Long-Term Slowdown of Ocean Carbon Uptake by Alkalinity Dynamics

Oceanic absorption of atmospheric carbon dioxide (CO2) is expected to slow down under increasing anthropogenic emissions; however, the driving mechanisms and rates of change remain uncertain, limiting our ability to project long-term changes in climate. Using an Earth system simulation, we show that the uptake of anthropogenic carbon will slow in the next three centuries via reductions in surface alkalinity. Warming and associated changes in precipitation and evaporation intensify density stratification of the upper ocean, inhibiting the transport of alkaline water from the deep. The effect of these changes is amplified threefold by reduced carbonate buffering, making alkalinity a dominant control on CO2 uptake on multi-century timescales. Our simulation reveals a previously unknown alkalinity-climate feedback loop, amplifying multi-century warming under high emission trajectories.

Automated summary

Oceanic absorption of atmospheric carbon dioxide is expected to slow down due to increasing anthropogenic emissions. Through an Earth system simulation, it has been found that reductions in surface alkalinity will cause a slowdown in anthropogenic carbon uptake in the next three centuries. Changes in precipitation, evaporation, and warming intensify the stratification of the upper ocean, hindering the transport of alkaline water from the deep. These changes are further amplified by reduced carbonate buffering, indicating the dominance of alkalinity in controlling CO2 uptake on multi-century timescales. The simulation also reveals a previously unknown alkalinity-climate feedback loop, amplifying multi-century warming under high emission trajectories.