Iron (Fe) is an essential micronutrient. Its low supply has been shown to limit phytoplankton growth in the large parts of world’s surface ocean. Previous works have shown that solubility and bioavailability of iron both are a function of its chemical speciation, which is dominantly controlled by the organic complexation by organic matter. The ocean is currently experiencing acidification, warming, deoxygenation and stratification, yet the impact of changing seawater chemistry conditions (e.g. decreasing pH) as a consequence on iron speciation is still poorly understood. Absence of pH and temperature dimensions in the current approach by previous studies pose severe limitations on data interpretation regarding how seawater chemistry impact iron speciation. Here I use an ion paring-organic matter (NICA-Donnan) model to investigate the impact of pH, temperature and dissolved organic matter on iron speciation and apparent iron solubility at ambient conditions. This talk will focus on iron speciation study on samples collected across the Peruvian shelf and slope, and basin-scale comparisons between the Pacific and Atlantic Oceans. I will show that the impact of pH and temperature on organic iron complexation is as important as the characterization of Fe-binding ligands for the speciation and solubility of iron, since the global distributions of Fe-binding ligand (and DOC concentrations) are relatively invariant at the basin scale.
Dr. Kechen Zhu received both his Bachelor’s and Master’s degrees in Agriculture at China Agricultural University, and a Ph.D. degree in Chemical Oceanography at GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany. Dr. Zhu has been working as a postdoc researcher at GEOMAR since Jan 2021, and will soon be joining Southern University of Science and Technology as a postdoctoral researcher. His research focuses on the impacts of climate change and seawater chemistry (e.g. pH) on iron speciation, as well as the thermodynamic interactions between trace metals and organic matter. As a junior researcher, Dr. Zhu has participated several German DFG projects, is a leading author in three SCI publications and a co-author in a book chapter by Elsevier.