9 September 2018

At the racetrack

Zooming in on our zig zag

During the past two days, we’ve continued profiling with our FastCTD winch, but we’ve switched to using a different instrument, the MMP. MMP stands for Modular Microstructure Profilers. It’s the tool we use to measure turbulent mixing in the water. It can carry a few different types of instruments, but the most important for mixing are the shear probes. These probes convert small deflections caused by velocity shear in the water to a measure of turbulence.

Yesterday we completed a straight transect off the shelf using the MMP and found turbulence heightened in the usual places: at the surface and near the sea floor. We also saw an elevated mixing region at the interface between Atlantic Water and Pacific Water below a depth of about 200 m. This is something we’ll dive into deeper once we’re back on dry land. How much of the Atlantic Water heat is being mixed into shallower depths? How quickly is that heat moving?

Today we chose a small box, 8 km long and 1 km wide to sample repeatedly with the MMP (green box on the map between depths of about 100 and 150 m). The ship drove around “the racetrack” three times while a Wave Glider circled the ship, following its own box pattern 10 km long and 1 km wide. Tomorrow we’ll shift the box into deeper water and complete another few laps. The Wave Glider will continue its current course. It has been trouble staying on track since the sea has been so calm. The gentle swell and near-zero wind makes standing on the back deck in the Arctic air quite pleasant, but Wave Gliders rely on surface waves to propel themselves in the direction they want to go. Without strong enough waves, they can easily get swept up in a current and be carried off course. We’ll be shifting the box into an area with a stronger current which will be even more difficult for the Wave Glider to navigate. Since the winds aren’t likely to pick up significantly for another couple days, it’s safer to keep the Wave Glider on its current mission while the ship takes us into deeper waters.