Terrestrial Organic Matter Contributes to CO2 Production From Siberian Shelf Sediments

Arctic climate warming is causing permafrost thaw and erosion, which may lead to enhanced inputs of terrestrial organic matter into Arctic Ocean shelf sediments. Degradation of terrestrial organic matter in sediments might contribute to carbon dioxide production and bottom water acidification. Yet, the degradability of organic matter in shallow Arctic Ocean sediments, as well as the contribution of terrestrial input, is poorly quantified. Here, potential organic matter degradation rates were investigated for 16 surface sediments from the Kara Sea, Laptev Sea, and the western East Siberian Sea and compared with physicochemical sediment properties including molecular biomarkers, stable and radioactive carbon isotopes, and grain size. Aerobic oxygen and carbon dioxide fluxes, measured in laboratory incubations of sediment slurry, showed high spatial variability and correlated significantly with organic carbon content as well as with the amount and degradation state of terrestrial organic matter. The dependency on terrestrial organic matter declined with increasing distance from land, indicating that the presence of terrestrial organic matter is likely a constraining factor for organic matter degradation in shallow shelf seas. However, sediment oxygen consumption rates, measured in incubations of intact sediment cores, also exhibited substantial spatial variability but were not related to organic carbon content or terrestrial influence. Oxygen consumption of intact sediments may be more strongly influenced by in situ redox conditions. Together with previous observations, our findings support that terrestrial organic matter is easily degradable in shelf sea sediments and might substantially contribute to aerobic carbon dioxide production and oxygen consumption. Plain Language Summary The Arctic climate is warming rapidly, which is leading to thawing of frozen deposits on land. These deposits contain large amounts of terrestrial organic matter that is being eroded and deposited into shallow ocean sediments. The breakdown of terrestrial organic matter in sediments might contribute to carbon dioxide release into the ocean water. There is insufficient knowledge on how fast this breakdown is happening and which parameters influence it. We investigated organic matter breakdown rates for sediment samples taken from shallow Siberian seas and compared them with sediment properties. Oxygen consumption and carbon dioxide release were measured in laboratory experiments and showed high variability between different samples. The release was related to the amount of terrestrial organic matter and its state of decomposition. This relationship decreased strongly for sediments further away from land. During a second incubation experiment, using intact sediment cores, oxygen consumption rates were measured and also showed high variability between samples. Oxygen consumption rates were not related to organic matter content. These findings support previous observations that terrestrial organic matter breaks down rapidly in shallow Arctic Ocean sediments and might also substantially contribute to the release of carbon dioxide and consumption of oxygen from the seawater. Key Points - Carbon dioxide fluxes from sediment slurry incubations showed high variability and were dependent on the input of terrestrial organic matter - Pronounced variability in oxygen consumption of intact sediment cores could not be explained by the input of terrestrial organic matter

Description

This article was originally published in Journal of Geophysical Research: Biogeosciences. The version of record is available at: https://doi.org/10.1029/2024JG008226. © 2025. The Author(s). This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Keywords

sediment CO2 release, sediment O2 consumption, molecular biomarkers, Laptev Sea, Kara Sea, East Siberian Sea

Citation

Sauerland, L., Ray, N., Martens, J., Tesi, T., Dudarev, O., Gustafsson, Ö., et al. (2025). Terrestrial organic matter contributes to CO2 production from Siberian shelf sediments. Journal of Geophysical Research: Biogeosciences, 130, e2024JG008226. https://doi.org/10.1029/2024JG008226

URI

https://udspace.udel.edu/handle/19716/35713

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