Observation-constrained estimates of the global ocean carbon sink from Earth system models

[摘要] The ocean slows global warming by currently taking uparound one-quarter of all human-made CO 2 emissions. However, estimatesof the ocean anthropogenic carbon uptake vary across variousobservation-based and model-based approaches. Here, we show that the globalocean anthropogenic carbon sink simulated by Earth system models can beconstrained by two physical parameters, the present-day sea surface salinityin the subtropical–polar frontal zone in the Southern Ocean and the strengthof the Atlantic Meridional Overturning Circulation, and one biogeochemicalparameter, the Revelle factor of the global surface ocean. The Revellefactor quantifies the chemical capacity of seawater to take up carbon for agiven increase in atmospheric CO 2 . By exploiting this three-dimensionalemergent constraint with observations, we provide a new model- andobservation-based estimate of the past, present, and future global oceananthropogenic carbon sink and show that the ocean carbon sink is 9 %–11 %larger than previously estimated. Furthermore, the constraint reducesuncertainties of the past and present global ocean anthropogenic carbon sinkby 42 %–59 % and the future sink by 32 %–62 % depending on the scenario,allowing for a better understanding of the global carbon cycle and better-targeted climate and ocean policies. Our constrained results are in goodagreement with the anthropogenic carbon air–sea flux estimates over the last three decadesbased on observations of the CO 2 partial pressure at the ocean surfacein the Global Carbon Budget 2021, and they suggest that existing hindcastocean-only model simulations underestimate the global ocean anthropogeniccarbon sink. The key parameters identified here for the ocean anthropogenic carbon sinkshould be quantified when presenting simulated ocean anthropogenic carbonuptake as in the Global Carbon Budget and be used to adjust these simulatedestimates if necessary. The larger ocean carbon sink results in enhanced oceanacidification over the 21st century, which further threatens marineecosystems by reducing the water volume that is projected to beundersaturated towards aragonite by around 3.7×10 6 – 7.4×10 6  km 3 morethan originally projected.

[学科分类] 大气科学