Autonomous underwater gliders (AUGs) are an established platform for conducting direct microstructure measurements of turbulent kinetic energy (TKE) dissipation rate (ε). This technique requires measuring the velocity shear (δu/δz) at a high rate (~512 Hz) which generates raw data orders of magnitude greater in size than autonomous platforms can wirelessly transfer to shore while deployed. Consequently, microstructure shear data has only been processed into turbulent dissipation rate estimates after vehicle recovery, which carried a risk of total dataset loss should the vehicle not be recoverable, and could not be used for adaptive sampling efforts during deployment. We solve this problem by equipping Slocum G2 gliders with a low-power embedded computer to conduct in-situ data processing and near real-time telemetry of TKE dissipation rate. We demonstrate the technical readiness of this novel system based on data collected by two vehicles during approximately three months of sea trials southwest of Iceland and northwest of Guam, which were conducted for the Office of Naval Research's NISKINE (Near Inertial Shear and Kinetic Energy in the North Atlantic Experiment) and ARCTERX (Island Arc Turbulent Eddy Regional Exchange) Departmental Research Initiatives (DRIs).

The NORSE DRI focuses on characterizing the key physical parameters and processes that govern the predictability of upper-ocean rapid evolution events occurring in the ice-free high latitudes. The goal is to identify which observable parameters are most influential in improving model predictability through inclusion by assimilation, and to field an autonomous observing network that optimizes sampling of high-priority fields. The overall goal is to demonstrate improvements in the predictability of the upper ocean physical fields associated with acoustic propagation over the course of the study. This Science Plan describes the specific objectives and implementation plan.

The interaction of flow with steep island and ridge topography at the Palau island chain leads to rich vorticity fields that generate a cascade of motions. The energy transfer to small scales removes energy from the large-scale mean flow of the equatorial current systems and feeds energy to the fine and microstructure scales where instability mechanisms lead to turbulence and dissipation. Until now, direct assessments of the turbulence associated with island wakes have received only minimal attention. Here, we examine data collected from an ocean glider equipped with microstructure sensors that flew in the island wake of Palau. We use a combination of submesoscale modeling and direct observation to quantify the relationship between vorticity and turbulence levels. We find that direct wind-driven mixing only accounts for about 10% of the observed turbulence levels, suggesting that most of the energy for mixing is extracted from the shear associated with the vorticity field in the island’s wake. Below the surface layer, enhanced turbulence correlates with the phase and magnitude of the relative vorticity and strain levels of the mesoscale flow.