Preprints
https://doi.org/10.5194/egusphere-2025-3727
https://doi.org/10.5194/egusphere-2025-3727
20 Aug 2025
 | 20 Aug 2025
Status: this preprint is open for discussion and under review for Biogeosciences (BG).

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.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Biogeosciences.

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

Status: open (until 12 Oct 2025)

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

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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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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