This is a location map. Black rectangle delineates the area shown in Figures 1B and 2. (B) Map of surface chlorophyll from June 22, 2012 (day 174), emphasizing the phytoplankton patch as a distinct area of high chlorophyll concentration. Thick black lines mark the main attracting Lagrangian coherent structures from calculation of finite-size Lyapunov exponents. To facilitate the presentation, we plotted only the highest 20 percent of FSLEs (for the entire FSLE field, see Figure 2C). Thin black contour outline region of strong Chl gradient is used to define patch boundaries. Magenta diamonds mark the position of Argo floats used for extracting the mixed layer depth in the patch vicinity. Green diamonds mark the location of the sampling stations.