Radioactive tracers as a tool in coastal oceanography: An overview of the MAST-52 project

Abstract

Radionuclides (99Tc, 125Sb, 90Sr, 137Cs) discharged from La Hague in France have been used to trace advection and dispersion of water masses in the “European Coastal Current” from the English Channel to the Baltic. Time-series of radionuclide measurements in water samples taken in the English Channel, at the Netherlands coast, in the German North Sea sector and in Danish waters have been compared with reported discharge values. The prospects for using 129I measured by accelerator mass spectrometry (AMS) as an oceanographic tracer have been evaluated as positive. The 99Tc analytical procedure have been improved and background levels of 99Tc, 137Cs and 90Sr in open North Atlantic seawater without influence from European discharges have been determined. An intercomparison programme have documented the quality of the measured 99Tc and 125Sb data. Transit times and transfer factors from La Hague to different locations in the study area have been estimated. It is concluded, that 10% of the La Hague discharge is transported through Kattegat and that 13 of the inflowing Kattegat bottom water originates from the coastal current. Three fundamentally different numeric models have been further developed under the project. The measured data have then been compared with values simulated by the three models. Models as well as measured data indicate, that a close coastal transport with longer transit times and often higher concentrations than seen in the open water main current is taking place. This coastal transport is important when contaminant transport is monitored. It is concluded, that the collected data gives a unique opportunity to evaluate models on advection and dispersion of coastal water masses and contaminants. The database will be made available as a tool for the evaluation of such models.