ALBERT

Description: High latitude terrestrial ecosystems are key components in the global carbon (C) cycle. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify stocks of soil organic carbon (SOC) in the northern circumpolar permafrost region (18.7 × 106 km2). The NCSCD is a digital Geographical Information systems (GIS) database compiled from harmonized regional soil classification maps, in which data on soil coverage has been linked to pedon data from the northern permafrost regions. Previously, the NCSCD has been used to calculate SOC content (SOCC) and mass (SOCM) to the reference depths 0–30 cm and 0–100 cm (based on 1778 pedons). It has been shown that soils of the northern circumpolar permafrost region also contain significant quantities of SOC in the 100–300 cm depth range, but there has been no circumpolar compilation of pedon data to quantify this SOC pool and there are no spatially distributed estimates of SOC storage below 100 cm depth in this region. Here we describe the synthesis of an updated pedon dataset for SOCC in deep soils of the northern circumpolar permafrost regions, with separate datasets for the 100–200 cm (524 pedons) and 200–300 cm (356 pedons) depth ranges. These pedons have been grouped into the American and Eurasian sectors and the mean SOCC for different soil taxa (subdivided into Histels, Turbels, Orthels, Histosols, and permafrost-free mineral soil taxa) has been added to the updated NCSCDv2. The updated version of the database is freely available online in several different file formats and spatial resolutions that enable spatially explicit usage in e.g. GIS and/or terrestrial ecosystem models. The potential applications and limitations of the NCSCDv2 in spatial analyses are briefly discussed. An open access data-portal for all the described GIS-datasets is available online at: http://dev1.geo.su.se/bbcc/dev/v3/ncscd/download.php. The NCSCDv2 database has the doi:10.5879/ECDS/00000002.

Description: High-latitude terrestrial ecosystems are key components in the global carbon (C) cycle. Estimates of global soil organic carbon (SOC), however, do not include updated estimates of SOC storage in permafrost-affected soils or representation of the unique pedogenic processes that affect these soils. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify the SOC stocks in the circumpolar permafrost region (18.7 × 106 km2). The NCSCD is a polygon-based digital database compiled from harmonized regional soil classification maps in which data on soil order coverage have been linked to pedon data (n = 1778) from the northern permafrost regions to calculate SOC content and mass. In addition, new gridded datasets at different spatial resolutions have been generated to facilitate research applications using the NCSCD (standard raster formats for use in geographic information systems and Network Common Data Form files common for applications in numerical models). This paper describes the compilation of the NCSCD spatial framework, the soil sampling and soil analytical procedures used to derive SOC content in pedons from North America and Eurasia and the formatting of the digital files that are available online. The potential applications and limitations of the NCSCD in spatial analyses are also discussed. The database has the doi:10.5879/ecds/00000001. An open access data portal with all the described GIS-datasets is available online at: http://www.bbcc.su.se/data/ncscd/.

Description: High latitude terrestrial ecosystems are key components in the global carbon (C) cycle. Estimates of global soil organic carbon (SOC), however, do not include updated estimates of SOC storage in permafrost-affected soils or representation of the unique pedogenic processes that affect these soils. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify the SOC stocks in the circumpolar permafrost region (18.7 × 106 km2). The NCSCD is a polygon-based digital database compiled from harmonized regional soil classification maps in which data on soil order coverage has been linked to pedon data (n = 1647) from the northern permafrost regions to calculate SOC content and mass. In addition, new gridded datasets at different spatial resolutions have been generated to facilitate research applications using the NCSCD (standard raster formats for use in Geographic Information Systems and Network Common Data Form files common for applications in numerical models). This paper describes the compilation of the NCSCD spatial framework, the soil sampling and soil analyses procedures used to derive SOC content in pedons from North America and Eurasia and the formatting of the digital files that are available online. The potential applications and limitations of the NCSCD in spatial analyses are also discussed. The database has the doi:10.5879/ecds/00000001. An open access data-portal with all the described GIS-datasets is available online at: http://dev1.geo.su.se/bbcc/dev/ncscd/.

Description: High-latitude terrestrial ecosystems are key components in the global carbon cycle. The Northern Circumpolar Soil Carbon Database (NCSCD) was developed to quantify stocks of soil organic carbon (SOC) in the northern circumpolar permafrost region (a total area of 18.7 × 106 km2). The NCSCD is a geographical information system (GIS) data set that has been constructed using harmonized regional soil classification maps together with pedon data from the northern permafrost region. Previously, the NCSCD has been used to calculate SOC storage to the reference depths 0–30 cm and 0–100 cm (based on 1778 pedons). It has been shown that soils of the northern circumpolar permafrost region also contain significant quantities of SOC in the 100–300 cm depth range, but there has been no circumpolar compilation of pedon data to quantify this deeper SOC pool and there are no spatially distributed estimates of SOC storage below 100 cm depth in this region. Here we describe the synthesis of an updated pedon data set for SOC storage (kg C m−2) in deep soils of the northern circumpolar permafrost regions, with separate data sets for the 100–200 cm (524 pedons) and 200–300 cm (356 pedons) depth ranges. These pedons have been grouped into the North American and Eurasian sectors and the mean SOC storage for different soil taxa (subdivided into Gelisols including the sub-orders Histels, Turbels, Orthels, permafrost-free Histosols, and permafrost-free mineral soil orders) has been added to the updated NCSCDv2. The updated version of the data set is freely available online in different file formats and spatial resolutions that enable spatially explicit applications in GIS mapping and terrestrial ecosystem models. While this newly compiled data set adds to our knowledge of SOC in the 100–300 cm depth range, it also reveals that large uncertainties remain. Identified data gaps include spatial coverage of deep (〉 100 cm) pedons in many regions as well as the spatial extent of areas with thin soils overlying bedrock and the quantity and distribution of massive ground ice. An open access data-portal for the pedon data set and the GIS-data sets is available online at http://bolin.su.se/data/ncscd/. The NCSCDv2 data set has a digital object identifier (doi:10.5879/ECDS/00000002).

Description: Soils and other unconsolidated deposits in the northern circumpolar permafrost region store large amounts of soil organic carbon (SOC). This SOC is potentially vulnerable to remobilization following soil warming and permafrost thaw, but stock estimates are poorly constrained and quantitative error estimates were lacking. This study presents revised estimates of the permafrost SOC pool, including quantitative uncertainty estimates, in the 0–3 m depth range in soils as well as for deeper sediments (〉3 m) in deltaic deposits of major rivers and in the Yedoma region of Siberia and Alaska. The revised estimates are based on significantly larger databases compared to previous studies. Compared to previous studies, the number of individual sites/pedons has increased by a factor ×8–11 for soils in the 1–3 m depth range,, a factor ×8 for deltaic alluvium and a factor ×5 for Yedoma region deposits. Upscaled based on regional soil maps, estimated permafrost region SOC stocks are 217 ± 15 and 472 ± 34 Pg for the 0–0.3 m and 0–1 m soil depths, respectively (±95% confidence intervals). Depending on the regional subdivision used to upscale 1–3 m soils (following physiography or continents), estimated 0–3 m SOC storage is 1034 ± 183 Pg or 1104 ± 133 Pg. Of this, 34 ± 16 Pg C is stored in thin soils of the High Arctic. Based on generalised calculations, storage of SOC in deep deltaic alluvium (〉3 m to ≤60 m depth) of major Arctic rivers is estimated to 91 ± 39 Pg (of which 69 ± 34 Pg is in permafrost). In the Yedoma region, estimated 〉3 m SOC stocks are 178 +140/−146 Pg, of which 74 +54/−57 Pg is stored in intact, frozen Yedoma (late Pleistocene ice- and organic-rich silty sediments) with the remainder in refrozen thermokarst deposits (±16/84th percentiles of bootstrapped estimates). A total estimated mean storage for the permafrost region of ca. 1300–1370 Pg with an uncertainty range of 930–1690 Pg encompasses the combined revised estimates. Of this, ≤819–836 Pg is perennially frozen. While some components of the revised SOC stocks are similar in magnitude to those previously reported for this region, there are also substantial differences in individual components. There is evidence of remaining regional data-gaps. Estimates remain particularly poorly constrained for soils in the High Arctic region and physiographic regions with thin sedimentary overburden (mountains, highlands and plateaus) as well as for 〉3 m depth deposits in deltas and the Yedoma region.

Description: Permafrost deposits in the Beringian Yedoma region store large amounts of organic carbon (OC). Walter Anthony et al. (2014) describe a previously unrecognized pool of 159 Pg OC accumulated in Holocene thermokarst sediments deposited in Yedoma region alases (thermokarst depressions). They claim that these alas sediments increase the previously recognized circumpolar permafrost peat OC pool by 50 %. It is stated that previous integrated studies of the permafrost OC pool have failed to account for these deposits because the Northern Circumpolar Soil Carbon Database (NCSCD) is biased towards non-alas field sites and that the soil maps used in the NCSCD underestimate coverage of organic permafrost soils. Here we evaluate these statements against a brief literature review, existing datasets on Yedoma region soil OC storage and independent field-based and geospatial datasets of peat soil distribution in the Siberian Yedoma region. Our findings are summarised in three main points. Firstly, the sediments described by Walter Anthony et al. are primarily mineral lake sediments and do not match widely used international scientific definitions of peat or organic soils. They can therefore not be considered an addition to the circumpolar peat carbon pool. Secondly, independent field data and geospatial analyses show that the Siberian Yedoma regions is dominated by mineral soils, not peatlands. Thus, there is no evidence to suggest any systematic bias in the NCSCD field data or maps. Thirdly, there is spatial overlap between these Holocene thermokarst sediments and previous estimates of permafrost soil and sediment OC stocks. These carbon stocks were already accounted for by previous studies and cannot be added to the permafrost OC count. We suggest that statements made in Walter Anthony et al. (2014) resulted from misunderstandings caused by conflicting definitions and terminologies across different geoscientific disciplines. A careful cross-disciplinary review of terminologies would help future studies to appropriately harmonize definitions between different fields.

Description: In permafrost soils, the temperature regime and the resulting cryogenic processes are decisive for the storage of organic carbon (OC) and its small-scale spatial variability. For cryoturbated soils there is a lack in the assessment of pedon-scale heterogeneity in OC stocks and the transformation of functionally different organic matter (OM) fractions such as particulate and mineral-associated OM. Therefore, pedons of 28 Turbels across the Siberian Arctic were sampled in five meter wide soil trenches in order to calculate OC and total nitrogen (TN) stocks within the active layer and the upper permafrost based on digital profile mapping. Density fractionation of soil samples was performed to distinguish particulate OM (light fraction, LF, 1.6 g cm−3), and a mobilizable dissolved pool (mobilizable fraction, MoF). Mineral-organic associations were characterized by selective extraction of pedogenic Fe and Al oxides and the clay composition was analyzed by X-ray diffraction. Organic matter transformation in bulk soil and density fractions was assessed by the stable carbon isotope ratio (δ13C) and element contents (C and N). Across all investigated soil profiles, total OC stocks were calculated to 20.2 ± 8.0 kg m−2 (mean ± SD) to 100 cm soil depth. Of this average, 54% of the OC was located in active layer horizons (annual summer thawing layer) showing evidence of cryoturbation, and another 35% was present in the permafrost. The HF-OC dominated the overall OC stocks (55%) followed by LF-OC (19% in mineral and 13% in organic horizons). During fractionation about 13% of the OC was released as MoF, which likely represents the most bioavailable OM pool. Cryogenic activity combined with an impaired biodegradation in topsoil horizons (O and A horizons) were the principle mechanisms to sequester large OC stocks in the subsoil (16.4 ± 8.1 kg m−2; all mineral B, C, and permafrost horizons). About 22% of the subsoil OC stock can be attributed to LF material subducted by cryoturbation, whereas migration of soluble OM along freezing gradients appeared as principle source for the dominating HF (63%) in the subsoil. The large proportion of MoF (15%) in the subsoil suggests a pool of weaker mineral-organic associations as result of the low acidity and presence of basic cations, reductive dissolution of Fe(III) oxides, and the frequent freezing-thawing cycles. Despite the unfavourable abiotic conditions, substantial microbial OM transformation in the subsoil was indicated by low C/N ratios and high δ13C values but this was not reflected in altered LF and HF pool sizes. Partial least square regression analyses suggest that OC accumulates in the HF fraction due to coprecipitation with multivalent cations (Al, Fe) and association with poorly crystalline Fe oxides and clay minerals. Our data show that across all permafrost pedons, mineral-associated OM represents the most important OM fraction but the reactivity of this pool under changing future environmental conditions warrants further attention.

Description: In permafrost soils, the temperature regime and the resulting cryogenic processes are important determinants of the storage of organic carbon (OC) and its small-scale spatial variability. For cryoturbated soils, there is a lack of research assessing pedon-scale heterogeneity in OC stocks and the transformation of functionally different organic matter (OM) fractions, such as particulate and mineral-associated OM. Therefore, pedons of 28 Turbels were sampled in 5 m wide soil trenches across the Siberian Arctic to calculate OC and total nitrogen (TN) stocks based on digital profile mapping. Density fractionation of soil samples was performed to distinguish between particulate OM (light fraction, LF, 〈 1.6 g cm−3), mineral associated OM (heavy fraction, HF, 〉 1.6 g cm−3), and a mobilizable dissolved pool (mobilizable fraction, MoF). Across all investigated soil profiles, the total OC storage was 20.2 ± 8.0 kg m−2 (mean ± SD) to 100 cm soil depth. Fifty-four percent of this OC was located in the horizons of the active layer (annual summer thawing layer), showing evidence of cryoturbation, and another 35 % was present in the upper permafrost. The HF-OC dominated the overall OC stocks (55 %), followed by LF-OC (19 % in mineral and 13 % in organic horizons). During fractionation, approximately 13 % of the OC was released as MoF, which likely represents a readily bioavailable OM pool. Cryogenic activity in combination with cold and wet conditions was the principle mechanism through which large OC stocks were sequestered in the subsoil (16.4 ± 8.1 kg m−2; all mineral B, C, and permafrost horizons). Approximately 22 % of the subsoil OC stock can be attributed to LF material subducted by cryoturbation, whereas migration of soluble OM along freezing gradients appeared to be the principle source of the dominant HF (63 %) in the subsoil. Despite the unfavourable abiotic conditions, low C / N ratios and high δ13C values indicated substantial microbial OM transformation in the subsoil, but this was not reflected in altered LF and HF pool sizes. Partial least-squares regression analyses suggest that OC accumulates in the HF fraction due to co-precipitation with multivalent cations (Al, Fe) and association with poorly crystalline iron oxides and clay minerals. Our data show that, across all permafrost pedons, the mineral-associated OM represents the dominant OM fraction, suggesting that the HF-OC is the OM pool in permafrost soils on which changing soil conditions will have the largest impact.