Date of Award

Summer 2024

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Alexander Yankovsky

Abstract

ABSTRACT River plumes play a crucial role in coastal ecosystems by influencing land-ocean interactions, primary production, water quality, and ocean circulation. This study presents observations of a buoyant river plume off Winyah Bay, South Carolina (USA), conducted in 2020 and 2021. Observations comprised CTD casts and shipborne ADCP profiles as well as near surface flow measurements from a floating platform and microstructure profiles in uprising mode. This research focuses on the offshore transport of the buoyant water through Ekman dynamics under upwelling-favorable conditions. Under varying wind forcing and stratification scenarios, the Winyah Bay plume either remains near the coast or moves offshore. Light to moderate upwelling- favorable winds cause the plume to turn offshore and separate from the coast through Ekman dynamics, which is the most efficient cross-shelf transport mechanism. Offshore Ekman transport can be shut down when surface and bottom boundary layers merge due to excessive wind stress and tide induced mixing. When surface and bottom boundary layers merge on the inner shelf, horizontal velocity tends to change linearly with depth. Hence, we hypothesize that the magnitude of its second derivative u_zz at the base of the plume can be used as a metric for the buoyant layer decoupling from the interior. To test this hypothesis, we compare the maximum absolute value of the horizontal velocity second derivative against the gradient Richardson number and the veering of the horizontal velocity vector estimated at the same depth. Large values of the Richardson number and the horizontal vector veering with depth indicate decoupling and the possibility of Ekman dynamics. In addition, we compare these characteristics with turbulent kinetic energy dissipation rates. To further test our hypothesis, these metrics are related to forcing conditions, such as the wind stress, tides, and freshwater content. We find that u_zz is an effective metric to indicate the detachment of the buoyant layer from the inner shelf.

Rights

© 2024, Isabella Moore

Download

Share

COinS