The Paris Agreement aims to limit global temperature rise to within 1.5-2°C. While reducing greenhouse gas emissions is crucial, ocean-based negative emissions are increasingly recognized as essential for achieving this climate goal. Ocean alkalinity enhancement (OAE) is a promising strategy for promoting negative emissions without exacerbating ocean acidification. In this study, we employed the carbon-centric Grid Enabled Integrated Earth system model (cGENIE) to assess the global climate and carbon cycle responses to OAE, incorporating the microbial carbon pump (MCP) into the simulations. We explored OAE scenarios under varying CO₂ emission pathways and found that the magnitude of surface alkalinity increase depends on the region of application. Global or subpolar OAE resulted in the smallest net surface alkalinity increase, whereas the North Pacific Subtropical Gyre (NPSG) showed the greatest retention of added alkalinity in the upper ocean, indicating it as the most effective region for OAE deployment. Under higher emission scenarios, greater stratification led to enhanced surface layer alkalinity retention. Additionally, OAE contributed to reduced atmospheric CO₂ concentrations, lowered global surface temperatures, and mitigated ocean acidification. Finally, comparisons of refractory dissolved organic carbon (RDOC) trends before and after OAE across emission scenarios revealed that MCP-mediated RDOC dynamics act as a bidirectional regulator of climate change.
 

climate change, ocean alkalinity enhancement, Earth system model, microbial carbon pump