Surface relative vorticity in April and September with superposed points of origin of particles. The color scale indicates relative vorticity normalized by the Coriolis parameter, ζ/f, at the ocean surface in April (left panels) and September (right panels), averaged over the time interval when the particles with sinking velocities equal to 30 m d–1 (a and b), 50 m d–1 (c and d) and 100 m d–1 (e and f) were also at the surface. Negative (positive) relative vorticity indicates anticyclonic (cyclonic) rotation. Points of origin of particles collected at GC600 (AT357) in black (green) in one ensemble member for each speed and collection period are also shown. DOI: https://doi.org/10.1525/elementa.292.f4