The solubility and deposition flux of East Asian aerosol metals in the East China Sea: The effects of aeolian transport processes

Aerosol dissolvable metals are considered to be readily bioaccessible so that their input would influence the growth and composition of marine phytoplankton and affect elemental cycling globally. However, it is highly challenging to measure or estimate reliable deposition fluxes of aerosol dissolvable metals in the ocean partially due to the impacts of complicated processes involved in pre- and post-deposition of aerosols. We have collected lithogenic dust from major Chinese deserts and size-fractionated aerosols from the East China Sea (ECS) to study the variations of their dissolvable metals by using three operationally defined leaching protocols (ultrapure water, buffer, and Berger leaches). We have systematically investigated the changes of the distribution patterns of the metals to evaluate the potential impacts of the transport processes on the flux estimates of different elements. In addition to the extremely high solubilities observed for anthropogenic type elements, we found variations for solubilities of lithogenic type elements (Ti, Al, Fe) increase with increasing sizes by the three leaching treatments. Without knowing the size specific information (mass and solubility), our observations indicate that the deposition fluxes of lithogenic type elements would be significantly overestimated. Compared with the solubility of the desert dust, we found that all solubilities for lithogenic type elements in the largest aerosols were significantly enhanced. For example, the Fe solubilities increased up to 68, 6, and 3 folds for ultrapure water, buffer, and Berger treatments, respectively. Attributed to the difference of the impacts of the transport processes in different regions, the extent of the enhancement would be region specific. Comparing some other recent laboratory studies, we argue that the solubilities obtained by buffer and Berger leaches are more realistic to represent aerosol solubility in the ocean than ultrapure water leach. It would be essential to carry out similar field studies in other regions as this study to obtain region specific parameters of dissolvable aerosol metals to achieve better global modeling estimates on the fluxes of dissolvable aerosol metals in the ocean.