Learning About the Ocean Carbon Cycle from Observational Constraints and Model Simulations of Multiple Tracers
Long Cao¹and Atul K. Jain¹

¹ University of Illinois, Urbana-Champaign, Illinois, USA

The reliability of ocean models in the prediction of oceanic CO2 uptake is fundamentally dependent on their skills in simulating ocean circulation and air-sea gas exchange. In this study we demonstrate how the credibility of ocean carbon cycle models can be improved through the simulation of multiple tracers and utilization of a variety of observational data. This study is conducted using an earth system model of intermediate complexity, whose ocean circulation is constrained by the simulation of delta-14C. First, through the simulation of ocean biogeochemical cycles we identify weak isopycnal diffusivity not detected by the modeling of delta-14C. The modeled phosphate distribution is significantly improved by replacing the uniform isopycnal diffusivity with a depth-dependent profile. Second, the recalibration of air-sea gas exchange rate based on updated bomb delta-14C inventory data at the ocean basin scale greatly improves simulated inventories of transient tracers in the Southern Ocean. Third, the simulation of CFC-11 reveals excessive upwelling in the Southern Ocean, a problem not clearly shown in the modeling of bomb delta-14C and anthropogenic CO2. Modified parameterizations of eddy-induced circulation based on the simulation of CFC-11 further improve the simulated uptake of transient tracers in the Southern Ocean. The series of modifications made in the model improve the model’s credibility in simulating ocean circulation and carbon uptake, particularly in the Southern Ocean, and has significant consequence for the predicted CO2 uptake. Under the IPCC IS92a projection of CO2 concentrations, by year 2100 the revised model predict a cumulative oceanic uptake of anthropogenic CO2 that is 80 and 33 PgC lower in the Southern and global Ocean respectively, relative to the previous model constrained by the simulation of delta-14C alone.

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Last updated: 12 Feb 2007