Subsurface eddies

The Antarctic Circumpolar Current (ACC) is the world’s strongest current. As its name would suggest, it circles the entire Antarctic continent flowing eastward. The Antarctic Peninsula juts out northward, so the current flows directly adjacent to the continental shelf on its western side. Warm water from this current provides a source of heat to the continental shelf, where water temperatures have been rising in recent decades. Below the permanent pycnocline, at depths of about 200-500 m, is a water mass called Upper Circumpolar Deep Water. With temperatures 3° – 4°C above freezing, this water mass is considered very warm for the Antarctic.

In order for the heat to be transported from the swiftly flowing ACC to the shelf, water must somehow be diverted onto it. At least some of this transport is accomplished via subsurface eddies. Instabilities occur in the flow in places where the current encounters a sharp change in bathymetry, like over the mouth of a subsurface canyon. This can cause deep eddies to spin off the main current like whirls over the stones in a creek.



At about 10 km wide, these eddies are relatively small compared to typical hydrographic sampling resolution. Ocean gliders, which move slowly from the surface to the ocean floor and back can make multiple passes through a single eddy as they “fly” through the water. Over the course of four deployments during austral summers 2010-11, 2011-12, and 2012-13, Rutgers gliders covered a distance of over 5,000 km on the shelf and flew through several of these features. The eddies were most frequently found within or along the edges of the two major cross-shelf canyons in the region.



Publications

Couto, N., J. Kohut, D. Martinson, O. Schofield (2017), Distribution of Upper Circumpolar Deep Water on the warming continental shelf of the West Antarctic Peninsula, Journal of Geophysical Research: Oceans, doi:10.1002/2017JC012840.