Several scientific projects have been carried out in the Baltic and North Sea to assess the possible threat to the marine environment through dumped munitions, mainly after the two World Wars. For example, it is now known that munitions dumpsites are hotspots of chemical pollution. Toxic substances, such as TNT, are released into the seawater. The last 60 years led to extensive metal shell corrosion and resulted in munition compounds' leakage. Therefore, it is crucial not only for the protection of the marine environment but also for the safety of the offshore infrastructure to map the dumpsites, prepare samples for disposal, and propose remediation and clearance measures. Oceanographic modeling is a powerful and indispensable tool to understand the processes controlling the dispersion of munitions compounds in seawater (e.g., TNT). Oceanographic models are widely used to simulate the state of the ocean. They can also be used to simulate and predict the distribution and dispersion of munitions compounds. Numerical models allow us to identify and prioritize contaminant sources, produce risk maps, and ultimately provide decision-making recommendations. In CONMAR, the Leibniz Institute for Baltic Sea Research (IOW) is responsible for oceanographic modeling. To be able to simulate the Baltic Sea and the Western Baltic Sea in a regional nest with higher resolution, we use the General Estuarine and Transport Model (GETM), a state-of-the-art numerical coastal ocean model, and an attached TNT module. More than 30 tracers have been released into the virtual ocean to model the release of TNT from potential munitions disposal sites. The locations of these sources correspond to known and documented munitions disposal sites. Since some munitions dump sites have yet to be discovered or have been inadequately sampled, the model results are also used to detect such potential sources. Sensitivity experiments and numerical simulations will be performed to evaluate the contribution and magnitude of individual munitions disposal sites to total TNT contamination. We will use these results to develop a priority list of contaminated sites.
To improve the model performance, plenty of observational data are necessary. In-situ observations are commonly used to validate and calibrate numerical models. Here, the observational data that were collected during dedicated field campaigns are used to evaluate and boost the GETM performance. The ship-based measurements are also used to constrain the simulated TNT release and achieve more consistent results. The first numerical experiments indicate that the existing model can serve as a predictive tool for the spread and dispersion of munitions-related chemicals.
Dissolution and degradation experiments are also planned in order to quantify the rate at which chemicals enter the marine environment. This will be incorporated into the numerical model for the first time. The model will also be used to study the potential effect of climate change on marine munitions since it is currently unknown to which degree the sea-dumped munitions can be affected by increased ocean temperatures or altered storm activity. Further model developments are planned to account not only for the dissolved but also for the particulate munition compounds.
Ulf Graewe, IOW
The video at https://www.youtube.com/watch?v=cvrD8027izU shows TNT concentration in the near bottom layer for the year 2018. Please note the non-linear color coding.