Sproul Pt. Sal survey

Since the first Intensive Operations Period (IOP 1) in September/2017, results from the different groups have been coming together to reveal a complicated plot around Pt. Sal, with lots of topographic wakes, recirculation south of the point, ridiculously sharp fronts and some really aggressive high-frequency internal waves.

Between about noon on the 12th until 9 am on the 13th, we tagged along the other vessels, repeating an L-shaped track in between the Sally Ride and the Oceanus. The collective goal of our Inner Shelf Armada was to observe the flow around the cape and try to understand, among other things, how vorticity is produced by the separating tidal flow and how a background, subtidal along-shelf flow might influence this process.

R/V Sproul’s track with flow-through temperature.

All vessel tracks during the Pt. Sal survey (~12th-14th Sep/2017).

We crossed what looks like some high-frequency internal wave packets, visible in temperature, velocity and acoustic backscatter. A very sharp front (an internal bore?) with ~2 C change across just two neighboring uCTD profiles was encountered next, with a step-like signature also in the deep chlorophyll maximum and ADCP backscatter. There was a persistent, generally southward larger-scale flow for the entire survey, which lasted for almost a complete tidal cycle.

We had business in the Oceano Array and had to leave early on the second day of surveying, but hopefully by stitching the measurements above together with those from the other 5 vessels (see here, here, here and here) we will learn something about the phenomenology of sharp fronts, headland eddies and incoming high-frequency internal waves around Pt. Sal.