Seawater Mg/Ca has oscillated markedly over the Phanerozoic, closely associated with secular variations in sedimentation, icehouse-greenhouse fluctuations, and the evolution of calcifying invertebrates. However, the drivers of these long-term oscillations remain unresolved. Here, we develop an inverse model that couples seawater Mg concentration and Mg isotope composition variations. By exploiting the contrasting Mg isotopic fractionation associated with Mg-silicate formation and dolomitization, this model quantifies the major marine Mg sinks. Model results show that increases in seawater Mg/Ca during supercontinent assembly were explained by reduced rates of silicate alteration and dolomitization. In contrast, decreases in seawater Mg/Ca during periods of supercontinent stasis and early breakup were driven by intensified Mg-silicate formation and dolomitization. Variations in marine Mg-silicate and dolomite formation were further regulated by seafloor spreading, continental configuration, and climate throughout the supercontinent cycle. Together, our results identify the supercontinent cycle as a first-order regulator of Phanerozoic seawater Mg/Ca through its control on marine Mg-silicate and dolomite fluxes. An element-isotope coupled inverse model quantifies marine Mg removal rates via silicate and dolomite formation, linking Phanerozoic seawater Mg/Ca oscillations to supercontinent-driven tectonic and climatic changes.
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Pan Zhang
Mark A. Kendrick
Yigui Han
Nature Communications
The University of Queensland
University of Hong Kong
Northwest University
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Zhang et al. (Fri,) studied this question.
www.synapsesocial.com/papers/69bf86ecf665edcd009e9051 — DOI: https://doi.org/10.1038/s41467-026-70649-z