Ideas and perspectives: Max MACS – constraining the potential global scale of Marine Anoxic Carbon Storage for CO <sub>2</sub> removal

Abstract. Marine Anoxic Carbon Storage (MACS) is a potential strategy for enhancing atmospheric CO2 removal (CDR) by sequestering organic carbon produced by terrestrial plants in stable, anoxic marine reservoirs. Initial results suggest that MACS could, in theory, operate at the gigatonne scale that would be required to impact global climate, with limited environmental risk and promising opportunities for co-benefits. However, several outstanding knowledge gaps make it challenging to quantify the actual potential global scale of MACS with confidence. To inform decisions about climate mitigation and trade-offs in the future, it is essential that we know how MACS implementation at scale would impact critical environmental and economic systems in the context of likely future scenarios. Building on the results of a workshop in Bucharest, Romania in 2025, we discuss the potential impacts of MACS activities on the ecology, biogeochemistry, economy, and community around the Black Sea, seafloor brines, and other anoxic marine sites. Quantifiable limits to the potential maximum feasible scale of MACS for CDR are organized into five criteria: (1) Durable storage site capacity; (2) Biomass sources and logistics; (3) Greenhouse gas balance; (4) Oxygen and sulfide impacts at the redoxcline; and (5) Impacts on dissolved organic matter or nutrients in the oxic zone. For each criterion, we evaluate the factors that could limit scale, our current state of knowledge, and the priority knowledge gaps that, if addressed, would improve our ability to estimate the potential global scale of MACS for CDR. Research is needed to understand its potential impacts at scale, but MACS is nonetheless worthy of serious consideration as a potential pathway for climate mitigation in coming decades.

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Publication Details

Journal
Biogeosciences
Published
2026-06-08
DOI
https://doi.org/10.5194/bg-23-3755-2026
Primary Topic
CO2 Sequestration and Geologic Interactions
Type
article
Field-Weighted Citation Impact
0.00

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article

Ideas and perspectives: Max MACS – constraining the potential global scale of Marine Anoxic Carbon Storage for CO 2 removal

JP Barry, Natalya Evans, Yoana G. Voynova, Daniel L. Sanchez et al.
Biogeosciences
CO2 Sequestration and Geologic Interactions
article

Ideas and perspectives: Max MACS – constraining the potential global scale of Marine Anoxic Carbon Storage for CO 2 removal

JP Barry, Natalya Evans, Yoana G. Voynova, Daniel L. Sanchez, Dror L. Angel, Selma Menabit, Sebastian Haas, Morgan Reed Raven, Tiia Luostarinen, Laura Boicenco, Mihaela Mureşan, Jean-Daniel Paris, Nitai Amiel, Peter Krost, Florence Schubotz, Antoine Crémière, Aaron M. Martinez, Adrian Stănică, Nora Gallarotti, Tina Treude, Allison Matzelle, Pranay Lal, Nikolaos D. Zarokanellos, Violeta Slabakova, Andrew K. Sweetman, Jan-Hendrik Hehemann, Thomas M. Blattmann, David Lordkipanidze, Nick Reynard, Christopher R. Pearce, Andreas Neumann, Elena Stoica
article en

Abstract

Abstract. Marine Anoxic Carbon Storage (MACS) is a potential strategy for enhancing atmospheric CO2 removal (CDR) by sequestering organic carbon produced by terrestrial plants in stable, anoxic marine reservoirs. Initial results suggest that MACS could, in theory, operate at the gigatonne scale that would be required to impact global climate, with limited environmental risk and promising opportunities for co-benefits. However, several outstanding knowledge gaps make it challenging to quantify the actual potential global scale of MACS with confidence. To inform decisions about climate mitigation and trade-offs in the future, it is essential that we know how MACS implementation at scale would impact critical environmental and economic systems in the context of likely future scenarios. Building on the results of a workshop in Bucharest, Romania in 2025, we discuss the potential impacts of MACS activities on the ecology, biogeochemistry, economy, and community around the Black Sea, seafloor brines, and other anoxic marine sites. Quantifiable limits to the potential maximum feasible scale of MACS for CDR are organized into five criteria: (1) Durable storage site capacity; (2) Biomass sources and logistics; (3) Greenhouse gas balance; (4) Oxygen and sulfide impacts at the redoxcline; and (5) Impacts on dissolved organic matter or nutrients in the oxic zone. For each criterion, we evaluate the factors that could limit scale, our current state of knowledge, and the priority knowledge gaps that, if addressed, would improve our ability to estimate the potential global scale of MACS for CDR. Research is needed to understand its potential impacts at scale, but MACS is nonetheless worthy of serious consideration as a potential pathway for climate mitigation in coming decades.

BiogeosciencesVol. 23(11)
Tbilisi State University (GE), Centre National de la Recherche Scientifique (FR), Dalhousie University (CA), Planetary Science Institute (US), Monterey Bay Aquarium Research Institute (US), Cyprus Institute (CY), Ifremer (FR), University of California, Santa Barbara (US), University of California, Los Angeles (US), Université de Bretagne Occidentale (FR), Nanyang Technological University (SG), University of Bremen (DE), Georgia State University (US), National Oceanography Centre (GB), Bulgarian Academy of Sciences (BG), Université Paris-Saclay (FR), Georgian National Museum (GE), Central Adoption Resource Authority (IN), GeoEcoMar (RO), Balearic Islands Coastal Observing and Forecasting System (ES), Laboratoire des Sciences du Climat et de l'Environnement (FR), Helmholtz-Zentrum Hereon (DE), Carbon180 (US), Society of Swedish Literature in Finland (FI), Institutul Naţional de Cercetare Dezvoltare Marină Grigore Antipa (RO), Institute of Oceanology (BG), Reuth TLV Rehabilitation Hospital (IL), Department of Earth Sciences (RU), Clinical Research Center Kiel (DE), Scottish Association For Marine Science (GB), University of Haifa (IL), University of California, Berkeley (US)
Grantham Foundation for the Protection of the Environment, European Commission, University of California, Santa Barbara, Horizon 2020 Framework Programme
Climate action
Openalex Percentile: Top 10%
CO2 Sequestration and Geologic Interactions
DOIOpen Access PDFOpenAlex
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