The composition of perennially frozen deposits holds
information on the palaeo-environment during and following deposition. In
this study, we investigate late Pleistocene permafrost at the western coast
of the Buor Khaya Peninsula in the south-central Laptev Sea (Siberia),
namely the prominent eastern Siberian Yedoma Ice Complex (IC). Two Yedoma IC
exposures and one drill core were studied for cryolithological (i.e. ice and
sediment features), geochemical, and geochronological parameters. Borehole
temperatures were measured for 3 years to capture the current thermal
state of permafrost. The studied sequences were composed of
ice-oversaturated silts and fine-grained sands with considerable amounts of
organic matter (0.2 to 24 wt %). Syngenetic ice wedges intersect the
frozen deposits. The deposition of the Yedoma IC, as revealed by radiocarbon
dates of sedimentary organic matter, took place between 54.1 and 30.1 kyr BP.
Continued Yedoma IC deposition until about 14.7 kyr BP is shown by dates
from organic matter preserved in ice-wedge ice. For the lowermost and oldest
Yedoma IC part, infrared-stimulated luminescence dates on feldspar show
deposition ages between 51.1
In recent years, considerable research on Quaternary permafrost has focused on a prominent feature of late Pleistocene deposit that is named in stratigraphic terms as Yedoma Ice Complex (IC), according to Tumskoy (2012) and Schirrmeister et al. (2013). The Yedoma IC formed in non-glaciated Beringia between approx. 60 and 12 kyr BP (marine isotope stages (MIS) 4 to 2), including stadial and interstadial stages of the late Pleistocene, although the ages of preserved deposits vary from site to site (Schirrmeister et al., 2011b). Yedoma IC formed in polygonal tundra environments with syngenetic ice-wedge growth. Ice wedges originate from repeated frost cracking of frozen ground in winter and subsequent crack filling by snowmelt water in spring and its re-freezing in the ground. The presence of huge syngenetic ice wedges (up to decametres tall and metres wide) is recognized as characteristic for Yedoma IC, while the depositional processes and sediment sources are still under debate (e.g. Murton et al., 2015). Different depositional regimes are assumed to produce polymodal grain-size distributions, which are commonly found in Yedoma IC (Schirrmeister et al., 2011b). But similar landscape and relief characteristics (poorly drained flat accumulation plains with polygonal patterned ground), cold-arid climate conditions, periglacial processes, such as cryoturbation, frost cracking, syngenetic freezing, and short-path transport of mineral material control Yedoma IC formation (Sher, 1997).
The modern periglacial surface exposes Yedoma IC remnants in Alaskan and
eastern Siberian lowlands next to widely distributed thermokarst basins
(alases). They were formed after late-glacial–Holocene warming had
eroded up to 70 % of the original IC distribution by thawing in an area of
more than 1 000 000 km
Numerous case studies have applied multi-proxy approaches at several sites in north-eastern Siberia including the stratotype outcrop for Yedoma IC at Duvanny Yar, which is exposed at the Kolyma River bank (e.g. Gubin and Zanina, 2013; Murton et al., 2015; Strauss et al., 2012). Poorly sorted silts and fine-grained sands compose Yedoma IC deposits, which are ice rich with segregation ice contents between 40 and 60 wt % (Schirrmeister et al., 2011b), and are intersected by ice wedges, which constitute between 31 and 63 vol % of the Yedoma IC (Ulrich et al., 2014). The total ice content of Yedoma IC reaches up to 80 vol %. Lens-like (lenticular) or net-like (reticulated) intrasedimentary ice structures (cryostructures) alternating with horizontal ice bands indicate ice segregation near the permafrost table and syngenetic freezing shortly after deposition. Pronounced ice-wedge shoulders indicate the stepwise transformation of seasonally unfrozen into perennially frozen deposits due to varying thaw (active) layer depths during formation of syngenetic permafrost.
Yedoma IC is rich in well-preserved floral and faunal fossils, and represents late Quaternary Beringian tundra–steppe environments. Palaeontological proxies, such as testate amoebae (Bobrov et al., 2004; Müller et al., 2009), pollen (Andreev et al., 2011), plant macrofossils (Kienast et al., 2005), ostracods (Wetterich et al., 2005), and insect fossils and bones of the mammoth fauna (Sher et al., 2005; Wetterich et al., 2008), give insights into past ecosystem and climate conditions, mainly for the summer season. Winter climate during IC formation is commonly deduced from ice-wedge stable water-isotope signatures (e.g. Meyer et al., 2002a, b; Vasil'chuk et al., 2001; Vasil'chuk, 2013) that differentiate at least interstadial and stadial stages of the last glacial period (Wetterich et al., 2011b, 2014). The combination of summer and winter proxies sheds light on seasonal trends of past climate and their roles in environmental dynamics.
Eroding Yedoma IC deposits are considered as a major source of terrigenic organic carbon transfer into the Arctic Ocean (Vonk et al., 2012; Winterfeld et al., 2015; Bröder et al., 2016) and represent the terrestrial end-member of organic matter (OM) on the East Siberian Arctic Shelf (Bischoff et al., 2016). Buried cryosols of Yedoma IC enriched in OM are striking and contribute to a mean total organic carbon (TOC) content of 3 wt % in Yedoma IC (Strauss et al., 2013), which mainly varies between 1 and 5 wt % (Schirrmeister et al., 2011a). Using TC values, Shmelev et al. (2017) estimated 0.6 to 2.1 % TC of carbon storage in permafrost of north-eastern Yakutia. The fossil OM of Yedoma IC is the subject of ongoing research to estimate the permafrost-locked carbon pool (Hugelius et al., 2014) and its potential feedback to recent climate warming (Schneider von Deimling et al., 2015). The baseline TOC estimates are of further use to study OM quality (Strauss et al., 2015; Stapel et al., 2016) and potential availability for microbial turnover of thawing carbon pools to greenhouse gas emissions in a warming Arctic (Knoblauch et al., 2013). Yedoma IC is considered to be an important pool of OM and potential source of carbon, nitrogen, and nutrient release under current warming (Zimov et al., 2006). Therefore, analysis of OM preserved in Yedoma IC can improve quantification and prediction of permafrost feedbacks to climate warming.
The cryolithology of several Yedoma IC sites in the Laptev Sea region is summarized in Schirrmeister et al. (2011b) and Tumskoy (2012). But studies of Yedoma IC in north-eastern Siberia started already several decades earlier (e.g. Tomirdiaro, 1980; Kaplina, 1981; Gubin and Zanina, 2013, 2014, and quotations therein); Yedoma IC with very similar characteristics to north-eastern Siberian sites is reported from the Alaskan Itkillik River in the Arctic foothills (Kanevskiy et al., 2011). Studies of eastern Beringian Yedoma IC were undertaken in permafrost tunnels near Fairbanks (Hamilton et al., 1988; Shur et al., 2004; Bray et al., 2006; Kanevskiy et al., 2008; Schirrmeister et al., 2016). IC of MIS 4 age is well-documented in central Yukon through the presence of the Sheep Creek-K tephra (approx. 80 kyr old; Froese et al., 2009). Further, the presence of IC deposits is known from the Klondike area (Sanborn et al., 2006).
Study area in the central Laptev Sea region (
This study summarizes cryolithological (i.e. ice and sediment features), geochemical, and geochronological data of three Yedoma IC sequences from the Buor Khaya Peninsula in the southern Laptev Sea (Fig. 1). We aim to fill a spatial gap in Yedoma IC research in western Beringia between the intensively studied western and central Laptev Sea regions (including the Lena Delta) to the west (e.g. Schirrmeister et al., 2002, 2008; Wetterich et al., 2008) and the Dmitry Laptev Strait and the New Siberian Archipelago to the east (Andreev et al., 2009).
By capturing the internal variation of Yedoma IC characteristics, the study deduces stratigraphy and correlates the Buor Khaya Yedoma IC records on a regional scale for Beringia. Since cryolithological properties of Yedoma IC vary from site to site and only about 20 Arctic and subarctic sites have been studied in detail so far, any new record provides important data for Beringian palaeo-environmental research. Yedoma IC formation processes have been under discussion for decades and each new sedimentary record gives insights into source material, transport, and deposition processes of this unique stratum, which represents a valuable archive and is a main focus in Arctic permafrost and palaeo-environmental research.
The Buor Khaya Peninsula is part of the Yana-Indigirka coastal lowlands and is located at the south-central Laptev Sea coast (Fig. 1). The vegetation of the Buor Khaya Peninsula is mostly erect dwarf-shrub tundra, with, in places, tussock-sedge and moss tundra (CAVM, 2003). The northernmost part of the peninsula is covered by sedge, moss, and dwarf-shrub wetlands. In total, 77 vascular plant species were recorded during fieldwork in 2010 (Yakshina, 2011).
The subarctic climate is continental, with low precipitation, long harsh
winters, and short cold summers. The mean annual air temperature at the
closest meteorological station (WMO station 218240, Tiksi, 1981 to 2010) is
The region is underlain by continuous permafrost with ground temperatures of
less than
The Yana-Indigirka coastal lowlands are part of the late Pleistocene accumulation plains of western Beringia. Late-glacial–Holocene warming triggered thermokarst and thermo-erosion, which both have significantly reworked the upper permafrost and shaped the modern surface morphology. Yedoma IC remnants cover 15 % of the area, which consists mainly of coalesced thermokarst basins (alases) and are often occupied by shallow lakes. Yedoma hills reach up to 37 m above sea level (a.s.l.), and thermokarst basins reach 9 to 14 m a.s.l. (Günther et al., 2013b).
The fieldwork on two Yedoma exposures on the western coast of the Buor Khaya
Peninsula (Buo-02, 71.384
Drilling at site BK-8 took place at a distance of approx. 100 m from the cliff
edge on top of a 34.2 m (a.s.l.) high Yedoma hill (71.4203
Ground temperature was measured in the borehole using a 40 m GeoPrecision
thermistor string with 15 PT1000 sensors, installed shortly after
drilling. The sensors were calibrated in a purified water (electrical
conductivity (EC) < 1
Sediment samples were freeze-dried, homogenized, and split into sub-samples
for further analyses. The volume and weight of frozen and freeze-dried
sub-samples were determined for analysis of bulk and dry density and total
volumetric moisture content (ice and water). Grain-size analyses were
carried out using an LS 200 laser particle analyser (Beckman Coulter, Inc.) after
removing OM with hydrogen peroxide (3 %). The used grain-size
classification is according to Reineck and Sing (1980) and Wenthworth
(1922). Total carbon (TC) and total nitrogen (TN) contents were measured
with a VARIO-EL-III Element Analyzer, while TOC content was measured with
the VARIO MAX C. Total sulfur (TS) was measured with a carbon–sulfur determinator (Eltra CS 200).
Using the TOC and TN values, the TOC
An end-member modelling analysis (EMMA) was used to determined characteristic
grain-size subpopulations that compose the polymodal grain-size
distributions at each site. A robust EMMA was run using the EMMAgeo
R package version 0.9.4. EMMAgeo is based on an algorithm developed by
Dietze et al. (2012) that relies on principles of factor analyses and
includes different transformation steps to determine a few interpretable
grain-size subpopulations (loadings, i.e. contribution of grain-size classes
to each end-member). Robust end-members (rEMs) are defined as grain-size
subpopulations that appear independent of model parametrization (related to
a priori unknown numbers of end-members and weight transformation limits;
Dietze et al., 2014). Mean rEM loadings and a weight transformation limit of
zero were used to calculate mean scores (i.e. relative contribution of an
end-member to each sample and their scaled variances) and to model the
data set. Then, goodness-of-fit parameters could be calculated (mean total,
class, and sample-wise explained variances, i.e.
Minimum, mean (red), and maximum ground temperatures
based on almost 3 years (from 11 May 2012 to 27 April 2015) of
measurements made at 4 h intervals. Dashed lines show the approximate
freezing temperature (0
Overview photo and scheme of the Buo-02 Yedoma IC exposure with sample positions and main cryolithological features (modified from Strauss and Schirrmeister, 2011).
Radiocarbon dating was performed on plant macro remains by accelerator mass
spectrometry (AMS) at the Poznan Radiocarbon Laboratory, Poland (1.5
SDH-Pelletron Model “Compact Carbon AMS”), for 10 samples of the Buor Khaya
exposure profiles (Buo-02 and Buo-04), and at the CologneAMS laboratory,
Germany (6 MV Tandetron), for 14 samples of the Buor Khaya drill core (BK-8).
Samples were prepared using standard methods including acid–base–acid
extraction with 1 % HCl and 1 % NaOH. Extraction times with HCl and NaOH
were reduced if the plant fragments were small and fragile to avoid sample
destruction or loss. The clean and dry samples were combusted and the
CO
Three frozen segments of the drill core were separated for luminescence
dating in order to determine sediment deposition ages (e.g. Aitken, 1998).
Luminescence dating was applied because the method allows for dating of material
beyond the limits of radiocarbon dating or evaluating results, when the
radiocarbon method reaches the non-finite range of ages. The segments were
taken from the lowermost part of the BK-8 drill core (with sample IDs
referring to the sample depth in m b.s., BK-8_12.95-12.8,
BK-8_16.55-16.25 m b.s., and BK-8_18.90-18.70).
Under subdued light, the outer 2 cm layer of material was removed during
controlled thawing to retrieve the inner core part that was not exposed to
light during drilling and core preparation. The outer material was used for
ice/water content measurements and high-purity Germanium (HPGe), low-level
gamma spectrometry of the sediment's radionuclide content. The inner core
part was processed for quartz and feldspar. The lack of pure extractable
quartz and coarse-grain material (> 100
Preparation of aliquots was done on aluminium discs of 4, 2, and 1 mm
diameter, depending on the trade-off between small amounts of material and
luminescence signal intensities. The infrared-stimulated luminescence
(IRSL) of feldspars was measured using the TL/OSL DA-20 Reader
(Bøtter-Jensen et al., 2003), equipped with a
The element (cation) content of ground ice was analysed by inductively coupled plasma
optical emission spectrometry (ICP-OES; Perkin-Elmer Optima
3000 XL), while the anion content was determined by ion chromatography;
Dionex DX-320). Hydrogen carbonate concentrations were measured by titration
with 0.01 M HCl using an automatic titrator (Metrohm 794 Basic Titrino).
Pore-water EC and pH were measured using a WTW MultiLab 540 multi-parameter
device equipped with a TetraConTM 325 cell referenced to 20
Ground temperatures measured at 4 h intervals for almost 3 years,
from 11 May 2012 to 27 April 2015, ranged between
Two composite profiles of Yedoma IC sections (Buo-02 and Buo-04) were studied in 2010 at coastal outcrops on the western shore of Buor Khaya Peninsula (Strauss and Schirrmeister, 2011). The Buo-02 profile extended approximately 10 m from the cliff edge down to a thermo-terrace where deeper-lying permafrost deposits were buried by talus material (Fig. 3). Several 2–3 m wide and 5–7 m deep exposed ice wedges were present at a approx. 150 m wide thaw slump. The top of the Yedoma hill was marked with a trigonometric point (30.5 m a.s.l.) approximately 100 m away.
Soil and organic matter properties of the Buo-02 profile (note that due to overlapping sub-profiles, different values may be displayed at similar heights).
The composite Buo-02 profile started at 23 m a.s.l. and has four overlapping sub-profiles (A to D; Fig. 3). Summary of the characteristic sediment parameters are given in supporting online material (SOM 1; see Supplement). The active layer of Buo-02 was 0.7 m thick and was composed of brownish sand including recent roots. The lowermost part of the active layer at 22.7 to 22.3 m a.s.l. consisted of grey and silty sand with several larger plant fragments. Below the permafrost table, from 22.3 to 21.8 m a.s.l., the cryostructure of sub-profile A was horizontally banded (< 1 cm thick bands) and composed of densely layered ice lenses (SOM 2). Fine ice lenses and vertical veins were observed between the ice bands. The sediment was brownish-grey fine-sandy silt, with sporadic iron oxide patches. At 21 m a.s.l. larger organic patches occurred giving evidence for a cryoturbated palaeosol. The uppermost part of sub-profile B was marked by concentric organic-rich patches and plant detritus indicating another palaeo-cryosol horizon. Around these organic patches the sediment was composed of grey-brown silts and fine-sandy silt containing vertical filament roots. The cryostructure was banded, especially visible at 19.5 m a.s.l. (SOM 2). In the lower part, lens-like to structureless cryostructures were found. Here at 18 m a.s.l., a palaeo-cryosol with tongues of light-brown material occurred. Sub-profile C was composed of grey to brownish silty fine sand. The uppermost sample was ice-saturated with ice veins up to 10 mm thick. At the underlying parts down to 16.1 m a.s.l., the cryostructures were coarse-to-fine lens-like (SOM 2). In sub-profile D, a remarkable heterogeneity of sediment composition was observed. In the upper part at 18.5 m a.s.l. the sediment was composed of greyish silt with brown patches and larger plant fragments. From 17.5 to 17 m a.s.l., a peat layer and peat inclusions appeared, along with vertical and diagonal ice veins. Below the peat layer, the sediment consisted of brownish silty sand with several plant fragments. The cryostructure was micro-lens-like with some ice veins (SOM 2).
The measured absolute ice contents varied between 20 and 90 wt % (Fig. 4);
ice oversaturation was connected to organic-rich palaeo-cryosol horizons.
The grain-size distributions were dominated by fine (18–32 %), medium
(5–22 %), and coarse (15–31 %) silt with a clay component (7–14 %),
and fine (8–30 %), medium (5–30 %), and small coarse (0.1–1.4 %) sand
fractions. The mean grain size varied between 26.6 and 69.9
Bulk density (BD) values varied around 1 g cm
Comparison of robust grain-size end-members, their explained
variances of scores, and performance of original vs. modelled data (using the
mean robust end-members,
Overview photo and scheme of the Buo-04 Yedoma IC exposure with sample positions and main cryolithological features (modified from Strauss and Schirrmeister, 2011).
Soil and organic matter properties of the Buo-04 profile (note that due to overlapping sub-profiles, different values may be displayed at similar heights).
The second composite profile Buo-04 was a 15 m long sequence, which was surveyed downwards starting in front of a steep wall at the cliff edge, crossing the thermo-terrace, and ending at a large thermokarst mound at beach level (Fig. 5). Sub-profiles from two thermokarst mounds overlapped. The uppermost sub-profile A (18.5 to 13.6 m a.s.l.) was exposed at a steep wall between two longitudinal cut-ice wedges. A summary of the characteristic sediment parameters is given in SOM 1. The uppermost sample was taken from the active layer in the zone of modern vegetation and roots. The frozen deposits consisted of greyish-brown silty fine sand with a lens-like cryostructure and with horizontal ice bands in several parts. The sediments and the ice bands bent on both sides towards the ice wedges. The nearby studied syngenetic ice wedge was diagonally cut by the exposure wall (10 m apparent width). Here, 21 ice-wedge samples were taken at 0.5 m intervals (SOM 3). The light-grey ice wedge contained gas bubbles and several mm wide vertical sediment stripes. Sub-profile B (10.0 to 7.6 m a.s.l.) consisted of greyish-brown silty fine-grained sand. The cryostructure was layered with ice bands < 2 mm thick. Between the ice bands, horizontally oriented ice lenses occurred (SOM 3). Coarse plant and wood fragments were visible at 9 m a.s.l. The lowermost thermokarst mound (sub-profile C) was sampled in three places (SOM 3). The uppermost part of sub-profile C between 9 and 7 m a.s.l. was characterized by greyish-brown silty fine-grained sand and the occurrence of plant detritus, much root material, and smaller plant stems. At 8.5 m a.s.l. coarse lens-like ice bands occurred. These bands appeared at 5 cm intervals and ice lenses (< 1 mm thick and 0.5 to 1 cm long) in the sediment interlayers were reticular oriented. At 8 m a.s.l., a matrix of greyish-brown silty fine sand contained a peaty cryoturbated palaeosol. Plant detritus was layered at 7 m a.s.l. The sediment in the middle part of sub-profile C between 6.8 and 5.5 m a.s.l. became sandier with depth. The peaty-bedded and horizontally bedded layers continued. In addition, coarse plant and wood fragments were found at 6.5 to 6.0 m a.s.l. At 6.8 m a.s.l., the deposits were ice super-saturated and the cryostructure was composed of coarse ice lenses surrounding plant fragments. Ice bands less than 0.5 to 4 mm thickness occurred. The lowest part of sub-profile C (5 to 4 m a.s.l.) was sandier and drier. Here a yellowish light-grey matrix with iron oxide spots and broken ice lenses as well as horizontal ice fissures indicated a disturbance of the deposits (SOM 3).
The absolute ice contents of the Buo-04 sequence varied between 22 and 59 wt %.
The grain-size distribution was again dominated by fine (10–25 %),
medium (7–25 %), and coarse (26–41 %) silt fractions and a clay
component (6–14 %). The sand contents were low (4–10 wt %) in the
uppermost sub-profile A (18.5 to 13.6 m a.s.l.) but similar to the Buo-02
sequence (21–43 wt %) in the B and C sub-profiles (9.6 to 4.3 m a.s.l.). This
was also mirrored in the mean grain-size values between 21.2 and 27.5
BD values varied between 0.5 and 1.5 g cm
Scheme of the BK-8 permafrost core including the main cryolithological units. The legend is given in Figs. 3 and 5.
Soil and organic matter properties of the BK-8 Yedoma IC core.
According to a detailed cryolithological description (SOM 4 and 5), the BK-8
core was sub-divided in the field into five segments completed by a sixth
segment characterized by specific pore-water composition (Fig. 7).
Characteristic sediment parameters are summarized in SOM 1. The
Radiocarbon dating on plant macro remains (and two sediment samples containing plant remains: COL2945 and COL2796). Calibrations were done using Calib 7.0.2 and the IntCal13 curve (Reimer et al., 2013). Ranges marked with a * are suspect due to impingement on the end of the calibration data set. Depth is given in metres below surface level (m b.s.l.) and height in metres above sea level (m a.s.l.). Poz: Poznan Radiocarbon Laboratory, Poland; COL: CologneAMS, Germany. The bold marked samples are from the ice wedge in BK-8.
The absolute ice contents of the BK-8 core varied between 66 and 84 wt %
(Fig. 8). The grain-size distribution was relatively uniform, dominated by
fine (12–20 %), medium (11–24 %), and coarse (23–33 %) silt and
containing clay (9–15 %), fine-sand (5–15.8 %), medium-sand (7–20 %),
and a small fraction of coarse-sand (1–8 %) components. The mean grain
size varied between 31.2 and 73.6
BD values varied between 0.6 and 1.6 g cm
Radiocarbon dates were obtained from five Buo-02 profile samples between 16
and 22.3 m a.s.l., and ranged between 45.0
Samples were selected from the BK-8 14 drill core for radiocarbon dating,
including four plant fragments and OM samples that were isolated from the
ice wedge (Table 2). The five ages from above the ice wedge between 3.35 and
0.3 m b.s. (30.65 and 33.7 m a.s.l.) covered the late-glacial period with ages of
11.4
Results of IRSL dating from three BK-8 core samples using
different feldspar grains on 4 mm aliquots (
Measurements of ice content, isotope ratios, electrical conductivity (EC), pH, and solutes over height in m a.s.l. for samples from the Buo-02 exposure.
Measurements of ice content, isotope ratios, electrical conductivity (EC), pH, and solutes over height in m a.s.l. for samples from the Buo-04 exposure.
Measurements of ice content, isotope ratios, electrical conductivity (EC), pH, and solutes over depth for samples from the BK-8 core.
The Yedoma IC below the ice wedge was dated by IRSL at three depths:
12.95–12.8, 16.55–16.2, and 18.9–18.7 m b.s. The dating results for
different grain-size fractions are summarized in Table 3. Applying the CAM,
the deposition ages of the 12.95–12.8 m b.s. core interval are 46.1
Stable isotope ratios of Buo-02 pore ice ranged between
Stable Buo-04 pore ice isotope ratios showed a trend from lower values
(around
The pore-space solution from the BK-8 core showed considerable hydrochemical
variability with depth (Fig. 11). Stable isotope ratios were the highest in
the active layer, and were lower and decreased in the late-glacial–early
Holocene cover above the ice wedge. Isotope ratios in the ice wedge were
lower (
Stable isotope ratios for the Buo-02 and Buo-04 exposures and the BK-8 core samples. For reference, they are plotted together with precipitation and meteoric water lines, both global (GMWL; solid line) and local (LMWL; dashed line).
Compilation of geochronological results of Yedoma IC obtained in two profiles (Buo-02, Buo-04) and one drill core (BK-8) at the western coast of Buor Khaya Peninsula.
Anion concentrations in the active layer and the late-glacial–early
Holocene cover were dominated by Cl
Stable isotope ratios are grouped based on source and on their relationship
to one another. Samples from BK-8 and the exposures range from
The chronostratigraphy of the Buor Khaya Yedoma IC and its overlying
late-glacial–early Holocene cover is based on 24 radiocarbon dates and
three IRSL datings of the lowermost BK-8 core Yedoma IC unit (Fig. 13).
The Buo-04 profile and the BK-8 core deposits below the ice wedge exhibit
radiocarbon ages between 54.1
Continued Yedoma IC formation is assumed by sedimentary radiocarbon ages of
the Buo-02 profile between 45.0
Generally, studying permafrost stratigraphies in palaeo-environmental research by sampling coastal exposures in sub-profiles and drill cores introduces certain considerations that must be accounted for during data interpretation. The preservation of late Pleistocene ice-rich permafrost depends not only on predominant climate dynamics but also on palaeo-relief conditions and the past spatial distribution of accumulation and erosion areas. To capture the kilometre-scale spatial variability, sampling of coastal exposures advances our understanding of this variability, or at least provides the chance to relate records of the same age spatially. As shown in Fig. 13 the oldest Yedoma IC units with non-finite radiocarbon ages were found at different altitudes, below 15 m a.s.l. for profile Buo-04 and between 16 and 9 m a.s.l. for core BK-8; this points to different deposition heights within the former surface morphology. The Buo-04 and Buo-02 Buor Khaya Yedoma IC profiles, even though they were sampled at similar altitudes, cover different periods of Yedoma IC deposition; the Buo-04 represents formation > 49 kyr BP, and the Buo-02 represents deposition between approx. 45 and 30 kyr BP. The exposure accessibility and technical difficulties encountered in keeping the sampled material frozen during summer field campaigns as well as the lower sampling resolution, if compared to permafrost drilling in springtime, limit the quality of exposure data. The drilling approach allows for higher sampling resolution of frozen material and better borehole instrumentation for, e.g., ground-temperature measurements. The core material is also limited since it is difficult to choose a drilling location from the ground surface that gives a representative sample and avoids ice wedges. This study attempts to combine the advantages of both stratigraphic sampling methods.
The Buo-02 and Buo-04 profiles (Figs. 3 to 6) show no distinct internal
stratification that allows cryolithological units to be defined within both
sequences. However, palaeo-cryosol horizons at 17 to 18 m a.s.l. in Buo-02 and at
6 to 8 m a.s.l. in Buo-04 are remarkable in ice content, BD, TOC, TOC
Results of the end-member analysis of the studied
Buo-02, Buo-04, and BK-8 sequences;
The BK-8 core is divided into six cryolithological units, according to field
observations, core descriptions, and analytical data sets. The active layer
(34.0–33.45 m a.s.l.) is characterized by the lightest stable water-isotope
values (
According to the end-member analysis (Fig. 14) each Yedoma IC sequence is
characterized by a specific robust end-member (rEM) signature. However,
three typical end-members (rEM1 to rEM3) with similar patterns are modelled
in all three records. The fine-silt rEM1 (main mode at 3–5
The Yedoma IC formation comprises primary soil accumulation and cryogenic processes, for instance cryogenic weathering, ice segregation, syngenetic ice-wedge growth, secondary sediment deformation, and reworking due to cryoturbation. Such processes were supported by the long-lasting severe continental climate conditions of the late Pleistocene. Moreover, the formation of large polygon ice-wedge nets and thick continuous ice-rich permafrost deposits was related to the existence of stable, poorly drained accumulation plains with low inclination. In contrast to the loess hypotheses of Yedoma IC formation (e.g. Tomirdiaro, 1980; Murton et al., 2015), the proposed cryolithogenetic concept integrates several previous formation concepts and, in particular, takes into account the important role of ground ice in the deposit formation process. Generally, this corresponds to the polygenetic character of Yedoma IC formation. It also includes the potential for several sediment sources, weathering processes, and pathways by which sediments in typical periglacial landscapes can build up the Yedoma IC.
Comparison of major ion composition of
Organic matter characteristics of the Buor Khaya Yedoma.
Left: correlation of the TOC content and the TOC
Whereas the EC of pore solutions in Buo-02, Buo-04, and most of BK-8 is less
than 3000
We suggest that the saline layer at the bottom of BK-8 is the result of
Rayleigh fractionation during the re-freezing of a thawed layer from above.
There are numerous points to support this interpretation. First, neither
the age nor the composition of the BK-8 mineral component show changes
correlated with the more concentrated solution, with the possible exception
of somewhat higher MS. Second, the concomitant increase in
We therefore suggest that during the warm and moist summer conditions of the MIS 3 interstadial period (Andreev et al., 2011; Wetterich et al., 2014), a talik horizon more than 2.5 m thick developed and subsequently re-froze making it post-depositional epigenetic permafrost. Such thawing and re-freezing can be observed, for example, in thaw bulbs beneath small water bodies such as polygon ponds (Langer et al., 2011). Our borehole was not deep enough to capture the lower boundary of this post-deposition re-freezing process nor to determine how local this phenomenon is.
According to pollen data from Zimmermann et al. (2016), the saline layer
segment of the BK-8 core is characterized by increasing wetness (e.g. algae
and spores) but also increasing shrub and tree taxa (
Our comprehensive cryolithogenetic concept of polygenetic Yedoma formation (Schirrmeister et al., 2013) combines cryogenic weathering, periglacial material transport and accumulation, and relief shaping under cold-arid climate conditions and considers two general formation processes: (1) primary accumulation in low-centred ice-wedge polygons and (2) syngenetic freezing and ice-wedge growth. Following this concept, the Yedoma IC represents a specific periglacial facies, whose formation is controlled by the interaction of climate, landscape, and geological preconditions typical for non-glaciated Arctic and subarctic lowlands and foothills.
Comparing the records of the Buor Khaya Yedoma IC with the well-studied profiles of the Bykovsky Peninsula (Fig. 1; e.g. Schirrmeister et al., 2002; Sher et al., 2005; Grosse et al., 2007) approx. 100 km west, the study sites of Mus Khaya on the Yana River approx. 150 km south-east (Konishchev, 2013) as well as the coastal exposure from Bol'shoy Lyakhovsky Island (Fig. 1; Andreev et al., 2009; Wetterich et al., 2011a, b, 2014) approx. 350 km north-east of Buor Khaya Peninsula, we come to the conclusion that these sections formed during the same period between approx. 60 and 12 kyr BP (late MIS 4 to MIS 2), which is typical for Yedoma IC formation (Schirrmeister et al., 2011b). The cryostructures observed at the studied Yedoma IC sequences as well as the major cryolithological parameters are also similar in range and internal variations. In this sense the Buor Khaya Yedoma IC generally belongs to the same late Pleistocene palaeo-environment and was formed under similar palaeo-climatological and palaeo-geographical conditions as Yedoma IC remains around the Laptev Sea.
The ground-temperature record (Fig. 2) does not show any specific variations due to palaeo-warming signals or heat transfer from the Laptev Sea. However, the typical warming of cold permafrost around the Arctic (Romanovsky et al., 2010) and in Siberian Yedoma boreholes at Cape Mamontov Klyk in the western Laptev Sea (Overduin et al., 2008) or at the Mamontovy Khayata site on the Bykovsky Peninsula (Kholodov, 2009) was not observed here.
Summarizing the OM characteristics, the Yedoma IC deposits from the Buor
Khaya Peninsula contain
When considering that the Yedoma IC exposed at the Laptev Sea coasts
provides source material for marine deposits and is a terrigenic end-member
of organic carbon on the eastern Siberian shelf, the study of the composition
and formation of Yedoma IC is essential to understanding the fate of
terrigenous OM across the Laptev Sea as studied by Bröder et al. (2016),
whose marine transect began in the Buor Khaya Bay. The
The studied Yedoma IC permafrost exposed at the western coast of the Buor
Khaya Peninsula in the central Laptev Sea accumulated from approx. 54.1
The data in this article are available at
The authors declare that they have no conflict of interest.
The study presented here is part of the Helmholtz–Russia Joint Research Group. We gratefully acknowledge the German Federal Ministry of Education and Research (BMBF) for funding this study as part of the joint German–Russian research project CARBOPERM (03G0836B, 03G0836F). Moreover, we acknowledge the support by the European Research Council (starting grant no. 338335) and the Initiative and Networking Fund of the Helmholtz Association (no. ERC-0013). We thank our colleagues, who helped during fieldwork in 2014, especially Dmitry Mel'nichenko and colleagues from the Hydrobase Tiksi, and Waldemar Schneider from AWI Potsdam, who greatly supported the logistics of this expedition. The analytical work in the AWI laboratories was expertly conducted by Ute Bastian, Dyke Scheidemann, Antje Eulenburg, Hanno Meyer, and Lutz Schönicke. We are grateful to Marcus Richter (TU Dresden) and to Ingrid Stein (TU Bergakademie Freiberg) for IRSL analyses, and to Jörg Erzinger, Sabine Schumann (GFZ Potsdam), and Torben Windirsch (University of Potsdam) for TS measurements. Finally, the paper benefited from the reviews of Mikhail Kanevskiy (University of Alaska Fairbanks) and one anonymous reviewer with constructive comments, and English language corrections from Candace O'Connor (Fairbanks Alaska).The article processing charges for this open-access publication were covered by a Research Centre of the Helmholtz Association. Edited by: A. V. Eliseev Reviewed by: M. Kanevskiy and one anonymous referee