Harnessing Deep-Ocean Carbon Sequestration via Enhanced Mineral Weathering

Exploring Accelerated Silicate Mineral Reactions in Oceanic Environments

1. The Geochemical Basis of Oceanic Carbon Sequestration

Silicate mineral weathering represents Earth's natural carbon sink mechanism, operating on geological timescales. The fundamental reaction for olivine (Mg₂SiO₄), one of the most reactive silicates, follows:

Mg₂SiO₄ + 4CO₂ + 4H₂O → 2Mg²⁺ + 4HCO₃⁻ + H₄SiO₄

This process sequesters CO₂ as dissolved inorganic carbon (DIC) in seawater, ultimately precipitating as carbonate minerals. In oceanic environments, several factors accelerate these reactions:

• High surface area-to-volume ratios of finely ground minerals
• Continuous seawater replenishment maintaining chemical gradients
• Catalytic effects of saline solutions on dissolution kinetics
• Microbial mediation in benthic environments

2. Oceanographic Advantages for Enhanced Weathering

The deep ocean offers distinct physicochemical advantages over terrestrial applications:

Parameter	Terrestrial EW	Oceanic EW
pH stability	Variable (4-8)	Consistent (7.8-8.3)
Temperature	Seasonal fluctuations	Stable 2-4°C (deep ocean)
CO₂ partial pressure	~400 ppm	Higher at depth (increased solubility)

3. Mineral Selection and Reaction Kinetics

Not all silicates exhibit equal reactivity. The relative weathering rates follow the Bowen reaction series inversely:

1. Olivine (Mg₂SiO₄): 10⁻¹⁰ to 10⁻¹¹ mol cm⁻² s⁻¹ at 25°C
2. Wollastonite (CaSiO₃): 10⁻¹¹ to 10⁻¹² mol cm⁻² s⁻¹
3. Basaltic glass: 10⁻¹³ mol cm⁻² s⁻¹

Recent studies demonstrate that grain size reduction to <10 μm increases reaction rates by 2-3 orders of magnitude through:

• Increased reactive surface defects
• Reduced diffusion path lengths
• Enhanced mineral-fluid contact area

4. Hydrodynamic Considerations for Mineral Deployment

Effective oceanic deployment requires overcoming three transport barriers:

4.1 Vertical Mixing

The ocean's stratified layers demand engineered solutions:

• Density currents: Utilizing mineral slurries with adjusted salinity
• Langmuir circulation: Leveraging wind-driven vortices in surface waters
• Artificial upwelling: Pipe systems transporting deep water

4.2 Horizontal Dispersal

Models suggest optimal dispersal occurs at:

• Mesopelagic zone (200-1000m) for carbonate saturation control
• Continental shelf edges for sediment trapping
• High-nutrient regions to stimulate biological pump synergy

5. Carbon Accounting and Verification

Quantifying sequestered carbon requires multi-method verification:

Method	Measurement Target	Uncertainty Range
Alkalinity anomaly	ΔTA per ton mineral	±5-10%
Isotopic tracers (δ¹³C, Δ¹⁴C)	Carbon source attribution	±2-3‰
Mineral surface analysis	Reaction progress rind thickness	±15-20%

6. Potential Environmental Impacts and Mitigation

Large-scale implementation requires addressing several ecological considerations:

6.1 Trace Metal Release

Olivine contains 0.2-0.3% nickel and 0.1-0.2% chromium by weight. Dissolution could release:

• ~2-3 kg Ni per ton olivine weathered
• ~1-2 kg Cr per ton olivine weathered

6.2 Plume Dynamics and Light Attenuation

Modeled effects show:

• 10% PAR reduction within 100m of surface plumes
• Settling velocities of 0.1-1 cm/s for 10-100μm particles

7. Technological Implementation Pathways

7.1 Mineral Processing Requirements

Industrial-scale deployment necessitates:

• Grinding energy: ~50-100 kWh/ton to reach 10μm particle size
• Material transport