The cooling potential of biological pump carbon after temperature overshoot

In the event of insufficient mitigation efforts, net-negative CO₂ emissions may be required to return to acceptable limits of climate warming as defined by the Paris Agreement. The ocean is an important carbon sink under increasing atmospheric CO₂ levels,when physico-chemical carbon-uptake dominates. However, the processes that govern the marine carbon sink under net-negative CO₂-emission regimes are unclear. Recent work with an Earth System model of intermediate complexity has shown that under idealized temperature overshoot scenarios CO₂ from physical-chemical uptake was partly lost from the ocean at times of net-negative CO₂-emissions, while storage associated with the biological carbon pump (DICremin) continued to increase and may even dominate marine excess CO₂ storage on multi-centennial time scales (Koeve et al. 2014, Nature Geosciences, https://doi.org/10.1038/s41561-024-01541-y).

Here we extend this work and estimate, for the first time, the cooling potential associated with CO₂-storage attributable to the biological carbon pump on centennial time scales, with a focus of conditions of net-negative CO₂-emissions. In our approach we use the UVic Earth System model, complemented with explicit model tracers of DICremin and preformed DIC. Changes of these tracers since preindustrial conditions can be traced to either the biological carbon pump or the physical-chemical uptake of anthropogenic CO₂, respectively. We quantify the cooling potential of biological pump carbon based on emission pathways perturbed by the change in DICremin since the preindustrial model state. The warming potential of anthropogenic carbon lost from the ocean during times of negative emissions is quantified from emission pathways perturbed by changes of preformed DIC since preindustrial.