Sedimentary insights into organic matter alteration in Arctic Alaska&rsquo;s saline permafrost

Seemann, Fabian; Zech, Michael; Jenrich, Maren; Grosse, Guido; Jones, Benjamin M.; Treat, Claire; Schirrmeister, Lutz; Liebner, Susanne; Strauss, Jens

doi:10.5194/egusphere-2025-3727

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https://doi.org/10.5194/egusphere-2025-3727

Preprints

20 Aug 2025

| 20 Aug 2025

Sedimentary insights into organic matter alteration in Arctic Alaska’s saline permafrost

Fabian Seemann, Michael Zech, Maren Jenrich, Guido Grosse, Benjamin M. Jones, Claire Treat, Lutz Schirrmeister, Susanne Liebner, and Jens Strauss

Abstract. In Arctic coastal lowland regions such as northernmost Alaska, thermokarst landscapes are often underlain by saline marine deposits, a factor frequently overlooked when assessing permafrost thaw risks. To evaluate the influence of thaw and salinity on organic matter degradation and landscape dynamics, we analyzed six sediment cores from representative landforms near Utqiaġvik (Barrow Peninsula, Alaska) using a multiproxy, carbon-focused approach, with emphasis on n-alkane biomarkers. Undisturbed tundra uplands contained well-preserved, organic-rich Holocene sediments (~140 cm thick) overlying brackish Lateglacial deposits, indicating the presence of saline permafrost. Thermokarst lake subsidence into these substrates led to enhanced carbon degradation, as reflected by lower n-alkane carbon preference index (CPI) values. While West Twin Lake talik sediments exhibited brackish porewater, East Twin Lake sediments were characterized by predominantly saline porewater, indicating the presence of a cryopeg driven by salt-induced thaw-point depression. Lagoonal environments, receiving both terrestrial and lacustrine inputs, accumulate sediments under unfrozen hypersaline conditions, presenting a high potential for organic carbon degradation. Carbon proxy signatures statistically distinguish perennially frozen uplands, unfrozen lakes, refrozen drained lake basins, and lagoonal settings. Our results demonstrate that salt-bearing deposits, as found in all investigated sites, are vulnerable to active layer deepening, talik and cryopeg formation, and shoreline erosion. These processes accelerate organic matter degradation and alter landscape trajectories. Our study underscores the need to better understand the role of saline permafrost in Arctic coastal lowlands and its broader implications under ongoing climate change.

Received: 31 Jul 2025 – Discussion started: 20 Aug 2025

Competing interests: At least one of the (co-)authors is a member of the editorial board of Biogeosciences. The peer-review process was guided by an independent editor, and the authors also have no other competing interests to declare.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

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Journal article(s) based on this preprint

03 Jun 2026

Sedimentary insights into organic matter alteration in Arctic Alaska's saline permafrost

Fabian Seemann, Michael Zech, Maren Jenrich, Guido Grosse, Benjamin M. Jones, Claire Treat, Lutz Schirrmeister, Susanne Liebner, and Jens Strauss

Biogeosciences, 23, 3675–3695, https://doi.org/10.5194/bg-23-3675-2026,https://doi.org/10.5194/bg-23-3675-2026, 2026

Short summary

Fabian Seemann, Michael Zech, Maren Jenrich, Guido Grosse, Benjamin M. Jones, Claire Treat, Lutz Schirrmeister, Susanne Liebner, and Jens Strauss

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-3727', Anonymous Referee #1, 12 Dec 2025

This study provides valuable insights into how organic matter is altered within saline permafrost sediments in Arctic Alaska—an important contribution to understanding carbon cycling and permafrost–climate feedbacks. While the dataset is strong, the manuscript would benefit from clearer explanations of the sampling design, the rationale for data grouping (Table 3), and the broader significance of saline permafrost thaw in a warming Arctic. Improved figure presentation (Figure 1) and an expanded discussion of methane and carbon dynamics in the broader climate context would further enhance the clarity and impact of the study.

Citation: https://doi.org/10.5194/egusphere-2025-3727-RC1
- AC1: 'Reply on RC1', Fabian Seemann, 08 Jan 2026
  
  Dear reviewer,
  Thank you very much for your very constructive and valuable review. Please find attached our response letter.
  Best regards,
  Fabian Seemann, on behalf of the author team
  
  Citation: https://doi.org/10.5194/egusphere-2025-3727-AC1
RC2:
'Comment on egusphere-2025-3727', Anonymous Referee #2, 16 Dec 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3727/egusphere-2025-3727-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-3727-RC2
- AC2: 'Reply on RC2', Fabian Seemann, 08 Jan 2026
  
  Dear reviewer,
  Thank you very much for your very constructive and valuable review. Please find attached our response letter.
  Best regards,
  
  Fabian Seemann, on behalf of the author team
  
  Citation: https://doi.org/10.5194/egusphere-2025-3727-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-3727', Anonymous Referee #1, 12 Dec 2025

This study provides valuable insights into how organic matter is altered within saline permafrost sediments in Arctic Alaska—an important contribution to understanding carbon cycling and permafrost–climate feedbacks. While the dataset is strong, the manuscript would benefit from clearer explanations of the sampling design, the rationale for data grouping (Table 3), and the broader significance of saline permafrost thaw in a warming Arctic. Improved figure presentation (Figure 1) and an expanded discussion of methane and carbon dynamics in the broader climate context would further enhance the clarity and impact of the study.

Citation: https://doi.org/10.5194/egusphere-2025-3727-RC1
- AC1: 'Reply on RC1', Fabian Seemann, 08 Jan 2026
  
  Dear reviewer,
  Thank you very much for your very constructive and valuable review. Please find attached our response letter.
  Best regards,
  Fabian Seemann, on behalf of the author team
  
  Citation: https://doi.org/10.5194/egusphere-2025-3727-AC1
RC2:
'Comment on egusphere-2025-3727', Anonymous Referee #2, 16 Dec 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-3727/egusphere-2025-3727-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-3727-RC2
- AC2: 'Reply on RC2', Fabian Seemann, 08 Jan 2026
  
  Dear reviewer,
  Thank you very much for your very constructive and valuable review. Please find attached our response letter.
  Best regards,
  
  Fabian Seemann, on behalf of the author team
  
  Citation: https://doi.org/10.5194/egusphere-2025-3727-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Reconsider after major revisions (20 Jan 2026) by Cindy De Jonge

AR by Fabian Seemann on behalf of the Authors (26 Jan 2026) Author's response Author's tracked changes Manuscript

ED: Reconsider after major revisions (02 Feb 2026) by Cindy De Jonge

Dear authors,

in preparation for my editorial assessment, I evaluated the revised manuscript.

I have several minor comments on the writing, which I evaluated until L 521. Please correct these instances and do a careful reading of the rest of the discussion. Following up on these corrections I will send the paper out for another round of reviews.

Minor editiorial comments on revised version:
L 35: Rephrase, sentence is not correct. Perhaps: three times as much as global vegetation?
L 39. In newly drained lake basins, instead of ‘in newly developed drained lake basins’?
L 45. Write pore ice in two words, poreice is difficult to read.
L 45. This is not logical to me. The thawing point is increased, or the freezing point is depressed. Thawing point depressed would mean that melts less quick.
L 48. Intensified compared with? Specify in the text. Then, improve the connection with the next sentence.
L 59: suggest to rephrase: systems that are characterized by …
L 61. Briefly introduce how Giest and co-authors quantified the degradation signal (which method?).
L 62. Consider using: across different salinity levels.
L 71-73: Don’t include question marks halfway through the sentence.
L 87. “Today’s vegetation communities are dependent on landscape position.”, rephrase to make the English accurate. The composition of local vegetation depends on the position in the landscape? But then also, I wonder if this sentence can be left out.
L 89. Consider if you can write ‘degraded lake basin’ in full throughout the text, to improve the readability. The abbreviation DLB can then be used only for the specific site name.
L 90. Instead of the ground: the soil? The subsurface?
L 114. Use determine instead of decipher.
L 254. Perhaps include a more typical range of CPI for plant material, for you reader’s reference. 82 is extremely high value.
L 226: Please include the original reference for the CPI calculation.
L 260. What would the Paq reflect in your permafrost core?
L 263: “lagoonal”
L 284: “is not affected”, or maybe more accurate: ‘is apparently not affected’? There is a connecting few words missing.
L 309. Specify permafrost upland.
L 310. The n-alkane ratio (which one?). Consider introducing this ratio by a different name in your methods, and otherwise always refer to the ratio by explaining what it reflects.
L 317. At the lake bottom = in the surface sediment? Rewrite to make clear what is meant.
Section 4.1.1. For the reader the term ‘upland’ is not clear. Specify briefly what you mean (fi in L 434) to help with the understanding. Fi: upland permafrost?
L 444 Late glacial in two words (also elsewhere in the ms).

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AR by Fabian Seemann on behalf of the Authors (04 Feb 2026) Author's response Author's tracked changes Manuscript

ED: Reconsider after major revisions (20 Feb 2026) by Cindy De Jonge

ED: Referee Nomination & Report Request started (31 Mar 2026) by Cindy De Jonge

RR by Anonymous Referee #2 (23 Apr 2026)

RR by Anonymous Referee #3 (04 May 2026)

RR by Anonymous Referee #4 (14 May 2026)

Suggestions for revision or reasons for rejection

This manuscript by Seemann et al. titled ‘Sedimentary insights into organic matter alteration in Arctic Alaska’s saline permafrost’ investigates organic matter composition and degradation status across a thermal and saline gradient in northernmost Alaska. This study provides new insights into local organic matter dynamics in a transect covering drained lake basins, lagoons, thermokarst lakes and tundra. I suggest this manuscript for publication with the minor corrections addressed, see below.

General comments:
1. Could the authors visualize the correlations (C/N and d13C) in the supplement? Also, correlation analysis has not been mentioned in the method section (include relevant details such as which correlation analysis was used).
2. Could the authors add a supplementary table on the results of the Kruskal Wallis tests, and report test statistic, degrees of freedom in addition to only p-values (as now given in the text).
3. Just a note that the discussion section tends to repeat the results making it a bit heavy to read, and could benefit from shortening in these terms. In the section ‘4.3 implications and outlook’ the writing is more in the style of discussion and reads well.

Minor comments (line numbers refer to the tracked changed document):
Line 42: Are the authors able to give an estimate of the extent of these saline deposits in e.g. km2? This would give the reader a better idea how significant these saline deposits are.
Line 62: ‘Biogeochemical analyses’ sounds vague, why not just write ‘using lipid biomarkers’ as aren’t those the main analyses showing degradation status in Giest et al. 2025?
Line 67: Also citing some of the earlier biomarker work in the region would be appropriate here e.g., Goñi et al. 2000.
Line 69: As the authors say, these are widely applied so would be good to cite some of this work done outside your research group as well.
Line 74: Should this be Utqiaġvik Peninsula (following the official name Utqiaġvik) instead of Barrow Peninsula? Using this name would also distinct your study area from Barrow Peninsula, Canada.
L83: I suggest removing ‘significant’
Line 95: This sentence is a bit confusing, perhaps: ‘ Both lakes investigated in this study, West Twin …’
Line 110: There is an extra g in ‘Utqiaġvik’.
Line 126: Were these cores kept chilled (if not frozen)?
Line 135: The word ‘treated’ does not sound quite right, perhaps ‘prepared’ or ‘processed’ if that is what the authors mean.
Line 137: Perhaps use the word ‘taken’ instead of ‘divided’ or: ‘sediment cores were subsampled in adjusted steps..’
Line 162: The word treated does not sound quite right here either. It sounds like something was actively done to the samples, perhaps instead: ‘All samples were kept at 4 °C.’
Line 175: Presumably the Solitoc and N analyzer are from Elementar? Include this information.
Line 190: I suggest writing ‘Alfred Wegener Institute (AWI)’ as mentioned here for the first time (not just abbreviation).
Line 205: Add a reference for the standard acid-base-acid treatment. Not all readers might be familiar with this.
Line 280: Are the groups based on thermal and salinity condition the same as mentioned above? Please clarify as now it sounds like new groups were created.
Line 288: Are these standard deviations that are given with the mean values (also elsewhere in this chapter)? Perhaps mention somewhere here or in methods how the results are reported.
Line 298: Add correlation analysis in the method section.
Lines 307-311: Could the authors add standard deviations (if that is used in the paragraph above) also to this paragraph as now only means are given.
Line 464: Remove the word ‘much’.
Line 482: Has the abbreviation ETL been introduced previously ?
Line 487: Young radiocarbon ages? Add a description of the radiocarbon units .
Lines 544-545: The CPI seems very similar in these lakes with only 0.7 difference. Can this be considered as stronger degradation??
Line 545: This sentence is not clear. So, CPI is similar to Yedoma and stronger with other thermokarst lake sediments?
Line 553: I suggest replacing ‘near-significant’ with ‘non-significant’.
Line 582: Should ‘and’ be ‘where’ instead? So saline deposits underlay Holocene deposits in permafrost uplands?
Line 584: Could the authors give a rate for the active layer deepening here?
Line 611: Is there a reference for these microbial community differences between the lakes?

Figures:
Fig. 1 Is the thermokarst lagoon here the same as the semi-open lagoon that is referred in the text (e.g., lines 103, 118). I suggest using the same name consistently.
Fig 3. How about adding the core section units (I-V) to this figure as well?

References:
Goñi, M. A., Yunker, M. B., MacDonald, R. W., and Eglinton, T. I.: Distribution and sources of organic biomarkersin arctic sediments from the Mackenzie River and Beaufort Shelf, Mar. Chem., 71, 23–51, https://doi.org/10.1016/S0304-4203(00)00037-2, 2000.

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ED: Publish subject to minor revisions (review by editor) (18 May 2026) by Cindy De Jonge

AR by Fabian Seemann on behalf of the Authors (25 May 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (26 May 2026) by Cindy De Jonge

AR by Fabian Seemann on behalf of the Authors (26 May 2026)

Journal article(s) based on this preprint

03 Jun 2026

Sedimentary insights into organic matter alteration in Arctic Alaska's saline permafrost

Fabian Seemann, Michael Zech, Maren Jenrich, Guido Grosse, Benjamin M. Jones, Claire Treat, Lutz Schirrmeister, Susanne Liebner, and Jens Strauss

Biogeosciences, 23, 3675–3695, https://doi.org/10.5194/bg-23-3675-2026,https://doi.org/10.5194/bg-23-3675-2026, 2026

Short summary

Fabian Seemann, Michael Zech, Maren Jenrich, Guido Grosse, Benjamin M. Jones, Claire Treat, Lutz Schirrmeister, Susanne Liebner, and Jens Strauss

Supplement

https://doi.org/10.5194/egusphere-2025-3727-supplement

Data sets

Sediment and pore water investigations in thermokarst terrain near Utqiagvik, Alaska Fabian Seemann et al. https://doi.pangaea.de/10.1594/PANGAEA.983965

n-Alkane biomarker, carbon, nitrogen and d13C data from the Barrow Peninsula (northern Alaska) before and after a one-year long incubation experiment Fabian Seemann et al. https://doi.pangaea.de/10.1594/PANGAEA.983966

Fabian Seemann, Michael Zech, Maren Jenrich, Guido Grosse, Benjamin M. Jones, Claire Treat, Lutz Schirrmeister, Susanne Liebner, and Jens Strauss

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Month	HTML	PDF	XML	Total
Aug 2025	3,255	100	20	3,375
Sep 2025	7,457	198	28	7,683
Oct 2025	240	110	40	390
Nov 2025	193	80	25	298
Dec 2025	205	165	40	410
Jan 2026	488	233	39	760
Feb 2026	156	150	24	330
Mar 2026	236	156	7	399
Apr 2026	59	38	5	102
May 2026	29	38	5	72
Jun 2026	5	4	1	10

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Short summary

Arctic coastal landscapes, like those in northernmost Alaska, often contain saline sediments that are more prone to thawing. We studied six sediment cores to understand how thawing and salinity affect organic carbon breakdown and land change. Our results show that salinity speeds up organic matter loss when permafrost thaws. This highlights the overlooked risk of salinity in shaping Arctic landscapes and carbon release as the climate continues to warm.


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