Encountering shoaling internal waves on the dispersal pathway of the pearl river plume in summer

Abstract

Fundamentally, river plume dynamics are controlled by the buoyancy due to river effluent and mixing induced by local forcing such as winds and tides. Rarely the influence of far-field internal waves on the river plume dynamics is documented. Our 5-day fix-point measurements and underway acoustic profiling identified hydrodynamic processes on the dispersal pathway of the Pearl River plume. The river plume dispersal was driven by the SW monsoon winds that induced the intrusion of cold water near the bottom. The river effluent occupied the surface water, creating strong stratification and showing on-offshore variability due to tidal fluctuations. However, intermittent disruptions weakened stratification due to wind mixing and perturbations by nonlinear internal waves (NIWs) from the northern South China Sea (NSCS). During events of NIW encounter, significant drawdowns of the river plume up to 20 m occurred. The EOF deciphers and ranks the contributions of abovementioned processes: (1) the stratification/mixing coupled by wind-driven plume water and NIWs disruptions (81.7%); (2) the variation caused by tidal modulation (6.9%); and (3) the cold water intrusion induced by summer monsoon winds (5.1%). Our findings further improve the understanding of the Pearl River plume dynamics influenced by the NIWs from the NSCS.

Land-Ocean Interaction Affected by the Monsoon Regime Change in Western Taiwan Strait

“…A multivariate technique Empirical Orthogonal/Eigen Function (EOF) analysis was used to characterize the correlations (standardized covariability) of variables in the upper water column and near-bottom water column and radioisotopes in seafloor sediment. This technique is based on internal correlations (Resio and Hayden, 1975), which present the statistical characteristics of a group of data through the spatial or temporal correlation of the data (Du and Liu, 2017;Liu et al, 2019;Lee et al, 2021). Each eigenmode in the EOF result was ranked according to the quotient between the eigenvalue of the eigenmode and the sum of all the eigenvalues.…”

“…Variables from the upper water column included water-mass properties (temperature, salinity, fluorescence, DO, and nutrients), suspended sediment attributes (SSC, VC of four size-groups), tidal height (tidal forcing), and N-S and E-W wind velocity components. In the water-sediment interface, analyzed variables included watermass properties (temperature, salinity, fluorescence, DO, and nutrients), suspended sediment attributes (SSC, VC of four sizegroups), surface sediment proxies ( 210 Pb ex and 7 Be), tidal height (tidal forcing), and N-S and E-W wind velocity components (Lee et al, 2016(Lee et al, , 2021Liu et al, 2019).…”

“…Major rivers in the world contribute approximately 40% of fresh water and particulate material to the global ocean (Milliman and Meade, 1983;Corbett et al, 2004;Dagg et al, 2004). The impact of fluvial discharge by major rivers can extend hundreds of kilometers beyond the river mouth such as the Amazon River, Columbia River, Changjiang (Yangtze) River, and Zhujiang (Pearl) River (Berdeal et al, 2002;Bai et al, 2014Bai et al, , 2015Lee et al, 2021;Liu et al, 2021;Nittrouer et al, 2021). The fate of river exported material in the distal marine environments is dominated by marine processes such as wind, tide, and coastal currents (Berdeal et al, 2002;Liu et al, 2002Liu et al, , 2009Liu et al, , 2021Nittrouer et al, 2021).…”

Internal Solitary Waves Observed on the Continental Shelf in the Northern South China Sea From Acoustic Backscatter Data

“…The red arrows indicate the directions of the survey lines. The solid circles show the locations of two XBT sites (red), CTD stations (magenta, Chen et al, 2017), and taut-line mooring station ZHJ2 (blue, Lee et al, 2021).…”

“…This study shows that the duration of ISWs is a few minutes, and the vertical displacements and vertical velocities are on the order of ∼10 m and 10 cm/s, respectively. For example, ISWs recorded that the vertical displacement was up to 20 m at a period of ∼6-8 h at station ZHJ2 (Figure 1; Lee et al, 2021).…”