Carbon Stocks in Permafrost-Affected Soils of the Lena River Delta

The soil organic carbon stock (S_SOC) of soils in arctic permafrost regions is known to be significant but is insufficiently investigated so far. Previous S_SOC studies report mainly the gravimetric carbon (C) contents and are limited to the active layer depth at the time of sampling. Since C deposits in permafrost regions are likely to become a future C source, more detailed investigations of the presently frozen likely carbon-rich sediment and soil layers are of importance. Our investigations were performed on Samoylov Island in the southern-central part of the Lena River Delta (32,000 km²) which is the largest arctic delta and the fifth largest delta worldwide. Samoylov Island is representative for the Lena River Delta's first terrace and the active floodplains. Within this study a new portable Snow-Ice-Permafrost-Research-Establishment (SIPRE) auger was used during a spring field session to obtain 1 m deep frozen soil cores (n = 29) distributed over all known soil and vegetation units. These cores are analyzed for bulk contents of nitrogen (N) and C, ice content and bulk density (BD) and to determine the S_SOC including the rarely investigated currently permanently frozen layers up to 1 m depth on Samoylov Island. Our study provides evidence for high S_SOC for a depth of 1 m for the investigated area ranging between 7 kg m^-2 and 48 kg m^-2. Considering the spatial extent of different soil units on the two geomorphological units of Samoylov Island, the area-weighted average S_SOC were 29 kg m^-2 (n = 22) for the first terrace and 14 kg m^-2 (n = 7) for the active floodplain. For the correspondent soil units of Turbels and Orthels in circumpolar permafrost regions a mean S_SOC of 27 kg m^-2 (min: 0.1 kg m^-2, max: 126 kg m^-2) for a depth of 1 m was reported [1]. For up-scaling solely over the soil-covered areas of the Lena River Delta, we excluded all water bodies >3,600 m² from the geomorphological units studied (first river terrace and the active floodplains) and additionally corrected the extent of the first terrace's land area by reducing it by the percentage of small water ponds and cracks by 14% detected by high-resolution aerial photography for Samoylov Island. We scaled the area-weighted S_SOC averages estimated for the two geomorphological units of Samoylov Island across the corrected total land areas of the Lena River Delta's first terrace (9,430 km²) and the active floodplains (3,470 km²) leading to total organic soil carbon storage estimates for a depth of 1 m of ~278 ± 98 Tg C and ~47 ± 26 Tg C, respectively [2]. References [1] Tarnocai, C., Canadell, J.G., Schuur, E.A.G., Kuhry, P. Mazhitova, G. & Zimov, S., 2009. Soil organic carbon pools in the northern circumpolar permafrost region. Global Biogeochemical Cycles 23, GB2023: 11p. [2] Zubrzycki, S., Kutzbach, L., Grosse, G., A. R. Desyatkin & E.-M. Pfeiffer (in prep.). Soil Organic Carbon Stocks in the Lena River Delta. In preparation for BGS.