Postdoc Seminar: "Mapping the Efficiency of Abiotic Marine CO2 Removal Approaches" - Mengyang Zhou

To limit global warming to below 2°C by 2100, CO2 removal from the atmosphere will be necessary. Abiotic marine CO2 removal (mCDR) approaches have received significant attention for their potential to remove climate-relevant amounts of atmospheric CO2. These approaches operate through different pathways. Ocean alkalinity enhancement (OAE) and direct ocean removal (DOR) can induce a pCO2 deficit in the surface ocean to drive additional CO2 uptake from the atmosphere. In contrast, enhanced rock weathering (ERW) removes atmospheric CO2 via silicate or carbonate rock dissolution applied to soils or onboard ships, with the resulting bicarbonate-rich solution ultimately discharged into the surface ocean. This discharge can induce a pCO2 excess in the surface ocean, leading to a CO2 outgassing that partially offsets the CO2 captured in the upstream processes. A key metric for evaluating the viability of these approaches at scale is their efficiency, or the amount of CO2 removal per unit of intervention. Since air sea CO2 equilibration is slow and ocean circulation can subduct the pCO2 anomalies before the full equilibration is realized, the efficiency of mCDR deployments is expected to vary geographically and with seasonal and interannual variability in ocean conditions. Here, we develop a theoretical basis that enables effective comparison of efficiencies across OAE, DOR and ERW (its ocean component), and produce global efficiency maps for these approaches using ocean model simulations. Together, these efficiency maps can help to identify optimal regions and seasons for abiotic mCDR deployments and support meaningful intercomparison across approaches.