Ice sheets extending over parts of the East Siberian
continental shelf have been proposed for the last glacial period and during
the larger Pleistocene glaciations. The sparse data available over this
sector of the Arctic Ocean have left the timing, extent and even existence of
these ice sheets largely unresolved. Here we present new geophysical mapping
and sediment coring data from the East Siberian shelf and slope collected
during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish – Russian – US
Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions). The
multibeam bathymetry and chirp sub-bottom profiles reveal a set of glacial
landforms that include grounding zone formations along the outer continental
shelf, seaward of which lies a
The glacial history of the Siberian continental shelf of the East Siberian Sea is poorly known and marine geological and geophysical data from this region are scarce. Most of the area is shallower than 120 m, implying that it was exposed during the sea level low stand of the Last Glacial Maximum (LGM) and the larger glaciations following the mid-Pleistocene transition (Lambeck et al., 2014; Rohling et al., 2014), even considering glacial isostatic adjustments (Klemann et al., 2015) (Fig. 1). One consequence of the shallowness of the East Siberian shelf is that submarine glacial landforms, signifying the presence of an ice sheet (Dowdeswell et al., 2016), may have been eroded during regressive and transgressive cycles.
Map of the Arctic Ocean showing the maximum extent of Quaternary glaciations (red dashed line) (Jakobsson et al., 2014). The 120 m isobath is highlighted across the Siberian, Chukchi and Beaufort seas to highlight the potential extent of exposed land during the global eustatic low stand of the LGM. Yellow arrows indicate the direction of ice flow inferred from the orientation of glacial landforms on the deep Arctic seafloor (Jakobsson et al., 2016). Glacial extents and flow directions around the New Siberian Islands (NSI) and De Long Islands (DLI) are redrawn from Basilyan et al. (2008). Dashed lines across the East Siberian shelf and hatching on the Chukchi Borderland (CB) indicate areas of probable glacial ice in the late Quaternary (Jakobsson et al., 2014). Known glacially excavated cross-shelf troughs (blue) and trough mouth fans (brown) are redrawn from Batchelor and Dowdeswell (2014) – the exception is the single trough on the East Siberian shelf, which is described in this paper. AP – Arlis Plateau; AR – Alpha Ridge; BS – Beaufort Sea; FS – Fram Strait; MR – Mendeleev Ridge; LR – Lomonosov Ridge.
On formerly glaciated margins, areas of fast-streaming glacial ice are recognized by the presence of glacially excavated cross-shelf troughs (CSTs) (Batchelor and Dowdeswell, 2014). CSTs and their sedimentary archives are diagnostic features for the presence of former ice sheets (Dowdeswell et al., 2016) and extensively used to reconstruct ice sheet dynamics (Polyak et al., 1997; Anderson et al., 2002; Winsborrow, et al., 2010; Jakobsson et al., 2012a; Kirshner et al., 2012; Hogan et al., 2010, 2016). Their association with fast-streaming ice is supported by the common presence of mega-scale glacial lineations (MSGL) within them (Clark, 1993; Stokes and Clark, 2002; Ó Cofaigh et al., 2002; Ottesen et al., 2005; King et al., 2009). MSGL are stream-lined, trough-parallel sedimentary landforms that range from kilometers to tens of kilometers in length (Stokes and Clark, 2002) and have been observed forming beneath active ice streams in West Antarctica (King et al., 2009). Within a CST, large asymmetrical sedimentary wedges oriented transversely to the ice flow direction mark stillstands in the streaming-ice and are known as grounding zone wedges (GZWs) (Batchelor and Dowdeswell, 2015). They are formed by high rates of subglacial sediment delivery to the grounding zone and can occur at vertical or lateral pinning points in the trough bathymetry or near the shelf break (Batchelor and Dowdeswell, 2015). MSGL are often found beneath and/or on top of GZWs (Jakobsson et al., 2012a), which supports the interpretation that GZW formation occurs during stillstands of fast-streaming ice. GZWs typically have much larger length-to-height ratios than terminal moraines, which are more commonly found in inter-ice stream regions on glaciated margins and are associated with slower ice flow velocities (Ottesen and Dowdeswell, 2009; Batchelor and Dowdeswell, 2015; Dowdeswell et al., 2016).
Ice streams within CSTs terminate in a calving front where large volumes of icebergs are discharged into the ocean or feed into ice shelves. Seaward of the shelf break, large volumes of subglacial sediments are discharged onto the slope in front of CSTs and form bathymetrically prominent trough mouth fans (TMFs) (Ó Cofaigh et al., 2003; Batchelor and Dowdeswell, 2014). These are composed of stacked glacio-genic debris flows, deposited while the ice was at or near the shelf break and are interbedded with ice-distal or open-water marine sediments (Laberg and Vorren, 1995; Elverhøi et al. 1997; Taylor et al., 2002). TMF development is more prominent in front of CSTs that have hosted repeated ice stream activity across numerous glacial cycles and where sediment is delivered to relatively shallow continental slopes (Batchelor et al., 2014).
Twenty glacially excavated troughs emptying directly into the Arctic Ocean are identified in existing bathymetric and seismic data from north of Fram Strait (Batchelor and Dowdeswell, 2014) (Fig. 1). Several of these can be traced back into tributary fjords on adjacent landmasses, or towards the center of former ice sheets, and are particularly pronounced along the Barents–Kara and North American margins (Batchelor and Dowdeswell, 2014; Jakobsson, 2016) (Fig. 1). By contrast, the shallow shelves of the East Siberian and Chukchi seas lack any identified CSTs. Despite the absence of these diagnostic features, ice sheets extending over parts of the East Siberian continental shelf have been proposed in literature during the LGM (Toll, 1897; Hughes et al., 1977; Grosswald, 1990), MIS 6 (Basilyan et al., 2008, 2010; Jakobsson et al., 2016) and the larger Pleistocene glaciations that followed the mid-Pleistocene transition (Colleoni et al., 2016; Niessen et al., 2013).
The existence of an ice sheet on the New Siberian Islands was first proposed
by Toll (1897) based on the widespread
occurrence of ice wedges, which he interpreted as relict glacial ice.
Although ice wedges are today known to be formed in permafrost by the
refreezing of water flowing into cracks, glacio-tectonized Cretaceous and
Cenozoic sediments on the New Siberian Islands do contain thick inclusions of
ice interpreted to originate from an ice sheet and are overlain by
conformable Quaternary sediments (Basilyan et al., 2008, 2010). The
orientation of the glacio-tectonic features indicates that glacial ice on the
New Siberian Islands flowed from a north-northeast direction and likely
nucleated over the De Long Islands, where small glaciers remain today
(Basilyan et al., 2008) (Fig. 1). Uranium–thorium
(
Another line of evidence for glacial ice on the Siberian continental shelf is
the presence and orientation of glacio-genic features and sedimentary
deposits mapped on the seafloor in the adjacent Arctic Basin. These glacial
features are mapped on the lower slope of the East Siberian Sea and on the
crest of shallower ridges and plateaus of the Arctic Ocean (Niessen et al.,
2013; Jakobsson et al., 2016). Streamlined glacial lineations on the seabed
of the Arlis Plateau and the base of the East Siberian continental slope have
orientations that indicate ice flow from the East Siberian shelf (Niessen et
al., 2013; Jakobsson et al., 2016) (Fig. 1). Niessen et al. (2013) speculate
that the modern water depths of these features, ranging between about 900 m
and 1200 m below sea level (m b.s.l.), imply an ice thickness on the East
Siberian continental shelf of up to 2 km. Glacial lineations also exist on a
heavily ice-scoured crest of the southern Lomonosov Ridge (81
Despite the mounting evidence for glacial ice on the East Siberian shelf, our ability to define its extent and timing remains limited. In part this is due to the lack of glacial morphology on the shelf that could be used to link the terrestrial observations with marine mapping results in deeper water settings of the Arctic Ocean. However, the sparse data availability across the East Siberian shelf implies that the absence of known submarine geomorphological features does not preclude their existence. Here we present new geophysical and sedimentological evidence for a glacial trough north of the De Long and New Siberian Islands on the outer margin of the East Siberian shelf. The trough was most likely occupied by glacial ice during MIS 6 and certainly free from glacial ice during the LGM.
Ship track and coring sites during SWERUS-C3-L2. Location of the geophysical data and sediment cores discussed in this paper is highlighted.
The data presented in this paper were acquired on Leg 2 of the SWERUS-C3
2014 Expedition on IB
Detail of study area showing ship track with the yellow and orange lines indicating portions of the chirp sub-bottom data presented in Figs. 4 and 5. Locations of sediment cores discussed in the text are shown. Blue and brown shading represents the bounds of the glacial trough and trough mouth fan deposits (respectively) as interpreted from the geophysical data collected during SWERUS-C3-L2. Bathymetry from IBCAO (Jakobsson et al., 2012b), with 50 m major contour intervals.
Composite chirp sub-bottom profile from the shallow East Siberian
shelf to the shelf break at
A brief summary of the geophysical mapping methods during the SWERUS-C3
expedition is included here; further details are described in Jakobsson et
al. (2016). Multibeam bathymetry and sub-bottom profiles were collected with
the Kongsberg EM 122 (12 kHz, 1
Four sediment cores (inner diameter of 100 mm) are presented in this study
(Table 1). They were collected using either a piston (PC) or gravity (GC)
corer, both rigged with a 1360 kg core head. The unsplit sediment cores were
allowed to equilibrate to room temperature (20
Location and length of sediment cores discussed in this paper.
The undrained shear strength was calculated using the cone geometry, weight
and penetration:
Shore-based measurements on the split cores were conducted at the Department of Geological Sciences, Stockholm University. These included additional magnetic susceptibility measurements, grain size and x-ray fluorescence (XRF)-core scanning. The magnetic susceptibility was remeasured on the MSCL using a Bartington point sensor. Compared to the loop sensor measurements on the whole core, the point sensor provides superior horizontal resolution (lower effective sensor length) but only measures the susceptibility of sediments in the upper few millimeters from the split core surface.
Sediment grain size (2
Elemental abundances were measured on the archive half of the split cores using a Cox Analytical Systems Itrax XRF-core scanner core scanner. Analyses were
made with a Mo tube set to 55 kV and 50 mA, a step size of 2 mm and a
counting time of 20 s. The data were normalized by the
incoherent
Accelerator mass spectrometry (AMS) radiocarbon measurements were made on
samples containing the planktonic foraminifer
The sub-bottom stratigraphy from the outer shelf 20-GC1 (77
Location of sediment cores 22-PC1, 23-GC1 and 24-GC1 along the composite chirp sub-bottom profile. The interpreted profile is offset by 200 ms TWT from the true depth. The location of the profile is shown in Fig. 3.
Radiocarbon dates and calibrations from sediment cores 20-GC1,
23-GC1 and 24-GC1. All dates were calibrated with the Marine13 calibration
curve (Reimer et al., 2013), with
The base of Unit 3 is defined by a hummocky reflector (R2) that overlies two
acoustically transparent facies (Units 4 and 5). The thickness of Unit 4
varies considerably along the track line, in places infilling v-shaped
wedges, and near the shelf break, thickening into two prominent sedimentary
deposits, here referred to as mounds M1 and M2 (Figs. 4, 5). Although the
exact lengths cannot be determined because of the orientation of the ship
track, M1 is
Units 4 and 5 are similar in appearance but separated by an often strong and
planar reflector (R3), which exists seaward of 360 m b.s.l. (480 ms TWT).
A third sedimentary deposition, mound M3, is recognized within Unit 4 and
lies landward of M1 and M2 within seismic Unit 5 (Figs. 4, 5). It is
At the shelf break, the base of units 4 and 5 are separated by a distinct
acoustically transparent, wedge-shaped sediment package (Unit 6) whose upper
boundary is defined by R3 and whose lower boundary is defined by R5
(Figs. 4, 5). Seaward of the shelf break, only the uppermost acoustically
laminated unit (Unit 3) can be laterally traced (Fig. 5). It overlies a
complex sequence of strong undulating, discontinuous acoustically laminated
sections, interspersed with thicker acoustically transparent intervals
(Fig. 6). This sequence extends to the maximum depth of the surveyed area
(
Representative acoustic stratigraphy of the continental slope, where a thin acoustically laminated veneer of sediments overlies a series of stacked acoustically transparent intervals. Some of the acoustically transparent intervals are laterally continuous but all exhibit substantial downslope variations in thickness. The location of the profile is shown in Fig. 3.
Multibeam mapping results.
The seabed above water depths of 280–320 m b.s.l. is heavily ice scoured. Below
320 m b.s.l., iceberg scouring becomes less prevalent. With the exception of the
iceberg scours, there are no prominent morphological seafloor features
distinguishable along the transect, where a single swath of multibeam
bathymetry was collected (Fig. 7). Where the small survey was made in the
vicinity of coring site 23-GC1, the three sedimentary mounds identified in
the sub-bottom profiles (Fig. 4) are visible as morphological seafloor
expressions (Fig. 7). The multibeam bathymetry reveals that the mounds
extend laterally as far as the survey covers (
The bathymetry from the International Bathymetric Chart of the Arctic Ocean
(IBCAO) (Jakobsson et al., 2012b)
is shown as a backdrop in Fig. 7. The depth difference between the newly
collected multibeam bathymetry with IB
Three of the sediment cores presented in this study penetrated to the base of acoustic Unit 3 (22-PC1, 23-GC1 and 24-GC1), while the shallowest core (20-GC1) sampled sediments from acoustic Unit 1. The bases of 22-PC1, 23GC-1 and 24GC-1 all contained a dark grey, poorly sorted sequence of coarser-grained sediments (sedimentary unit B) interpreted as a diamict (Fig. 8). The transition into this lower sedimentary unit is abrupt and is reflected by a substantial increase in sediment bulk density, compressional-wave velocity and magnetic susceptibility (Fig. 8). The undrained shear strength increases in Unit B but remains relatively low, only exceeding 15 kPa in 23-GC1 (Fig. 8). Point and loop sensor susceptibility measurements coincide throughout sedimentary Unit A and diverge in the coarser-grained Unit B (Fig. 8). This likely reflects the presence of larger magnetic clasts irregularly distributed within the coarse grained sediments. Benthic and planktic foraminifera are found within Unit B in both 22-PC and 24-GC.
Detailed view of sub-bottom data, penetration and physical property measurements of cores 22-PC1, 23-GC1 and 24-GC1. All cores penetrate down to a strong reflector that marks the top of an acoustically transparent interval. The base of all the cores recovered a coarser-grained, poorly-sorted unit displaying a higher bulk density and magnetic susceptibility. This is interpreted as a diamict.
Stratigraphic correlation of core 20-GC1, 22-PC1, 23-GC1 and 24-GC1,
based on MSCL, XRF-scanning, digital images and radiocarbon dating results.
The acoustically laminated sediments of Unit 3 (Figs. 4 and 5) are
represented by sedimentary Unit A in cores 22-PC1, 23-GC1 and 24-GC1. These
undisturbed sediments overlie the glacial diamict of Unit B, which
corresponds to acoustic Unit 4. The base of Unit A is older than
In the upper 50 cm of 22-PC1, 23-GC1 and 24-GC1, a less pronounced
coarser-grained interval is present, again displaying higher bulk density but
with no notable change in the magnetic susceptibility. Although notable, for
the purpose of this paper, this interval has not been classified as a
distinct sedimentary unit. Correlation between the two sedimentary units (A
and B) in 22-PC1, 23-GC1 and 24-GC1 is straightforward using the grain size
and physical property data (Fig. 9). It is further refined by incorporating
the Ca
Core 20-GC1, obtained from the shallow shelf, also contained a
coarser-grained, dark grey facies at its base, transitioning into
lower-density and susceptibility sediments above 0.5 m b.s.f. Six
radiocarbon dates were obtained from below 0.55 m b.s.f. in this core and
indicate that the basal sequence is younger than 14 cal kyr BP and was
deposited after sea level transgression of this site following the last
glacial cycle (Cronin et al., this volume). Although the base of the core has
similar sedimentary characteristics to Unit B in 22-PC1, 23-GC1 and 24-GC1,
it is not syndepositional. Radiocarbon dates from a mollusk shell in 23-GC1
(1.69–1.86 m b.s.f.) and a foraminiferal bearing interval in 24-GC1
(1.91–1.93 m b.s.f.) return ages of 33 200
Based on the combined chirp, swath-bathymetry and sediment core data, a
summary of the acoustic units and their interpretation is made. Unit 1 is
interpreted as iceberg-scoured postglacial sediments overlying a sharp
peneplained seafloor on the shallow shelf (
Unit 1 thickens in deeper water depths where it incorporates preglacial and
glacial sediments reworked by sea level lowering during the last glacial
cycle (Fig. 4). The depth of reworking in response to sea level lowering lies
between 260 and 300 m b.s.l. Below this depth, Unit 1 gradually merges with
Unit 3, which can then be traced as a continuous acoustically laminated unit
extending seaward of the shelf break and downslope to water depths of
The acoustically transparent Unit 4, is interpreted as subglacially deposited
sediment (till). It can be traced laterally to the shelf break, where it
forms two prominent sedimentary mounds oriented transverse to the track
profile. These mounds are evident in the bathymetry data (Fig. 7) and extend
laterally beyond the surveyed regions, exceeding widths of
The wedge-shaped acoustically transparent Unit 6, found at the shelf break
and separating the two till sequences, is interpreted as
either a mass wasting deposit or an ice-proximal fan (Dowdeswell et al., 2016), deposited in front
of the ice margin between the advances that formed M3 and M1/2. Downslope,
the acoustically laminated sediments forming Unit 3 drape a
The geophysical data collected from the outer shelf and slope of the East Siberian Sea, north of the De Long Islands, are sparse but contain evidence for many elements commonly associated with a CST. These include grounding line deposits found near the shelf break in a pronounced bathymetric depression that extends landward for more 100 km, seaward of which lies a recognizable TMF. This provides the first evidence for a CST on the Siberian shelf that we hereafter refer to as the De Long Trough. The dimensions of the De Long Trough and associated glacio-genic features are comparable to those from other Arctic glacial troughs recently compiled by Batchelor and Dowdeswell (2014, 2015) and are discussed in the following subsections.
The limited mapping of the interpreted grounding line deposits makes the
absolute discrimination between M1 and M2 uncertain, as is their
interpretation as either GZWs or terminal moraines (Fig. 7). For example, the
outermost sedimentary mound (M2), which is mapped in most detail, displays
pronounced lateral variations in thickness (Fig. 7) that may more closely
resemble a series of terminal moraines than a GZW (Batchelor and Dowdeswell,
2015). On the other hand, length-to-height ratios of all the sedimentary
mounds range between 165 : 1 (5 km
As both GZWs and terminal moraines are grounding line deposits, either interpretation supports the more general conclusion that an ice sheet existed on the outer East Siberian continental shelf. However, as terminal moraines are commonly associated with deposition beneath slowly retreating ice margins, while GZWs are associated with stillstands in fast-streaming ice, the existing data are not capable of unambiguously describing retreat dynamics of the grounded ice. The absence of other diagnostic features for fast-streaming ice (i.e., MSGL), further adds to this ambiguity. However, we cannot rule out the possibility that streamed-lined trough parallel lineations may exist in this region but were simply not captured due to the limited extent of mapping.
The location of the grounding line deposits within a broad bathymetric depression that ends at the shelf break, suggests that they are features preserved within a glacially excavated trough. This trough can be identified in IBCAO Version 3.0 (Jakobsson et al., 2012b) (Fig. 3). In this area IBCAO is completely based on digitized contours from the Russian bathymetric maps published by the Head Department of Navigation and Oceanography (HDNO) in 1999 and 2001 (Naryshkin, 1999, 2001). The source data of the Russian HDNO maps are not publicly available. Given the broad similarity between our mapping results and those portrayed in IBCAO V. 3.0, the identified glacial features in the sub-bottom data, and the more detailed mapping of the grounding line formations near the shelf break, there is no reason to believe that a glacially scoured bathymetric trough is overinterpreted from the source data.
At the same time, bathymetric mapping during SWERUS-C3 does reveal substantial differences in water depth compared to IBCAO Version 3.0 (Fig. 7a). Results from mapping indicate a lower gradient along the base of the trough between 400 and 500 m b.s.l., where the grounding line deposits are mapped, and a steeper slope beyond them, between 500 and 1000 m b.s.l. The dimensions of the De Long Trough at the shelf break, derived from IBCAO, are between 40 and 70 km wide, with a depth of 140 m (Fig. 3). The true depth at the shelf break is closer to 100 m given the new mapping data (Fig. 7a). Although many of the larger Antarctic CSTs and some found off southern Greenland deepen landward, there is no evidence of a reverse gradient within the De Long Trough. This is similar to other high Arctic CSTs in the Barents and Kara seas (Batchelor and Dowdeswell, 2014).
The dimensions of 75 Arctic CSTs, reviewed by Batchelor and Dowdeswell (2014), have modal lengths of 150–200 km (with more than 50 % of them being between 50 and 200 km), widths of 20–40 km and depths of 300–400 m. Batchelor and Dowdeswell (2014) suggest that trough width and length are controlled by the volume of ice and sediment flowing through it, which depends on drainage basin size and the duration/number of times that a paleo-ice stream was active. Conversely, trough depths are more variable and probably controlled by the number of past glaciations, the underlying geology and the tectonic setting. Although the length of the interpreted trough is not accurately defined by the new mapping data (Fig. 3), the distance between 22-PC1 and 23-GC1 is 105 km and provides a minimum estimate for its length. Its width (40–70 km) falls within the modal range of other Arctic troughs, while its depth (100–140 m) is substantially shallower than any recognized Arctic CSTs. Additional bathymetric mapping is required to generate a more accurate and complete representation of the trough dimensions and the glacial features within it.
TMFs are formed when fast-streaming ice delivers large volumes of subglacial sediments to the shelf edge, which is then remobilized and forms a stacked sequence of glacio-genic debris flows (Elverhøi et al., 1997; Laberg and Vorren, 1995; Taylor et al., 2002; Batchelor and Dowdeswell, 2014). The acoustic stratigraphy and morphology of the continental slope seaward of the grounding line deposits is typical of TMF sediments described on other high-latitude continental margins (Ó Cofaigh et al., 2003; Dowdeswell et al., 2016; Batchelor and Dowdeswell, 2014). The laterally discontinuous lenses of acoustically transparent material are glacio-genic debris flows and are interspersed with segments of acoustically laminated sediments, deposited when the ice stream retreated from the shelf edge.
Trough mouth fans can usually be identified in generalized bathymetric charts
by a bulge in bathymetric contours along the continental slope, and a similar
morphology is evident in IBCAO V. 3.0 seaward of the De Long Trough (Fig. 3).
TMFs commonly approach areas of 10
The radiocarbon date from 24-GC indicates that the last episode of glacial
activity in the De Long Trough occurred before
46 300
The absence of glacial ice during the LGM is consistent with the existence of permafrost across much of the submarine East Siberian shelf (Romanovskii et al., 2004; Nicolsky et al., 2012), the reported absence of ice on Wrangel island during the LGM (Gaultieri et al., 2005) and the comparatively limited extent of the Kara ice sheet on the Barents Sea (Möller et al., 2015). The lack of glacial ice in the East Siberian Sea and the Kara Sea during the LGM are both ascribed to generally arid conditions due to a reduction in atmospheric moisture supply to these regions (Gaultieri et al., 2005; Möller et al., 2015). Glacial landforms indicating ice flow from the East Siberian shelf that are mapped on the continental slope of the East Siberian Sea, Arlis Plateau and southern Lomonosov Ridge were also formed prior to the LGM (Niessen et al., 2013; Jakobsson et al., 2016) and are consistent with the absence of glacial ice in the De Long Trough during this time.
The De Long Trough notably connects to the reconstructed ice extents around
the De Long and New Siberian Islands (Basilyan et al., 2008, 2010) (Fig. 1).
Therefore, it is reasonable to assume that glacial activity in the trough is
associated with known glaciations of the New Siberian Islands.
Uranium–thorium (
The current data do not allow us to dismiss the possibility that a smaller local ice cap developed over the De Long Islands and fed an ice stream in the De Long Trough during a stadial of MIS 5. Late Quaternary glacial extents in the Kara Sea, specifically over the Taimyr Peninsula and the Severnaya Zemlya archipelago, were considerably larger during MIS 5d (109 ka) and 5b (87 ka), compared to the MIS 4 and LGM extents (Möller et al., 2015). However, when considering the most recent estimates for the age of glacial ice on the New Siberian islands (Basilyan et al., 2008, 2010) and the date of deep-water glacial features that indicate ice flow directions from the East Siberian shelf (Jakobsson et al., 2016), the most plausible explanation is that an ice stream was active in the De Long Trough during MIS 6. Additional research needs to focus on (1) establishing the connection between glacial ice in the De Long Trough and the existence of a larger ice sheet that covered much of the East Siberian shelf (Fig. 1) and (2) acquiring more detailed dating of the sedimentary sequences overlying the glacial deposits to determine if ice reoccupied the trough during a stadial of MIS 5.
One of the remarkable observations based on the stratigraphy of sediment
cores 22-PC1, 23-GC1 and 24-GC1 is that there does not appear to be a
dramatic increase in sediment delivery to the outer shelf and slope during
the last glacial cycle. This is despite fluctuating eustatic levels that
would have seen the repeated exposure and flooding of the shelf. This is at
odds with observations in the river-dominated Laptev Sea (Bauch et al., 2001)
and the generally inferred influx of sediments to the outer shelf and slope
during periods of transgression (Wegener et al., 2015). Reworking of
sediments above
Geophysical and sediment coring data collected on Leg 2 of the 2014 SWERUS-C3 expedition reveal a set of grounding line deposits at the shelf break of the East Siberian Sea that lie within a distinct bathymetric depression interpreted as a glacial trough. This provides the first evidence for a glacially excavated trough on the East Siberian continental shelf and direct evidence for an ice sheet on the Siberian shelf. The dimensions of the grounding line deposits and glacial trough conform to the dimensions on the smaller Arctic cross-shelf troughs and the grounding zone wedges mapped within them. A thick sequence of glacio-genic debris flows exist seaward of the grounding line deposits and form a notable trough mouth fan. The ice stream occupying the trough was likely connected to glacial ice over the De Long and New Siberian Islands. Multiple lines of evidence indicate that the trough was occupied by an ice stream during the penultimate glaciation (MIS 6).
Data shown in the article acquired during the SWERUS-C3 expedition in 2014
are available through the Bolin Centre for Climate Research database:
The authors declare that they have no conflict of interest.
This article is part of the special issue “Climate–carbon–cryosphere interactions in the East Siberian Arctic Ocean: past, present and future (TC/BG/CP/OS inter-journal SI)”. It is not associated with a conference.
We thank the supporting crew and Captain of I/B