Organic carbon characteristics in ice-rich permafrost in alas and Yedoma deposits, central Yakutia, Siberia
<p>Permafrost ground is one of the largest repositories of terrestrial organic carbon and might become or already is a carbon source in response to ongoing global warming. With this study of syngenetically frozen, ice-rich and organic carbon (OC)-bearing Yedoma and associated alas deposits in...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-07-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/17/3797/2020/bg-17-3797-2020.pdf |
| Summary: | <p>Permafrost ground is one of the largest repositories of
terrestrial organic carbon and might become or already is a carbon source in
response to ongoing global warming. With this study of syngenetically
frozen, ice-rich and organic carbon (OC)-bearing Yedoma and associated alas
deposits in central Yakutia (Republic of Sakha), we aimed to assess the local sediment
deposition regime and its impact on permafrost carbon storage. For this
purpose, we investigated the Yukechi alas area (61.76495<span class="inline-formula"><sup>∘</sup></span> N,
130.46664<span class="inline-formula"><sup>∘</sup></span> E), which is a thermokarst landscape degrading into Yedoma in
central Yakutia. We retrieved two sediment cores (Yedoma upland, 22.35 m
deep, and alas basin, 19.80 m deep) in 2015 and analyzed the biogeochemistry,
sedimentology, radiocarbon dates and stable isotope geochemistry. The
laboratory analyses of both cores revealed very low total OC (TOC) contents
(<span class="inline-formula"><0.1</span> wt %) for a 12 m section in each core, whereas the
remaining sections ranged from 0.1 wt % to 2.4 wt % TOC. The core sections
holding very little to no detectable OC consisted of coarser sandy material were
estimated to be between 39 000 and 18 000 BP (years before present) in age. For this
period, we assume the deposition of organic-poor material. Pore water stable
isotope data from the Yedoma core indicated a continuously frozen state
except for the surface sample, thereby ruling out Holocene reworking. In
consequence, we see evidence that no strong organic matter (OM)
decomposition took place in the sediments of the Yedoma core until today.
The alas core from an adjacent thermokarst basin was strongly disturbed by
lake development and permafrost thaw. Similar to the Yedoma core, some
sections of the alas core were also OC poor (<span class="inline-formula"><0.1</span> wt %) in 17 out
of 28 samples. The Yedoma deposition was likely influenced by fluvial
regimes in nearby streams and the Lena River shifting with climate. With its
coarse sediments with low OC content (OC mean of 5.27 kg m<span class="inline-formula"><sup>−3</sup></span>), the Yedoma deposits in the Yukechi area differ from other Yedoma sites in
North Yakutia that were generally characterized by silty sediments with
higher OC contents (OC mean of 19 kg m<span class="inline-formula"><sup>−3</sup></span> for the non-ice
wedge sediment). Therefore, we conclude that sedimentary composition and
deposition regimes of Yedoma may differ considerably within the Yedoma
domain. The resulting heterogeneity should be taken into account for future
upscaling approaches on the Yedoma carbon stock. The alas core, strongly
affected by extensive thawing processes during the Holocene, indicates a
possible future pathway of ground subsidence and further OC decomposition
for thawing central Yakutian Yedoma deposits.</p> |
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| ISSN: | 1726-4170 1726-4189 |