In-situ detection and tracking of oil in the water column

Abstract

Standard tracer techniques, known from work with radioactive tracers and fluorescent dyes, have been applied for full scale studies of the distribution of oil in the water column. The study was part of oil spill experiments conducted off the coast of Norway in June 1985 under the research program ‘Dispersion of Oil on Sea’ Light scattering of oil droplets in water and UV-fluorescence of dissolved oil components were used for in-situ detection of oil in water. By UVfluorescence measurements, being the more sensitive of the two methods, it was demonstrated that dissolved components of oil were present 15 m below the slick less than one hour after the surface release of 10 tonnes of Statfford crude oil (premixed with 2% dispersant). By tracking a submerged UV-fluorimeter through the elongated oil patch it wasfound that the maximum concentration of dissolved components occurred below the central part of the slick. It was experienced that in-situ UV-fluorimeter recordings provide detailed information on the relative distribution of dissolved oil compounds in the water column below a slick.

By laboratory calibration of the UV-fluorimeter it is possible to establish a reliable estimate on the physical dilution of the released oil within a working range of 5 to about 10 000 μl m⁻³ oil in water. However, at the present state of work, the working range is only tested on oil with a residence time of less than six hours in sea water.