Hawaiian beaches as natural analogues for enhanced silicate weathering of olivine

Abstract

Silicate weathering induces atmospheric CO2 sequestration through alkalinity release, which is Earth's prime mechanism for regulating the climate. Marine enhanced rock weathering (mERW) seeks to accelerate this process by distributing fast-weathering silicate minerals like olivine in coastal environments, thus targeting deliberate carbon dioxide removal. However, the efficiency and environmental impact of mERW remain uncertain, as experimental studies are not capable of tracking the CO2 sequestration rate and ecological effects over sufficiently long timescales. Natural coastal environments with olivine-rich sands enable insight into long-term weathering and may serve as analogues envisioned for mERW applications. Papak & omacr;lea Beach (Hawai'i) is one of the few beaches across the world with olivine-rich sands (>80% by weight), thus providing a unique mERW analogue. We examined in situ weathering and biogeochemical cycling at Papak & omacr;lea as well as in the nearby mixed volcanic/coral sands of Richardson Ocean Park. Flow-through sediment incubations examined olivine dissolution kinetics, alkalinity release, and the fate of weathering products. High-resolution scans of weathered grains characterized olivine dissolution and surface alteration processes. Alkalinity generation from Papak & omacr;lea's olivine sands and carbonate dissolution in Richardson Ocean Park was observed alongside dissolved inorganic carbon increases, suggesting CO2 sequestration occurs in this near-shore marine setting. However, complex biogeochemical interactions impede a precise quantification of olivine dissolution. Our findings highlight the complexity and challenges of monitoring, reporting, and verification for mERW applications in dynamic coastal settings.