Reactions of microbial communities to enhanced benthic weathering (EBW) as a CDR strategy

Enhanced benthic weathering (EBW) is a promising carbon dioxide removal (CDR) strategy. In the Baltic Sea, seasonally hypoxic bottom waters are considered ideal settings for EBW. Addition of alkaline minerals (calcite and dunite) to the seafloor accelerates weathering, releases alkalinity to the water column and fosters CDR. However, feedbacks of microbial metabolisms currently remain unknown.               

RETAKE I - Enhanced benthic weathering of carbonate and olivine in the Baltic Sea (AP1.4) (2021-2024)

In the first phase of RETAKE I, the focus was on identifying which alkaline mineral (i.e. calcite or dunite) would be more favorable and efficient for CDR when artificially added to organic-rich Baltic Sea sediments. To assess the carbon dioxide uptake potential, related to enhanced weathering of calcite or dunite (i) laboratory sediment core incubations exposed to fully oxic or low oxygen bottom water conditions as well as (ii) long-term benthocosm experiments were conducted (cf. Fuhr et al. 2024, Fuhr et al. 2025, Dale et al. 2024). One of the major findings of these experiments was that calcite had an up to 10-fold higher carbon dioxide uptake efficiency than dunite (Fuhr et al. 2025).

To assess the effects that EBW has on the benthic microbial community and its metabolisms, 16S amplicon sequencing, CARD-FISH, cell counts as well as metagenomic and transcriptomic analyses are combined. Based on RNA-profiling the shifted microbial communities showed no distinct pattern in relation to alkaline mineral additions when exposed to fully oxic bottom water conditions (Fuhr et al. 2024). In contrast, later work on sediment core incubations under low oxygen conditions clearly demonstrated that a distinct shift within the microbial consortium was apparent (as indicated by metagenomics and transcriptomics) correlating with calcite addition and low oxygen bottom water conditions - further promoting alkalinity production (Bährle et al. in review)

Work on benthocosms is currently still be evaluated with respect to impacts of EBW on microbial community compositions and functionality.

RETAKE I - Team

Principal Investigators
Sonja Geilert (Biogeochemistry) (Lead: 2021-2023)
Mirjam Perner (Geomicrobiology)
Andy Dale (Biogeochemistry)

Doctoral candidates
Michael Fuhr (Biogeochemistry) (2021-2024)
Isabel Diercks (Geomicrobiology) (09/2021-05/2023)
Rebecca Bährle (Geomcirobiology) (2022-2024)

Associated
Frank Ohnemüller (Lime & Morter Industry)
Frank Melzner (Invertebrates)

RETAKE II - Enhanced benthic weathering of carbonate rocks: Experiments in seasonal and permanent anoxic bottom waters of the Baltic Sea (AP1.4) (2024-2027)

In the first phase the experimental data and predictions from complex numerical models exhibited considerable discrepancies for the CDR potential. This Is likely due to deviations in bottom water mineral saturation, redox conditions and microbial community succession related to incubation of sediment cores under laboratory conditions. Consequently, experiments under in situ field conditions were necessary.

Experiments with the BIGO (Biogeochemical Observatory) Lander systems will be conducted in regions of the Baltic Sea that are exposed to seasonal hypoxia (Boknis Eck, Eckernförde Bight) and permanent anoxic (Gotland Basin) bottom water conditions. The BIGO Systems contain two benthic chambers, various sensors and the ability to collect and fix subsamples in situ during the experiment from the chamber waters. A newly developed calcite addition system will enable injection of calcite to one of the chambers while the other benthic chamber will serve as control and remain unamended. This will enable us to monitor chemical and microbial changes at the seafloor after calcite addition over a period of three weeks. At the end of the BIGO in situ experiments the sediments will be brought up for further microbial and geochemical analyses.

For these BIGO experiments three research cruises are envisioned:

AL626 (L25-02b, MzB Helmsand, MzB HELIOS) - February 2025 (chief scientist: Mirjam Perner)
ALKOR (July 2025) (chief scientist: Andy Dale)
ALKOR Spring 2026 (chief scientist: Nicole Adam-Beyer)

RETAKE II - Team

Principal Investigators
Mirjam Perner (Geomicrobiology)
Andy Dale (Biogeochemistry)

PostDoc
Michael Fuhr (Biogeochemistry) (2024-2025)

Scientist
Stefanie Böhnke-Brandt
Katja Laufer-Meiser
Nicole Adam-Beyer

Associated
Frank Ohnemüller (Lime & Morter Industry)
Frank Melzner (Invertebrates)

Related publications/presentations:

RETAKE II

Perner, M. et al. (2025) Calcite addition to surface sediments as a CO2 removal strategy in seasonal hypoxic coastal waters promotes cable bacteria and alters the biogeochemical cycle. [Talk] FEMS Microbiol. Milan, Italy

Fuhr, M., Wallmann, K., Perner, M. & A. Dale (2025). In situ incubation experiments to assess the potential for calcite based ocean alkalinity enhancement. [Talk] College de Liège

Bährle, R. J., Baaske, R., Bornemann, T. L. V., Fuhr, M., Böhnke, S., Soares, A., Dale, A. W., Probst, A. J., Geilert, S. und Perner, M. (in review) Calcite addition to surface sediments as a CDR strategy in seasonal hypoxic coastal waters promotes cable bacteria and changes element cycling. ISME Communications: New Developments in Microbial Ecology

Fuhr, M., Dale, A. W. , Wallmann, K. , Bährle, R. J., Kalapurakkal, H. T., Sommer, S., Spiegel, T., Dobashi, R., Buchholz, B., Schmidt, M., Perner, M. und Geilert, S. (2025) Calcite is an efficient and low-cost material to enhance benthic weathering in shelf sediments of the Baltic Sea. Communications Earth & Environment, 8 . Art.Nr. 106 (2025). DOI 10.1038/s43247-025-02079-6.

Perner, M. (2025) Field-experiments for enhanced benthic weathering and its consequences in the German coastal SW Baltic Sea (Seafloor AE) - Cruise report FK Littorina, Cruise L25-02b (prev. AL626), MzB Helmsand and MzB HELIOS, 06. February - 24. February 2025. GEOMAR Helmholtz Centre for Ocean Research Kiel, 6 pp.

Perner, M. , Bährle, R. J., Baaske, R., Bornemann, T. L. V., Fuhr, M., Böhnke, S., Soares, A., Dale, A. W. , Probst, A. J. und Geilert, S. (2025) Enhanced benthic weathering as a CO2 removal strategy in seasonal hypoxic coastal waters of the Baltic Sea is influenced by cable bacteria activity after re-ventilation of bottom waters. [Talk] In: Annual Conference of the Association for General and Applied Microbiology, 23.-26.03.2025, Bochum, Germany.

Dale, A. W. , Geilert, S. , Diercks, I., Fuhr, M., Perner, M. , Scholz, F. und Wallmann, K. (2024) Seafloor alkalinity enhancement as a carbon dioxide removal strategy in the Baltic Sea. Communications Earth & Environment, 5 . Art.Nr. 452. DOI 10.1038/s43247-024-01569-3.

Bährle, R., Böhnke-Brandt, R., Fuhr, M., Dale, A. and M. Perner (2024). Reactions of the microbial community in benthic alkalinity enhancement experiments. [Talk] In: Annual Conference of the Association for General and Applied Microbiology. VAAM, 02.-05.06.2024, Würzburg, Germany.

RETAKE I

Fuhr, M., Wallmann, K., Dale, A. W. , Diercks, I., Kalapurakkal, H. T., Schmidt, M. , Sommer, S., Böhnke, S., Perner, M.und Geilert, S.(2023) Disentangling artificial and natural benthic weathering in organic rich Baltic Sea sediments.  Frontiers in Climate, 5 . Art.Nr. 1245580. DOI 10.3389/fclim.2023.1245580.

Diercks, I.,Geilert, S., Böhnke-Brandt, S., Dale, A.W., Fuhr, M., Perner, M. (2022). Interactions between microbial activity and enhanced benthic weathering of carbonate and olivine in the Baltic Sea. ePoster auf der VAAM Jahrestagung 2022

Diercks, I.,Geilert, S., Dale, A.W., Fuhr, M. and Perner, M. (2022). Interactions between microbial activity and enhanced benthic weathering in the Baltic Sea to analyse the potential, benefits and risks of a marine CDR strategy. YOUMARES13, Berlin.