Dina Ebouel, Ferdinand J. , Bineli Betsi, Thierry , Eiche, Elisabeth , Norra, Stefan , Eze, Peter N.
2026-05-08 FRONTIERS IN ENVIRONMENTAL SCIENCE 2026 14(卷), null(期), (null页)
Pedogenic carbonates provide valuable archives of past environmental conditions through their elemental and isotopic compositions. This study integrates stable carbon (delta 13C) and oxygen (delta 18O) isotopes, obtained from carbonate features alongside manganese (Mn) and iron (Fe) concentrations in carbonate features and soil horizons across four pedosedimentary sections (SC01-SC04), to reconstruct vegetation dynamics, climatic stability, and local hydrological variability. Elemental concentrations of Mn and Fe are reported in molar percent (mol%). Soil profiles exhibit low Mn content (0.04%-0.11%), in contrast to higher Fe concentrations (2.68%-7.47%). Carbonate features are systematically depleted in Fe relative to their host matrices (0.42%-3.13%), while Mn is selectively enriched in several nodules, reaching up to 0.22% (Nd07, SC02). Stable isotope data reveal tightly clustered values within each section. delta 13C values range from -3.17 parts per thousand to -0.24 parts per thousand for nodules, which is consistent with a C4-dominated savannah ecosystem. However, deep-seated pseudomycelia exhibit a distinct delta 13C signature of -6.85 parts per thousand, interpreted as a biogenic signal from C3 shrub roots in a closed, riparian sub-surface environment rather than a vegetation shift. delta 18O values display a narrow range of -5.52 parts per thousand to -3.39 parts per thousand across all sections, indicating limited variability in meteoric water composition and evaporative conditions. High Mn/Fe ratios correlate with depleted delta 18O values (<=-5 parts per thousand), marking periods of increased freshwater input and seasonal waterlogging. Crucially, the decoupling of redox signals in some nodules, characterised by a combined high Mn/Fe ratio with delta 18O enrichment, highlights the occurrence of episodic fluvial pulses and overbank flooding superimposed on a generally semi-arid background. These findings demonstrate that while the regional macro-climate remained stable, local hydrology was highly dynamic, driven by high-frequency fluctuations in river-water influence.