Big decisions from small experiments: observational strategies for biomass-based marine carbon storage

Abstract Biomass-based CO 2 removal (CDR) with marine storage aims to harness photosynthesis to remove excess CO 2 from the atmosphere and sequester that fixed carbon in a long-lived marine reservoir. To guide decision-making around testing, deploying, and regulating CDR as part of a portfolio of climate mitigation strategies, we need to better understand how the deep sea and broader Earth system would respond to increased biomass addition. The central processes driving this response are sensitive to choices about biomass type and storage site, and they span spatial and temporal scales from microns to kilometers and from minutes to millennia. To organize this interdisciplinary challenge, we define five generalizable phases for biomass-based marine carbon storage projects: inputs, placement, short-term response, long-term response, and functional stability. Each phase is associated with observational needs with characteristic spatial and temporal scales that could be met through direct field measurements, investigations of analog sites, experiments, and/or models. Predicting the effects of potential interventions over global and centennial scales will require the strategic integration of diverse observational types into process-based Earth System models that can be used to support planning. Beyond assessing carbon storage and ensuring regulatory compliance, future research should therefore prioritize generating the data required to improve models for impacts of biomass-based marine carbon storage at climatically-relevant scales.