Mineral Influence of a Northern Estuary on the Retention of Aquatic and Land-derived Stabilized Organic Carbon (MINERALS-OC)

The global carbon cycle encompasses reservoirs and the dynamic fluxes of carbon within and among them. These reservoirs include the atmosphere, lithosphere, biosphere, and hydrosphere, each contributing to or receiving carbon in spatially and temporally varying ways. Marine sediments represent a critical sink for organic carbon (OC), with coastal and deltaic sediments playing a dominant role in sequestering OC. These sediments receive terrestrial and marine OC in varying proportions along the land-to-ocean continuum, where their preservation is strongly influenced by protective associations with reactive minerals, particularly iron (hydr)oxides and clay minerals. Despite their importance, the combined effects of iron and clay minerals in preferentially stabilizing specific types of OC remain poorly understood, particularly under changing redox conditions. The extent to which these mineral OC associations are formed in-situ within sediments as opposed to pre-depositional formation on land also remains to be determined. To address these knowledge gaps, this study employs dual isotopic (δ¹³C, Δ¹⁴C) and molecular approaches to explore the combined roles of clays and reactive iron in OC stabilization across both temporal and spatial gradients. By analyzing total, iron-associated, clay-associated, and non-soluble residual OC fractions in oxic and anoxic sediment layers along gradients of terrestrial and marine OC inputs, this research will (i) quantify the relative contributions of clays and iron oxides to OC stabilization in surface (0–3 cm) and diagenetically stabilized deep (26–31 cm) sediments and (ii) resolve the preferential preservation of marine versus terrestrial OC within mineral-associated fractions through isotope and biomarker analyses. The findings of this study provide critical insights into the source-to-sink fate of mineral-associated OC in coastal sedimentary systems and elucidate their implications in the global carbon cycle, advancing our understanding of carbon sequestration in dynamic environments.