Carbon and nitrogen pools in thermokarst-affected permafrost landscapes in Arctic Siberia

• Main Authors: M. Fuchs, G. Grosse, J. Strauss, F. Günther, M. Grigoriev, G. M. Maximov, G. Hugelius
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-02-01
• Series: Biogeosciences
• Online Access: https://www.biogeosciences.net/15/953/2018/bg-15-953-2018.pdf

Ice-rich yedoma-dominated landscapes store considerable amounts of organic carbon (C) and nitrogen (N) and are vulnerable to degradation under climate warming. We investigate the C and N pools in two thermokarst-affected yedoma landscapes – on Sobo-Sise Island and on Bykovsky Peninsula in the north of eastern Siberia. Soil cores up to 3 m depth were collected along geomorphic gradients and analysed for organic C and N contents. A high vertical sampling density in the profiles allowed the calculation of C and N stocks for short soil column intervals and enhanced understanding of within-core parameter variability. Profile-level C and N stocks were scaled to the landscape level based on landform classifications from 5 m resolution, multispectral RapidEye satellite imagery. Mean landscape C and N storage in the first metre of soil for Sobo-Sise Island is estimated to be 20.2 kg C m⁻² and 1.8 kg N m⁻² and for Bykovsky Peninsula 25.9 kg C m⁻² and 2.2 kg N m⁻². Radiocarbon dating demonstrates the Holocene age of thermokarst basin deposits but also suggests the presence of thick Holocene-age cover layers which can reach up to 2 m on top of intact yedoma landforms. Reconstructed sedimentation rates of 0.10–0.57 mm yr⁻¹ suggest sustained mineral soil accumulation across all investigated landforms. Both yedoma and thermokarst landforms are characterized by limited accumulation of organic soil layers (peat). <br><br> We further estimate that an active layer deepening of about 100 cm will increase organic C availability in a seasonally thawed state in the two study areas by  ∼  5.8 Tg (13.2 kg C m⁻²). Our study demonstrates the importance of increasing the number of C and N storage inventories in ice-rich yedoma and thermokarst environments in order to account for high variability of permafrost and thermokarst environments in pan-permafrost soil C and N pool estimates.