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 three-fold 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.

Key Points

  • Oceanic uptake of carbon could slow in upcoming centuries through previously unidentified alkalinity-climate feedback
  • Reduced upwelling and carbonate buffer enhance the influence of alkalinity on the increase in surface ocean carbon dioxide
  • Reductions in surface alkalinity will reduce the rate of carbon uptake on multi-century timescales

Chikamoto M. O., DiNezio P. & Lovenduski N., 2023. Long-term slowdown of ocean carbon uptake by alkalinity dynamics. Geophysical Research Letters 50: e2022GL101954. doi: 10.1029/2022GL101954. Article.

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