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Variations in the flow of ice streams and outlet glaciers are a primary control on ice sheet stability, yet comprehensive understanding of the key processes operating at the ice-bed interface remains elusive. Basal resistance is critical, especially sticky spots-localized zones of high basal traction-for maintaining force balance in an otherwise well-lubricated/high-slip subglacial environment. Here we consider the influence of subglacial gas-hydrate formation on ice stream dynamics, and its potential to initiate and maintain sticky spots. Geophysical data document the geologic footprint of a major palaeo-ice-stream that drained the Barents Sea-Fennoscandian ice sheet approximately 20,000 years ago. Our results reveal a ∼250 km2 sticky spot that coincided with subsurface shallow gas accumulations, seafloor fluid expulsion and a fault complex associated with deep hydrocarbon reservoirs. We propose that gas migrating from these reservoirs formed hydrates under high-pressure, low-temperature subglacial conditions. The gas hydrate desiccated, stiffened and thereby strengthened the subglacial sediments, promoting high traction-a sticky spot-that regulated ice stream flow. Deep hydrocarbon reservoirs are common beneath past and contemporary glaciated areas, implying that gas-hydrate regulation of subglacial dynamics could be a widespread phenomenon.
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LETTERS
PUBLISHED ONLINE: 11 APRIL 2016 | DOI: 10.1038/NGEO2696
Regulation of ice stream flow through subglacial
formation of gas hydrates
Monica Winsborrow*, Karin Andreassen, Alun Hubbard, Andreia Plaza-Faverola,
Eythor Gudlaugsson and Henry Patton
Variations in the flow of ice streams and outlet glaciers are
a primary control on ice sheet stability, yet comprehensive
understanding of the key processes operating at the ice–bed
interface remains elusive. Basal resistance is critical, especially
sticky spots—localized zones of high basal traction—for main-
taining force balance in an otherwise well-lubricated/high-slip
subglacial environment1. Here we consider the influence of
subglacial gas-hydrate formation on ice stream dynamics, and
its potential to initiate and maintain sticky spots. Geophysical
data document the geologic footprint of a major palaeo-
ice-stream that drained the Barents Sea–Fennoscandian ice
sheet approximately 20,000 years ago. Our results reveal a
250 km2sticky spot that coincided with subsurface shallow
gas accumulations, seafloor fluid expulsion and a fault complex
associated with deep hydrocarbon reservoirs. We propose that
gas migrating from these reservoirs formed hydrates under
high-pressure, low-temperature subglacial conditions. The gas
hydrate desiccated, stiened and thereby strengthened the
subglacial sediments, promoting high traction—a sticky spot—
that regulated ice stream flow. Deep hydrocarbon reservoirs
are common beneath past and contemporary glaciated areas,
implying that gas-hydrate regulation of subglacial dynamics
could be a widespread phenomenon.
Ice stream flow is largely determined by the degree to which
gravitational driving stress is resisted by lateral shear at its margins
and friction at its base. The primary resistive force is lateral drag
from adjacent slower-moving ice, but this is insufficient to balance
the driving stress, and the spatial distribution of subglacial traction
is critical to overall ice stream stability. Consequently, variations
in basal friction will cause variations in ice stream velocity, with
a well-lubricated, weak bed promoting fast flow. Observations
from the Siple Coast ice streams, West Antarctica, indicate that
basal shear stress is disproportionally focused on localized areas
of high basal traction, or so-called sticky spots, surrounded by
a well-lubricated deformable bed of weaker strength1. Sticky spot
distribution and extent thus plays a critical role in regulating ice
stream flow, with ice stream shutdown observed to follow their
widespread development2,3.
Sticky spots can form if subglacial sediments are desiccated and
stiff, or if freezing conditions prevail at the ice–bed interface1,4.
Subglacial sediment shear strength is directly related to normal
effective stress (ice load minus basal water pressure, although, in
the case of basal sediments we are explicitly referring to pore-water
pressure). This means that a small reduction in basal pore-water
pressure causes a significant increase in sediment strength. This
initial change in water pressure can be triggered by two processes
First, reorganization of, or changes in, the availability of subglacial
10° W
75° N
70° N
65° N
60° N
0°10° E20° E30° E
Longitude
Latitude
40° E50° E
Russia
Sklinnadjupet
ice stream
Limited
data
availability
Håkjerringdjupet
ice stream
Barents
Sea
Ice stream
Water depth (m)
5,0000
100 km
Norway
Norway
Finland
Sweden
Russia
Fig. 2
7019/1-1
Russia
Maximum
ice extent
Hydrocarbon
field or find
Figure 1 | Last Glacial Maximum ice extent of the Eurasian ice sheet
complex8.The ice sheet complex was drained by multiple fast-flowing ice
streams9,30, many of which flowed over hydrocarbon reservoirs.
Hydrocarbon information from the Norwegian Petroleum Directorate
(www.npd.no) and the British Government (www.gov.uk/oil-and-gas).
meltwater ‘water piracy’3,5, or second, basal freeze-on caused by
changes in ice thickness or the increased advection of cold surface
ice to the bed2,6,7. On the basis of observations from a palaeo-ice-
stream bed on the Norwegian continental shelf, we introduce a
third mechanism for sticky spot formation: pore-water piracy and
sediment stiffening due to subglacial gas-hydrate accumulation.
Håkjerringdjupet is a glacially overdeepened cross-shelf trough
in the southwest Barents Sea (Fig. 1). At the Last Glacial Maximum
(24,000 years ago) the entire Barents Sea and Norwegian
continental shelf were covered in ice8, with Håkjerringdjupet
draining ice westwards from the mainland to an ice margin located
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CAGE—Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geology, UiT The Arctic University of Norway, 9037 Tromsø, Norway.
*e-mail: monica.winsborrow@uit.no
370 NATURE GEOSCIENCE | VOL 9 | MAY 2016 | www.nature.com/naturegeoscience
NATURE GEOSCIENCE DOI: 10.1038/NGEO2696 LETTERS
70° 40 N
70° 30 N
18° E 19° E
Longitude
Latitude
>4002000
Water depth (m)
Older glacigenic sediments
Deglacial glacigenic and
Holocene marine sediments
5 km
100 ms
Bedrock/glacigenic sediments boundary
West East
Rafted sediments
a
b
Source depression
Fault complex
Bedrock
10 km
N
Rafted
sediments
GZW
GZW
MSGLs
MSGLs
Source
depression
Fig. 3
Fig. 2b
Troms−Finnmark
Fault Complex
MSGLs
Figure 2 | Past ice streaming and glacitectonic deformation in Håkjerringdjupet. a, Bathymetric map showing landforms indicating fast-flowing ice
(MSGLs: mega-scale glacial lineations, black lines and GZW: grounding zone wedge deposits) and glacitectonic landforms indicating slow-flowing ice
(rafted sediments and source depression). b, Profile based on analogue two-dimensional (2D) seismic data showing the overdeepened source depression
associated with the Troms–Finnmark Fault Complex. Within the source depression older glacigenic sediments are largely absent. Upstream, east of the
fault complex, these sediments are widespread and undisturbed; whereas downstream (west of the fault complex), rafted blocks of older glacigenic
sediments form hummocky glacitectonic hills (Supplementary Fig. 1)16.
at the shelf edge9. The trough is dissected by the Troms–Finnmark
Fault Complex, and the sea floor is characterized by a complex
glacial landform assemblage (Fig. 2a). Most widespread are highly
elongated (lengths over 50km and widths of the order of 500 m),
streamlined sedimentary deposits, aligned parallel to the trough
axis (Fig. 2a). These are observed across the whole trough, with
the exception of the northern part, west of the fault complex and
are interpreted as mega-scale glacial lineations (MSGLs), formed
beneath a fast-flowing ice stream10,11. Aligned transverse to the
trough axis are two broad wedge-shaped deposits with asymmetrical
profiles (steeper down-ice slopes) and MSGLs on their surface
(Fig. 2a). These have been interpreted to be grounding zone wedges
(GZWs), formed during standstills or readvances in the course of
ice margin retreat12,13. Landform assemblages of MGSLs and GZWs
have been identified widely across formerly glaciated continental
shelves, their formation attributed to the rapid, episodic retreat of
ice streams14.
Unusual for a palaeo-ice-stream bed is the hummocky mor-
phology of the northern part of Håkjerringdjupet (Fig. 2a), which
comprises a broad depression, bounded laterally by the margins of
the Troms–Finnmark Fault Complex and by an area of irregular
hills beyond the western margin of the fault complex (Fig. 2a).
The depression covers approximately 250km2, and represents an
overdeepening of 90m from the sea floor east of the fault complex.
The bedrock–glacigenic sediment boundary is also overdeepened
and rough beneath the seafloor depression (Fig. 2b). The irregular
hills cover an area similar to that of the depression and have a maxi-
mum elevation of approximately 80 m relative to the surrounding
sea floor. Older glacigenic sediments, deposited before deglacia-
tion15, have both a uniform thickness and stratified acoustic signa-
ture across much of Håkjerringdjupet, but are largely absent from
the depression, and have an unusually great and varying thickness
within the hummocky hills (Fig. 2b and Supplementary Fig. 1).
Furthermore, within the hills, the older glacigenic sediments have a
chaotic seismic reflection pattern comprised of blocks of randomly
oriented, acoustically stratified sediments (Supplementary Fig. 1).
Consistent with previous work16, we interpret this to be a glacitec-
tonic hill–hole pair, formed from rafted subglacial sediment and
bedrock which have been displaced (creating a source depression),
transported with the overlying ice, and deposited, forming irregular
hills. Glacitectonic rafting of sediment/bedrock occurs along a low-
strength decollement, which may represent the boundary between
consolidated and soft sediment, or frozen and non-frozen sedi-
ment. These processes imply slow ice flow on a high-traction/low-
slip subglacial environment, in contrast to the rest of the Håkjer-
ringdjupet palaeo-ice-stream bed, which records fast ice flow on a
low-traction/high-slip subglacial environment. In the geomorphic
record, sticky spots are suggested to appear as a disruption to the
classic pattern of parallel MSGLs formed by streaming ice flow4.
Therefore, we conclude that the glacitectonic source depression and
rafted sediments are the geologic imprint of a sticky spot on the
Håkjerringdjupet ice stream bed.
NATURE GEOSCIENCE | VOL 9 | MAY 2016 | www.nature.com/naturegeoscience
© 2016 Macmillan Publishers Limited. All rights reserved
371
LETTERS NATURE GEOSCIENCE DOI: 10.1038/NGEO2696
5 km
Troms−Finnmark
Fault Complex
N
Rafted
sediments Source
depression
Fig. 3f
Fig. 3g
Fig. 3c
Fig. 3d
Fig. 3e
Fig. 3b
Source depression
North
South
2 km
100 ms
Fault complex
Bedrock
Seafloor
reflection
a
f
g
b
c
d
e
Rafted sediments
West
East
Fault complex
source depression
2 km
100 ms
Phase-reversed
reflection
Bedrock
500 m 500 m
500 m 500 m
Figure 3 | Focused fluid flow and shallow gas accumulations. a, Central Håkjerringdjupet bathymetry showing glacitectonic landforms and mega-scale
glacial lineations (black lines). be, Hillshaded bathymetry showing abundant, large pockmarks within the source depression (b), smaller, less dense
pockmarks east of the fault complex (c), abrupt transition from pockmarked source depression to the adjacent, unpockmarked sea floor (d) and no
pockmarks within the rafted sediments (e). f,g, 3D seismic profiles showing phase-reversed reflections (black circles) indicative of shallow gas and fluid
flow (black dashed arrows), localized to the fault complex, beneath the source depression. Black line indicates boundary between glacial sediments and
sedimentary bedrock.
Numerous small circular depressions (typically <50 m diameter
and <7 m deep) are evident across the sea floor of Håkjerringdjupet
(Fig. 3a–e) and are interpreted as pockmarks, formed by focused
fluid flow through the sea floor. The presence of pockmarks is
consistent with the current or past migration of hydrocarbons from
an underlying reservoir17. Their distribution and size is not uniform,
with the highest density and largest examples found in the source
depression, within the fault complex (Fig. 3b). Pockmarks are also
observed east of the fault complex, where they tend to be smaller
and less dense (Fig. 3c). There is a sharp boundary between areas
of sea floor with and without pockmarks (Fig. 3d), and pockmarks
are largely absent from the rafted sediments (Fig. 3e), the grounding
zone wedges and the area of MSGLs in the southern part of
the trough.
Seismic data from central Håkjerringdjupet show multiple
faults and the presence of high-amplitude, phase-reversed
reflections along dipping layers that are classical indicators of gas
accumulations and migration from deeper reservoirs along faults
(Fig. 3f,g). These shallow gas accumulations are restricted to the
substrate underlying the pockmarked source depression, which
is also the zone of maximum fault displacement. In the southern
part of the trough, the fault escarpment is less abrupt, no deep
seafloor depression is seen (Fig. 2) and pockmarks and shallow
gas accumulations are largely absent (Fig. 3). We therefore infer
a link between structurally controlled gas migration from deeper
reservoirs and the formation of the Håkjerringdjupet sticky spot.
Indeed, a discovery well drilled 15 km north of Håkjerringdjupet
(Wellbore 7019/1-1, Fig. 1) proved gas in two reservoirs (Middle
Jurassic and Lower Cretaceous), and the Troms–Finnmark Fault
Complex is associated with multiple major hydrocarbon discoveries
in the southwestern Barents Sea (Norwegian Petroleum Directorate
2015; www.npd.no).
Thermogenic gas from deep reservoirs is less dense than either
water or sediments, and migrates upwards, along faults and
permeable sediment layers. In the Arctic, migrating gas from leaking
petroleum systems may be trapped in the shallow subsurface in
the form of gas hydrates, ice-like solids that form under the high-
pressure, low-temperature conditions found in marine sediments
and permafrost18. In Håkjerringdjupet, present-day pressure and
temperature conditions are just outside the boundary for methane-
hydrate formation (Supplementary Fig. 2). However, under glacial
conditions, ice was grounded in Håkjerringdjupet (as evidenced
372
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NATURE GEOSCIENCE DOI: 10.1038/NGEO2696 LETTERS
Rafted sediments Source depression
East
West
Gas
migration
Faulted
bedrock
Subglacial
water Glacier ice
Håkjerringdjupet
ice stream
Bedrock
1,200 m 400 m
Gas
hydrate Fault complex
Sediments
Gas-hydrate stability zone
Free gas zone
Figure 4 | Conceptual model of subglacial gas-hydrate formation in
Håkjerringdjupet at the Last Glacial Maximum. The fault complex
facilitates focused fluid flow from deeper reservoirs to the ice–bed
interface. This migrating gas formed concentrated patches of gas hydrates
within the gas-hydrates stability zone (calculated on the basis of numerical
modelling, Supplementary Fig. 2), associated with faults, fractures and
porous sediments.
by subglacial bedforms such as mega-scale glacial lineations),
creating the low-temperature, high-pressure conditions necessary
for a thick zone (400m) of methane-hydrate stability beneath
the ice stream (Supplementary Fig. 2). Migrating gas entering the
region of methane-hydrate stability would have combined with pore
water under high pressure within the subglacial sediments and
shallow sedimentary bedrock, forming hydrates (Fig. 4). Given the
heavily faulted and fractured bedrock and the heterogeneous nature
of the subglacial sediments within Håkjerringdjupet15, rather than
forming a continuous layer, gas hydrate is expected to have formed
in patches of high saturation, localized around faults and fractures
and in areas of porous sediments (Fig. 4).
Gas hydrate desiccates and stiffens host sediments as a result of
pore-water piracy into the gas-hydrate cage structure, cementation
of grains, and the greater strength and lower volume of gas hydrate
compared with its constituent gas and ice19–22. Gas-hydrate-bearing
sediments from the Mackenzie Delta, northern Canada, show a
more than eightfold increase in sediment shear strength when gas
hydrate develops (Supplementary Fig. 3), from an initial shear
strength of 0.8 to 6.7MPa with 60% hydrate saturation20. Assuming
a similar relative increase in shear strength, the strength of gas-
hydrate hosting sediments and shallow bedrock in Håkjerringdjupet
would have been far in excess of that of ‘weak’ till recovered from
beneath the Siple Coast ice streams, West Antarctica23 and typical
driving stresses of active ice streams, which tend not to exceed
20 kPa (ref. 24).
Patches of desiccated, stiff gas-hydrate-hosting sediments and
shallow bedrock beneath the Håkjerringdjupet ice stream would
have locally enhanced basal friction, thereby providing resistance to
the flow of the overlying ice. These high-shear-strength sediments
would probably have formed a strong frictional bond with the
overlying ice, favouring glacitectonic decollement deeper within
the substrate. Thrusting and subsequent deposition of hydrate-
bearing sediments and shallow bedrock by the slow-moving ice
created the glacitectonic hill–hole pair visible on the present-day
sea floor.
Major hydrocarbon reservoirs exist across the shelf areas
previously glaciated by the last Eurasian ice sheet complex, and
several palaeo-ice-streams flowed over substrates associated with
confirmed hydrocarbon systems (Fig. 1). The high-pressure, low-
temperature subglacial conditions that prevailed beneath these ice
streams would have promoted widespread gas-hydrate formation,
particularly at leaking reservoirs with focused gas migration, and
consequent regulation of ice stream basal thermomechanics and
flow. Multiple observations across the footprint of the palaeo-
ice-sheet may now require reinterpretation on the basis of this
hypothesis. For example, the large glacitectonic landforms and
heavily overconsolidated till associated with the Sklinnadjupet ice
stream9,25 which flowed over the extensive hydrocarbon reservoirs
(Fig. 1 and Supplementary Fig. 4), and the widespread occurrence
of overconsolidated glacial sediments across the southwestern
Barents Sea26 are consistent with gas-hydrate regulation of ice
stream flow.
Abundant gas-hydrate accumulations are proposed to exist
beneath the Antarctic and Greenland ice sheets, based on the
presence of extensive sedimentary basins and modelling studies27,28.
Furthermore, gas hydrates have been identified in ice-core samples
from above subglacial Lake Vostok, East Antarctica29. So far, the
role of potentially widespread gas-hydrate reservoirs in modifying
the critically sensitive thermomechanical regime at the base of
contemporary ice sheets, along with their impact on ice stream
force balance and dynamics, has not been recognized. Given current
lack of knowledge regarding subglacial gas-hydrate distribution, this
previously unforeseen control represents a significant unknown in
attempts to model the current and future discharge and evolution
of contemporary ice sheets, along with their contribution to global
sea-level rise.
Methods
Methods and any associated references are available in the online
version of the paper.
Received 27 August 2015; accepted 10 March 2016;
published online 11 April 2016
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Acknowledgements
This work was partly supported by the Research Council of Norway through its Centres
of Excellence funding scheme, project number 223259; the PetroMaks project
‘Glaciations in the Barents Sea area, GlaciBar’ (grant 200672) and the European
Commission FP7-People 2012- Initial Training Networks ‘Glaciated North Atlantic
Margins, GLANAM’ (grant 317217). We thank the Norwegian Mapping Authority and
the Geological Survey of Norway for providing the high-resolution bathymetry data set
through the MAREANO programme, TGS for providing the 3D seismic data set and
SINTEF Petroleum Research for providing analogue and digital 2D seismic data.
Author contributions
K.A. developed the study. M.W. interpreted the geophysical data sets and wrote the paper.
A.H. contributed to the writing and editing of the paper, advised on its scope and wrote
the code for the ice sheet model. H.P. modelled ice thickness and basal temperature.
K.A., A.P.-F. and E.G. helped with the interpretation and analysis. M.W. and H.P.
prepared the figures. All authors discussed ideas and commented on the paper.
Additional information
Supplementary information is available in the online version of the paper. Reprints and
permissions information is available online at www.nature.com/reprints.
Correspondence and requests for materials should be addressed to M.W.
Competing financial interests
The authors declare no competing financial interests.
374
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NATURE GEOSCIENCE DOI: 10.1038/NGEO2696 LETTERS
Methods
Stability plots for methane hydrate were calculated using gas-hydrate phase
boundaries assuming pure methane18 and a geothermal gradient of
0.038 C m1, suggested to be an average value for the Barents Sea31.
A present-day bottom water temperature of 6 C was used, based on a large
data set of conductivity–temperature–density (CTD) casts acquired
within Håkjerringdjupet in the years 2000–2015, downloaded from the
World Ocean Database. Estimates of ice thickness and basal temperature
during the Last Glacial Maximum were extracted from a high-resolution
(10 km) simulation of the Eurasian ice sheet complex, calculated using a
first-order, three-dimensional (3D) thermomechanical ice flow model
(UiT model32). Explicit technical details on the derivation and implementation
of the model can be found from its previous application to the
Celtic Ice Sheet33.
Data availability. The multibeam swath bathymetry data set used in this study is
available from the Norwegian Mapping Authority via the website www.mareano.no.
The 3D seismic data set (FP12_PRCMIG) was acquired from TGS, and 2D seismic
data sets (analogue and digital) were acquired from SINTEF Petroleum Research.
References
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33. Hubbard, A. et al. Dynamic cycles, ice streams and their impact on the extent,
chronology and deglaciation of the British-Irish ice sheet. Quat. Sci. Rev. 28,
758–776 (2009).
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... It is possible that extensive glacial erosion of the continental shelf has enabled connections to be made to migration pathways for methane and other gases generated from source rocks, which, in this location, include Mesozoic marine shales , Niemann et al. 2009). The pockmarks could also be produced by the dissociation of gas hydrates that were formed when migrating thermogenic gas entered a subsurface zone of gas-hydrate stability (Hovland et al. 2002, Winsborrow et al. 2016. Although the presence of gas hydrates has not been confirmed on the north-east Antarctic Peninsula margin, it has been inferred previously from the detection of methane within sea-floor sediments adjacent to Seymour Island ( Fig. 1; del Valle et al. 2017). ...
... Although the presence of gas hydrates has not been confirmed on the north-east Antarctic Peninsula margin, it has been inferred previously from the detection of methane within sea-floor sediments adjacent to Seymour Island ( Fig. 1; del Valle et al. 2017). Gas-hydrate destabilization on glaciated margins has been linked to depressurization by the removal of grounded ice and the increase in ocean temperature that accompanied the last deglaciation (Solheim & Elverhøi 1993, Winsborrow et al. 2016, Böttner et al. 2019). The post-glacial age of the pockmarks on the north-east Antarctic Peninsula is consistent with an origin through gas-hydrate dissociation. ...
... Where a thermogenic origin is confirmed, the identification and monitoring of active pockmark fields on glaciated margins is important for predicting how global gas-hydrate reserves may evolve in a warming climate (Wadham et al. 2012(Wadham et al. , 2019. Given that gas-hydrate destabilization and methane release have been linked to past periods of ocean warming and ice-sheet retreat (Solheim & Elverhøi 1993, Winsborrow et al. 2016, Böttner et al. 2019), a future increase in ocean-water temperature and/or reduction in the extent of grounded ice around Antarctica could act as positive feedbacks on 9 POCKMARKS ON THE ANTARCTIC PENINSULA MARGIN climate warming (Wadham et al. 2012(Wadham et al. , 2019. Conversely, higher rates of glacimarine sedimentation under warmer ocean and atmospheric conditions could reduce the flux of greenhouse gases from deep reservoirs to the sea floor by burying fluid-escape structures such as pockmarks, causing them to become inactive. ...
... The fresh appearance of the pockmarks on the seafloor, and their overprinting of deglacial landforms including small GZWs ( Fig. 7c and d), suggests that they are relatively recently formed. Their development may be linked to fluid flow from gas-hydrate destabilisation following the last deglaciation, which has been suggested to be a key factor in pockmark formation on glaciated margins (Winsborrow et al., 2016;Mazzini et al., 2017). ...
... An additional factor that could have influenced ice-sheet dynamics on the mid-Norwegian margin is the formation of gas hydrates during the last deglaciation e a process that has been linked to depressurisation during ice-sheet retreat (Solheim and Elverhøi, 1993;Winsborrow et al., 2016). The 'fresh' appearance of the pockmarks on the mid-Norwegian shelf ( Fig. 7c and d) suggests that these features formed during or subsequent to the retreat of grounded ice, and is consistent with an origin through gas-hydrate dissociation. ...
... The 'fresh' appearance of the pockmarks on the mid-Norwegian shelf ( Fig. 7c and d) suggests that these features formed during or subsequent to the retreat of grounded ice, and is consistent with an origin through gas-hydrate dissociation. The widespread occurrence of pockmarks in innermid Sklinnadjupet ( Fig. 7c and d) suggests that the presence of several glaciotectonically formed hill-hole pairs in this region (Figs. 2 and 4) could be linked to the development of 'sticky spots' where subglacial sediments were strengthened by gas hydrate formation (Winsborrow et al., 2016). ...
Article
The analysis of glacial landforms preserved on mid- and high-latitude continental margins provides insights into the patterns and processes of sedimentation beneath contemporary ice sheets and aids predictions of the future resilience of ice sheets to ocean and atmospheric drivers of change. However, most previous high-resolution investigations of submarine glacial landforms have utilised data that are focused only on relatively small areas of the seafloor. Here we use an extensive database of high-resolution marine-geophysical data to map and interpret the distribution of glacial landforms over an 80,000 km² area along a ∼600 km-long section of the mid-Norwegian margin. Our glacial-geomorphological mapping shows that the Scandinavian Ice Sheet displayed highly dynamic behaviour, including readvances and changes in ice-flow direction, during the last glacial-interglacial cycle. The shallow banks briefly became dynamic centres of ice flow during deglaciation, with ice readvances from these banks linked to the loss of ice-sheet buttressing through the early deglaciation of grounded ice in the deeper troughs. The geometry of the continental shelf, especially its troughs and banks, exerted an important control on the pattern of ice-sheet retreat. The distribution of small grounding-zone wedges shows that frequent, small-magnitude still-stands or readvances within overall ice-stream retreat were prevalent on prograding slopes that limited the flux of ice across the grounding zone. Although the pattern of ice-sheet retreat along the mid-Norwegian margin is now relatively well-understood, future marine sediment coring efforts are needed to better constrain the timing of these deglacial events.
... On the Mid-Norwegian Shelf for example, several hundred kilometers northeast of the Norwegian Channel ice stream trough where Utsira Nord is located, bathymetric and seismic data indicate the presence of at least three ice stream troughs running from the coast of Mid-Norway towards the Norwegian Sea (Traenadjupet, Suladjupet and Sklinnadjupet, Ottesen et al. 2002;Dowdeswell et al. 2006;Montelli et al. 2017). Further north, offshore northern Norway and Svalbard, the continental shelf has also been shaped by ice streaming e.g., the Håsjerringsdjupet trough (Winsborrow et al. 2016) and the Bear Island trough (Vorren and Laberg, 1997;Ottesen et al. 2005a;Andreassen et al. 2004Andreassen et al. , 2008. In the United Kingdom and Ireland, where the offshore wind industry has been rapidly expanding in recent years, seabed troughs have been carved out by at least 17 ice streams related to the British-Irish Ice Sheet (BIIS) during the last glaciation (Gandy et al. 2019). ...
Article
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Conceptual geological models of the shallow subsurface that integrate geological and geotechnical information are important for more strategic data acquisition and engineering at offshore wind sites. Utsira Nord is an offshore wind site in the Norwegian North Sea suitable for floating turbines, with an average water depth of 267 m. It covers a 23 km x 43 km area within the Norwegian Channel, a trough formed by repeated ice streaming. The goal of this study is to present a preliminary conceptual geological model for the site, which combines an overview of previous knowledge about the ice streaming history of the Norwegian Channel with key observations from bathymetric data, 2D acoustic data, and shallow cores. Despite limited data, four units with different geotechnical properties can be defined: 1) exposed glacimarine to marine sediments, 2) buried to exposed subglacial traction till, 3) buried lodgement till and 4) shallowly buried to exposed crystalline bedrock. The model serves as a basis for planning site surveys at Utsira Nord and as a reference for offshore wind sites on other formerly glaciated coasts where ice streaming has been an important land-forming process, such as the northern coastlines of North America and the United Kingdom.
... On the Mid-Norwegian Shelf for example, several hundred kilometers northeast of the Norwegian Channel ice stream trough where Utsira Nord is located, bathymetric and seismic data indicate the presence of at least three ice stream troughs running from the coast of Mid-Norway towards the Norwegian Sea (Traenadjupet, Suladjupet and Sklinnadjupet, Ottesen et al. 2002;Dowdeswell et al. 2006;Montelli et al. 2017). Further north, offshore northern Norway and Svalbard, the continental shelf has also been shaped by ice streaming e.g., the Håsjerringsdjupet trough (Winsborrow et al. 2016) and the Bear Island trough (Vorren and Laberg, 1997;Ottesen et al. 2005a;Andreassen et al. 2004Andreassen et al. , 2008. In the United Kingdom and Ireland, where the offshore wind industry has been rapidly expanding in recent years, seabed troughs have been carved out by at least 17 ice streams related to the British-Irish Ice Sheet (BIIS) during the last glaciation (Gandy et al. 2019). ...
... Subsequent degassing has been used to explain pockmarks and mounds on submarine beds of former ice sheets (Crémière et al., 2016;Mazzini et al., 2017;Nixon et al., 2019) and doughnut-shaped ring forms (blowouts) around glacitectonic features in Alberta (Evans et al., 2020). Moreover, glacitectonic rafts and hill-hole pairs on the bed of the former Barents Sea Ice Sheet are argued by Winsborrow et al. (2016) to be sticky spots related to porewater piracy and sediment stiffening in response to subglacial gas-hydrate accumulation. ...
Article
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Landforms and sediments on the palaeo-ice stream beds of central Alberta record glacitectonic raft production and subsequent progressive disaggregation and moulding, associated substrate ploughing, and grooving. We identify a subglacial temporal or developmental hierarchy that begins with incipient rafts, including en échelon hill-hole complexes, hill-hole pairs, and strike-slip raft complexes, all of which display patterns typical of transcurrent fault activation and pull apart. Many display jigsaw puzzle-style fragmentation, indicative of substrate displacement along shallow décollement zones and potentially related to patchy ice stream freeze-on. Their gradual fragmentation and smoothing produces ice flow-transverse ridges (ribbed moraine), hill-groove pairs, and paraxial ridge and groove associations. Initiator scarp and megafluting associations are indicative of raft dislodgement and groove ploughing, leading to the formation of murdlins, crag-and-tails, stoss-and-lee type flutings and drumlins, and Type 1 hogsback flutings. Downflow modification of rafts creates linear block trains (rubble stripes), stoss-and-lee type megaflutings, horned crag-and-tails, rubble drumlinoids, and murdlins, diagnostic of an immature palaeo-ice stream footprint. Lateral ice stream margin migration ingests disaggregated thrust masses to form ridged spindles, ladder-type morphologies, and narrow zones of ribbed terrain and Type 2 hogsback flutings, an assemblage diagnostic of ice stream shear margin moraine formation.
... CO 2 hydrates have a higher melting temperature at subglacial pressures than ice, and in massive forms have superior mechanical properties. Methane hydrates may have contributed to 'sticky spots' in palaeoglacial ice streams under the present Barents Sea (Winsborrow et al., 2016). Bed drying by hydrate formation sequesters CO 2 from the atmosphere, however exothermicity of hydrate formation would require supplemental basal refrigeration to avoid melting adjacent ice. ...
Article
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It is remarkable that the high-end sea level rise threat over the next few hundred years comes almost entirely from only a handful of ice streams and large glaciers. These occupy a few percent of ice sheets’ coastline. Accordingly, spatially limited interventions at source may provide globally-equitable mitigation from rising seas. Ice streams control draining of ice sheets; glacier retreat or acceleration serves to greatly increase potential sea level rise. While various climatic geoengineering approaches have been considered, serious consideration of geotechnical approaches has been limited – particularly regarding glaciers. This study summarises novel and extant geotechnical techniques for glacier restraint, identifying candidates for further research. These include draining or freezing the bed; altering surface albedo; creating obstacles: retaining snow; stiffening shear margins with ice; blocking warm sea water entry; thickening ice shelves (increasing buttressing, and strengthening fractured shelves against disintegration); as well as using regional climate engineering or local cloud seeding to cool the glacier or add snow. Not all of these ideas are judged reasonable or feasible, and even fewer are likely to be found to be advisable after further consideration. By describing and evaluating the potential and risks of a large menu of responses – even apparently hopeless ones – we can increase the chances of finding one that works in times of need.
... 2D/3D seismic/core (very rare) (Rüther et al., 2013;Winsborrow et al., 2016) Shear margin moraine Ridge of sediments formed subglacially at the boundary between slow-moving is and fast-moving ice (ice stream). 10s m high, 100-1000s m wide and 10s km long. ...
Article
Glaciogenic sediments are present in many hydrocarbon-producing basins across the globe but their complex nature makes it difficult to characterise the reservoir-quality sedimentary units. Despite this, Ordovician glacial deposits in North Africa, and Carboniferous-Permian glaciogenic sequences in the Middle East, have been proven to host significant, economical, hydrocarbon accumulations. Additionally, discoveries have been made in the shallow (<1000 m below seabed), glacial, Pleistocene sedimentary succession of the North Sea (e.g. Peon and Aviat). This paper provides a predictive exploration framework in the form of a conceptual model of glaciogenic sediment-landform distributions. The model is based on the extensive onshore glacial sedimentary record integrated with available offshore data. It synthesises the published knowledge, drawing heavily on glacial landsystem models, glacial geomorphology and sedimentology of glaciogenic deposits to provide a novel conceptual model allowing for the efficient description and interpretation of glacial sediments and landforms in the subsurface. Subsequently, land-terminating and water-terminating ice sheet depositional systems are described and discussed, with respect to ice advance and retreat cycles. This detailed description focuses on the macro-scale stratigraphic organisation of glacial sediments with relation to the ice margin, aiding the prediction of glaciogenic sediment distributions, and their likely geometry, architecture and connectivity as reservoirs.
Chapter
The Kara Sea shelf is an offshore continuation of the extensive West Siberia hydrocarbon province that stretches from the Novaya Zemlya archipelago (bordering the Barents Sea) to the Severnaya Zemlya archipelago (bordering the Laptev Sea). The Kara Sea shelf comprises several regions featuring drastically different bathymetric, oceanographic, geological, glaciological and permafrost settings. Due to the extremely limited availability of empirical data, the best tool for estimating gas hydrate potential on the shelf is gas hydrate stability zone modeling coupled with permafrost evolution modeling. This will also allow for the forecasting of areas where gas hydrate systems may be found in the future, through either bottom simulating reflection identification or direct sampling. Deep water troughs (>350 m water depth) in the South and North Kara Sea are zones where pressure and temperature conditions are suitable for the formation and preservation of gas hydrates. The Novaya Zemlya Trough also hosts a suite of hydrocarbon-bearing structures that may supply hydrocarbon gas to the gas hydrate stability zone. The shallow areas of the South Kara Sea (to the west and north of the Yamal peninsula) contain only discontinuous permafrost and cannot bear stable gas hydrate accumulations. The North Kara Sea, in contrast, features a thicker layer of permafrost (circa 100–300 m thick) formed during the LGM and a weaker thermal impact caused by the subsequent sea transgression. In this region, permafrost exceeding 250 m in thickness allows for stable permafrost-related gas hydrate accumulations.
Chapter
The Last Glacial Maximum (LGM) extent of the European Ice Sheet Complex (EISC) has been the subject of intense research for over a century. Today, the landscapes that locate the former limits of the ice sheets of the EISC at their respective maximum coverage are recognised as time-transgressive; each ice sheet reached its maximum extent at different times, indeed within each ice sheet different sectors also exhibit variations in timing of advance and retreat. Here we give an overview of the dimensions, geometry, and evolution of the EISC during the LGM (29–19 ka) to provide an ice-sheet scale context for the landscape evidence described in Chapters 48–53. We reflect on the historical development of ideas and approaches to constrain the dimensions and chronology of the EISC during the LGM. As for the pre-LGM period (Chapter 28), the majority of evidence is found along the former ice-sheet margins with glimpses of the internal structure of the LGM ice sheets predominantly restricted to locations preserved under cold-based ice. We examine how landscapes of the EISC have played a key role in recognising the spatiotemporal complexity of the subglacial thermal regime of ice sheets and outline routes for understanding the role of cold-based ice in landform genesis as well as a means of landscape preservation. Establishing the detailed geometry and precise volume of the three ice sheets comprising the EISC remains an active field of research.
Article
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Projections of ice sheet behavior hinge on how ice flow velocity evolves and the extent to which marine-based grounding lines are stable. Ice flow and grounding line retreat are variably governed by the coupling between the ice and underlying terrain. We ask to what degree catchment-scale bed characteristics determine ice flow and retreat, drawing on paleo-ice sheet landform imprints from 99 sites on continental shelves worldwide. We find that topographic setting has broadly steered ice flow and that the bed slope favors particular styles of retreat. However, we find exceptions to accepted “rules” of behavior: Regional topographic highs are not always an impediment to fast ice flow, retreat may proceed in a controlled, steady manner on reverse slopes and, unexpectedly, the occurrence of ice streaming is not favored on a particular geological substrate. Furthermore, once grounding line retreat is under way, readvance is rarely observed regardless of regional bed characteristics.
Article
Water piracy by Ice Stream B, West Antarctica, may have caused neighboring Ice Stream C to stop. The modern hydrologic potentials near the upstream end of the main trunk of Ice Stream C are directing water from the C catchment into Ice Stream B. Interruption of water supply from the catchment would have reduced water lubrication on bedrock regions projecting through lubricating basal till and stopped the ice stream in a few years or decades, short enough to appear almost instantaneous. This hypothesis explains several new data sets from Ice Stream C and makes predictions that might be testable.
Article
The basal shear stress of an ice stream may be supported disproportionately on localized regions or “sticky spots”. The drag induced by large bedrock bumps sticking into the base of an ice stream is the most likely cause of sticky spots. Discontinuity of lubricating till can cause sticky spots, but they will collect lubricating water and therefore are unlikely to support a shear stress of more than a few tenths of a bar unless they contain abundant large bumps. Raised regions on the ice-air surface can also cause moderate increases in the shear stress supported on the bed beneath. Surveys of large-scale bed roughness would identify sticky spots caused by bedrock bumps, water-pressure measurements in regions of thin or zero till might reveal whether they were sticky spots, and strain grids across the margins of ice-surface highs would show whether the highs were causing sticky spots. Sticky spots probably are not dominant in controlling Ice Stream Β near the Upstream Β camp, West Antarctica.
Article
Microscopic observation of air-hydrate crystals was carried out using 34 deep ice-core samples retrieved at Vostok Station, Antarctica. Samples were obtained from depths between 1050 and 2542 m, which correspond to Wisconsin/Sangamon/Illinoian ice. It was found that the volume and number of air-hydrate varied with the climatic changes. The volume concentration of air-hydrate in the interglacial ice was about 30% larger than that in the glacial ice. In the interglacial ice, the number concentration of air-hydrate was about a half and the mean volume of air-hydrate was nearly three times larger than that in the glacial-age ice. The air-hydrate crystals were found to grow in the ice sheet, about 6.7 × 10−12 cm3 year-1, in compensation for the disappearance of smaller ones. The volume concentration of air-hydrate was related to the total gas content by a geometrical equation with a proportional parameter α. The mean value of α below 1250 m, where no air bubbles were found, was about 0.79. This coincided with an experimentally determined value of the crystalline site occupancy of the air-hydrate in a 1500 m core obtained at Dye 3, Greenland (Hondoh and others, 1990). In the depth profile of calculated α for many samples, α in the interglacial ice was about 30% smaller than that in the glacial-age ice.
Article
Water piracy by Ice Stream B, West Antarctica, may have caused neighboring Ice Stream C to stop. The modern hydrologic potentials near the upstream end of the main trunk of Ice Stream C are directing water from the C catchment into Ice Stream B. Interruption of water supply from the catchment would have reduced water lubrication on bedrock regions projecting through lubricating basal till and stopped the ice stream in a few years or decades, short enough to appear almost instantaneous. This hypothesis explains several new data sets from Ice Stream C and makes predictions that might be testable.
Article
The 3D geometrical evolution of the Barents Sea Ice Sheet (BSIS), particularly during its late-glacial retreat phase, remains largely ambiguous due to the paucity of direct marine- and terrestrial-based evidence constraining its horizontal and vertical extent and chronology. One way of validating the numerous BSIS reconstructions previously proposed is to collate and apply them under a wide range of Earth models and to compare prognostic (isostatic) output through time with known relative sea-level (RSL) data. Here we compare six contrasting BSIS load scenarios via a spherical Earth system model and derive a best-fit, χ 2 parameter using RSL data from the four main terrestrial regions within the domain: Svalbard, Franz Josef Land, Novaya Zemlya and northern Norway. Poor χ 2 values allow two load scenarios to be dismissed, leaving four that agree well with RSL observations. The remaining four scenarios optimally fit the RSL data when combined with Earth models that have an upper mantle viscosity of 0.2-2 × 1021 Pa s, while there is less sensitivity to the lithosphere thickness (ranging from 71 to 120 km) and lower mantle viscosity (spanning 1-50 × 1021 Pa s). GPS observations are also compared with predictions of present-day uplift across the Barents Sea. Key locations where relative sea-level and GPS data would prove critical in constraining future ice-sheet modelling efforts are also identified.
Article
This paper presents results of shear strength and acoustic velocity (p-wave) measurements performed on: (1) samples containing natural gas hydrate from the Mallik 2L-38 well, Mackenzie Delta, Northwest Territories; (2) reconstituted Ottawa sand samples containing methane gas hydrate formed in the laboratory; and (3) ice-bearing sands. These measurements show that hydrate increases shear strength and p-wave velocity in natural and reconstituted samples. The proportion of this increase depends on (1) the amount and distribution of hydrate present, (2) differences, in sediment properties, and (3) differences in test conditions. Stress-strain curves from the Mallik samples suggest that natural gas hydrate does not cement sediment grains. However, stress-strain curves from the Ottawa sand (containing laboratory-formed gas hydrate) do imply cementation is present. Acoustically, rock physics modeling shows that gas hydrate does not cement grains of natural Mackenzie Delta sediment. Natural gas hydrates are best modeled as part of the sediment frame. This finding is in contrast with direct observations and results of Ottawa sand containing laboratory-formed hydrate, which was found to cement grains (Waite et al. 2004). It therefore appears that the microscopic distribution of gas hydrates in sediment, and hence the effect of gas hydrate on sediment physical properties, differs between natural deposits and laboratory-formed samples. This difference may possibly be caused by the location of water molecules that are available to form hydrate. Models that use laboratory-derived properties to predict behavior of natural gas hydrate must account for these differences.
Article
The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1) the Late Saalian (>140 ka), (2) the Early Weichselian (100–80 ka), (3) the Middle Weichselian (60–50 ka) and (4) the Late Weichselian (25–15 ka). The reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in Russia and Siberia, and with marine seismic- and sediment core data. The Barents-Kara Ice Sheet got progressively smaller during each glaciation, whereas the dimensions of the Scandinavian Ice Sheet increased. During the last Ice Age the Barents-Kara Ice Sheet attained its maximum size as early as 90–80,000 years ago when the ice front reached far onto the continent. A regrowth of the ice sheets occurred during the early Middle Weichselian, culminating about 60–50,000 years ago. During the Late Weichselian the Barents-Kara Ice Sheet did not reach the mainland east of the Kanin Peninsula, with the exception of the NW fringe of Taimyr. A numerical ice-sheet model, forced by global sea level and solar changes, was run through the full Weichselian glacial cycle. The modeling results are roughly compatible with the geological record of ice growth, but the model underpredicts the glaciations in the Eurasian Arctic during the Early and Middle Weichselian. One reason for this is that the climate in the Eurasian Arctic was not as dry then as during the Late Weichselian glacial maximum.
Article
The dynamic behavior of the West Antarctic ice sheet is of interest because of the possibility that it may change and cause rapid sea-level rise. Attention is focused on the fast-moving and rapidly responding ice streams that drain the ice sheet. One of these, ice stream C, largely stopped about a century ago, and some models for this shutdown postulate negative feedbacks that would tend to stabilize the ice-sheet. Here, new data are presented indicating that the slowdown of the ice stream is restricted to its lower part, and occurred because of loss of lubrication on localized “sticky spots” at the bed of the ice stream. The increased friction probably arises from a topographic accident of the glacier bed that has directed lubricating water to the neighboring ice stream B, together with slow drawdown of the ice sheet, rather than from any general stabilizing feedbacks.