Advancing Ocean Modelling Tools to Constrain Marine CDR Effectiveness by Testing Air-Sea Equilibration Timescales

Most Marine Carbon Dioxide Removal (mCDR) methods rely on creating a deficit in seawater CO₂ concentrations and partial pressure (pCO₂), quantified as a deficit in dissolved inorganic carbon (DIC). This DIC deficit drives atmospheric CO₂ uptake or reduces CO₂ outgassing.

The success of mCDR depends on efficient air-sea CO₂ equilibration before the DIC deficit becomes isolated from the atmosphere through water mass subduction. Since equilibration spans vast ocean regions, in situ measurements are impractical, making numerical modeling essential.

This study utilizes the ACCESS-OM2 model at three resolutions (0.1°, 0.25°, and 1°) to investigate how equilibration timescales vary with resolution, ranging from non-eddying to eddy-rich. Inter-model comparisons with CESM2 and ECCO indicate that model resolution has limited impact in the tropics but a stronger influence in polar regions. Furthermore, intra-model differences (due to resolution) are smaller than inter-model differences.

To improve accessibility, we introduce a computationally inexpensive virtual particle tracking method. This innovative approach offers a low-cost alternative to traditional, HPC-dependent ocean modeling, enabling easier testing of air-sea equilibration timescales, particularly for non-specialists.

These findings advance model-based assessments of air-sea CO₂ equilibration timescales and provide a practical, accessible tool for enhancing mCDR effectiveness.