WHOI PO

Title: Fluid Mechanics in Marine Carbon Dioxide Removal

Abstract: 

Ocean alkalinity enhancement (OAE), a potentialapproach for atmospheric carbon dioxide removal (CDR), can involve introducingmilled mineral particles into the ocean to promote carbon dioxide uptake. Theeffectiveness of this method relies on particles remaining in the ocean mixedlayer while dissolution takes place, which depends on particle settling rates.Conventionally, particle settling rates are assessed using the Stokes settlingvelocity in stagnant conditions. However, recent numerical modelling revealsthat in dynamic, stratified ocean environments, sediment vertical transport canbe up to an order of magnitude faster than Stokes settling because of two typesof fluid instabilities that can take place at the mixed layer base. Here, weestimate effective settling velocities in the presence of these instabilitiesand assess the implications for the efficacy of this particular OAE approachfor CDR. The new effective settling rate estimates are sufficiently rapid thatthere is negligible particle dissolution before particles settle out of themixed layer. This result is independent of initial particle size for the rangeof sizes considered here. Findings underscore the importance of consideringocean dynamics and stratification in assessing particle settling rates andprovide valuable insights for optimizing OAE applications in diverse marinesettings.