Near-bottom Oxygen observations from Western Baltic Sea

The provided dataset includes the near-bottom oxygen observations (NBO) from the western Baltic Sea (8.5-16°E and 53.67-57.5°N) and is presented in detail by Friedland, Vock, Piehl (2023, https://www.mdpi.com/2073-4441/15/18/3235).

The provided data consists of a couple of individual dataset from several freely usable sources: IOW measurement database, ICES Dataset of Hydrography, Boknis Eck time series, EU Copernicus Marine Data Store and the databases of the Mecklenburg Western Pomerania state office for Environment, Conservation and Geology (LUNG-MV) and the Schleswig-Holstein state office for the Environment (LfU-SH) respectively. From the different databases, we extracted the measured dissolved oxygen concentrations (or the measured oxygen saturation, which was converted following Weiss (1970)), location (longitude, latitude, water depth) and depth of the measurement. Aiming to unify the data in the joint dataset, the different datasets were transformed to mg/l, duplicates were removed and measurements at the same time and location obtained by different methods were averaged. Due to many inconsistencies between the measurement depth and bathymetric depth as well as large variations in the measured bathymetric depth of the respective measuring stations, the measured bathymetric depth given in the datasets was replaced by the bathymetric depth retrieved from iowtopo and EMODnet Bathymetry. The datasets mentioned above, included measurements of dissolved oxygen from the whole water column. To sort out the NBO, the deepest measurement was used, if it was close enough to the bottom using as threshold: for water depths below 16m, measurements within the lower 25% of the water column and for water depths above 16m measurements from a maximum of 4 meters above the sea floor were selected.