the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Sep 2026
Ideas and perspectives: the biogeochemical role of taliks
Abstract. Taliks, unfrozen ground within permafrost, sustain year-round biogeochemical processes, mobilizing carbon, nutrients, and contaminants through lateral and open taliks, while closed and isolated taliks confine reactions locally. Yet, while talik physical and thermal dynamics have been increasingly documented, their biogeochemical processes remain understudied, particularly in winter. In this manuscript, we argue that taliks represent a critical and overlooked driver of Arctic and sub-Arctic biogeochemical processes. We put forward three testable hypotheses to advance the study of talik biogeochemical functioning and we propose a related road map: year-round sampling, standardized protocols, pan-Arctic talik mapping, and community-building.
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Status: open (until 10 Nov 2026)
- RC1: 'Comment on egusphere-2026-5453', Anonymous Referee #1, 12 Oct 2026 reply
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RC2: 'Comment on egusphere-2026-5453', Anonymous Referee #2, 19 Oct 2026
reply
I agree with the report of Referee 1, in particular on the overstated novelty claim, the weakness of the three “testable hypotheses”, the contradiction between residence-time arguments, and the quality of Figs. 1 and 4.
I also share the view that the sub-aerial focus, the talik-type/function framework and the pan-Arctic inventory idea are the manuscript’s most useful elements. I will not repeat these points. The topic is timely and relevant to the permafrost carbon feedback. The hydrological-connectivity framing is useful. The winter-sampling gap is real, and the roadmap is constructive. A perspective paper that organizes the field around testable questions would be welcome.
My additional concerns are complementary:
1. The manuscript never discusses the zero-curtain period or unfrozen water in frozen soil, which sustain winter microbial activity at sites without taliks. Without this, the added value of a talik cannot be defined.
2. The manuscript is not soil-centred. Soil properties (texture, pH, mineralogy, reactive Fe/Al phases, organic versus mineral horizons, ice content) are largely absent. This matters for a perspective claiming a “biogeochemical role”. Evidence from sub-lake, peatland, boreal hillslope and Yedoma taliks is also merged as if equivalent.
3. Several citations do not support the sentences they accompany, and some quantitative statements lack scenario or model context (see below).
4. The roadmap lacks methodological depth, omits existing initiatives such as GTN-P, and does not address ethics, geographic bias, or self-citation balance.
Specific comments
Introduction and Fig. 1. “Seasonally frozen layer”, “active layer” and “seasonally frozen ground” are used interchangeably. Introduce and define “active layer” (the seasonally thawed layer) and use the terms consistently.
L19–25 and Fig. 1. Five classification axes are introduced, but only connectivity is used afterward. “Open” is a position-based class (a through talik) but is listed beside connectivity categories. Clarify the typology, ideally in a table (definition, thermal state, expected hydrology and expected biogeochemistry for each class).
L27–31. The sub-aerial growth rate (~0.13–0.25 m yr⁻¹) is compared with sub-lake talik rates over centuries. These involve different mechanisms, timescales and metrics. Explain how the sub-aerial rate was derived.
L67–70. Closed taliks are described as surrounded by frozen ground on all sides. For supra-permafrost closed taliks, closure may be partial or seasonal, and connectivity can differ strongly between thaw and freeze seasons. Maybe add seasonality to the typology?
L72–76. No quantification of winter hydraulic gradients, flow path lengths or travel times is offered. How much solute flux can be transferred laterally under a frozen cap with little recharge?
L90–92. The statement that closed taliks promote reactions through longer contact time cites Ma et al. 2019, a DOC review that does not address taliks. Cryoconcentration of solutes when a closed talik refreezes (brine exclusion, increased ionic strength, pH shifts) is not considered.
L96–98. “Nutrients” should be specified (N, P, base cations?).
L98–100. Temperatures just above 0 °C may only weakly stimulate microbial activity in absolute terms. Provide measured talik temperatures and temperature sensitivities if available.
L103–105. Mineral-bound OC can also be released by reductive dissolution of Fe(III) phases in anoxic taliks (Patzner et al. 2022; Voggenreiter et al. 2025). This tension between protection and release is central to the argument but only glossed.
L123–127. Provide quantitative hydraulic conductivity ranges by texture, and consider that partially frozen, ice-impeded soils may behave like closed taliks.
L133–134. Schwab et al. 2020 concerns aging of DOC in large Arctic rivers and does not implicate taliks specifically.
L134–137. The logic that released mineral elements destabilize mineral-bound DOC via photo-oxidation is unclear. Photo-oxidation can occur only after export to sunlit surface water, not in winter subsurface taliks. Lawrence & Slater 2008 is a land-surface-model paper and does not support a statement about DOC mineralization by lateral taliks. Can you clarify this statement?
L144–155. The contaminant section mixes atmospheric deposition, industrial pollution and infrastructure-induced thaw, and mostly describes transport rather than biogeochemical processing. Mercury (the principal legacy contaminant in permafrost) and persistent organic pollutants are missing. Contaminant speciation, sorption and redox control are not discussed.
L222–227 and Fig. 3. The roadmap lacks sequencing, feasibility, costs and success metrics. The mapping of hypotheses to priorities in Fig. 3 (H3→1, H2→2, H1→3, H2→4) is not convincingly justified.
L265–268. Section 5.2 is too short to count as a roadmap item. List minimum analytes and methods (filtration size, preservation, DOC, ions, Fe(II)/Fe(III), isotopes) and ancillary soil data (texture, pH, SOC, reactive Fe/Al, ice content), and propose reference materials and interlaboratory comparisons.
L269–270. Si isotopes are described as “known to be sensitive to freeze–thaw cycling”. They also respond to weathering, secondary phases and plant uptake, so they are not talik-specific.
L284–295. I agree the inventory is the strongest proposal, but it needs more detail. Existing sensors are not randomly sited and are mostly shallow, so specify a minimum depth, sensor accuracy and unfrozen water content. A two-year minimum conflicts with the emphasis on interannual to decadal intermittency (H1).
L289–299. The Global Terrestrial Network for Permafrost (GTN-P) and other existing ground temperature databases are not mentioned, though they would be the natural starting point. Remote sensing and airborne geophysics could support spatial extrapolation?
L300–315. Broaden geographic scope (Siberia, Tibetan Plateau, Fennoscandia, mountain permafrost)? and address ethics: co-production with Indigenous and local communities, land access and data sovereignty.
Missing topics/ideas suggestion:
- Snow. Snow insulation is a primary control on winter ground temperature and on supra-permafrost talik occurrence, yet it is not discussed.
- Weathering and inorganic carbon. DIC, alkalinity and base cation export are absent.
- Ground ice and thermokarst. These control saturation and redox and should be linked to talik types.
- Icings (aufeis) and springs. They are direct manifestations of winter groundwater discharge through taliks and potential monitoring targets.Citation: https://doi.org/10.5194/egusphere-2026-5453-RC2 -
RC3: 'Comment on egusphere-2026-5453', Élise Devoie, 19 Oct 2026
reply
The article “Ideas and perspectives: the biogeochemical role of taliks” is a concise and well-written overview of what we don’t know about talik processes, especially over winter. The article is a call to action to investigate (1) the transient nature, (2) the hydrologic controls and (3) the coordinated measurement of taliks. While the article does not present new findings, it does set forth objectives for future studies.
One main consideration that was discussed only to a limited extent could be heterogeneity, and the differences in thaw patterns. Primarily sub-aerial taliks were discussed, but contrasting these with sub-aqueous taliks, as well as those formed laterally or vertically from below might create anoxic talk environments with the potential for autotrophy.
There are diverse microbiological groups that may lead to carbon export, but may also lead to carbon capture, some nuance may be helpful in that conversation. As an article calling for a biogeochemical investigation, the emphasis is on physical processes and the biogeochemistry is discussed less than expected. I would suggest including recent work such as https://doi.org/10.3389/fmicb.2021.757812, and/or clarifying the title/purpose.
Finally, this discussion has a focus on taliks, which do not contain pore ice, though they may be cryptic. What about warming permafrost where SFCCs may drive significant unfrozen water content where similar processes may also be taking place?
In addition, there are several minor revisions I would suggest:
Resolution of Fig 1 is lacking. The caption repeats content from the text, which is likely unnecessary.
L 96 :”liquid water activates microorganisms and also unlocks considerable amounts of carbon and nutrients that can be used for their accelerated growth” - what do you mean by “unlocks”, makes bioavailable through redox conditions? Please revise language.
L 100: It is not clear if “ (Δ14C-DOC from ‐180 to -573‰; Kelley et al., 2026)” is evidence of microbial decomposition of DOC in a talk - could you please add context?
L 106: “occur alongside a broader pattern of winter carbon emissions” sourced from …
L 130 Is it surface water flow the mobilizes AL nutrients, or rather shallow groundwater flow?
L 142 … remains largely unconsidered? unconstrained seems like an odd word choice here
L145 the long-range transport of contaminants is hinted at but should be specifically stated
Section 3.2 does not note the many contamination sources (sumps, landfills, …) which rely on permafrost to maintain a hydraulic barrier. In these cases the formation and expansion of talks enables the mobilization of these contaminants.
Figure 3 caption - the “modelling effort” is not clearly defined above. The link between these (4) objectives, and hypotheses (especially H2) is a bit tenuous. I’m not sure they need to be linked? Might make it a bit more straightforward…
L 318: suggest to revise to “… peer through that window”
Citation: https://doi.org/10.5194/egusphere-2026-5453-RC3
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- 1
Review of „Ideas and perspectives: the biogeochemical role of taliks”
This topic is timely and fits very well to Biogeosciences Ideas and perspectives category. However, at this moment the manuscript is more a succinct review calling to actions, but no an ideas manuscript. According the main view of the manuscript, the geophysical aspects are very solid, but the biogeochemistry is the weaker part (in my point of view), which is not a problem in fact, but the title calls the “the biogeochemical role of taliks”. I would expect more about the last part in the manuscript. Below I leave some comments that may improve the manuscript.
There are some parts in the manuscript that I find overstated the novelty of the manuscript, for example in Lines 34-37 indicate the biogeochemical role of taliks “has not yet been investigated”, but own references several manuscripts in which contradicts this statement, e.g., Heslop et al. 2015, Meisel et al. 2021, Waler Anthony et al. 2024, Bergamn et al. 2025, Parazoo et al. 2018. Even, beyond your references, thermokarst lakes (Sub-aqueos talik, Fig. 1) carbon dynamics has been studied for several decades. But, it does mean that it is a new contribution, good things in the manuscript are the focus of sub-aerial, supra-permafrots taliks in winter, the neat way to compare isolated taliks as confined reactors versus open taliks, and the CALM-like pan-Arctic talik inventory built proposal. So please town down it and also make a deeper literature review of the topic and avoid to claiming a blank field.
The most useful as perspective manuscript in the clear conceptual link between talik type and function (2.1), together with the winter focus, and the clear gap about the CO2 loss during the cold seasons, and the contaminant and infrastructure is something that demands to explore in a scientific way. Additional, the inventory proposal in section 5.3 is the strongest, concrete, cheap, and realistic actionable part.
However, the to my point of view the main flaws are the “testable hypotheses”, which are not clear hypotheses (section 4, only one in part). Because: (i) H1 is already observed in a manuscript of one of the authors of this manuscript (Farquharson et al. 2022). But it is more a sampling limitation, not a biogeochemical hypothesis, (ii) H2 is trivially true, (iii) H3 it is the closest to a hypothesis. The reason to this opinion is that testable hypothesis would specify with measurable predictions, for example, the D14C from DOC and DIC of winter stream becomes older as lateral talik connectivity increase.
Another important topic that you should correct is the idea that production is confounding as emission to the atmosphere (section 2.2). In supra-permafrost talik, however, the seasonally frozen layer is acting as barrier, so the CH4 ad CO2 can be stored and some released in spring ice-out, other dissolved part lateral transported in streams and CH4 can be used as substrate by anaerobic or aerobic methane oxidation, which is never mentioned and this manuscript, which the main talk is about biogeochemical processes. The entire manuscript never talk about the transport pathway of CH4 and CO2 to the atmosphere, yet, it is necessary to determines whether talik biophysical processes contributes to the atmosphere in winter or only shift the time of these gas emissions. I recommend then, to separate explicit the production, storage, and atmospheric emission explicitly (even I would introduce N2O in the talk, as missed greenhouse gas in main studies).
About the “hotspot”, this argument does not have a quantitative foundation, I know it is incredible high in such low temperatures, but argue that taliks has “disproportionately high reaction rates” is not completely true (compared to tropic ecosystems is minimal). Taliks biochemistry is working close to zero degrees Celcius (very low for optimal microbial activity), so the importance is more related to the duration and the volume of the talik, but not rates. Perhaps you can compare for example to compare the talik volume per rate per length of the cold season, to active layers of annual microbial mineralization.
Finally, there is a problem with the resident time between closed and open taliks. While you state that close taliks promote reactions by longer period times (section 2.2), the section 3 says that lateral taliks enhance mineralization. Both of course can be true, but, you need to argue that closed systems have longer residence time and my become limited in substrate and electron acceptors. Open systems have short residence times but resupply substrate. You may need a statistical or model to formulate reaction timescales vs. transport timescales.
Other comments:
• The sub-aqueous taliks are missing. Beneath thermokarst lakes and rivers are the most documented talik biogeochemistry. It cannot be possible that a manuscript about this is not talking about it. Sub-aerial taliks are completely missing.
• Sorry but, Rhizons are not adequate to dissolved greenhouse gases or other redox sensitive compounds (Fig. 4), perhaps you can include other methods for it, or acknowledge this problem. Because, in line 245 you state that those gases are priority measurements.
• You may need to improve Figures 1 and 4, they are not kinder than the other Figures.