Coastal Circulation in a Western Boundary Current Using Gliders and a Wirewalker

Abstract

We deployed a propulsion system-aided Slocum G3 glider in a high current environment off the Florida shelf fitted with an Acoustic Doppler Current Profiler (ADCP), a Conductivity-Temperature-Depth (CTD) sensor, and optics channel sensors to obtain measurements of current velocities, salinity, temperature, pressure, dissolved organic matter (DOM), chlorophyll, and backscatter. We also used a Wirewalker, a wave-powered profiling platform, fitted with both an ADCP and a CTD to obtain measurements at a 120-m isobath nearby off the Florida shelf. CTD measurements, glider coordinates, and aligned temporal windows of relevant profiles were used to validate velocity comparisons between both ADCPs. Different processing procedures were also used to motion-correct velocity measurements from both devices. Glider optics channels were used to evaluate changes through time in particle distributions associated with the meandering of the currents. Wirewalker velocity measurements qualitatively coincided with the glider’s ADCP overall, albeit not perfectly quantitatively. However, this coherence was partly dependent on whether the platform’s upcasts or downcasts were compared, as well as distance from the glider. Both ADCPs’ velocity measurements show clear evidence of a southward-flowing intermittent undercurrent jet previously reported by Soloviev et al. (2017). This undercurrent’s effects are also seen through the glider’s optics channels, with influence in DOM and chlorophyll distributions. Changes in backscatter were seen to a much lesser degree and probably influenced by the diel vertical migration (DVM) of zooplankton. The volume transport by the southward flow is relatively small compared to the Florida Current’s transport. Nevertheless, the processes that maintain and account for the variability of the southward flow are important for a number of practical applications including the propagation of pollution and genetic information against the Florida Current.