the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Mar 2026
The International Soil Radiocarbon Database (ISRaD) version 2: Synthesis, data gaps, and future directions of soil radiocarbon data
Abstract. Soil radiocarbon (14C) measurements are crucial for understanding soil carbon cycling over timescales ranging from years to millennia. However, the global synthesis and comparison of radiocarbon data has been limited due to the variety of measurement methodologies and data formats. The International Soil Radiocarbon Database (ISRaD) is an open-access, community-driven archive designed to compile soil radiocarbon data and facilitate large-scale research on soil carbon dynamics. Here, we present ISRaD version 2 (v2), which has grown significantly since its initial release in 2020. It now contains data from 515 unique studies spanning 1,669 sites globally, with over 20,000 radiocarbon observations across multiple hierarchical levels, including bulk soil layers, soil fractions, laboratory incubations, interstitial carbon in soil pores, and in situ fluxes of CO2 and CH4. Major updates include expanded metadata structures to capture emerging measurement techniques and an improved soil fractionation template to better capture diverse methods. There has also been a substantial increase in data from underrepresented ecosystems, including urban and cultivated soils, as well as wetlands. Despite this growth, significant geographic and data-type gaps persist. Tropical and arid regions, soils deeper than 100 cm, and certain types of measurements, including incubation, interstitial, and flux, are severely undersampled. We discuss the scientific advances enabled by ISRaD v1 and the major updates to the database and data representation. We also explore future opportunities for ISRaD and the soil radiocarbon community. ISRaD v2 continues to serve as a living archive and dynamic platform for the soil radiocarbon research community. It supports synthesis efforts that are critical for predicting how soil carbon will respond to environmental and climatic changes.
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Status: final response (author comments only)
- RC1: 'Comment on essd-2025-753', Anonymous Referee #1, 07 Apr 2026
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RC2: 'Comment on essd-2025-753', Anonymous Referee #2, 13 Apr 2026
General comments
This manuscript presents a version 2 of the International Soil Radiocarbon Database (ISRaD), a major expansion of a community-driven, open-access resource compiling global soil radiocarbon data. The updated version substantially increases the number of studies, sites, and observations, while introducing improvements in database structure, metadata standardization, and accessibility tools. The paper also highlights scientific advances enabled by ISRaD v1 and outlines future research directions. The database has clear potential to support large-scale syntheses, model benchmarking, and improved understanding of soil carbon dynamics across spatial and temporal scales. The effort toward standardization and community engagement is particularly commendable.
However, the manuscript is descriptive and would benefit from a more critical and integrative perspective. Several important processes influencing radiocarbon data interpretation are insufficiently discussed and there is a lack of arguments of the choices made by authors:
- the role of radiocarbon-dead carbon (not only geogenic) inputs is insufficiently considered, despite their significance for data interpretation and recent work using the version 1,
- the consideration of parent material, land use change and forestry which may limit the robustness of global-scale interpretations,
- soil classification and the consideration of mangrove and salt marshes as soils,
- some methodologies used in soil sciences are missing and future direction could be refined.
- the absence of formal governance and long-term funding raises concerns regarding database sustainability and maintenance.
In summary, this is a valuable and timely contribution for soil science communities, but the manuscript would benefit from a more critical and comprehensive discussion of limitations and from clarification of several methodological and conceptual aspects. At this stage I recommend a major revision and these following major comments need to be developed in the new version of the ms.
Major comments
- Incomplete consideration of processes on radiocarbon interpretation
The manuscript does not sufficiently address key processes that can strongly influence soil radiocarbon signatures and interpretation. In particular, the role of radiocarbon-dead carbon, that encompass not only geogenic OC, is largely overlooked. Given the growing body of literature on these processes, their omission represents (only a sentence in the text) a significant conceptual gap that may lead to misinterpretation of compiled data. Indeed, recent works clearly show the importance of these dead-C contribution in soils, leading to a clear misunderstanding of soil C dynamics, with apparent aged SOC cause by this dilution of this dead-C. This ancient C contribution should be clearly considered as a new set of variables in this v2. In detail and throughout the ms:
L124: why there is no mention of radiocarbon dead-C contribution is the new version of ISRaD? since this contribution can reach 50% and more in deepsoils and a quarter in subsoils (see Copard et al., 2025)
L153f: again, why there is no mention of radiocarbon dead-C contribution… this contribution can reach 50% and more in deep soils? in fact, as stated recently by these works, not only C from sedimentary rocks but also from surficial deposits (e.g. loess) and C with low energy (Kleber's work). Authors should give more details about these origins that modify the C dynamics and some conclusions made by previous authors cited at the beginning of this section. Additionally, authors should consider the conclusions of these papers.
L181: section 4.1: why there is no mention of the radiocarbon-free SOC there ? it is now relatively easy to calculate the contribution of this SOC component. In the new version of ISRaD, I suggest to give this crucial info when it is possible.
L278f: see also the stock given in Copard et al. 2025 about ancient free14C stock in sub and deepsoil - suggest to add this important detail.
L605f: I insist on the fact that ISRaD should focus on parent material and used the previous recent results in this database, notably since these works used profils from ISRaD database.... - in addition, and in this sentence, this concerns not only climate datasets but also land use change trajectory which could greatly help the understanding of 14C distribution with depth.
- Absence of the major factors controlling soil C processes
Although the manuscript acknowledges data gaps (e.g., tropical regions, deep soils), important controlling factors are not fully considered compared to climate. A more comprehensive discussion of biases - including geological, land-use change is necessary.
L147: numerous studies already published state that land use change, and forestry modify SOC persistence, I think authors should give some words there.
L440f: why such a database cannot unlock the question of the best-practice? - also why talking about climate feedback only, why not land use change and/or even impact of the parent material feedbacks?
L535-section 7.2: the nature of parent material and if possible, the OC content of this material should be also a key variable.
- Mangroves and salt marshes and soils classification
L445: manyresearchers belong to the soil and geology communities consider that mangrove and salt marsh are not soils but consist in sediment deposits only, why are the arguments used by authors to consider that as soils?
L175-177, L243, figure 2: what the authors mean? soil classification (group, class)? Why not replace by soil group and why authors use this soil classification rather than an international one (WRB).
L351f: before in the text, it was order, now type, I suggest to use class or group, the soil classification used needs to be added and argued (the best would be to use an international classification, as WRB), nb: usda is only cited in the figure caption;
- Integration of recent methodological advances, methodological recommendation and future direction
The manuscript does not fully incorporate recent approaches relevant to soil carbon characterization as Rock-Eval 6 pyrolysis. Including such approaches would improve the completeness and forward-looking perspective of the database.
L198: authors should also consider the numerous works using Rock-Eval method applied to SOC.
L192: I didn't check on the first version, but and prior isolation fractions, methods (because there are different methods, from acids concentration, fumigation etc) to isolate Corg could be also described and authors could provide recommendation (best-practice) too in order to avoid a loss of light SOC fractions during these treatments.
L492: since the understanding of vertical C dynamics is still debated with the C exchanges between atmosphere, biosphere, pedosphere and lithosphere reservoirs - effort and lateral C fluxes within the LOAC are a bit premature - the priority for ISRaD should be to well understand and better consider the vertical ones; especially the recent works about the incorporation of parent material in soils which disturb the SOC age and dynamics.
L592f: put e.g.; the authors should refer to the fundamental (precursor) papers dealing with this point (notably Meybeck, Raymond, Bianchi works etc).
L595 : as said previously, ISRaD should focus on vertical fluxes first, what happens in river system is by far completely different than soil processes, however, since river system are, most of time, anthropized, soil can develop along these systems (why not give a word on these unknown young soils)? understanding the 14C data in river system is by far different since rivers act as a conduit grouping all the eroded sources coming from the catchments (different soils, rocks, surficial formations, combustion residues, human-derived OM (wasted material), and NPP from river) - other suggestion is to focus on plastics in soils...All in all, there is a lot of to do before an adventure in rivers system.
L611f: focus on river won't help about the ability to predict soil C response face to env. changes.
- Sustainability and governance concerns
The manuscript acknowledges that ISRaD operates without formal governance or stable funding. While community-driven approaches are valuable, the long-term sustainability of the database remains uncertain. This issue should be more explicitly discussed, including potential strategies for ensuring continuity and data quality.
Minor comments
L46: precise if organic, inorganic or both.
L50 - 53: need reference(s) at the end of these sentences.
L50: a bit evasive, do the authors meant soil carbon dynamics?
L87: acronym no defined (GLOSIS).
L120: see major comment 1 ; not only, but also origin, as geogenic etc, see comments line 155
L124: give 1 or 2 examples about these new concepts.
L177 and 184-185: sentences is a bit useless since these ideas were already given many times before.
L218: what is this information you want to increase?
L253: not agree, there are azonal soils which escape from this rule.
Figure 2: this is an interesting figure; however geology is missing at the profile scales, it could be interesting to know if all the parent materials (geology, surficial formations) on which the soils are developing were considered in this database.
L275f: rephrase with topsoil, I don't understand, subsoil concerns 30-100cm, here there is a mix between sub and deepsoils, could you clarify?
Figure 3: the koeppen-Geiger zone is hard to follow in 3a and 3c – also I suggest to label b by c and vice versa.
L392: in this subsection 5, there are some statements about future research direction, I suggest to put all these in the appropriate section (7) or delete these sentences if it is also given in this section 7 to avoid redundancy.
L394f: could you explain better what do you mean there, why this comparison is important for you and what is upland for you? - this sentence is a bit unclear and disconnected from the other...alternatively, suggest to delete.
L402: what do you mean by macrofossils, come from parent material?, old macrorests? Not clear since it is not defined.
Figure 5: in this figure, FA and HA quantification is an old soil science concept no longer used actually - I am not sure if these distinctions still remain suitable, the best is to group in HS. Or at least, authors should explain their choice to keep this old terminology.
L610: modelling of what?
Citation: https://doi.org/10.5194/essd-2025-753-RC2
Data sets
International Soil Radiocarbon Database (ISRaD) version 2 J. Beem-Miller et al. https://zenodo.org/records/17860507
Model code and software
International Soil Radiocarbon Database (ISRaD) version 2 data analysis S. von Fromm et al. https://zenodo.org/records/17859527
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This is excellent piece of work. The text accompanying it should be a first port of call for anyone who wants to seek direction for novel work using 14C radiocarbon.
As a soil scientist I find the delta unit uninformative, a kind of disconnect, now we have a double delta delta 14C per mil. I would be happy to just see somewhere in the text what -100, -500 and -1000 means in terms of years (approxiately). Also there are no measurements it seems below -1000 so you can stop the scale there I guess. The lack of compound specific 14C dates seems worrying and still only lipids suggest the field is not moving forward or too difficult or complex ? I wonder why there no recorded dates on compound specific PLFAs in the database.