Misconceptions of the marine biological carbon pump in a changing climate: Thinking outside the “export” box

Output of Earth system model simulations in support of the publicationI. Frenger, A. Landolfi, K. Kvale, C. J. Somes, A. Oschlies, W., Yao, and W. KoeveMisconceptions of the marine biological carbon pump in a changing climate: Thinking outside the “export” boxGlobal Change Biology (GCB-23-1265.R1) accepted for publication, 2023The marine biological carbon pump (BCP) stores carbon in the ocean interior, locked away from exchange with the atmosphere. As the BCP commonly is equated with the flux of organic material to the ocean interior, referred to as “export flux”, a change in export flux is perceived to directly impact atmospheric CO2, and thus climate. This Perspective recaps how this perception contrasts with current understanding of the BCP, emphasizing the lack of a direct relationship between global export flux and atmospheric CO2. We suggest instead to use the storage of carbon of biogenic origin in the ocean interior as a diagnostic that directly relates to atmospheric CO2, as a way forward to quantify the changes of the BCP in a changing climate. The diagnostic is conveniently applicable to both climate model data and increasingly available observational data. It can explain a seemingly paradoxical response under anthropogenic climate change: Despite decreasing export flux the BCP intensifies and provides a negative feedback to atmospheric CO2. This feedback is notably small compared to anthropogenic CO2emissions and other carbon-climate feedbacks. We hope our perspective will serve to promote a comprehensive view of the BCP’s impact on atmospheric CO2, which will better inform biological marine CO2 removal approaches.Methods are described in detail in docu/METHODS.pdf.All model experiments have been carried out on the CAU NEC cluster.For questions arrising, please contact [e-mail]