UC San Diego

Abstract The ocean plays a major role in controlling atmospheric carbon at decadal to millennial timescales, with benthic carbon representing the only geologic‐scale storage of oceanic carbon. Despite its importance, detailed benthic ocean observations are limited and representation of the benthic carbon cycle in ocean and Earth system models (ESMs) is mostly empirical with little prognostic capacity, which hinders our ability to properly understand the long‐term evolution of the carbon cycle and climate change‐related feedbacks. The Benthic Ecosystem and Carbon Synthesis (BECS) working group, with the support of the US Ocean Carbon & Biogeochemistry Program (OCB), identified key challenges limiting our understanding of benthic systems, opportunities to act on these challenges, and pathways to increase the representation of these systems in global modeling and observational efforts. We propose a set of priorities to advance mechanistic understanding and better quantify the importance of the benthos: (a) implementing a model intercomparison exercise with existing benthic models to support future model development, (b) data synthesis to inform both model parameterizations and future observations, (c) increased deployment of platforms and technologies in support of in situ benthic monitoring (e.g., from benchtop to field mesocosm), and (d) global coordination of a benthic observing program (“GEOSed”) to fill large regional data gaps and evaluate the mechanistic understanding of benthic processes acquired throughout the previous steps. Addressing these priorities will help inform solutions to both global and regional resource management and climate adaptation strategies. Plain Language Summary The ocean plays a large role in shaping atmospheric carbon at timescales from decades to millennia, and ocean sediments not only influence the processes involved but also constitute a long‐term storage of oceanic carbon. Despite its importance, benthic (sediment) observations are limited, making it difficult to represent sediment‐water interface in climate models and improve our understanding of climate feedbacks. In this manuscript, the Benthic Ecosystem and Carbon Synthesis (BECS) working group recommends a set of priorities to further accelerate sediment research. These include comparing existing sediment models, synthesizing available data, prioritizing cost‐effective and informative variables for sampling, and coordinating global field campaigns to increase observations in areas where data is lacking. Key Points New observations should prioritize easier‐to‐collect variables to rapidly increase temporal and spatial coverage of benthic data Multi‐variable data sets need to be harmonized to provide comprehensive data sets that can inform gaps in the carbon cycle Sediment model comparison is needed to establish recommendations for processes and parameterizations, and support varied modeling efforts