12 Apr 2023
 | 12 Apr 2023
Status: a revised version of this preprint is currently under review for the journal BG.

Ecosystem-specific patterns and drivers of global reactive iron mineral-associated organic carbon

Bo Zhao, Amin Dou, Zhiwei Zhang, Zhenyu Chen, Wenbo Sun, Yanli Feng, Xiaojuan Wang, and Qiang Wang

Abstract. Reactive iron (Fe) oxides are vital for long-term soil/sediment organic carbon (SOC) storage. However, the patterns and drivers of Fe‐associated organic carbon (Fe-OC) over global geographic scales under various ecosystem types remain largely controversial. Here, we provided for the first time a systematic assessment of the distribution patterns and determinants of Fe-OC content and its contribution (ƒFe-OC) by assembling a global dataset comprising 862 observations from 325 sites in distinct ecosystems. We found that Fe-OC content across global ecosystems ranged from 0 to 83.3 g/kg (ƒFe-OC ranged from 0 to 82.4 %), reflecting the high variability of the Fe-OC pool. Fe-OC contents varied with ecosystem type, being greater in wetlands with a high molar ratio of Fe-OC/dithionite-extractable Fe (Fed) compared with marine and continental ecosystems. Furthermore, ƒFe-OC in wetlands was significantly lower than that in other ecosystems due to rich OC. In contrast with climate variables and soil pH, the random forest modelling and multivariate analysis showed that the Fe-OC:Fed and SOC were the predominant predictors of Fe-OC content and ƒFe-OC in wetlands and continents, whereas Fed content was a primary driver in marine ecosystems. Based on upper estimates of global SOC storage in various ecosystem types, we further estimated that 83.84 ± 3.86 Pg, 172.45 ± 8.74 Pg, and 24.48 ± 0.87 Pg of SOC were preserved by association with Fe oxides in wetlands, continental and marine ecosystems, respectively. Taken together, our findings highlighted the importance of reactive Fe oxides in global SOC preservation, and their controlling factors were ecosystem-specific.

Bo Zhao et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-59', Anonymous Referee #1, 20 Jul 2023
    • AC1: 'Reply on RC1', Qiang Wang, 07 Sep 2023
  • RC2: 'Comment on bg-2023-59', Anonymous Referee #2, 05 Aug 2023
    • AC2: 'Reply on RC2', Qiang Wang, 07 Sep 2023

Bo Zhao et al.


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Short summary
This study provided a comprehensive analysis of the spatial variability and determinants of Fe-bound organic carbon (Fe-OC) among wetland, continental and marine ecosystems, and its governing factors globally. We illustrated that reactive Fe was not only an important sequestration mechanism for OC in continents, but also an effective “rusty sink” of OC preservation in wetland and marine ecosystems, i.e., a key factor for long-term OC storage in global ecosystems.