The use of photolytic rhodamines WT and sulpho G as conservative tracers of dispersion in surface waters

Abstract

We describe the use of sulpho rhodamine G (SG) and rhodamine WT (WT) as oceanographic tracers in tidally active waters of the southeastern North Sea. Ten kilograms of SG and 5 kg of WT dissolved in 1,000 liters of sea water were released to produce an initial tracer patch ∼10 × ∼0.5 km. Tracer dispersal was monitored for 11 d by high-performance liquid chromatography analysis of samples collected close to the patch center. The patch center was initially identified during surveys for sulfur hexafluoride released simultaneously, and its position was subsequently confirmed by use of a two-dimensional tracer dispersion model. Temporal changes in the SG/WT ratio were undetectable, so photolytic tracer losses were not directly quantified. A simple photolysis model was used to correct to conservative behavior for WT. Results are compared with the dispersal of spores of Bacillus globigii var. niger released simultaneously. Photolytic tracer pairs are ideally suited to tracer experiments in unconstrained water masses.