Anoxic Marine Storage of Terrestrial Biomass: Mechanisms and Monitoring Approaches as Informed by the Geologic Record

Since the publication of the 2022 IPCC WG report and the 2022 National Academies Report on Research Strategies for Ocean-Based CO2 Removal and Sequestration, substantial attention has been paid to the research gaps and potential monitoring strategies associated with cultivating and sinking marine biomass as a means to sequester atmospheric CO2 in the deep ocean. However, a comparable effort for the marine sequestration of terrestrial biomass products, particularly crop wastes, has been lacking. Because terrestrial biomass presents several potential advantages as a carbon sink relative to marine materials, most notably its direct uptake of atmospheric (rather than dissolved) CO2, its utilization of extant agricultural infrastructure, and its relatively high resistance to microbial breakdown, a research framework for evaluating the risks and potential of this CDR approach is urgently needed. Here, we integrate insights from both laboratory experiments and the geologic record, which provide valuable analogs for understanding the mechanisms of long-term organic matter storage in marine sediments. These data inform best practices for the optimization and measurement of biomass carbon sequestration as they constrain the local geochemical and ecological conditions most conducive to enhancing biomass recalcitrance through natural processes. Monitoring and verification of terrestrial biomass CDR installations can apply knowledge of these geologic mechanisms to target reactive components of terrestrial biomass (e.g., glucans), the products of their breakdown (e.g., dissolved organic matter, sulfide), and their potential transformations under a range of environmental redox conditions. We provide a summary of the state of CDR science related to terrestrial biomass sequestration in the ocean and identify critical research needs for future development of monitoring and verification technologies.