Deoxygenation of the Baltic Sea during the last millennium

Over the last 1,000 years, changing climate strongly influenced ecosystem of coastal oceans such as Baltic Sea. Sedimentary records revealed that temperatures could be linked to oxygen levels, spreading anoxic, oxygen-free areas in However, attribution levels remains challenging. This work simulates a preindustrial period 850 covering Medieval Climate Anomaly (MCA) and Little Ice Age using coupled physical-biogeochemical model. We conduct set sensitivity studies allow us disentangle contributions different biogeochemical processes increasing hypoxia during millennium. find temperature-dependent mineralization rate is key process contributing formation MCA. Faster enhances vertical phosphorus flux leading higher primary production. Our results question hypothesis increased cyanobacteria blooms are reason for Sea Moreover, strong contribution suggests role current projections should revisited.