Trends and Drivers of Soluble Iron Deposition from East Asian Dust to the Northwest Pacific: A Springtime Analysis (2001–2017)

Abstract. Recent shifts in dust emissions and atmospheric compositions in East Asia may have a significant impact on the deposition of soluble iron from dust over the Northwest Pacific. This study investigates the trends and driving factors behind this phenomenon during the springs of 2001–2017 using an enhanced version of the Community Atmosphere Model version 6 with comprehensive stratospheric chemistry (CAM6-chem). We improved the model to account for desert dust mineralogy and atmospheric chemical processes that promote iron dissolution, allowing for an in-depth analysis of the evolution of dust iron. Our findings indicate a decreasing trend in dust soluble iron deposition from East Asia to the Northwest Pacific by 2.4 % per year, primarily due to reduced dust emissions driven by declining surface winds over dust source regions. Conversely, the solubility of dust iron showed an increasing trend, rising from 1.5 % in 2001 to 1.7 % in 2017. This increased iron solubility is linked to the acidification of coarse mode aerosols and in-cloud oxalate-ligand-promoted dissolution. Sensitivity model simulations reveal that the increase in anthropogenic NO_x emissions, rather than the decrease in SO₂, plays a dominant role in enhancing dust aerosol acidity. This study highlights a dual trend: a decrease in the overall deposition of soluble iron from dust, but an increase in the solubility of the iron itself. It underscores the critical roles of both dust emission and atmospheric processing in promoting iron dissolution, which further influences soluble iron deposition and marine ecology.