Passive CO₂ Sequestration via Basaltic Iron Fertilization and Diatom Silica Export: A Self-Financing, Zero-Energy Approach to Atmospheric Carbon Removal at Gigaton Scale

We propose a passive, zero-energy, self-financing system for atmospheric CO₂ removal at gigaton scale, based on the coupled dissolution of iron- and silica-rich volcanic rocks (basalt, olivine) in High-Nutrient Low-Chlorophyll (HNLC) ocean regions, and the resulting stimulation of diatom blooms. Diatoms — silica-mineralizing microalgae responsible for ~25% of global primary production — uniquely combine photosynthetic CO₂ fixation with permanent biomineral carbon export: their silica frustules sink rapidly to abyssal sediments, physically removing organic carbon from the fast carbon cycle for centuries to millions of years. Unlike Direct Air Capture (DAC), which requires 1–5 GWh per tonne CO₂ and costs $100–300/tCO₂, the proposed system consumes no external energy (solar-driven), produces no chemical waste (residue = natural diatomite mineral), and generates no CO₂ during operation. Its sole consumable is crushed basalt or olivine rock ($5–15/tonne). We estimate sequestration costs of $9–70 per tonne CO₂ at scale, compared to $100–300/tonne for DAC. Critically, this system is economically self-financing through voluntary carbon markets, currently pricing high-quality sequestration credits at $20–200 per tonne CO₂. At a deployment scale of 1–5 GtCO₂/year, gross carbon credit revenues would reach $20–500 billion USD annually, requiring zero government subsidies. This economic structure creates market-driven incentives that circumvent the political deadlocks that have slowed climate action for three decades. We present the geochemical and biological foundations, a mass balance, scale estimates, risk analysis, and a staged experimental protocol. All data, protocols, and intellectual content are released under CC BY 4.0 for immediate open use.