Knowledge gaps in quantifying the climate change response of biological storage of carbon in the ocean

The ocean is responsible for taking up approximately 25% of anthropogenic CO2 emissions and stores > 50 times more carbon than the atmosphere. Biological processes in the ocean play a key role, maintaining atmospheric CO2 levels 200 ppm lower than they would otherwise be. The ocean’s ability to take up and store CO2 is sensitive to climate change, however the key biological processes that contribute to ocean carbon storage are uncertain, as are their response and feedbacks to climate change. As a result, biogeochemical models vary widely in their representation of relevant processes, driving large uncertainties in the projections of future ocean carbon storage. This review identifies key biological processes that affect how carbon storage may change in the future in three thematic areas: biological contributions to alkalinity, net primary production, and interior respiration. We undertook a review of the existing literature to identify processes with high importance in influencing the future biologically-mediated storage of carbon in the ocean, and prioritised processes on the basis of both an expert assessment and a community survey. Highly ranked processes in both the expert assessment and survey were: for alkalinity – high level understanding of calcium carbonate production; for primary production – resource limitation of growth, zooplankton processes and phytoplankton loss processes; for respiration – microbial solubilisation, particle characteristics and particle type. The analysis presented here is designed to support future field or laboratory experiments targeting new process understanding, and modelling efforts aimed at undertaking biogeochemical model development.