| 23 Feb 2026
Munition Piles in the German Baltic Sea: Inventory and Maritime Hazard Perspectives
Abstract. For the first time, this paper presents two datasets that detail the distribution of piles of dumped munitions in the German Baltic Sea (Lübeck Bay and north of Kiel Fjord). Multibeam echosounder data and photomosaics were collected between 2017 and 2024. Dataset A contains basic information on 484 known and potential munition piles and their geographic context, with a focus on maritime activities in their surroundings. Dataset B is a subset of the former, where visual investigation enabled the detailed assessment of 39 munition piles by experts, so that a greater level of detail on the properties of the munitions was collected. The paper contextualises the data in terms of the munitions' properties and their geospatial surroundings. It identifies a "typical" munition pile to be inhomogeneous, most likely layered, with partially buried objects and munition casings that are weakly corroded. Munition pile properties were found to differ between dump sites—particularly in terms of the number and size of objects on a pile. Based on the information in datasets A and B, it was possible to extrapolate the number of objects on all (potential) munition piles across Lübeck Bay. The assessment demonstrates that survey data do not match historic recordings in archival documents. Distance measurements reveal that munition piles are located close to protected areas and sediment deposit sites, while subsea cables are located furthest away. The paper identifies six clusters of munition piles, two of which are located in areas with very high traffic density (> 2,000 vessels annually). These data are presented to encourage scientific debate on holistic management strategies, clearance approaches, cost estimates, policy relevance, and prioritisation of remediation activities. The findings show that several munition piles require attention by the respective authorities.
General comments
The authors present two datasets describing the occurrence of munition piles and their spatial distribution in relation to maritime activities. Dataset A is publicly available. However, within the manuscript, a non-public link is cited, while the publicly accessible link is provided only in the Data Availability section. This inconsistency should be harmonized (see also specific comments).
Dataset B, which represents a subset analyzed in greater detail, is not yet accessible. Consequently, statements based on this dataset cannot be reviewed properly.
Overall, the manuscript is understandable and methods are described in great detail, aside from minor issues (see specific comments).
Specific comments
Chapter 1:
Chapter 3: Which area is covered by MBES data. Please highlight in Figure 2. Including Lübeck Bay. See also comment for Figure 2.
Chapter 3.1: The Authors refer the description of the dump sites to other publications. Nevertheless, a short summary would be good.
Chapter 3.1.2, line 181: please spell out the term OFOP.
Chapter 3.2, line 210: Frey et al. 2026b is reference not public available. In my opinion, this is critical because details about the data origin are important information.
Chapter 3.2, line 211 f: I’m wondering which parameter are discussed in this manuscript. Please elaborate. I guess the authors describe this later. However, here the reader is left in the dark.
Chapter 3.2, line 230 f: I guess using ship type depending traffic density from one year is principally ok, but it is not true that 2022 is the only available year. HELCOM provides ship density maps, distinguishing vessel types, since 2006.
Chapter 3.2., line 241 f: The HELCOM data were converged into three categories. Why were these three categories choosen? Why was the category fishing vessels not choosen? I guess fishing activities are more impacted by munition than for example passenger vessels.
Figure 2: It is inconsistent that the maritime activities are only shown for Lübeck Bay and not for Kiel Bay.
Chapter 4.1, line 268 f: By whom or which method have been the munition piles confirmed? Please clarify.
Chapter 4.1, line 293 “In summary, a typical munition pile in the German Baltic Sea …”: There are much more dumping sites in the German Bight (e.g. Mecklenburg Bigth, Pommeranian Bight). Are sure, that these have similar characterized. Otherwise replace German Baltic Sea by “study area”
Figure 3, legend: Number of piles instead of objects?
Chapter 5, line 401 f: replace German Baltic Sea by study area (see comment above)
Chapter 5, line 409: The historical data don’t match with this study. Summarize shortly why.
Technical corrections
Values and units are not consistently separated from one another. Some are separated by spaces, while others are not.
Thousands separators are not used consistently