[Department of Ocean Science] PhD Qualifying Examination Defense Seminar: Dynamics and variability of the circulation-plume-front in the coastal waters off Pearl River Estuary
 

Abstract:

Ocean fronts serve as dynamic hotspots in ocean circulation through submesoscale dynamics in the complex shelf-estuary circulation system. At fronts, surface convergence generates intense vertical velocity and drives an ageostrophic secondary circulation (ASC), while submesoscale instabilities also redistribute energy across scales. Although these processes have been extensively studied in the open ocean and marginal seas, their dynamics in shelf-estuary system, where freshwater discharge, strong tidal forcing, wind-driven current over complex coastal topography jointly regulate multi-scale variability, remain comparatively underexplored. The Pearl River Estuary (PRE) connects with the adjacent shelf and jointly forms a shelf-estuary system in the Greater Bay Area (GBA). The system receives substantial freshwater discharge from the Pearl River and forms a dynamic plume-front that interacts with wind- and tidal-driven circulation over the shelf. Driven by high river runoff and wind-driven upwelling circulation, the summer plume spreads southeastward and forms distinct plume-fronts over the shelf. Conversely, downwelling circulation and reduced discharge during winter confine the plume-front to the coastline as a narrow and bottom-attached plume-front. The plume-front greatly modulates the wind-driven shelf circulation involving, for example, the 3D submesoscale characteristics and distinct instability, pathways of substance and energy transport. Combining process-oriented numerical simulations, observations, Lagrangian particle tracking, and analysis of geophysical fluid dynamics, this study aims to achieve three interlinked objectives: (O1) characterize the 3D structures of circulations and submesoscale instabilities of the plume-fronts during upwelling; (O2) investigate the plume-front dynamics under controls of coastal topography and tidal forcing during downwelling; and (O3) map the 3D pathways of Lagrangian transport and assess the source-to-sink connectivity in plume-front under different physical controls. This thesis study will provide new insights into the characteristics and dynamics of time-dependent, 3D heterogeneous plume-front under combined wind, topographic and tidal modulation in the coupled shelf-estuary circulation.