Use constraints: Data can be used freely given that the source is cited (following creative commons license CC-BY). The source should be cited as: “HELCOM HOLAS 3 Dataset (2023).

The data used to produce the layer was provided by the Leibniz-Institut für Ostseeforschung Warnemünde (IOW) in 2022:

- areas (polygons) with hydrogen sulfide (H2S) based on point measurements and modeling. Five time periods/year, for years 2016-2021 (altogether 30 layers).

The polygons were converted to raster layers in a way that for each time period (6 years, 5 time periods each year), the areas with H2S got the value 0, while the other areas got the value 1. All layers were summed, (representing 6 years, 5 time periods each year, maximum value 30) and data was normalised. For more detailed information on the data used, please see Feistel et al. 2016.

Data source:

Polygon data on sulfidic areas was kindly provided by Leibniz-Institut für Ostseeforschung Warnemünde (IOW). Separate maps can be viewed at http://www.io-warnemuende.de/msr-2016-0100.html.

Reference:

Feistel, S., Feistel, R., Nehring, D., Matthhäus, W., Nausch, G., Nauman n, M., 2016: Hypoxic and anoxic regions in the Baltic Sea, 1969-2015. Meereswiss. Ber, Warnemünde, 100. doi:10.12754/msr-2016-0100

Data quality: The data is based on monitoring data and modeling. For further information, see reference.