Fuhr, Michael (2024) Experimental assessment of enhanced benthic weathering of calcite and dunite in the south western Baltic Sea. (PhD/ Doctoral thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 203 pp.

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Abstract

This thesis delves into the potential of enhanced benthic weathering (EBW), which has been proposed as a viable strategy for carbon dioxide removal (CDR) in the Baltic Sea. A series of three laboratory experiments and a long-term benthocosm study were therefore carried out. Experiments on dissolution kinetics of olivine in artificial seawater, revealed total alkalinity (TA) decline attributed to the precipitation of several secondary minerals. In light of these findings, processes within surface sediments were explored in the framework of an incubation experiment under oxygenated conditions to understand alkaline mineral dissolution in natural sediment. Experiments simulating late summer conditions showed that corrosive bottom waters with respect to calcite are the ultimate driver for dissolution kinetics. Calcite and dunite exhibited elevated dissolution rates, compared to the oxygenated experiment. Assessment of dissolution kinetics yielded rate constants consistent with literature values, supporting their applicability in EBW modeling efforts. During a long-term benthocosm experiment, mineral dissolution rates closely followed temperature as long as bottom waters were oxygenated. This, combined with the fact that the temperature sensitivity was stronger than reported for laboratory experiments in the absence of biota, substantiates the principle function of the benthic weathering engine in the investigated sediments. A modelling approach assessing the efficiency of EBW in a potential application area in Eckernförde Bay and subsequent economic analysis underscored the cost-effectiveness of calcite as a preferred material for EBW, offering promising prospects for marine CDR implementation in coastal environments in the Baltic Sea. Overall, the findings of this thesis provide insights into the efficiency of EBW as a practical approach for climate change mitigation in Baltic Sea sediments and, potential, to fine-grained coastal sediments in general.

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