Work

Secular evolution of marine carbonate δ66Zn and its implications for nutrient cycling through time

Year: 2026

Type: article

Abstract: The Zn isotope composition of marine carbonates provides a window into major reorganizations of the Earth surface system. Here, we present 185 new δ 66 Zn measurements from 176 carbonate samples spanning the Early Archean (3.48 Ga) to the Paleogene, integrated with 220 published analyses of carbonates, banded iron formations (BIF), sulfides, organic-rich sediments, and Fe–Mn crusts. The composite record reveals four first-order transitions: (1) a Late Archean decline in carbonate δ 66 Zn culminating near the Great Oxidation Event (GOE); (2) a reversal of the carbonate–BIF Zn isotope offset across the GOE; (3) relative Zn isotope stability during the mid-Proterozoic; and (4) a progressive rise in δ 66 Zn and amplification of isotopic variability from the Neoproterozoic onward.We argue that these secular trends reflect shifts in Zn partitioning among Fe-rich phases, carbonates, phosphates, and organic matter in response to evolving ocean chemistry and ecosystem structure, including the rise of eukaryotic algae. A single-reservoir Zn isotope mass-balance model, including sedimentary removal and exchange with diagenetic and hydrothermal fluids, is used to evaluate how changes in these fluxes and their isotope fractionations are expressed in the δ 66 Zn values of sedimentary rocks. Because the marine Zn cycle has a short residence time relative to the geological timescales considered here, the model supports interpretation of carbonate δ 66 Zn as a tracer of changes in Zn sources, sinks, and their coupling to continental weathering, phosphorus cycling, redox transitions, and biological innovation through Earth history.

Source: Geochimica et Cosmochimica Acta

DOI: 10.1016/j.gca.2026.09.021