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

Abstract

Abstract. 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 Holoceneage 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).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 icerich 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.

Sentinel-1 InSAR Measurements of Elevation Changes over Yedoma Uplands on Sobo-Sise Island, Lena Delta

“…Typically, the water/ice content in the active layer predominantly accounts for the seasonal elevation changes. The active layer thickness does not significantly vary among the Yedoma uplands [30]. Thus, the highest subsidence amplitudes over the top of Yedoma uplands suggest higher water/ice contents than in lower regions.…”

“…The vegetation coverage is sparse and characterized by moist to wet sedge-and moss-dominated tundra [32]. The vegetation growth period lasts from June to September and is roughly similar to the thaw season [30]. The maximum active layer thickness ranges from 20 cm to 50 cm on the Yedoma uplands.…”

“…based on RapidEye satellite imagery. As we focus on Yedoma uplands, we mask out the thermokarst basins and water bodies using this geomorphological classification [30]. Our study domain on Sobo-Sise thus consists of the classes flat undisturbed Yedoma uplands and partly degraded Yedoma slopes from [30].…”

“…The total area of Sobo-Sise is about 340 km 2 , accounting for 16% of the Yedoma coverage in the Lena Delta. Fuchs et al [30] classified and mapped different landforms (Yedoma uplands, thermokarst basins, water bodies, etc.) based on RapidEye satellite imagery.…”

“…Fuchs et al [30] classified and mapped different landforms (Yedoma uplands, thermokarst basins, water bodies, etc.) based on RapidEye satellite imagery.…”