In the event of insufficient mitigation efforts, net-negative CO₂ emissions may be required to return climate warming to acceptable limits as defined by the Paris Agreement. The ocean acts as an important carbon sink under increasing atmospheric CO₂ levels when the physico-chemical uptake of carbon dominates. However, the processes that govern the marine carbon sink under net-negative CO₂ emission regimes are unclear. Here we assessed changes in marine CO₂ uptake and storage mechanisms under a range of idealized temperature-overshoot scenarios using an Earth system model of intermediate complexity over centennial timescales. We show that while the fate of CO₂ from physico-chemical uptake is very sensitive to future atmospheric boundary conditions and CO₂ is partly lost from the ocean at times of net-negative CO₂ emissions, storage associated with the biological carbon pump continues to increase and may even dominate marine excess CO₂ storage on multi-centennial timescales. Our findings imply that excess carbon that is attributable to the biological carbon pump needs to be considered carefully when quantifying and projecting changes in the marine carbon sink.

如果缓解措施不足，可能需要净负CO ₂排放才能将气候变暖恢复到《巴黎协定》规定的可接受限度。当大气中CO ₂水平增加时，当碳的物理化学吸收占主导地位时，海洋充当重要的碳汇。然而，在净负CO ₂排放制度下控制海洋碳汇的过程尚不清楚。在这里，我们使用百年时间尺度的中等复杂性的地球系统模型评估了一系列理想化温度超调情景下海洋CO ₂吸收和储存机制的变化。我们表明，虽然物理化学吸收的 CO ₂的命运对未来的大气边界条件非常敏感，并且在 CO ₂净排放为负值时，CO ₂部分从海洋中损失，但与生物碳泵相关的储存继续在几个世纪的时间尺度上，海洋过量CO ₂储存量会增加，甚至可能占主导地位。我们的研究结果表明，在量化和预测海洋碳汇变化时，需要仔细考虑生物碳泵造成的过量碳。