The Evolution of Plume Fronts in the Rhine Region of Freshwater Influence. Issue 7 (7th July 2021)

• Record Type: Journal Article
• Authors: Rijnsburger, Sabine; Flores, Raúl P.; Pietrzak, Julie D.; Horner‐Devine, Alexander R.; Souza, Alejandro J.; Zijl, Firmijn
• Is Part Of: Journal of geophysical research. Volume 126:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-07
• Subjects: tidal plume fronts -- numerical model -- river plume -- advection -- straining; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2019JC015927
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The Rhine region of freshwater influence (ROFI) is strongly stratified, rotational, relatively shallow and has large tides, resulting in a dynamic field of fronts that are formed by multiple processes. We use a 3D numerical model to obtain a conceptual picture of the frontal structure and the processes responsible for generating this multiple front structure in the Rhine ROFI. The horizontal salinity gradient and numerical tracers are used to identify three different types of fronts: outer, inner, tidal plume and relic tidal plume fronts. Tidal plume front (TPF) trajectories together with the tracers demonstrate that TPFs exist for longer than one tidal cycle. A Lagrangian frontogenesis analysis shows that the fronts are strengthened mainly as a result of increased convergence, which is observed to occur at times when tidal straining is large. Additionally the alongshore tidal excursion and the dominance of the tidal currents over the intrinsic frontal propagation speed, trap TPFs within 20 km from the river mouth. Trapping and re‐strengthening maintain several fronts at a time in the mid‐field region, resulting in a multi‐frontal system. The observation of a complex river plume system is expected to be important for cross‐shore exchange, transport and coastal ecology. Plain Language Summary: Rivers transport sediments, nutrients, and contaminants into the coastal ocean. A river plume is formed when the freshwater enters the ocean, where the edges of this river plume are the boundary between river and ocean water. These boundaries are called fronts and relate to large horizontal density gradients. These fronts are important for the transport of freshwater away from the river mouth. Our study shows that multiple fronts are observed in the Rhine region of freshwater influence. These multiple fronts result in a complex system. Our study unravels which processes are responsible for the presence of multiple fronts, which will change the overall dynamics in coastal areas influencing the transport of sediments, nutrients and contaminants. Key Points: Tidal straining re‐strengthens fronts hours after their initial formation Tidal advection leads to the trapping of tidal plume fronts, generating a multi‐frontal system The persistence of Rhine plume fronts is due to convergence associated with bulk plume circulation