Measurements of Turbulence Generated by Wake Eddies Near a Steep Headland

Abstract

Currents impinging on islands, headlands and submarine ridges can lead to the generation of vortices and internal waves downstream (e.g., Chang et al., 2013;Edwards et al., 2004). These processes and the eventual transition to turbulence lead to the loss of kinetic energy and momentum in the wake and weaken the incident currents Wolanski et al., 1984). The vertical transport generated by mixing in the wake has been seen to increase chlorophyll concentrations and may also enhance biological productivity in the region (e.g., Gove et al., 2016;Heywood et al., 1990). It is therefore important to understand the turbulence and mixing generated in the lee of topographic features such as islands and headlands.This study was motivated by observations collected around Velasco Reef, a promontory at the northern end of the Pacific archipelago of Palau. The complex topography at this location, consisting of both a steep headland and a deep water ridge, leads to the formation of both wake eddies (MacKinnon et al., 2019) and lee waves (Voet et al., 2020). We are interested in understanding how these wake processes may head to turbulence downstream of the headland.Previous observations of turbulence at headlands and islands have often focused on measurements in the immediate vicinity of topographic obstacles to quantify the turbulent drag leading to flow separation (e.g., Edwards et al., 2004;MacKinnon et al., 2019). The few observational studies that have collected measurements of turbulent