Sensitivity of Atmospheric Carbon Dioxide to Dust Iron Solubility During the Last Glacial‐Interglacial Cycle

Abstract Iron (Fe) input into remote oceans strongly influences the effectiveness of the biological pump and atmospheric carbon dioxide (CO 2 atm ). Several pathways contribute to the delivery of Fe to the ocean surface, with mineral dust aerosols being fundamental beyond continental margins. The greatest variability in dust emissions occurs at glacial‐interglacial timescales. While the absolute amount of dust is important, another key variable is the amount of soluble Fe within dust particles. However, the effect of this variable on past ocean biogeochemistry is not well documented by observations. Using the cGENIE Earth system model, we conducted sensitivity simulations of the role of dust‐borne soluble Fe ocean inputs on the pre‐industrial and Last Glacial Maximum (LGM) global CO 2 atm concentration. We found that the progressive enhancement of dust‐borne Fe deposition and solubility in glacial oceans led to enhanced biological productivity. This shift in nutrient dynamics contributed to a 28% increase in global particulate organic carbon export. The resulting nonlinear drawdown in LGM CO 2 atm (compared to the Holocene) increases up to a saturation value of ∼30 ppmv, approximately one‐third of the documented 80–100 ppmv change in CO 2 atm between glacial and interglacial periods during the late Quaternary. The region between 35°S and the transition between the Subantarctic and Polar Fronts is particularly critical for regulating CO 2 atm . These results provide new insights into the role of Fe solubility in oceanic carbon fixation, emphasizing the need for a more complete understanding of dust particle mineralogy and its interactions with atmospheric and ocean chemistry in past and future climates.