ALBERT

Description: Many recent ocean modelling studies have demonstrated the added value of enhanced horizontal resolution, although it comes at a high computational cost. However, few modeling studies of ocean-based CDR have been done at high resolution. Here we assess the effects of model resolution on two simulated ocean-based CDR methods, unequilibrated ocean alkalinity enhancement (OAE) and the direct marine capture (DMC) of CO2 from seawater (with assumed permanent storage), in experiments with the FOCI Earth system model. To do this we utilized two FOCI configurations, one with a 1/2° ocean resolution and the other with a 1/10° ocean nest in the N. Atlantic. Both configurations were run in a series of “paired” experiments with identical climate forcing and CDR deployments. We show that model resolution does appear to matter when simulating OAE and DMC. For OAE, parameterization of physical processes in the coarse resolution version of the model appears to overestimate how long alkalized waters stay in contact with the atmosphere and where they are transported. This results in large differences in OAE efficacy with almost twice as much carbon sequestered when the model resolution is coarse. For the DMC simulations, at one site there were clear differences in the compensating CO2 flux induced by DIC removal, which was again higher with a coarse resolution, while at the other site variability was high and differences were difficult to determine. At both DMC sites there were clear differences in circulation with the two model resolutions, and thus on downstream biogeochemistry. We suggest that well resolving ocean physics may be necessary to best calculate unequilibrated OAE and DMC efficacies and side effects. These results should be confirmed using other models and with different resolutions.