[A-CG42] Projection and detection of global environmental change

[ACG42-09] The Energy Exascale Earth System Model version 2 (E3SMv2) Global Ocean Biogeochemical Simulations: Effects of Vertical Mixing on the Ocean Carbon Cycle

★Invited Papers

*Yohei Takano¹, Mathew Maltrud², Cara Nissen³, Katherine Smith², Nicole S. Lovenduski³, Alison R. Gray⁴, Katy Christensen³, LeAnn Conlon², Kristen Falcinelli⁴, Nicole Jeffery², Mark R. Petersen², Jade Sauvé⁴, Anirban Sinha⁵, Jonathan D. Wolfe² (1.British Antarctic Survey, 2.Los Alamos National Laboratory, 3.University of Colorado, 4.University of Washington, 5.Picarro Inc.)

Keywords:Earth System Model, global ocean carbon cycle, vertical mixing

Ocean biogeochemistry models have large uncertainties in simulating changes in the observed ocean carbon sink in recent decades. Vertical mixing is one of the major physical processes that is critical for controlling the exchange of biogeochemical tracers between the upper and deep ocean. This process is parameterized in ocean biogeochemistry models, which contributes to uncertainties in simulating the ocean carbon sink. We present ocean–sea ice–biogeochemical simulations based on the Department of Energy's Energy Exascale Earth System Model version 2 (E3SMv2-BGC), with a particular focus on the simulated historical ocean carbon cycle and the model’s latest features. The E3SMv2-BGC incorporates the Marine Biogeochemistry Library (MARBL) and additional improvements to the representation of ocean physics, the most significant being background vertical mixing in ocean biogeochemistry simulations. We performed forced ocean biogeochemistry simulations with and without background vertical mixing. A comparison of the two simulations suggests that additional vertical mixing improves the representation of the spatial patterns of air–sea CO₂ flux, nutrients, and dissolved oxygen in the thermocline. Moreover, enhanced thermocline mixing through additional background vertical diffusion leads to a slower accumulation of modeled dissolved inorganic carbon in the upper ocean over recent decades, contributing to enhanced ocean carbon uptake in subtropical and mid-latitude regions. The results highlight the importance of incorporating background vertical diffusion for improved ocean biogeochemistry and carbon cycle simulations.