Solubility of trace metals from patagonian dust in the future Southern Ocean

Dust input from the patagonian desert to the Southern Ocean (SO) has the potential to modify future global climate by supplying Fe (and other essential limiting micronutrients) to microalgae, hence stimulating the biological CO2 pump, as suggested in the past at the Last Glacial Maximum. Future projections indicate increased dust deposition in the subantarctic waters due to higher frequency and magnitude of storms. However, the solubility of dust in the future SO that supplies micronutrients available for the phytoplankton, is not known yet. The impact of future increased dust delivery on the efficiency of the biological carbon pump is thus poorly constrained. Furthermore, the SO will experience other environmental changes (increase of T, pCO2, light, and decrease of macronutrients) that can also impact dust solubility. Therefore, the individual and cumulative effects of increased dust deposition and predicted other changes on the solubility of trace metals contained in Patagonian dust were studied in laboratory experiments under controlled conditions. Natural surface seawater collected in the Indian sector of the Southern Ocean was used to carried out the experiments, as well as patagonian dust generated experimentally from a soil sampled in South America. The pH was regulated by CO2 injections to the required concentration. The rate constants of the dissolution reaction were assessed by analyzing the evolution of particulate trace metal concentrations during the course of the experiments (each lasting for 8 days). Results will present the different phases of the dissolution kinetics of Fe and other trace metals from Patagonian dust under present, future and two intermediate scenarios. They will also highlight the individual and interactive effects of the future changes on the dissolution rates of metals contained in patagonian dust. The potential impact of these changes on microorganisms in the SO will then be discussed.