Diatom-induced calcification in coastal marine environments: Biomineralization threshold and mechanism

Abstract

Diatoms play a pivotal role in the ocean, contributing approximately 40 % of marine primary production, with nearly half of the particulate organic carbon being exported. The recent discovery of a novel diatom-induced calcification pathway has attracted significant attention due to its implications for marine carbon, calcium, and silicon cycling. Despite its potential, the lack of a quantitative initiation threshold and comparative analysis with known calcifying organisms limit our ability to predict its ecological impact, particularly on carbon sequestration. This study addresses these gaps by cultivating the common diatom species, Skeletonema costatum, under simulated marine conditions to evaluate its CaCO₃ precipitation potential and define the biogeochemical threshold for calcification. The experimental results showed that S. costatum can induce calcification across a range of environmental conditions, including varying dissolved inorganic carbon (DIC 1837 to 2709 μmol·kg⁻¹), nitrogen sources (NH₄⁺ or NO₃⁻), and cell densities (10⁴ to 10⁵ cells·mL⁻¹). Calcification was initiated when the aragonite saturation state (Ω_arag) exceeded ∼8. The calcification rate exhibits a linear correlation with Ω_arag in the bulk solution, categorizing it as a “biologically induced” process. Our findings highlight similarities between the calcification mechanisms of S. costatum and other calcifying organisms, revealing the common ality of environmental drivers. This study advances our understanding of diatom-induced calcification, offering insights into its role in the marine carbon cycle and potential contributions to carbon sequestration strategies.