Geochemical indicators are emerging as important predictors of soil organic carbon (SOC) dynamics, but evidence concerning the role of calcium (Ca) is scarce. This study investigates the role of Ca prevalence in SOC accumulation by comparing otherwise similar sites with (CaCO₃-bearing) or without carbonates (CaCO₃-free). We measured the SOC content and indicators of organic matter quality (C stable isotope composition, expressed as δ¹³C values, and thermal stability) in bulk soil samples. We then used sequential sonication and density fractionation (DF) to separate two occluded pools from free and mineral-associated SOC. The SOC content, mass, and δ¹³C values were determined in all the fractions. X-ray photoelectron spectroscopy was used to investigate the surface chemistry of selected fractions. Our hypothesis was that occlusion would be more prevalent at the CaCO₃-bearing site due to the influence of Ca on aggregation, inhibiting oxidative transformation, and preserving lower δ¹³C values. Bulk SOC content was twice as high in the CaCO₃-bearing profiles, which also had lower bulk δ¹³C values, and more occluded SOC. Yet, contrary to our hypothesis, occlusion only accounted for a small proportion of total SOC (< 10%). Instead, it was the heavy fraction (HF), containing mineral-associated organic C, which accounted for the majority of total SOC and for the lower bulk δ¹³C values. Overall, an increased Ca prevalence was associated with a near-doubling of mineral-associated SOC content. Future investigations should now aim to isolate Ca-mediated complexation processes that increase organo-mineral association and preserve organic matter with lower δ¹³C values.

地球化学指标正在成为土壤有机碳 (SOC) 动态的重要预测指标，但有关钙 (Ca) 作用的证据却很少。本研究通过比较具有（含CaCO ₃）或不具有碳酸盐（不含CaCO ₃ ）的其他相似位点来研究Ca 流行在SOC 积累中的作用。我们测量了大块土壤样品中的 SOC 含量和有机质质量指标（C 稳定同位素组成，表示为δ ¹³ C 值和热稳定性）。然后，我们使用连续超声和密度分级 (DF) 将两个闭塞池与游离和矿物相关 SOC 分开。SOC 含量、质量和δ ¹³在所有级分中测定 C 值。X 射线光电子能谱用于研究选定馏分的表面化学。我们的假设是，由于 Ca 对聚集、抑制氧化转化和保持较低的δ ¹³ C 值的影响，在含有 CaCO ₃的位点，闭塞会更普遍。_{在含 CaCO 3}的剖面中，体积 SOC 含量是其两倍，其体积δ ¹³也较低C 值，多闭塞 SOC。然而，与我们的假设相反，遮挡仅占总 SOC 的一小部分（< 10%）。相反，它是含有矿物相关有机碳的重质馏分 (HF)，它占总 SOC 的大部分和较低的体积δ ¹³ C 值。总体而言，Ca 患病率的增加与矿物质相关的 SOC 含量几乎翻倍有关。未来的研究现在应该旨在分离 Ca 介导的络合过程，该过程增加有机矿物结合并保存具有较低δ ¹³ C 值的有机物。