Pyrogenic Carbon Degradation by Galvanic Coupling with Sprayed Seawater Microdroplets

Area of Science:

• Environmental Chemistry
• Oceanography
• Carbon Cycle Science

Background:

• Surface waves play a significant role in coastal processes influencing weather and climate.
• The chemical impact of surface waves, especially on pyrogenic carbon transformation, is not well understood.
• Pyrogenic carbon is typically considered to have minimal postformation alteration in its stable carbon isotope composition.

Purpose of the Study:

• To investigate the electrochemical interaction between pyrogenic carbon and seawater microdroplets generated by wave breaking.
• To understand the chemical transformation of refractory pyrogenic carbon under these conditions.
• To explore the implications for the carbon isotope discrepancy between riverine and marine black carbon and ocean carbon sequestration.

Main Methods:

• Examined the electrochemical interaction at the interfaces of seawater microdroplets and pyrogenic carbon.
• Investigated the galvanic coupling between water-carbon and water-vapor interfaces within microdroplets.
• Analyzed the resulting oxygenation and mineralization reactions of pyrogenic carbon.

Main Results:

• Identified a rapid degradation pathway for refractory pyrogenic carbon driven by electrochemical reactions in seawater microdroplets.
• Observed a significant enrichment of ~2.6‰ in ¹³C in pyrogenic carbon, exceeding previously assumed postformation alteration values (<0.5‰).
• Demonstrated that the unique chemical dynamics of seawater microdroplets drive these rapid transformations.

Conclusions:

• Seawater microdroplets facilitate rapid electrochemical degradation of pyrogenic carbon.
• This process significantly alters the carbon isotope signature of pyrogenic carbon, challenging existing assumptions.
• Coastal oceans may play a more substantial role in carbon sequestration through these microdroplet-mediated processes.