20 Jun 2022
20 Jun 2022
Status: this preprint is currently under review for the journal BG.

Observation-constrained estimates of the global ocean carbon sink from Earth System Models

Jens Terhaar1,2, Thomas L. Frölicher1,2, and Fortunat Joos1,2 Jens Terhaar et al.
  • 1Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland
  • 2Oeschger Centre for Climate Change Research, University of Bern, Switzerland

Abstract. The ocean slows global warming by currently taking up around one quarter of all human-made CO2 emissions. However, estimates of the ocean anthropogenic carbon uptake vary across various observation-based and model-based approaches. Here, we show that the global ocean anthropogenic carbon sink simulated by Earth System Models can be constrained by two physical parameters, the present-day sea surface salinity in the subtropical-polar frontal zone in the Southern Ocean and the strength of the Atlantic Meridional Overturning Circulation, and one biogeochemical parameter, the Revelle factor of the global surface ocean. By exploiting this three-dimensional emergent constraint with observations, we provide a new model- and observation-based estimate of the past, present and future global ocean anthropogenic carbon sink and show that the ocean carbon sink is 9–11 % larger than previously estimated. Furthermore, the constraint reduces uncertainties of the past and present global ocean anthropogenic carbon sink by 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. The here identified key parameters for the ocean carbon sink should be quantified when presenting simulated ocean anthropogenic carbon uptake as in the Global Carbon Budget and be used to adjust these simulated estimates if necessary. The larger ocean sink results in enhanced ocean acidification over the 21st century, which further threatens marine ecosystems by reducing the water volume that is projected to be undersaturated towards aragonite by around 3.7–7.4 million km3 more than originally projected.

Jens Terhaar et al.

Status: open (until 01 Aug 2022)

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Jens Terhaar et al.

Jens Terhaar et al.


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Short summary
Estimates of the ocean sink of anthropogenic carbon vary across various approaches. We show that the global ocean carbon sink can be estimated by three parameters, two of which approximate the ocean ventilation in the Southern Ocean and the North Atlantic, and one approximates the chemical capacity of the ocean to take up carbon. With observations of these parameters, we estimate that the global ocean carbon sink is 10 % larger than previously assumed and cut uncertainties in half.