A dye tracer reveals cross-shelf dispersion and interleaving on the Oregon shelf

[1] A fluorescent dye tracer was injected into the pycnocline on the Oregon shelf at a depth of 9–10 m. It spread rapidly cross-shelf as two distinct layers, one above the other in the water column, split by interleaving dye-free water. The vertical scale of these layers, and associated density steps, was 1–2 m, and the horizontal extent of interleaving exceeded 1.6 km after an inertial period. The upper dye layer was sharply peaked and embedded in a strong vertical density gradient. The lower layer was slablike and associated with weak stratification. Both layers were inclined slightly in density space. It is proposed that internal wave-induced mixing and the lateral collapse of mixing patches were important mechanisms. Analogies can be drawn between these dye structures and frequently-observed thin planktonic layers. By approximating the dye dispersion as a Fickian process, estimated isopycnal and diapycnal eddy diffusivities of kx = 4.1 m 2 s 1 and kz = 1.4 10 5 m s 1 are obtained. Citation: Dale, A. C., M. D. Levine, J. A. Barth, and J. A. Austin (2006), A dye tracer reveals cross-shelf dispersion and interleaving on the Oregon shelf, Geophys. Res. Lett., 33, L03604, doi:10.1029/2005GL024959.