the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Apr 2026
Experimental evidence that organo-mineral interactions regulate dissolved organic matter composition and lability across permafrost landscapes of northwestern Canada
Abstract. Increased land-water connectivity of northern landscapes driven by permafrost thaw is shifting the bioavailability of dissolved organic matter (DOM) in surface waters, with implications for northern food webs and regional and global carbon balances. However, sorption of DOM to previously frozen sediments has received little attention as a mechanism of regulating the bioavailability of organic matter in thaw-affected freshwater ecosystems. Using batch sorption experiments, we assessed sorption potential, water-extractable dissolved organic carbon (DOC) concentration, and the impact of sorption on DOM composition of six different permafrost sediment types common throughout northwestern Canada, reflecting variation in geologic and permafrost histories. A principal component analysis revealed that sediment biogeochemical characteristics reflected geologic origin, and past thaw increased within-type variation. Sorption was positively correlated with organo-reactive forms of Al and Fe and negatively correlated with sediment pH. Proportion of bulk sediment organic carbon released as water extractable DOC ranged from 1.0 % to 62.0 %, with yedoma sediments from the Klondike region releasing substantially more than sediments from other regions. Preferential sorption of larger, humic-like compounds and displacement of mineral-bound small, aliphatic molecules enriched the DOM pool in labile compounds. Bio-incubations verified that exposure to sediments increased rates of biodegradation, corresponding with shifts in DOM composition and increased nutrient concentrations. Our experiments demonstrate that organo-mineral interactions have the potential to decrease DOC concentrations while increasing DOM bioavailability following exposure to permafrost-origin sediments, but that the strength of this response varies with sediment characteristics that are reflective of landscape history.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-1844', Anonymous Referee #1, 12 May 2026
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RC2: 'Comment on egusphere-2026-1844', Anonymous Referee #2, 26 May 2026
The fate of carbon released from thawing permafrost landscapes is a subject of great concern with potential severe climate impacts, and knowledge on factors determining degradation of organic matter in these landscapes is still incomplete. This study investigates interaction between minerals and dissolved organic matter in a set of different sediment samples collected in geologically different regions of the permafrost zone of northern Canada. An impressive range of experiments and geochemical analyses were conducted. The manuscript is overall very well-written, nicely motivated and explained, and all results are clearly documented.
The analyses and experiments performed are extenisive, but nonetheless might fall short of providing sufficient evidence to address the objectives of the study. The large range of geochemical parameters obtained for the large number of samples exhibited broad variability not only between sampling sites but also between samples from the same unit. This is illustrated in Figure S4, where only few panels show significant differences between sample sets (in particular the clay content, here represented by grain-size distribution, not mineral analysis). Within sample set variability appears to be equally large, making it difficult to derive meaningful systematics. On the other hand, some sediment properties with strong impacts on sorption like mineral surface area or quantitative mineralogy are not reported for the sample set. This raises the question whether differences found between the sample sets can be attributed to the differences between the landscapes and are not due to random variability between individual sites. Related to this is the observation that none of the relationships found between sediment geochemistry and sorption coefficient appear to be particularly strong (Figure 6).
Sorption experiments were conducted on freeze dried, disaggregated and homogenized sediments. These were agitated with a DOM solution in a dilution series and the decrease in DOC concentration was used to determine sorption coefficients. I wonder how this can be unambiguously ascribed to sorption alone. Can biodegradation during these experiments be excluded? Were sediments sterilized before the sorption experiments? Initial biodegradation would be consistent with the observed enrichment of labile compounds in the DOM solution (or the loss of humic-like, aromatic compounds). Even in frozen till or Yedoma sediments, resting microbial communities can be readily re-activated when thawed and exposed to water.
Rather sophisticated statistical analyses were performed. The typical reader of a biogeochemical journal might appreciate more details on the methods.
In summary, the manuscript presents an ambitious study and an impressive data set. The conclusions drawn from the observations, however, should be formulated more carefully and the rather large unexplained variability observed in the data set should be acknowledged.
Specific comments:
Line 290-300: More details are needed to explain the PARAFAC analysis, including the number of dimensions. Later, in the results chapter, M, A and C peaks are described, which are not properly introduced.
Chapter 3.1: The way the mineral content is presented is a bit confusing, and I would encourage presentation of minerals in order of decreasing relative abundance. From Figure S3 it is evident that the dominant minerals (as expected) are the silicates (quartz, feldspar, muscovite and clay minerals), which occur in almost all samples. Some samples (dependent on bedrock geology, I presume) contain carbonates and sulfates and sulfites (the latter likely only in anoxic portions of the profiles). Anatase is likely only present in trace amounts, but is presented as one of the first minerals in the list. Overall, mineral occurrence will be tightly linked to bedrock, and may also be related to grain size (with coarser grain size lacking clays). It would be helpful to provide relative abundances of mineral classes, not only report occurrence. Different mineral classes have very different sorption capacities, and their abundance within a sample will determine the effectiveness of sorption. This is particularly true for clay minerals, which have charged surfaces.
Line 335: Be careful when ascribing causal relationships in a PCA – co-variation does not explain which is the driver and which is the cause. I would expect that high concentrations of Al (high in clay minerals with a high surface charge) and Fe and Mn (in oxides) are the causes for high SOC content, not the result, as those minerals are active sites of OC adsorption.
Chapter 3.2: Sorption coefficients seem to scale inversely with OC content. This is not mentioned.
Chapter 3.3: None of the relationships displayed in Figure 6 seem to be particularly strong, suggesting that they may not be the primary control on sorption. Did you obtain mineral surface area measurements for the samples? This is likely a strong control on the sorption of OC.
Chapter 3.5: Can you provide more details on the “common microbial pool”? Where was it derived from?
Chapter 4.3: Can a mechanism be proposed by which organo-mineral interactions may promote biodegradation? Is it perhaps by concentrating OM on mineral surfaces through sorption, while at the same time providing a hot-spot for microbial colonization increasing availability of OM?
Details, typos:
Line 119: what kind of sulfides are contained in the till?
Line 136: shouldn’t this be “siliciclastic“?
Citation: https://doi.org/10.5194/egusphere-2026-1844-RC2
Data sets
Biogeochemical characteristics and organic carbon sorption properties of permafrost-origin sediments from northwestern Canada Gabrielle K. F. Hatten et al. https://doi.org/10.5683/SP3/NFOPAF
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General comments:
Thawing of permafrost is one of the most obvious and severe effects of global change and has the potential to fundamentally change ecosystems at higher latitudes and elevations. The release, subsequent transport and biological metabolization of soluble organic carbon entrapped in permafrost layers has drawn substantial scientific interest over the last decades but knowledge on controlling factors is still far from completeness. The present study investigates the role sediment mineral properties in the regulation of amounts, composition, and microbial consumption of soluble/dissolved organic matter at landscape scale.
The study addressed sorptive interactions between sediments and soluble/dissolved organic matter across large gradients in sediment mineral properties. Extensive sorption experiments were combined with incubation experiments and spectroscopic (absorption/fluorescence) analyses. The resulting comprehensive dataset was carefully evaluated and revealed that the fractionation during sorption and desorption control composition and, thus, the bioavailability of dissolved organic matter. Sorptive interactions with minerals in sediments seemingly are important in regulating the fate and ecological impacts of soluble organic matter within permafrost landscapes.
The entire manuscript is well structured. It starts with a focused, still extensive and comprehensive summary of the scientific background, a detailed presentation of the environmental settings in the study area that, and, based on that, a straight-forward justification of the presented study. The Method section is extremely detailed, providing all necessary information to fully understand the scientific approach. The presentation of results, in the manuscript as well as in the supplement, is very neat, comprehensive, and logic. The discussion, as the rest of the manuscript, is also well-structured, easy to follow, with the arguments well presented (I like much the artwork and the figures), and the conclusions/implications well supported/justified by data and literature evidence. I enjoyed the reading very much, likely because it is in line with my own way of thinking. However, other people might consider some of the detailed reflections as too lengthy (see comments below).
Overall, I think the manuscript presents a great contribution to the field of carbon research in permafrost regions, with novel and important findings on organic matter processing at landscape scale. Also, I think it fits very well the focus and style of the journal and therefore recommend acceptance for publication after minor revision.
Specific comments