The planned joint project RETAKE II deepens the initiated investigations into potentials, feasibility, and side
effects of atmospheric CO2 removal through alkalinity enhancement (AE). The projects in RETAKE-D-II are
part of the joint project. Work Package 2.4 focuses on the Baltic Sea. In project phase I, the immediate
effects of a possible alkalinity release by dissolving introduced lime were investigated at two contrasting
Baltic Sea locations (Eckernförde Bay and Gotland Basin). Through simulations and the supplementary
collection of observational data, direct effects on CO2 uptake could be estimated. However, significant
uncertainties remained due to the limited transferability of the incubation experiments conducted by our
project partners to in-situ conditions, the neglect of possible indirect effects, and the natural background
alkalinity increase, presumably caused by the same process (the dissolution of calcite in the sediment).
These uncertainties are to be reduced in the second phase by answering: (1) How does the Baltic Sea
react according to our model when a calcite dissolution occurs analogous to the results of the lander
experiments conducted by the project partners, but scaled to realistic amounts for an intervention
(upscaling)? (2) How could benthic calcification and specifically the growth of mussels be influenced by a
higher saturation degree of calcite and how strongly would this slow down the desired effect of CO2
uptake? (3) Can new alkalinity data for the freshwater end-members reduce the uncertainties of the
background alkalinity increase and thus support a future attribution of the CO2 uptake through a possible
targeted lime input? Work Package 0.3 coordinates the data management of the research mission "Marine
Carbon Sinks in Decarbonization Paths" across the network.