28 Jun 2022
28 Jun 2022
Status: this preprint is currently under review for the journal CP.

Impact of iron fertilisation on atmospheric CO2 during the last glaciation

Himadri Saini1,2, Katrin J. Meissner1,2, Laurie Menviel1,3, and Karin Kvale4 Himadri Saini et al.
  • 1Climate Change Research Centre, University of New South Wales, Sydney, New South Wales, Australia
  • 2The Australian Research Council Centre of Excellence for Climate Extremes, Sydney, New South Wales, Australia
  • 3The Australian Centre for Excellence in Antarctic Science, University of Tasmania, Hobart, Tasmania 7001, Australia
  • 4GNS Science, 1 Fairway Drive, Avalon 5010, P.O. Box 30368, Lower Hutt 5040, New Zealand

Abstract. While several processes have been identified to explain the decrease in atmospheric CO2 during glaciations, a better quantification of the contribution of each of these processes is needed. For example, enhanced aeolian iron input into the ocean during glacial times has been suggested to drive a 5 to 28 ppm atmospheric CO2 decrease. Here, we constrain this contribution by performing a set of sensitivity experiments with different aeolian iron input patterns and iron solubility factors under boundary conditions corresponding to 70 thousand years before present (70 ka BP), a time period characterised by the first observed peak in glacial dust flux. We show that the decrease in CO2 as a function of the Southern Ocean iron input follows an exponential decay relationship. This exponential decay response arises due to the saturation of the biological pump efficiency and levels out at ∼21 ppm in our simulations. Using a best estimate of surface water iron solubility between 3 and 5 %, a ∼9 to 11 ppm CO2 decrease is simulated at 70 ka BP, while a plausible range of CO2 draw-down between 4 to 16 ppm is obtained using the wider but possible range of 1 to 10 %. This would account for ∼12–50 % of the reconstructed decrease in atmospheric CO2 (∼32 ppm) between 71 and 64 ka BP. We further find that in our simulations the decrease in atmospheric CO2 concentrations is solely driven by iron fluxes south of the Antarctic polar front, while iron fertilization elsewhere plays a negligible role.

Himadri Saini et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-46 by Juan Muglia', Juan Muglia, 12 Sep 2022
  • RC2: 'Comment on cp-2022-46', Anonymous Referee #2, 13 Oct 2022
  • RC3: 'Comment on cp-2022-46', Anonymous Referee #3, 17 Oct 2022

Himadri Saini et al.

Himadri Saini et al.


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Short summary
Understanding the variability in atmospheric CO2 during the past glacial cycle is crucial to understand the future impact of climate change. Previous research has hypothesised a key role of higher iron input into the Southern Ocean in influencing the global atmospheric CO2 levels by impacting the changes in the marine phytoplankton response. In this study we test this hypothesis using climate modelling and constraint the impact of ocean iron influence on global CO2 decrease.