Composition and plume gas interaction control iron fractional solubility more than particle size in volcanic ash: Implications for fertilization of the North Atlantic

Journal Article · Thu Aug 21 00:00:00 EDT 2025 · Global Biogeochemical Cycles

DOI:https://doi.org/10.1029/2025GB008560· OSTI ID:3015488

Cheng, Zezhen; Gaston, Cassandra J.; Ault, Andrew P.; Hornby, Adrian; Elliott, Hope E.; Blades, Edmund; Royer, Haley M.; Buck, Clifton; Kollman, Charlotte; Kukkadapu, Ravi K.; China, Swarup; Lata, Nurun Nahar; Engelhard, Mark H.; Bowden, Mark E.; Lahiri, Nabajit; Parham, Rebecca; Meagher, Lauren; Angstman, B; Dayton, Kyle; Gazel, Esteban

Deposition of volcanic ash is thought to impact marine biogeochemical cycling by adding soluble iron (Fe) to the surface ocean. The magnitude of this input is a function of the amount of ash deposited, the total Fe content in the ash, and ash-derived Fe’s fractional solubility. However, the relative importance of chemical composition, acidic processing by the volcanic plume, and ash particle size in determining solubility is unclear. We paired an aerosol leach meant to provide an upper limit for fractional Fe solubility with chemical analyses of ash from the Cumbre Vieja and La Soufrière eruptions, which both impacted the North Atlantic in 2021. Fe in the ash samples is <6% soluble, but Fe fractional solubility in Cumbre Vieja ash is approximately triple that of La Soufrière ash. Compared to La Soufrière, a larger proportion of the Fe in Cumbre Vieja ash is in silicate rather than oxide minerals, which release more soluble Fe. Elevated levels of surficial fluorine (F) also suggest that Cumbre Vieja ash was subjected to a more fluorine-rich eruption plume and underwent more acidic processing. Particle size does not appear to be a primary control on Fe release. We estimate that the Cumbre Vieja eruption had a much larger impact on dissolved Fe (DFe) concentration in the surface ocean than the La Soufrière eruption due to differences in soluble Fe content and particle deposition velocity. These differences may help explain why some eruptions elicit a biological response in the ocean while others do not.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 3015488
• Report Number(s): PNNL-SA-215190
• Journal Information: Global Biogeochemical Cycles, Journal Name: Global Biogeochemical Cycles Journal Issue: 8 Vol. 39
• Country of Publication: United States
• Language: English