In situ-measured benthic fluxes of dissolved inorganic phosphorus in the Baltic Sea

Abstract. Sedimentary recycling of phosphorus is a key aspect of coastal eutrophication. Here, we present data on benthic fluxes of dissolved inorganic phosphorus (DIP) from the Baltic Sea, an area with a long eutrophication history. The presented dataset contains 499 individual fluxes measured in situ with three types of benthic chamber landers at 59 stations over 20 years, and data cover most of the Baltic Sea sub-basins (Hylén et al., 2025; https://doi.org/10.5281/zenodo.14812160). The dataset further contains information about bottom-water dissolved oxygen (O₂) concentrations, sedimentary organic carbon (OC) content and sediment type. The DIP fluxes differ considerably between basins depending on OC loading and the level of O₂ depletion and generally increase from the coast to the central basins. Several stations have been visited on multiple occasions, also at times with different O₂ concentrations, which enables investigation of the immediate effects of shifting bottom-water O₂ concentrations on the benthic DIP release. The Baltic Sea-wide benthic DIP release is estimated to be 391 – 489 kton y^-1 based on a data integration based on sediment type and O₂ conditions during three years with varying extents of hypoxia and anoxia (2004, 2013 and 2018). The dataset reveals a lack of flux measurements in winter months, coastal areas and sandy sediments; these should be targeted in future studies. Overall, the data is of high quality and will be important for marine management and studies on mechanisms in benthic phosphorus cycling.