Vertical vorticity ζ normalized by f at the surface in the wintertime Gulf Stream after separation from the western boundary in a nested-subdomain simulation. Notice the meandering Stream in the centre, the northern warm anticyclonic and southern cold cyclonic mesoscale Rings, and the nearly ubiquitous submesoscale features of many types: North Wall ‘comma’ instabilities and streamers, Ring interior instabilities, cyclonic coherent vortices, and ‘submesoscale soup’ in-between. See J. C. McWilliams, Submesoscale currents in the ocean. Proc. R. Soc. A472: 20160117; http://dx.doi.org/10.1098/rspa.2016.0117. Image courtesy of J. Gula.