TY - JOUR

T1 - The Role of Fe(II) Minerals in Carbon Stabilization in Coastal and Estuarine Anoxic Environments

AU - Jagode, Jan

AU - Carstens, Jannis Florian

AU - Guggenberger, Georg

N1 - Publisher Copyright: © 2026. The Author(s).

PY - 2026/1/1

Y1 - 2026/1/1

N2 - Fe(III) (oxyhydr)oxides are well-known for their role in organic carbon (OC) stabilization in terrestrial soils. Coastal and estuarine soils typically act as iron sinks and receive a high input of OC. However, tidal submersion induces anoxic and reducing conditions that favor the microbial reductive dissolution of Fe(III) (oxyhydr)oxides, followed by the partial formation of Fe(II) minerals. However, the potential of these minerals—such as siderite, vivianite and iron sulfides—to stabilize C has only recently received attention. In this review, we (a) elucidate methodological constraints in Fe(II) mineral analysis, (b) highlight formation mechanisms of Fe(II) minerals and (c) their interactions with organic matter (OM) and inorganic C and (d) explore their role in C stabilization. Fe(II) minerals interact with OM through surface complexation, coprecipitation or physical entrapment, despite their typically low surface charge. These interactions are facilitated by surface-reactive chemical species such as potential-determining ions, divalent cations and functional surface groups, enabling Fe(II) minerals to bind or occlude OC in anoxic settings. During Fe(II) mineral formation, dissolved inorganic C can be exported as total alkalinity or precipitated as stable carbonates, both contributing to long-term inorganic C sequestration. Emerging research indicates that Fe(II) mineral interactions with organic and inorganic C likely binds 5.8–16.6 Tg C yr−1, a potential overlooked global C sink with yet unexplored long-term stability. This review thus emphasizes the geochemical relevance of Fe(II) minerals beyond transient redox products as they may constitute a persistent and quantifiable carbon sink in anoxic sediments, warranting further exploration.

AB - Fe(III) (oxyhydr)oxides are well-known for their role in organic carbon (OC) stabilization in terrestrial soils. Coastal and estuarine soils typically act as iron sinks and receive a high input of OC. However, tidal submersion induces anoxic and reducing conditions that favor the microbial reductive dissolution of Fe(III) (oxyhydr)oxides, followed by the partial formation of Fe(II) minerals. However, the potential of these minerals—such as siderite, vivianite and iron sulfides—to stabilize C has only recently received attention. In this review, we (a) elucidate methodological constraints in Fe(II) mineral analysis, (b) highlight formation mechanisms of Fe(II) minerals and (c) their interactions with organic matter (OM) and inorganic C and (d) explore their role in C stabilization. Fe(II) minerals interact with OM through surface complexation, coprecipitation or physical entrapment, despite their typically low surface charge. These interactions are facilitated by surface-reactive chemical species such as potential-determining ions, divalent cations and functional surface groups, enabling Fe(II) minerals to bind or occlude OC in anoxic settings. During Fe(II) mineral formation, dissolved inorganic C can be exported as total alkalinity or precipitated as stable carbonates, both contributing to long-term inorganic C sequestration. Emerging research indicates that Fe(II) mineral interactions with organic and inorganic C likely binds 5.8–16.6 Tg C yr−1, a potential overlooked global C sink with yet unexplored long-term stability. This review thus emphasizes the geochemical relevance of Fe(II) minerals beyond transient redox products as they may constitute a persistent and quantifiable carbon sink in anoxic sediments, warranting further exploration.

KW - anoxic soils

KW - blue carbon

KW - Fe(II) minerals

KW - iron-organic matter interactions

KW - pyrite

KW - siderite

UR - http://www.scopus.com/inward/record.url?scp=105026380013&partnerID=8YFLogxK

U2 - 10.1029/2025GB008709

DO - 10.1029/2025GB008709

M3 - Review article

AN - SCOPUS:105026380013

VL - 40

JO - Global biogeochemical cycles

JF - Global biogeochemical cycles

SN - 0886-6236

IS - 1

M1 - e2025GB008709

ER -