Holger Class leads new DFG funded research project on calcite dissolution

The German Research Foundation (DFG) approved the funding of the research project CL 190/4-1 entitled "Experimental and numerical investigations on density-driven dissolution of CO² and related carbonate dissolution in karst water". The proposal was jointly written with Bettina Strauch and Martin Zimmer from the Deutsches GeoForschungsZentrum in Potsdam. The project will start on 1 January 2023 and be funded for three years. SFB 1313 principal investigator Holger Class will be the project leader. The research project will contribute to the SFB 1313 vision topic on calcite dissolution in the subsurface.

Karst systems in carbonate rocks are formed in the presence of water that is charged with carbonic acid. It is common knowledge in karst hydrology that the main sources of this CO2 are the activity of microorganisms in the soil and root respiration. The biological activity in soil is subject to seasonal fluctuations (e.g. Dreybrodt, 1998; Ford & Williams, 2007; White, 2018; Klimchouk et al., 2000, and many others). These textbooks and papers also explain that meteoric water is percolating through the unsaturated zone, where it dissolves the CO2. Consequently, corrosion of carbonate rocks starts preferably close to the ground surface, where it causes karst denudation. Karst hydrologists are challenged in explaining why caves with often large cavities form also deep inside the rock. There are currently most notably two accepted explanations. The first one is denoted as ‘mixing corrosion’ and was introduced by Bögli (1980). Mixing corrosion is explained by the always calcite-aggressive behavior of water that is mixed from two water streams, which are each in calco-carbonic equilibrium. This can happen, for example, in joints. The calcite-aggressive mixing water then has new potential to dissolve more carbonates and form cavities. A second explanation assumes non- linear dissolution kinetics, which says that water would keep some of its remaining potential for dissolving carbonates while it is penetrating deep into the rock. This was discussed, e.g., by Gabrovsek & Dreybrodt, 2000; Ford & Ewers, 1978; Dreybrodt, 2004; Kaufmann et al., 2014. A third explanation for CO2 replenishment, in the absence of percolating meteoric water, was recently proposed by us (Class et al., 2021a) and is concerned with density-driven dissolution of CO2 at the epiphreatic karst-water table (Figure 1). We are confident that our preliminary work has demonstrated the plausibility of our hypothesis (see below), but more evidence is still needed in order to substantiate its relevance relative to ‘classical’ theories.