Atmospheric processing outside clouds increases soluble iron in mineral dust.

Area of Science:

• Geochemistry
• Atmospheric Chemistry
• Oceanography

Background:

• Iron (Fe) is a critical micronutrient for marine primary productivity.
• Dust deposition is a major source of oceanic iron, but much of it is biologically unavailable.
• Atmospheric processing of dust can increase bioavailable iron inputs, but these mechanisms are poorly understood.

Purpose of the Study:

• To experimentally simulate and model the cycling of iron-bearing dust in atmospheric aerosols and cloud droplets.
• To investigate the influence of pH on iron dissolution and speciation during atmospheric processing.
• To quantify the impact of atmospheric processing on the bioavailability of iron delivered to the ocean.

Main Methods:

• Experimental simulation of iron-bearing dust cycling between wet aerosols and cloud droplets.
• Chemical analysis of iron dissolution and speciation under varying pH conditions.
• Modeling of atmospheric iron-dust processing and its implications for oceanic iron supply.

Main Results:

• Insoluble iron in dust readily dissolves under acidic wet aerosol conditions.
• Higher pH in clouds causes dissolved iron to precipitate as nanoparticles.
• Redissolution of iron nanoparticles occurs upon return to acidic conditions, alongside gradual dissolution of refractory phases.

Conclusions:

• The duration of acidic wet aerosol stages increases the delivery of bioavailable iron to the ocean.
• Cloud conditions promote the formation of iron-rich nanoparticles in the atmosphere.
• Atmospheric processing significantly influences the form and bioavailability of iron transported to marine ecosystems.