Assessing the effective settling of mineral particles in the ocean with application to ocean-based carbon-dioxide removal

A. Yang, M. Timmermans
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Abstract

Ocean alkalinity enhancement (OAE), a potential approach for atmospheric carbon dioxide removal (CDR), can involve introducing milled mineral particles into the ocean to promote carbon dioxide uptake. The effectiveness of this method relies on particles remaining in the ocean mixed layer while dissolution takes place, which depends on particle settling rates. Conventionally, particle settling rates are assessed using the Stokes settling velocity in stagnant conditions. However, recent numerical modeling reveals that in dynamic, stratified ocean environments, sediment vertical transport can be up to an order of magnitude faster than Stokes settling because of two types of fluid instabilities that can take place at the mixed layer base. Here, we estimate effective settling velocities in the presence of these instabilities and assess the implications for the efficacy of this particular OAE approach for CDR. The new effective settling rate estimates are sufficiently rapid that there is negligible particle dissolution before particles settle out of the mixed layer. This result is independent of initial particle size for the range of sizes considered here. Findings underscore the importance of considering ocean dynamics and stratification in assessing particle settling rates and provide valuable insights for optimizing OAE applications in diverse marine settings.
评估矿物颗粒在海洋中的有效沉降并应用于海洋二氧化碳清除
海洋碱度增强(OAE)是去除大气中二氧化碳(CDR)的一种潜在方法,可将研磨过的矿物颗粒引入海洋,以促进二氧化碳的吸收。这种方法的有效性取决于颗粒在溶解过程中能否留在海洋混合层中,而这取决于颗粒的沉降速度。传统上,颗粒沉降速度是通过停滞条件下的斯托克斯沉降速度来评估的。然而,最近的数值建模显示,在动态的分层海洋环境中,由于混合层底部可能存在两种流体不稳定性,沉积物的垂直迁移速度可能比斯托克斯沉降速度快一个数量级。在此,我们估算了存在这些不稳定性时的有效沉降速度,并评估了这种特殊的 OAE 方法对 CDR 的影响。新的有效沉降速度估计值足够快,在颗粒沉降出混合层之前,颗粒的溶解可以忽略不计。对于本文考虑的颗粒大小范围,这一结果与初始颗粒大小无关。研究结果强调了在评估颗粒沉降率时考虑海洋动力学和分层的重要性,并为优化 OAE 在各种海洋环境中的应用提供了宝贵的见解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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