Author(s): Adam Jiankang Yang; Mary-Louise Timermans
Linked Author(s): Adam Yang
Keywords: Mixing in geophysical flows Carbon sequestration Particle-laden flows Kelvin-Helmholtz instability Rayleigh-Taylor instability
Abstract: Human-induced increases in atmospheric carbon dioxide (CO2) have led to significant global warming. With global temperatures already 1.1°C above pre-industrial levels and projected to surpass the 1.5°C threshold in the coming years, urgent action is needed to reduce emissions and implement carbon dioxide removal (CDR). One promising approach is ocean alkalinity enhancement (OAE), which involves adding minerals like pulverized silicates and carbonates to the ocean’s surface. Effective OAE relies on understanding how long particles remain suspended in the ocean's mixed layer, where velocity shear and air-sea gas exchange occur. Using direct numerical simulations, we investigate vertical sediment transport out of the surface mixed layer under varying shear strengths. Our results reveal that sediment transport is governed by a competition between the settling-driven convective instability (Rayleigh-Taylor) and the stratified shear instabilities. In weak shear conditions (characteristic velocity difference dU 0.05 m/s), rapid growth of stratified shear instabilities suppresses the Rayleigh-Taylor instability, significantly reducing effective particle settling and mass transport rates. These findings provide critical insights into the limitations of particle dissolution-based marine CDR approaches in the surface ocean, emphasizing the importance of considering shear dynamics in designing effective OAE strategies.
Year: 2025