Highly bioavailable dust-borne iron delivered to the Southern Ocean during glacial periods

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Shoenfelt, Elizabeth M., Winckler, Gisela, Lamy, Frank, Anderson, Robert F., Bostick, Benjamin C.
• Format: Text
• Language: English
• Published: National Academy of Sciences 2018
• Subjects: Physical Sciences; Southern Ocean
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6217405/; http://www.ncbi.nlm.nih.gov/pubmed/30322933; https://doi.org/10.1073/pnas.1809755115

Dust-borne iron fertilization of Southern Ocean phytoplankton contributes to lower glacial atmospheric CO2. Previous studies evaluating the impact of dust on climate estimate bioavailable iron using total iron fluxes in sediment cores. Thus, all iron is considered equally bioavailable over geologic time, despite evidence that glaciers mobilize highly bioavailable iron from bedrock, which winds can deliver to the Southern Ocean. Here we reconstruct dust-borne iron speciation over the last glacial cycle, showing that highly bioavailable iron(II) silicate minerals are a greater fraction of total iron reaching the Southern Ocean during glacial periods. The abundance of iron(II) silicates likely controls the bioavailable iron supply to the Southern Ocean and contributes to the previously observed increase in glacial productivity and CO2 drawdown.