Impact of iron fertilisation on atmospheric CO2 during the last glaciation

• Main Authors: Saini, Himadri, Meissner, Katrin J., Menviel, Laurie, Kvale, Karin
• Format: Text
• Language: English
• Published: 2022
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarc*
• Online Access: https://doi.org/10.5194/cp-2022-46; https://cp.copernicus.org/preprints/cp-2022-46/

While several processes have been identified to explain the decrease in atmospheric CO 2 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 CO 2 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 CO 2 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 CO 2 decrease is simulated at 70 ka BP, while a plausible range of CO 2 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 CO 2 (∼32 ppm) between 71 and 64 ka BP. We further find that in our simulations the decrease in atmospheric CO 2 concentrations is solely driven by iron fluxes south of the Antarctic polar front, while iron fertilization elsewhere plays a negligible role.