Incorporating Recalcitrant Dissolved Organic Carbon and Microbial Carbon Pump Processes into the cGENIE Earth System Model (cGENIEv0.9.35-MCP)

Abstract. Recalcitrant dissolved organic carbon (RDOC) is a significant component of dissolved organic carbon (DOC), produced through the microbial carbon pump (MCP), and plays a crucial role in long-term carbon sequestration. In this study, we extend the cGENIE Earth System Model by integrating the RDOC fraction and embedding MCP-driven transformations, resulting in the enhanced cGENIE-MCP model. We implement temperature-dependent limitations on nutrient uptake and organic matter remineralization to simulate MCP processes. Model outputs are compared with contemporary observations and previous cGENIE versions. The model effectively simulates the spatial distribution of concentrations and production rates of labile (LDOC), semi-labile (SLDOC), and RDOC. The cGENIE-MCP model demonstrates improved accuracy over previous versions, capturing spatial variability in DOC pools and quantifying MCP contributions to long-term carbon sequestration. For instance, sea surface DOC concentrations exhibit a latitudinal gradient, with values ranging from 65–80 μmol kg^-1 in tropical-subtropical zones to 40–50 μmol kg^-1 in subpolar regions. RDOC concentrations remain relatively stable at 40–50 μmol kg^-1 throughout the water column, while LDOC and SLDOC concentrations are typically below 10 μmol kg^-1 and 34 μmol kg^-1, respectively, in high-production areas. The model reveals a strong spatial correlation between primary production and LDOC production in upwelling zones, while RDOC production exhibits long-term carbon sequestration. These results emphasize the importance of incorporating MCP processes into Earth system models to better predict ocean carbon sink efficiency and biogeochemical responses to climate change. The cGENIE-MCP model provides a tool for studying the dynamics of ocean DOC and carbon cycle across timescales from paleo to future projections.