[A-OS13] Exploring Variability and Changes in Ocean Biogeochemical Cycles

[AOS13-02] Complex response of marine carbon pumps to global warming impacts atmospheric CO₂ on multi-centennial time scales

★Invited Papers

*Samar Khatiwala¹、Olivia Strachan²、Andreas Schmittner³ (1.Waseda University、2.University of Oxford、3.Oregon State University)

The ocean's capacity to absorb anthropogenic CO₂ is predicted to decrease with global warming, contributing to a positive climate-carbon cycle feedback. However, the precise nature of how climate change will impact the ocean's various carbon pumps and hence atmospheric CO₂ remains poorly constrained, especially on multi-centennial time scales. Here, we use an ocean biogeochemical model enabled with a suite of diagnostic tracers to robustly quantify the effect of climate change on the different marine carbon pumps between1765-2500 and their feedback on atmospheric CO₂. We show that under a high emission scenario, reduced carbon uptake and redistribution of alkalinity leads to ~505 ppm (30%) higher atmospheric CO₂ by 2500. Despite compensating changes in biological storage and air-sea disequilibrium, CO₂ is still 16% higher due to climate change. These changes are a net response to slowing circulation and increased stratification, which not only reduces carbon uptake but lengthens by hundreds of years the time anthropogenic and biologically-respired CO₂ are sequestered in the ocean. These results are essential for understanding and projecting long-term changes in global carbon cycle dynamics and climate, efforts to achieving Net Zero, and informing proposed marine carbon dioxide removal strategies.