Organic carbon sequestered in soil aggregate contributes significantly to the carbon preservation on the earth’s surface. However, the turnover of soil aggregate in high latitudes and cold zones is strongly affected by the frequency of freeze–thaw cycles and may be disturbed by climate change. Although the effects of recurrent freeze–thaw cycles on the size, structure, and stability of soil aggregate have been well studied, the aggregation of individual mineral particles adsorbed by organic carbon and its mechanism are not yet conclusive. Here, we report that more than 97 wt% of the humic acid-coated goethite (goethite-HA) particles can aggregate into aggregates of different sizes and morphologies through one freeze–thaw cycle (freezing at −24 °C for 12 h and thawing at 4 °C for 12 h). Combining electron microscopy, infrared absorption spectroscopy and thermogravimetric analysis, we revealed that goethite-HA particles could strongly complex with each other after one freeze–thaw cycle. Compared with previous studies, our results showed that both electrostatic repulsion and steric hindrance (known to prevent aggregation) were overcome by the internal thrust of ice exclusion during freezing, then goethite-HA particles could be interconnected through the carboxyl-iron and hydrogen bonding to form aggregates. We believe that aggregates formed during the freeze–thaw cycles in soils rich in iron (hydr)oxides can serve as shelters for soil organic carbon and may reduce CO₂ emissions in these soils.

土壤团聚体中的有机碳对地球表面的碳保存有重要贡献。然而，高纬度和寒冷地区土壤团聚体的周转受冻融循环频率的强烈影响，并可能受到气候变化的干扰。尽管反复冻融循环对土壤团聚体的大小、结构和稳定性的影响已经得到很好的研究，但有机碳吸附的单个矿物颗粒的团聚及其机制尚未定论。在这里，我们报告说，超过 97 wt% 的腐植酸包覆的针铁矿 (goethite-HA) 颗粒可以通过一个冻融循环（在 -24 °C 12 小时，并在 4 °C 下解冻 12 小时）。结合电子显微镜、红外吸收光谱和热重分析，我们发现针铁矿-HA 颗粒在一次冻融循环后可以强烈地相互复合。与之前的研究相比，我们的结果表明，在冷冻过程中，冰排斥的内部推力克服了静电排斥和空间位阻（已知可防止聚集），然后针铁矿-HA 颗粒可以通过羧基-铁和氢键相互连接到形成聚合体。我们相信，在富含铁（氢）氧化物的土壤中，在冻融循环过程中形成的聚集体可以作为土壤有机碳的庇护所，并可能减少这些土壤中的CO ₂排放。