Silicate weathering is the process that converts atmospheric CO₂ into bicarbonate (HCO₃^-) or alkalinity and is believed to occur primarily on land. In contemporary oceans, it has been suggested that the increase in alkalinity during deep oceanic flow results from the in-situ dissolution of carbonate. However, the carbon isotope composition of total dissolved inorganic carbon does not support carbonate dissolution as a source of alkalinity in present-day oceans, except in areas where the depth exceeds the carbonate saturation depth (CSD) (Ref. 1). Instead, the steady increase in alkalinity observed in intermediate waters during flow is better explained by silicate weathering in the oceans (OW). Even at depths below the CSD, OW remains the primary source of alkalinity. OW facilitates the conversion of CO₂ produced by the remineralization of organic matter in the water column into HCO₃^- ions, effectively retaining carbon in the water.
Recently, novel functions of diatoms have been described. Diatoms secrete viscous saccharoidal substances that entrap silicate mineral particles and dissolve them through saccharoidal chelation in tandem with proton pumping; lithogenic elements in the silicate minerals are then incorporated into their frustules (Ref. 2). These organisms are adept at fusing metals (from silicate minerals) with opal (in their frustules). The uniform relationship between silicic acid and alkalinity suggests that the dissolution of diatom frustules—into which these organisms have efficiently incorporated lithogenic elements from dust—likely contributes to alkalinity production in subsurface waters.
Carbonate dissolution as a source of alkalinity has been supported by sediment trap and suspended particle observations, which report a decrease in carbonate flux and an increase in lithogenic flux with depth. In sediment trap studies, it is assumed that lithogenic matter has no interaction with fauna. However, because diatoms constitute a significant portion of the planktonic phase in the oceans, accounting for half of oceanic primary production, and are directly grazed by fauna, the presence of lithogenic elements in diatom frustules may lead to misleading interpretations of settling particle observations.
Exploring an ocean influenced by OW qualitatively suggests that this process substantially facilitates the storage and release of carbon during glacial-interglacial cycles. It could also provide an explanation for the cyclic fluctuations observed without conflicting with reported geochemical records or the ice-land rebound mechanism. Furthermore, it will be demonstrated that an OW-equipped ocean can explain the emergence and development of glacial cycles.

Ref.
1.Akagi & Nishino, Evidence for weathering of silicate minerals in ocean columns as the primary source of oceanic alkalinity. Mar. Chem.. (2026)
2. Akagi et al. Diatom-driven processes lead to the assimilation of elements from silicate minerals into their frustules. Mar. Chem.., (2025)

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