Speaker

Agata Piffer Braga, Ph.D. candidate, UMass-Dartmouth

Frontal Evolution of a River Plume: Dynamics, Turbulence, and the Release of Solitary Waves

Abstract

Fronts are a common and crucial feature of our oceans, driving vertical transport and playing a key role in oceanic mixing. In coastal regions, river plume fronts can form from the interaction of fresh river water with denser ocean water. These fronts are regions of intense turbulence, with dissipation rates around 10⁻³ m²s⁻³, undergoing a fascinating evolution from gravity currents to geostrophic structures.

Sampling these fronts is challenging due to their rapid propagation and vast spatial and temporal scales. While existing literature focuses on isolated stages, our work provides a continuous, detailed view of river plume front evolution. Using a novel sampling strategy with an Autonomous Underwater Vehicle (T-REMUS) supported by a drone, drifters, and shipboard measurements, we achieved 33 frontal crossings of the Merrimack River Plume.

Through this innovative dataset, we captured the evolution of the frontal structure and its mixing dynamics in unprecedented detail. Microstructure shear probe measurements allowed us to quantify Turbulent Kinetic Energy dissipation rates, providing valuable insights into turbulence’s temporal and spatial progression within the frontal zone. Additionally, our observations reveal the intricate generation of internal solitary waves by these fronts. These waves not only transport energy and mass but also generate significant turbulence beyond the frontal region. Ultimately, we present the changes in the momentum balance and trace the fate of the front. This study provides insights into the evolution of ocean fronts and their mixing processes, which is essential for understanding the transport of nutrients and pollution.