A cruise survey of the Pearl River plume during southeasterly and southwesterly winds, two typical wind patterns in summer in Guangdong coastal waters, is reported and the cruise data are analyzed to unveil the plume dynamics. The Kelvin number is derived from the in situ data, revealing that the Pearl River plume exhibits two different scales in response to the two kinds of the wind forcing. Numerical model simulations based on the regional oceanic modeling system (ROMS) with nesting domains are implemented to explore details of the plume dynamics, validated by cruise observations and tidal gauge sea level data. Modeling results suggest that there is a subtidal, anticyclonic recirculation bulge on the west side out of the estuary mouth under southeasterly winds, showing a recirculating plume in the near-field. When the wind changes to the southwesterly, however, the recirculating plume vanishes. The distinct, supercritical tidal plume front occurs with southeasterly winds prevailing in spring tide due to the strong advection in the tidal plume. The tidal salt deficit flux can reach as high as 12.5% of the mean current flux, and illustrates the combined forcing of tide and wind.

Ocean tides are changing worldwide for reasons unrelated to astronomical forcing. Changes in tidal properties coupled with altered mean sea level (MSL) may yield higher peak water levels and increased occurrence of short‐term exceedance events, such as storm surge and nuisance flooding. Here we investigate the hypothesis that changes in relative sea level are correlated with alterations in tidal amplitudes. Our approach focuses on the correlation between short‐term (monthly to interannual) fluctuations in sea level with changes in tidal properties of major ocean tides (M₂, and K₁; S₂ and O₁) at 152 gauges. Results suggest that sea level variability is correlated to interannual tidal variability at most (92%) of tide gauges in the Pacific, with statistically significant rates between ±10 and ±500 mm per meter sea level rise observed. These tidal anomalies, while influenced by basin‐scale climate processes and sea level changes, appear to be locally forced (in part) and not coherent over amphidromic or basin‐wide scales. Overall, the Western Pacific shows a greater concentration of tide/sea level correlations at interannual time scales than the Eastern Pacific; 44% and 46% of gauges are significant in K₁ and O₁ in the west compared to 29% and 30% in the east, and 63% and 53% of gauges in the west are significant in M₂ and S₂ versus 47% and 32% in the east. Seasonal variation in tidal properties is less apparent in the empirical record, with statistically significant seasonal variations observed at only 35% of all gauges, with the largest concentrations in Southeast Asia.

Tropical cyclones may augment nutrients in the ocean surface layer through mixing, entrainment, and upwelling, triggering phytoplankton blooms in oligotrophic waters such as the South China Sea (SCS). Previous studies focused mainly on responses of marine environments to strong or slow‐moving typhoons in the SCS. In this study, we analyze variations of chlorophyll a (Chl a) and oceanic conditions in the continental shelf region east of Hainan Island during the fast‐moving tropical storm Washi and investigate its influences on phytoplankton bloom and related dynamic mechanisms. Results indicate that there was significant variation of Chl a concentration in the continental shelf region, with low values (about 0.1 mg m⁻³) before the storm and a 30% increase after the storm. This increase was spatially variable, much larger nearshore than offshore. Power spectral analysis of Acoustic Doppler Current Profiler (ADCP) data at a shelf site near the study region reveals strong near‐inertial oscillations (NIOs) in the upper layer, with a period of about 36 h, close to the local inertial period. The NIOs intensified mixing and modified the stratification of the upper layer, inducing uplift of nutrients and Chl a into the mixed layer from below, and leading to surface Chl a increase. The relatively shallow nutricline and thermocline in the continental shelf region before the storm were favorable for upwelling of nutrients and generation of NIOs. Advection of nutrients from enhanced runoff during and after the storm may be responsible for the larger increase of the Chl a nearshore.

Using satellite-based multi-sensor observations, this study investigates Chl-a blooms induced by typhoons in the Northwest Pacific (NWP) and the South China Sea (SCS), and quantifies the blooms via wind-induced mixing and Ekman pumping parameters, as well as pre-typhoon mixed-layer depth (MLD). In the NWP, the Chl-a bloom is more correlated with the Ekman pumping than with the other two parameters, with an R² value of 0.56. In the SCS, the wind-induced mixing and Ekman pumping have comparable correlations with the Chl-a increase, showing R² values of 0.4~0.6. However, the MLD exhibits a negative correlation with the Chl-a increase. A multi-parameter quantification model of the Chl-a bloom strength achieves better results than the single-parameter regressions, yielding a more significant R² value of 0.80, and a lower regression rms of 0.18 mg·m⁻³ in the SCS, and the R² value in the NWP is also improved compared with the single-parameter regressions. The multi-parameter quantification model of Chl-a blooms is more accurate in the SCS than in the NWP, due to the fact that nutrient profiles in the NWP are uniform from surface to a deep depth (300 m). Thus, the Chl-a blooms are more correlated with the upper ocean dynamical processes in the SCS where a shallower nutricline is found.

The detachment of low salinity water (LSW) from the Pearl River plume occurs frequently as revealed by in situ observations and satellite images, and plays an important role in cross‐shore transport of the nutrient‐rich plume water. In this study, the Regional Ocean Modeling System (ROMS) is used to simulate the LSW detachment process forced by realistic and idealized winds, and to explore its dynamical mechanisms. Modeling results show that the LSW detachment appears under a pulsed southwesterly wind, while tidal mixing modifies the size and salinity of the detached LSW. Strong pulsed wind causes the LSW to separate from the plume and move offshore quickly after the detachment. Under a pulsed northeasterly wind, however, the plume without separation of the LSW moves shoreward, indicating that the LSW detachment is sensitive to wind direction. In the plume region, upwelling develops under the forcing of the pulsed southwesterly wind, which transports high salinity bottom water to the surface layer, while the shear mixing in the upper layer further enhances the surface buoyancy flux, leading to appearance of high salinity water in the surface layer off the Pearl River estuary mouth, cutting off the eastward‐spreading plume water, and resulting in the plume LSW detachment. Further analysis shows that the pulsed southwesterly wind induces positive local salinity change rate in the LSW detachment area. The pulsed upwelling‐favorable wind with duration of 2–5 days is responsible for the detachment process.

The ocean responses to Typhoon Cimaron, which influenced the South China Sea (SCS) from 1 to 8 November 2006, are analyzed. Based on satellite-observed sea surface temperature (SST) and climatological temperature profiles in the SCS, mixed layer deepening, an important parameter characterizing turbulent mixing and upwelling driven by strong typhoon winds, is derived. Corresponding to the SST drop of 4.4°C on 3 November 2006, the mixed layer deepened by 104.5 m relative to the undisturbed depth of 43.2 m, which is consistent with a simulation result from a mixed layer model. Furthermore, baroclinic geostrophic velocity and vorticity are calculated from the surface temperature gradient caused by the typhoon. The negative vorticity, associated with the typhoon cooling, indicated an anticyclonic baroclinic circulation strongest at the base of the mixed layer and at the depth of 50 m, the geostrophic speed reached as high as 0.2 m s−1. Typhoon Cimaron proceeded slowly (1.7 m s−1) when it was making a southwestward turn on 3 November 2006, resulting in a subcritical condition with a Froude number (the ratio of typhoon translation speed to first baroclinic mode speed) of 0.6 around the maximum SST drop location and facilitating high SST cooling and mixed layer deepening because of the absence of inertial-gravity waves in the wake of the typhoon. Comparison of Argo buoy data with the climatological temperature suggests that the average uncertainty in the mixed layer deepening estimation caused by the difference between Argo and climatological temperature profiles is less than 10 m.