ALBERT

Description: Detailed calculations of ground-ice volumes in permafrost deposits are necessary to understand and quantify the response of permafrost landscapes to thermal disturbance and thawing. Ice wedges with their polygonal surface expression are a widespread ground-ice component of permafrost lowlands. Therefore, the wedge-ice volume (WIV) is one of the major factors to be considered, both for assessing permafrost vulnerability and for quantifying deep permafrost soil carbon inventories. Here, a straightforward tool for calculating the WIV is presented. This GIS and satellite image-based method provides an interesting approach for various research disciplines where WIV is an important input parameter, including landscape and ecosystem modeling of permafrost thaw or organic carbon assessments in deep permafrost deposits. By using basic data on subsurface ice-wedge geometry, our tool can be applied to other permafrost region where polygonal-patterned ground occurs. One is able to include individual polygon geomorphometry at a specific site and the shape and size of epigenetic and/or syngenetic ice wedges in three dimensions. Exemplarily, the WIV in late Pleistocene Yedoma deposits and Holocene thermokarst deposits is calculated at four case study areas in Siberia and Alaska. Therefor, we mapped ice-wedge polygons sizes on different landscape units by using very-high-resolution satellite data. This information was combined with literature or own field data of individual ice-wedge sizes. We demonstrate that the WIV can vary considerably, not only between different permafrost regions, but also within a certain study site. Calculated WIV maxima range from 63.2 vol% to 31.4 vol% in late Pleistocene Yedoma deposits and from 13.2 vol% to 6.6 vol% in Holocene thermokarst deposits in Siberia and Alaska. Maximum WIV can be more than twice as high as calculated minimum WIV at a site. Assuming an equivalent ground-ice thickness (EGIT) from the WIV we are further able to estimate the potential surface subsidence caused by complete thawing of ice wedges. For example, adopting a possible range in Yedoma deposits thickness of 5 to 50 m in northern permafrost regions, the EGIT related to our calculated WIV maximum would range from 3.2 m to 31.6 m, respectively. In accordance to possible thermokarst deposit thicknesses of 1 to 10 m, the maximum WIV calculated for Holocene thermokarst deposits corresponds to an EGIT of 0.1 to 2.0 m, respectively.

Description: Late Pleistocene Yedoma is often described as arctic loess, but its formation is still disputed in literature. Differences of interpretation remain between researchers of western and eastern Beringia. These differences largely center on the relevance of eolian processes for Yedoma formation. Researchers working in Yukon and Alaska often characterize Yedoma silts as primarily loess. In contrast, researchers working in Siberia have proposed several hypotheses about the origin of Yedoma, including alluvial, glaciolacustrine, deltaic, proluvial/colluvial, cryogenic-eolian, nival, and polygenetic processes. The polygenetic Yedoma origin combines two major processes, (1) sedimentation and (2) syngenetic freezing, which were largely controlled by similar landscape and relief characteristics, climate conditions, periglacial processes, and the occurrence of nearby sediment sources. Syngenetic freezing, including the presence of large syngenetic ice wedges, unique cryostructures of the frozen deposits as well as fossils of the late Pleistocene mammoth megafauna and tundra-steppe flora, is the overarching similarity of the Yedoma deposits. In addition to huge ice wedges, the frozen sediment sequences commonly contain excess ice, with gravimetric ice contents (ratio of the mass of liquid water and ice in a sample to the dry mass of the sample, expressed as a mass percentage) of 70 to 〉100 wt%; this corresponds to an absolute ice content (related to the wet sample weight) of 30 to 〉 60 wt% for the Yedoma sediment columns. Estimating that ice wedges occupy about 50% by volume (vol%), the total volumetric ground ice content of Yedoma sequences likely varies between 65 to 90 vol%. Therefore, the major component of the Yedoma deposits is ground ice, which is the main distinction from other loess sediment deposits. The clastic components of the Yedoma deposits are poorly sorted and range in grain size from dominant silt to fine--grained sand and gravel is encountered as well. Granulometric parameters differ from site to site as well as within horizons, but the grain size peaks of nearly all samples lie within the silt and fine sand range. Multi-modal grain-size distributions suggest a variety of transport processes, and underscore the importance of the re-deposition of silts with coarser grain sizes. Heavy-mineral analyses of Siberian Yedoma suggest significant differences in detrital composition between sites, indicating different local sediment sources in the hinterland. In conclusion, we answer the loess-question as follows: aeolian deposition is involved in Yedoma formation, but it is neither the single nor the major mechanism of sediment deposition in western and eastern Beringia.

Description: The estimation of the carbon pool stored in arctic permafrost and its biogeochemical characteristics are essential topics in today’s permafrost research. While the uppermost cryosoil horizons are well-studied and already recorded in the Northern Circumpolar Soil Carbon Database (NCSCD) there are still large uncertainties concerning the quality and distribution of deep (i.e. up to decameters) organic carbon stocks. Well-exposed permafrost sections along the arctic sea coast and river banks in northern Yakutia are excellent objects to study permafrost organic carbon characteristics in connection with cryolithogy, cryostratigraphy and past periglacial landscape dynamics. Organic carbon occurs in permafrost as large tree trunks, peat inclusions, twigs and root fragments, other solid plant remains, and finely distributed plant detritus, but also as fossil mammal remains, insects, aquatic zooplankton and -benthos, and soil microorganisms, and finally its decomposition and metabolic products in terms of particulate and dissolved organic matter. These different kinds of fossil organic matter were formed, deposited, frozen, thawed and partly degraded, and sometimes refrozen, under different paleoclimatic and paleogeographical conditions of the Quaternary past. Therefore, the deep permafrost organic carbon pool is far from homogeneous and strongly linked to depositional and permafrost dynamics as well as the ecological and climatic history. The archive of specific biogeochemical and cryolithological features of frozen ground is recorded in permafrost sequences of about the last 200.000 years in northern Yakutia. We present the variabilites of the spatial distribution of organic carbon and organic matter qualities between different stratigraphical units, between correlated stratigraphical units of several sites, and even within stratigraphic units at the same site. Especially the coverage and composition of the widely distributed late Pleistocene Yedoma horizons and its thermokarst-affected derivatives in alas depressions are of interest to climate modeling, microbiology or biochemistry. There are significant differences to former estimates of the area, thickness of the relevant frozen deposits, ground ice content and finally in organic carbon content that lead to a reassessment of the deep permafrost carbon pools of the northern high latitude Yedoma region.

Description: Permafrost deposits constitute a large organic carbon pool vulnerable to degradation and potential carbon release due to global warming. Permafrost sections along coastal and river bank exposures and subsea cores in northeastern Siberia were studied for organic matter characteristics and ice content. Organic matter stored in permafrost grew, accumulated, froze, partly decomposed, and refroze under different periglacial environments, reflected in specific biogeochemical and cryolithological features. For the studied individual strata (Saalian ice‐rich deposits, Pre‐Eemian floodplain, Eemian lake deposits, early to middle Weichselian fluvial sands, middle and late Weichselian Yedoma , Taberites, Holocene cover, Holocene thermokarst and thermoerosional sediments, submerged lagoon and fluvial deposits) organic matter accumulation, preservation, and distribution are strongly linked to a broad variety of paleoenvironmental factors and specific surface and subsurface conditions. Permafrost deposits include twigs, leaves, peat lenses, grass roots, fine-distributed plant detritus, and particulate and dissolved organic matter. The vertical distribution of total organic carbon (TOC) in exposures varies from 0.1 wt % in fluvial deposits up to 45 wt % in Holocene peats. High TOC, high C/N, and low 13C values reflect less decomposed organic matter accumulated under wet, anaerobic conditions characteristic of relative temperate interglacial and interstadial periods. Glacial and stadial periods are characterized by less variable, low TOC, low C/N, and high 13C values indicating stable periglacial environments with reduced bioproductivity but stronger decomposition of organic matter under dryer, aerobic conditions. We present an in‐depth studies of organic matter distribution for the arctic permafrost zone, indicating the variability of organic matter distribution between different stratigraphical units, between the same stratigraphical unit at different study sites, and even within stratigraphic units at the same site that need to be taken into account in future inventories.

Description: During the late Pleistocene, a large pool of organic matter (OM) accumulated in ice-rich deposits of the arctic permafrost zone. Because of the potential re-introduction of this stored carbon into the global cycle from degrading permafrost (i.e. decomposed OM) as climate-relevant gases, the OM inventory of ice-rich permafrost deposits is important to current concerns about global warming. The objective of this presentation is to deduce the quality of OM stored in the studied permafrost sediments. The approach to estimate the OM quality is to use degradation parameters (e.g. C/N, �13C) based on the assumption that low degraded OM is more labile and has higher vulnerability for decomposition. Standard sedimentological and a molecular marker (biomarker) approach are applied. The study site is located on the west coast of the Buor Khaya Peninsula (N 71.6�, E 132.2�), Laptev Sea (Russia). Stratigraphically, two sediment units are distinguished. The first unit is composed of late Pleistocene ice-rich permafrost (Yedoma). The second unit consists of Holocene thermokarst (Alas) deposits. The mean bulk density of sediments from both units is ca. 1 g/cm3. The average total organic carbon (TOC) content is 2.4 wt% for Yedoma, 2.8 wt% for thermokarst deposits. The volumetric organic carbon contents of the Yedoma and thermokarst deposits are 13+-11 kg/m3 and 22+-11 kg/m3, respectively. The degree of OM degradation from both units is low (mean C/N 10, mean �13C -26.5 h because the deposits accumulated at relatively fast rates and the OM underwent only a short time of decomposition before it was incorporated into permafrost. Originating from microorganisms, archaeal lipids like archaeol can be used as a marker for methanogenic microbial communities or as a proxy for past microorganism activity. The archaeol concentrations reveal higher microbial activity in thermokarst deposits than in Yedoma deposits. The n-alkane and n-fatty acid parameters (carbon preference index and average chain length) show source signal from vascular land plants and prove a minor degradation state of the OM. OM parameters such as the total amount of organic carbon and the C/N ratio and acetate concentrations indicate labile OM.