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

Abstract. Sedimentary recycling of phosphorus is a key aspect of 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 498 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 subbasins (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 389–484 kton yr−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 and coarse sediments; these should be targeted in future studies. Overall, intercomparisons between samplings and landers as well as rigorous data evaluation show that the data are of high quality. As such, this data set will, alone and together with other environmental data, be important for marine management and studies on mechanisms in benthic phosphorus cycling.