Baltic Sea primary production regional climatologies from SatBałtyk data

Baltic Sea primary production estimates for 2021-2022 were obtained from the SatBałtyk operational system (https://www.satbaltyk.pl/), which applies the regionally tuned DESAMBEM bio-optical model to derive daily, depth-integrated primary production from satellite-derived surface chlorophyll-a, sea surface temperature and photosynthetically available radiation. These data were used to calculate regional primary production monthly means. Monthly regional primary production means were derived from SatBałtyk daily GeoTIFF files after masking invalid pixels and excluding negative retrievals. For each day, a regional mean was calculated by averaging all valid pixels within the region’s bounding box. Monthly values were then computed as the arithmetic mean of the daily regional means within each calendar month. Regional time series were extracted for three basins: the Bornholm Basin (54.9–55.7°N, 15.0–16.5°E), the Gdansk Basin (54.3–55.0°N, 18.4–20.0°E), and the eastern Gotland Basin (56.6–58.5°N, 19.2–21.0°E). Uncertainty bands were computed as ±0.5 times the standard deviation of the daily regional means within each month (representing day-to-day variability within that month).