Abstract. Association of organic carbon (OC) with reactive iron (Fe_R) represents an important mechanism by which OC is protected against remineralisation in soils and marine sediments. Recent studies indicate that the molecular structure of organic compounds and/or the identity of associated Fe_R phases exerts a control on the ability of an OC-Fe_R complex to be extracted by the citrate-bicarbonate-dithionite (CBD) method. While many variations of this method exist in the literature, these are often uncalibrated to each other, rendering comparisons of OC-Fe_R values extracted by different method iterations impossible. Here, we created a synthetic ferrihdyrite sample coprecipitated with simple organic structures and subjected these to modifications of the most common CBD method. Method parameters (reagent concentration, time of the extraction and sample preparation methods) were altered and Fe_R recovery measured to determine which (if any) modifications resulted in the greatest release of Fe_R from the sediment sample. We provide an assessment of the reducing capacity of Na dithionite in the CBD method and find that the concentration of dithionite deployed can limit OC-Fe_R extractability for sediments with a high Fe_R content. Additionally, we show that extending the length of any CBD extraction offers no benefit in removing Fe_R. Finally, we demonstrate that for synthetic OC-Fe_R samples, the almost universal technique of freeze drying samples can significantly reduce OC-Fe_R extractability and we offer insight into how this may translate to environmental samples using Arctic Ocean sediments. These results provide a valuable perspective on how the efficiency of this extraction could be improved to provide a more accurate assessment of sediment OC-Fe_R content. Accurate determinations of OC-Fe_R in sediments and soils represents an important step in improving our understanding of, and ability to model, the global carbon cycle.

中文翻译：

---

技术说明：揭示方法变化对铁结合有机碳可萃取性的影响

摘要。有机碳（OC）与反应性铁（Fe _R）的结合代表了一种重要的机制，可以保护OC防止土壤和海洋沉积物中的再矿化。最近的研究表明，有机化合物的分子结构和/或相关的Fe _R相的身份控制着OC-Fe _R络合物通过柠檬酸盐-碳酸氢盐-连二亚硫酸盐（CBD）方法提取的能力。尽管文献中存在该方法的许多变体，但这些变体往往彼此未经校准，从而比较了OC-Fe _R通过不同方法迭代提取的值是不可能的。在这里，我们创建了与简单的有机结构共沉淀的合成铁锂铁矿样品，并对这些样品进行了最常见的CBD方法的修改。更改方法参数（试剂浓度，提取时间和样品制备方法），并测量Fe _R的回收率，以确定哪些（如果有）改性导致从沉积物样品中释放出最大的Fe _R。我们提供的Na连二亚硫酸盐的CBD法的还原能力的评估，并发现部署连二亚硫酸盐的浓度可以限制OC-铁_{- [R}萃取对于具有高铁沉积物_ř内容。此外，我们表明，延长任何CBD提取的长度对去除Fe _R都没有好处。最后，我们证明了对于合成OC-Fe _R样品，冷冻干燥样品的几乎通用技术会大大降低OC-Fe _R的可萃取性，并且我们将深入了解如何利用北冰洋沉积物将其转化为环境样品。这些结果为如何提高萃取效率提供了有价值的观点，以提供对沉积物OC-Fe _R含量的更准确评估。准确测定OC-Fe _R 沉积物和土壤中的碳黑代表了增进我们对全球碳循环的理解和建模能力的重要一步。