Observations of Dye Dispersion in the Gulf Stream Core and North Wall

We report on a series of four dye and drifter releases performed in the Gulf Stream core and along its north wall in Winter 2012, two near the surface (~25 m) and two at depth (~55 m, and ~120 m). The primary goal was to quantify and identify processes controlling submesoscale lateral dispersion across a strong front, including during strong forcing conditions. Dye injections were performed in concert with Lagrangian float deployments, each of which were tracked for 1 to 5 days. Sampling focused on hydrography, velocity, and dye distributions in a moving reference frame around the Lagrangian float, with repeat transects through the dye patch and across the stream. Results reveal pathways of transport and mixing of the dye, including evidence of rapid subduction along isopycnals due to symmetric instability, and the formation and detachment of streamers and/or filaments along the north wall. For symmetric instability cases, within hours after release the dye mixed throughout the mixed layer, and within 24–36 hrs it mixed below the mixed layer where isopycnals become more horizontal than vertical. For intra-thermocline eddy and north wall filament cases, analysis of towed transect data shows that the dye captured the main features of interest during these drifts. We estimate bounds on along- and cross-isopycnal dispersion on scales comparable to the dye patch, i.e., hundreds of meters to 10s of km, accounting for the fact that isopycnals varied from nearly vertical (outcropping) to nearly horizontal (main pycnocline).