Ocean convergence and the dispersion of flotsam

Prediction of their resulting distribution on the surface is a fundamental, long-standing, and practically important problem. The dominant paradigm is dispersion within the dynamical context of a nondivergent flow: objects initially close together will on average spread apart but the area of surface patches of material does not change.

Although this paradigm is likely valid at mesoscales, larger than 100 km in horizontal scale, recent theoretical studies of submesoscales (less than similar to 10 km) predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices. Here we show that such structures can dramatically concentrate floating material. More than half of an array of similar to 200 surface drifters covering similar to 20 x 20 km(2) converged into a 60 x 60 m region within a week, a factor of more than 105 decrease in area, before slowly dispersing.