Description: Highlights • A new description of sediment phosphorus dynamics was implemented in a 3D-model. • Oxygen consumption affects oxygen penetration in coastal sediments. • Low oxygen concentrations determine the oxygen penetration in deeper water sediments. • More than 80% of the phosphorus loads (1980–2008) are retained in the Baltic Sea. • Phosphorus is released from anoxic sediments and retained in oxic sediments. Abstract The new approach to model the oxygen dependent phosphate release by implementing formulations of the oxygen penetration depths (OPD) and mineral bound inorganic phosphorus pools to the Swedish Coastal and Ocean Biogeochemical model (SCOBI) is described. The phosphorus dynamics and the oxygen concentrations in the Baltic proper sediment are studied during the period 1980–2008 using SCOBI coupled to the 3D-Rossby Centre Ocean model. Model data are compared to observations from monitoring stations and experiments. The impact from oxygen consumption on the determination of the OPD is found to be largest in the coastal zones where also the largest OPD are found. In the deep water the low oxygen concentrations mainly determine the OPD. Highest modelled release rate of phosphate from the sediment is about 59 × 103 t P year− 1 and is found on anoxic sediment at depths between 60–150 m, corresponding to 17% of the Baltic proper total area. The deposition of organic and inorganic phosphorus on sediments with oxic bottom water is larger than the release of phosphorus, about 43 × 103 t P year− 1. For anoxic bottoms the release of total phosphorus during the investigated period is larger than the deposition, about 19 × 103 t P year− 1. In total the net Baltic proper sediment sink is about 23.7 × 103 t P year− 1. The estimated phosphorus sink efficiency of the entire Baltic Sea is on average about 83% during the period.

Description: The Baltic Sea is a marginal sea, located in a highly industrialized region in Central Northern Europe. Saltwater inflows from the North Sea and associated ventilation of the deep exert crucial control on the entire Baltic Sea ecosystem. This study explores the impact of anticipated sea level changes on the dynamics of those inflows. We use a numerical oceanic general circulation model covering both the Baltic and the North Sea. The model successfully retraces the essential ventilation dynamics throughout the period 1961–2007. A suite of idealized experiments suggests that rising sea level is associated with intensified ventilation as saltwater inflows become stronger, longer, and more frequent. Expressed quantitatively as a salinity increase in the deep central Baltic Sea, we find that a sea level rise of 1 m triggers a saltening of more than 1 PSU. This substantial increase in ventilation is the consequence of the increasing cross section in the Danish Straits amplified by a reduction of vertical mixing