4.1. Origin of the Yedoma Ice Complex at Duvanny Yar
 The studied Kolyma River cliff cut in vertically or diagonally polygonal ice-wedge systems. It is suggested that the Yedoma hills are remnants of former accumulation plains [e.g., Schirrmeister et al., 2012]. There is still no widely accepted concept of Yedoma ICs genesis, but it seems clear that neither glacial-related sedimentation, such as hypothesized by Nagaoka et al.  and Grosswald , nor shallow-marine sedimentation, such as postulated by Bol'shiyanov et al. , was involved. An overview of the different Yedoma ICs origin concepts is given by Vasil'chuk .
 It is agreed that Yedoma IC material was sub-aerially exposed most of the time and froze syngenetically during permafrost accumulation [Kanevskiy et al., 2011]. Based on more than 50 radiocarbon dates for adjacent sediments [Vasil'chuk et al., 2001], we know that the ice wedges at Duvanny Yar were formed between ∼37 and 13 ka BP by syngenetic freezing of permafrost deposits. Our studies confirm the syngenetic freezing process because lenticular and layered cryostructures occur. The average absolute ice content of all studied deposits is 35 wt%. Assuming that ice wedges can account for about 50 vol% in Yedoma IC sequences [Schirrmeister et al., 2002; Zimov et al., 2006a], the total absolute ground-ice content can constitute up to three quarters of the total outcrop volume. This clearly shows the vulnerability of Yedoma IC deposits to warming temperatures and surface subsidence during thawing.
 Three granulometric characteristics can be seen in the GSDs (Figure 5). First, a sand maximum, as shown by the sand maximum sample at 6.1 m a.r.l., could be caused by a higher energetic transport level such as increased streaming velocity during a flooding period, as has been suggested by our EM modeling. In some samples a distinct third small peak in the fine-sand fraction is obvious. This can be explained by an increased fraction of seasonal or temporal inundation of a floodplain due to stronger streaming conditions or increased aeolian activity resulting in enrichment of the fine-sand fraction by a larger fraction of saltating and rolling sediments [Reineck and Singh, 1980]. Second, an enrichment of the finer fractions, especially the medium-silt fraction, like in paleocryosol 5, can indicate ponding water, in which the settling velocity of the suspended medium-silt fraction allows for its deposition [Hjulström, 1939]. At this paleocryosol our EM 2 for alluvial, fluvial, and lacustrine processes rises to 100%. Additionally, the increased TOC could be caused by ponding water and boggy conditions in low-center polygons, under which the accumulation of organic matter is higher and the decomposition rate is lowered. Third, paleocryosols are characterized by more alternating mean grain sizes. This could be a consequence of faster environmental changes, increased plant growth, or thaw and cryoturbation processes during warmer periods. Despite these specific characteristics, the grain-size analysis and magnetic susceptibility data indicate stable sediment sources as well as persistent transport conditions.
 Loess material, formed as a result of cryogenic weathering and glacial grinding processes, is rather common in (peri)glacial environments and drifts from outwash plains via aeolian transport. Therefore, Pye  defined a sub-category of loess named ‘periglacial loess’. Moreover, Pye  states that the GSD of a ‘typical’ loess shows a pronounced mode in the 28 to 48 μm range and is positively skewed (toward the finer sizes). Smalley and Smalley  define loess-sized material as between 20 to 60 μm, which corresponds perfectly with the observed large peak of the studied deposits.
 Sub-aquatic fluvial and lacustrine silts can also be loess-like, as can some alluvial and colluvial deposits [Konishchev, 1987]. Especially the first peak, described by EM 2 and peak 5 + 4, cannot be explained by pure aeolian processes. Walger  states that products of each of the three basic transport and deposition mechanisms, namely suspension, saltation, and rolling, are represented in every single GSD. However, because of sediment variations and sampling uncertainties, polymodal GSDs are recorded. Due to the absence of visible layered structures, and considering Walger's hypothesis, IPF and EM modeling were conducted. The results of these modeling efforts clearly indicate that the GSD of each single sample is characterized by at least bimodal curves and consists of numerous single populations of monomodal GSDs, indicating the participation of various processes of transport and (re-)sedimentation during Yedoma IC formation in agreement with a polygenetic formation concept [Sher, 1995; Sher et al., 2005]. In this context, EM 2 is believed to be an alluvial, fluvial, and lacustrine signal, and EM 1 is interpreted as an aeolian component. IPF peak 4 + 5 is interpreted as the water-dependent analogue to EM 2, peak 3 + 2 as aeolian, and peak 1 as the fluvial/aeolian component (Figures 6b and 7).
 This interpretation of the GSDs is based on natural EMs like Chinese [Sun et al., 2002] and Alaskan loess (L. Schirrmeister, unpublished data, 2008), as well as on alluvial/fluvial/lacustrine deposits from northern China [Kaakinen and Lunkka, 2003; Kenkkilä, 2005]. Another EM for periglacial loess(-like) sediment was described by Zech et al.  at the Tumara palaeosol sequence in northeast Siberia.
 Both EM modeling and IPF reveal a relatively balanced proportion of the peaks/distributions interpreted as the alluvial/fluvial/lacustrine component (EM: 61 ± 21%; IPF: 43 ± 6%) and the aeolian component (EM: 39 ± 21%; IPF: 55 ± 7%).
 The consistency of the EM modeling and the IPF scores indicates stable accumulation conditions. Another process for producing fine-grained sediments could be in situ frost weathering of the material. After deposition, repeated freezing and thawing of ice/water-bearing sediments results in production of silt-sized particles [Konishchev and Rogov, 1993; Wright et al., 1998; Schwamborn et al., 2008]. When this process is significant, the post-depositional transformation conceals the primary transport and accumulation signal, distorting and complicating the interpretation. In addition, winnowing/eroding of the fine fraction by shallow overland flow caused by rain or thawing events could have altered the depositional GSDs [Farenhorst and Bryan, 1995].
 Due to the (very) poorly sorted polymodal sediments lacking in carbonates, and the absence of glaciers and ice sheets with their grinding processes [Seppälä, 2004] in northeast Siberian lowlands [Velichko et al., 1997; Hubberten et al., 2004; Svendsen et al., 2004], the Yedoma IC at Duvanny Yar is interpreted to be of polygenetic origin. Water-related (like floodplain overbank deposition) and aeolian deposition were the controlling processes. It is also likely that seasonally differentiated deposition occurs here. A possible scenario of seasonal deposition is flooding of alluvial areas after snowmelt and during periods of high river discharge (today around June, Kolymskoye Stream Discharge Station, ArcticRIMS). Aeolian deposition likely occurs in dryer seasons. During fall and winter, river discharge volume is extremely reduced. As a consequence, parts of the formerly submerged floodplain areas become susceptible to wind activity [e.g., Muhs and Bettis, 2003].
4.2. Changes in Organic Matter Parameters
 The TOC content of the homogenous parts of the studied Yedoma IC deposits is between 0.5 and 2.0 wt%, which is rather low compared to other Yedoma IC studies (∼4 wt% [Schirrmeister et al., 2011a]). The paleocryosols are characterized by TOC values of up to 10.5 wt%. The mean organic-carbon value for the whole profile is 1.5 ± 1.4 wt%, and the δ13C values range between −27.4 and −24.6 ‰. These parameters, in combination with high C/N ratios, suggest that fresh water and sub-aerial terrestrial environments were the dominant sources of organic matter during Yedoma IC formation. In the paleocryosol samples a higher input of terrestrial plant associations is revealed. The local environmental conditions under which the paleocryosol sequences were formed are likely to have been more humid and favorable for plant growth. Hence, the formation period of the lowermost paleocryosol sequence fits well into the Middle Weichselian (50 to 30 ka BP) interstadial period [Schirrmeister et al., 2002]. This hypothesis is based on the stratigraphical position, and on parameters such as high TOC contents, high C/N ratios, and low δ13C values (Figure 4). These are typical indications of interstadial periods with increased bioproductivity and moderate organic-matter decomposition under wet/moist conditions [e.g., Wetterich et al., 2009; Schirrmeister et al., 2011b]. Moreover, the alternating behavior observed in the paleocryosols can be explained, according to Gundelwein et al. , as the result of a patchy environment such as a distinctive mosaic-like polygonal tundra with moist anaerobic (lower δ13C) and dryer aerobic conditions (higher δ13C). On the contrary, in the homogeneously composed sediments of the Yedoma IC stadial periods were characterized by less variable, generally lower TOC contents and low C/N ratios (higher decomposition). Despite the low TOC values compared to other Yedoma IC studies, the Yedoma IC at Duvanny Yar contains a considerable organic-carbon inventory with a mean of 14 ± 8 kg/m3. Given that the Yedoma IC deposits accumulated at relatively fast rates and low temperatures, the organic matter had only a short time to decompose before it was incorporated into a permanently frozen state. Therefore, Yedoma IC deposits are believed to contain a labile and vulnerable carbon-matter stock. Applying broad upscaling, Zimov et al. [2006b] estimated the organic-carbon reservoir in Siberian ICs to be ∼500 Gt.
 Our data from Duvanny Yar show lower TOC content and lower bulk densities; therefore, we hypothesize that the Yedoma IC carbon inventory is lower than estimated by Zimov et al. [2006b]. Large-scale extrapolations should be considered as preliminary because of great uncertainties about the controlling factors, e.g., Yedoma IC distribution/area, thickness, and local heterogeneity. When considering the different studies of spatial variation of carbon-bearing Yedoma IC deposits [e.g., Walter et al., 2006; Zimov et al., 2006b; Tarnocai et al., 2009], it becomes obvious that our knowledge about the quantities and qualities of this organic-matter pool is insufficient for extrapolating possible effects of a warming climate on the Yedoma IC organic-carbon stock. Nevertheless, as a large carbon inventory that is vulnerable to release, the Yedoma IC deposits contain an important carbon pool, which is relevant to current discussions about the effect of global climate warming.