. Mixed layer depths in cyclonic eddies are on average 15 m shallower than those in anticyclonic eddies. The rotation of the composite cyclonic (anticyclonic) eddy generates meridional heat transport of 1.4 × 10 12 W (À3.1 × 10 12 W) and salt transport of À4.0 × 10 4 kg/s (5.6 × 10 4 kg/s). More than 90% of the heat and salt transports are concentrated in the upper 300 and 100 m, respectively. Compared to the meridional transports, the westward propagation of eddies results in zonal heat and salt transports on the same orders of magnitudes. The westward propagation of eddies also generates a basin-scale westward water transport of 1.4 Sv, equivalent to about 30% of the annual-mean Luzon Strait transport. HE ET AL.4906

Periodic Mesoscale Eddies in the South China Sea

“…Compared with the climatological result, the temperature shows an anomaly larger than 2.5°C at 100-200 m in the eddy center. The anomaly still reaches about 0.5°C at 600 m (Figure 3d), which is larger than the mean value of~0.1°C at 500 m for anticyclones in the SCS (Chen et al, 2011;He et al, 2018). This indicates that the WAE is vertically extending deeper than the mean shape of anticyclones in the SCS, consistent with the observation in 2004 (Figure 2).…”

“…Mesoscale eddies are quite active in the South China Sea (SCS) (Chen et al, ; He et al, ; Hwang & Chen, ; Wang et al, ). They have profound effects on heat and salt transport (e.g., (Chen et al, )), chlorophyll distribution (e.g., (He et al, ; Liu et al, )), primary productivity (Lin et al, ), variation of sea surface temperature and wind (Chow & Liu, ), inertial energy propagation (Chen et al, ), and so on.…”

Features of Slope Intrusion Mesoscale Eddies in the Northern South China Sea

“…Mesoscale eddies are active in the NSCS due to wind stress curl (Qu, ; Wang, Chen, et al, ), Kuroshio current loops (Jia et al, ; Zu et al, ), and the intrusion of western Pacific water masses (Hu et al, ; Wu & Chiang, ). Previous studies have investigated the spatiotemporal distribution, properties, motions, and structures of mesoscale eddies in the NSCS (Chen et al, ; He et al, ; Lin, Dong, et al, ; Wang et al, ; Xiu et al, ; Xie et al, ; Zhang et al, ). Wang et al () grouped eddies in the SCS into four geographic zones and found that mesoscale eddies originated mainly in the regions southwest of Taiwan, northwest of Luzon Strait, and offshore of central Vietnam.…”

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

“…species composition (EDDIES) in the Sargasso Sea off Bermuda [5], meso-and submesoscale processes in an intense front (AlborEx) [6] and the northwestern Pacific eddies, internal waves and mixing Experiment (NPEIM) [7], and so forth. Nowadays, main observation methods for field experiment include Argo floats, moored instrumentation, underwater gliders and shipboard survey.Argo profiling floats, which are designed to measure underwater ocean temperature and salinity (T/S) [8], are one of the effective methods to obtain 3D mesoscale eddy structures [9][10][11][12][13]. However, due to the drift features, the detailed structure of a specific eddy is difficult to acquire unless a large number of Argo floats are deployed inside the targeted mesoscale eddy.…”

“…Argo profiling floats, which are designed to measure underwater ocean temperature and salinity (T/S) [8], are one of the effective methods to obtain 3D mesoscale eddy structures [9][10][11][12][13]. However, due to the drift features, the detailed structure of a specific eddy is difficult to acquire unless a large number of Argo floats are deployed inside the targeted mesoscale eddy.…”