Inhibition of oil plume dilution in Langmuir ocean circulation

Oil spills from deep-water blowouts rise through and interact with the ocean mixed layer and Langmuir turbulence, leading to considerable diversity of oil slick dilution patterns observed on the ocean surface. Certain conditions can drive oil droplet plumes to organize into distinct bands called windrows, inhibiting oil dilution. Observations of blurred or even diffused plumes are also common, but conditions under which these various dilution regimes emerge are not well understood. Here we use large eddy simulations to explain and quantify the dilution patterns and their dependence on relevant physical parameters. Two mechanisms, the downwelling and dilution due to Langmuir cells and the inhibition of dilution due to buoyancy of oil droplets, compete. This competition can be characterized by the ratio of Stokes drift to droplet rise velocity - the drift-to-buoyancy parameter, Db. We find that plume appearance and quantitative measures of relative dilution depend mainly on Db. Key Points Applied high-fidelity LES to model oil dilution in ocean mixed layer Reproduced various observed oil dilution patterns, from fingered to diffused Introduced a non-dimensional parameter to characterize modes of oil dilution