To limit global warming to below 2 °C by 2100, CO₂ removal from the atmosphere will be necessary. One promising method for achieving CO₂ removal at scale is ocean alkalinity enhancement (OAE), but there are challenges with incomplete air–sea CO₂ equilibration, which reduces the efficiency of carbon removal. Here, we present global maps of OAE efficiency, and assess the seasonal variation in efficiency. We find that the equilibration kinetics have two characteristic timescales: rapid surface equilibration followed by a slower second phase, which represents the re-emergence of excess alkalinity that was initially subducted. These kinetics vary considerably with latitude and the season of alkalinity release, which are critical factors for determining the placement of potential OAE deployments. Additionally, we quantify the spatial and temporal scales of the induced CO₂ uptake, which helps identify the requirements for modelling OAE in regional ocean models.

为了到 2100 年将全球变暖限制在 2 °C 以下，必须从大气中去除 CO₂。实现大规模 CO₂ 去除的一种有前途的方法是海洋碱度增强 （OAE），但空气-海洋 CO₂ 平衡不完全存在挑战，这会降低碳去除效率。在这里，我们展示了 OAE 效率的全球地图，并评估了效率的季节性变化。我们发现平衡动力学具有两个特征时间尺度：快速表面平衡，然后是较慢的第二阶段，这表示最初被俯冲的过量碱度重新出现。这些动力学随纬度和碱度释放季节的变化而有很大变化，这是决定潜在 OAE 部署位置的关键因素。此外，我们量化了诱导 CO₂ 吸收的空间和时间尺度，这有助于确定在区域海洋模型中建模 OAE 的要求。