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Purpose <p>To address gaps in coastal settings of the northern South China Sea (NSCS) that lack major estuarine input, we investigated three bays and two lagoons east of the Pearl River Estuary (PRE). Our objectives are to (i) characterize spatial distributions and inter-regional differences of rare earth elements (REE) in nearshore regions of the NSCS, (ii) identify provenance controls on REE composition, and (iii) explain main factors and mechanisms governing REE mobility.</p> Materials and methods <p>Surface sediments (<i>n</i> = 86) were collected during field campaigns in May 2023 and July 2024 using a grab sampler. Grain size was determined by laser diffraction, REE concentrations by inductively coupled plasma optical emission spectrometry (ICP-OES), and major element oxides by fused-bead wavelength-dispersive X-ray fluorescence spectrometry (WDXRF). Inter-regional differences in REE geochemistry were assessed using statistical tests and multivariate analysis. Hydrodynamic controls on REE distribution were assessed using grain size indicators. Geochemical indicators, including the sum of REE (ΣREE), europium anomaly (Eu/Eu*), cerium anomaly (Ce/Ce*), enrichment factor (EF), discrimination factor (DF), and the chemical index of alteration (CIA), were calculated to infer provenance and assess REE mobility.</p> Results and discussion <p>ΣREE ranges from 75 to 453 ppm (mean 240 ppm). Inter-regional contrasts are driven by lagoons, showing weaker fractionation and stronger positive Ce/Ce*. Regionally, ΣREE increases with grain size indicators, consistent with alongshore transport and hydrodynamic sorting, whereas within-regional ΣREE-grain size relationships are weak. REE patterns, Eu/Eu*, DF, EF, and major elements indicate a dominant granitoid source. CIA increases from west to east and correlates positively with ΣREE, indicating weathering related clay enrichment. ΣREE rises with (Fe₂O₃-T + MnO) / Al₂O₃ in bays but not in lagoons, whereas Ce/Ce* decreases with this index in both. These trends suggest suboxic pore water processes weaken positive Ce/Ce* and decouple ΣREE from Fe-Mn abundance in lagoons, while in bays Fe–Mn oxides and clays remain effective sorbents.</p> Conclusions <p>Provenance exerts the first-order control on REE distributions, while hydrodynamic sorting, chemical weathering, and early-diagenetic Fe-Mn oxides modulate the signal. These findings provide valuable geochemical insights for sediment tracing and environmental assessment.</p>

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Provenance and geochemical behavior of rare earth elements in bay and lagoon surface sediments of the Northern South China Sea

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Jiajun Cao,
  • Qunfang Ye,
  • Sizheng Li,
  • Yang Wang,
  • Wanhu Wang,
  • Jie Zhao,
  • Li Cao,
  • Chenwei Luo,
  • Yunzhong Zhang,
  • Cong Lin

摘要

Purpose

To address gaps in coastal settings of the northern South China Sea (NSCS) that lack major estuarine input, we investigated three bays and two lagoons east of the Pearl River Estuary (PRE). Our objectives are to (i) characterize spatial distributions and inter-regional differences of rare earth elements (REE) in nearshore regions of the NSCS, (ii) identify provenance controls on REE composition, and (iii) explain main factors and mechanisms governing REE mobility.

Materials and methods

Surface sediments (n = 86) were collected during field campaigns in May 2023 and July 2024 using a grab sampler. Grain size was determined by laser diffraction, REE concentrations by inductively coupled plasma optical emission spectrometry (ICP-OES), and major element oxides by fused-bead wavelength-dispersive X-ray fluorescence spectrometry (WDXRF). Inter-regional differences in REE geochemistry were assessed using statistical tests and multivariate analysis. Hydrodynamic controls on REE distribution were assessed using grain size indicators. Geochemical indicators, including the sum of REE (ΣREE), europium anomaly (Eu/Eu*), cerium anomaly (Ce/Ce*), enrichment factor (EF), discrimination factor (DF), and the chemical index of alteration (CIA), were calculated to infer provenance and assess REE mobility.

Results and discussion

ΣREE ranges from 75 to 453 ppm (mean 240 ppm). Inter-regional contrasts are driven by lagoons, showing weaker fractionation and stronger positive Ce/Ce*. Regionally, ΣREE increases with grain size indicators, consistent with alongshore transport and hydrodynamic sorting, whereas within-regional ΣREE-grain size relationships are weak. REE patterns, Eu/Eu*, DF, EF, and major elements indicate a dominant granitoid source. CIA increases from west to east and correlates positively with ΣREE, indicating weathering related clay enrichment. ΣREE rises with (Fe₂O₃-T + MnO) / Al₂O₃ in bays but not in lagoons, whereas Ce/Ce* decreases with this index in both. These trends suggest suboxic pore water processes weaken positive Ce/Ce* and decouple ΣREE from Fe-Mn abundance in lagoons, while in bays Fe–Mn oxides and clays remain effective sorbents.

Conclusions

Provenance exerts the first-order control on REE distributions, while hydrodynamic sorting, chemical weathering, and early-diagenetic Fe-Mn oxides modulate the signal. These findings provide valuable geochemical insights for sediment tracing and environmental assessment.