Movie S2.

Animation of the passive numerical tracer (color) in the LES FRONT run, with contours of buoyancy (white, with interval equivalent to a change in density of 0.1 kg m⁻³). The bottom panel shows the net surface heat flux (red) and wind-stress vectors (black) calculated from shipboard observations. The stress vectors are shown in a coordinate system defined by the maximum depth-integrated currents, such that downstream is parallel, and cross-stream is orthogonal, to the Gulf Stream jet (as shown in the annotation). The current yearday is indicated by the vertical dashed line.