Marine munition in coastal seas: High-resolution numerical simulations of munition-related contaminants

After the Second World War, vast quantities of munitions were dumped in the world’s oceans. Over the years, the metal casings of these munitions have been corroded to the point where toxic substances such as TNT are continuously released into the seawater. The munition dumpsites are, therefore, hotspots of chemical pollution. However, predicting the distribution and spread of munition-related chemicals is challenging since (i) the associated dynamical processes are not well understood yet and (ii) some dumpsites are still unknown or poorly sampled. This study focuses on the Baltic Sea, which is estimated to contain more than 400,000 tons of conventional munitions, and particularly on the western Baltic Sea, a region with numerous documented or suspected dumpsites. We use high-resolution numerical simulations complemented by field measurements collected during several dedicated research campaigns to study the distribution and spread of munition-related contaminants. More than 45 virtual tracers have been released in the model to simulate the release of TNT from each contaminant source. Since the TNT release rates are unknown, we use inverse modeling and optimization techniques by combining the model results with the available observations. Thus, the simulated TNT is constrained, and we can obtain better estimates. Consistent with the observations, the simulated TNT distribution maps show elevated levels of TNT in the vicinity of the dumpsites. However, depending on the winds, the waves, and the ocean circulation, relatively high TNT levels are found throughout the western Baltic Sea. This indicates that this is not just a localized problem and that clearance operations are necessary to protect the marine environment. To further test the clearance strategies and prioritize the contaminant sources, we perform sensitivity experiments and construct risk maps.