Mobilization of organic carbon and nitrogen in a retrogressive thaw slump on Herschel Island, Yukon Territory, Western Canadian Arctic


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Hugues.Lantuit [ at ] awi.de

Abstract

Herschel Island, located in the southern Beaufort Sea, Western Canadian Arctic, shows a clear response to the global warming. Due to its ice-rich permafrost it is highly affected by environmental forcing and known for its high erosion rates and retrogressive thaw slump activity. Even though retrogressive thaw slumps have an effect on carbon and nitrogen cycling, until now there is not much known about the processes and carbon and nitrogen availability within a retrogressive thaw slump at a circumarctic scale. To provide new insides in this particular field, the retrogressive thaw slump “Slump D” on Herschel Island was divided into undisturbed (tundra zone, permafrost zone), and disturbed zones (mud pool zone, slump floor zone) and sampled via a fishnet grid. The tundra, mud pool and slump floor zones were sampled at 0 to 30 cm depth, for the permafrost zone permafrost profiles of up to 340 cm depth were sampled. In total 100 samples were analysed in their biogeochemical parameters (total organic carbon(TOC)-, total carbon(TC)-, total nitrogen(TN)-content) and stable isotope content (δ13Corg). The organic carbon source was determined for all zones to illustrate eventual differences in the deposition milieu. To show the degree of decomposition and degradation during the slumping process TOC/TN-ratio and δ13Corg were used as proxys. The results show that the tundra zone has the highest TC-, TOC- and TN-values follwed by the permafrost zone. The lowest values are determined for the slump floor and the mud pool zone. All of the zones show similar δ13Corg-values of -26.9‰but obvious differences in the TOC/TN-ratio. From the results it is concluded that the tundra zone shows a higher degradation than the permafrost zone but less than the mud pool and slump floor zone. Based on the high TOC/TN-values for the permafrost zone a vulnerable zone where carbon and nitrogen is available for decomposition during thawing processes is indicated. Due to the better quality of the organic matter within the permafrost zone labile carbon can be released right after thawing. The mud pool as well as the slump floor are highly degraded and store the more stable carbon which stays in the soil for several years. Within the slump floor zone no differences in degradation or composition are visible even though there is a mixture of old and new vegetated areas. With this findings the first step is made to understand the influence of degrading permafrost on carbon and nitrogen dynamics within a retrogressive thaw slump.



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Thesis (Master)
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Eprint ID
40213
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Ruttor, S. (2015): Mobilization of organic carbon and nitrogen in a retrogressive thaw slump on Herschel Island, Yukon Territory, Western Canadian Arctic Master thesis,


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