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Regulation of ice stream flow through subglacial formation of gas hydrates

April 2016
Nature Geoscience 9(5)

DOI:10.1038/ngeo2696

Authors:

Kain Andreassen

UiT The Arctic University of Norway

Alun Hubbard

UiT The Arctic University of Norway

Andreia Plaza

UiT The Arctic University of Norway

Show all 6 authorsHide

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.

| Last Glacial Maximum ice extent of the Eurasian ice sheet complex 8 . The ice sheet complex was drained by multiple fast-flowing ice streams 9,30 , 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).

…

| 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.

…

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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

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

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

Source depression

Fault complex

Bedrock

10 km

Rafted

sediments

GZW

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

371

LETTERS NATURE GEOSCIENCE DOI: 10.1038/NGEO2696

5 km

Troms−Finnmark

Fault Complex

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

Rafted sediments

West

East

Fault complex

source depression

2 km

100 ms

Phase-reversed

reﬂection

Bedrock

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). b–e, 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

NATURE GEOSCIENCE | VOL 9 | MAY 2016 | www.nature.com/naturegeoscience

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

References

1. Alley, R. B. In search of ice-stream sticky spots. J. Glaciol. 39, 447–454 (1993).

2. Tulaczyk, S., Kamb, W. B. & Engelhardt, H. F. Basal mechanics of Ice Stream B,

West Antarctica 2. Undrained plastic bed model. J. Geophys. Res. 105,

483–494 (2000).

3. Anandakrishnan, S. & Alley, R. B. Stagnation of Ice Stream C, West Antarctica

by water piracy. Geophys. Res. Lett. 24, 265–268 (1997).

4. Stokes, C. R., Clark, C. D., Lian, O. B. & Tulaczyk, S. Ice stream sticky spots:

a review of their identification and influence beneath contemporary and

palaeo-ice-streams. Earth Sci. Rev. 81, 217–249 (2007).

5. Alley, R. B., Anandakrishnan, S., Bentley, C. R. & Lord, N. A water-piracy

hypothesis for the stagnation of Ice Stream C, Antarctica. Ann. Glaciol. 20,

187–194 (1994).

6. Bougamont, M., Tulaczyk, S. & Joughin, I. Response of subglacial sediments to

basal freeze-on 2. Application in numerical modeling of the recent stoppage of

Ice Stream C, West Antarctica. J. Geophys. Res. 108, 2223 (2003).

7. Christoﬀersen, P. & Tulaczyk, S. Response of subglacial sediments to basal

freeze-on 1. Theory and comparison to observations from beneath the West

Antarctic ice sheet. J. Geophys. Res. 108, 2222 (2003).

8. Svendsen, J. I. et al. Late Quaternary ice sheet history of northern Eurasia.

Quat. Sci. Rev. 23, 1229–1271 (2004).

9. Ottesen, D., Dowdeswell, J. A. & Rise, L. Submarine landforms and the

reconstruction of fast-flowing ice streams within a large Quaternary ice sheet:

the 2500-km-long Norwegian-Svalbard margin (57◦–80◦N). Geol. Soc. Am.

Bull. 117, 1033–1050 (2005).

10. King, E., Hindmarsh, R. & Stokes, C. R. Formation of mega-scale glacial

lineations observed beneath a West Antarctic ice stream. Nature Geosci. 2,

585–588 (2009).

11. Stokes, C. R. & Clark, C. D. Geomorphological criteria for identifying

Pleistocene ice streams. Ann. Glaciol. 28, 67–74 (1999).

12. Ottesen, D., Stokes, C. R., Rise, L. & Olsen, L. Ice-sheet dynamics and ice

streaming along the coastal parts of northern Norway. Quat. Sci. Rev. 27,

922–940 (2008).

13. Winsborrow, M. C. M., Stokes, C. R. & Andreassen, K. Ice stream

flow-switching during the deglacation of the south-western Barents Sea. Geol.

Soc. Am. Bull. 124, 275–290 (2012).

14. Dowdeswell, J. A., Ottesen, D., Evans, J., Ò Cofaigh, C. & Anderson, J. B.

Submarine glacial landforms and rates of ice stream collapse. Geology 36,

819–822 (2008).

NATURE GEOSCIENCE | VOL 9 | MAY 2016 | www.nature.com/naturegeoscience

373

LETTERS NATURE GEOSCIENCE DOI: 10.1038/NGEO2696

15. Rokoengen, K., Bugge, T. & Løfaldli, M. Quaternary geology and deglaciation

of the continental shelf oﬀ Troms, north Norway. Boreas 8, 217–227 (1979).

16. Sættem, J. in Formation and Deformation of Glacial Deposits (eds Warren, C. R.

& Croot, D. C.) 95–113 (Balkema, 1994).

17. Hovland, M. & Judd, A. G. Seabed Pockmarks and Seepages: Impact on Geology,

Biology and the Marine Environment (Graham and Trotman, 1988).

18. Sloan, E. D. & Koh, C. Clathrate Hydrates of Natural Gases (CRC Press, 2008).

19. Waite, W. F. et al. Physical properties of hydrate-bearing sediments. Rev.

Geophys. 47, RG4003 (2009).

20. Winters, W. J., Pecher, I. A., Waite, W. F. & Mason, D. H. Physical properties

and rock physics models of sediment containing natural and

laboratory-formed methane gas hydrate. Am. Mineral. 89, 1221–1227 (2004).

21. Hyodo, M. et al. Mechanical behavior of gas-saturated methane

hydrate-bearing sediments. J. Geophys. Res. 118, 5185–5194 (2013).

22. Durham, W. B., Kirby, S. H., Stern, L. A. & Zhang, W. The strength and

rheology of methane clathrate hydrate. J. Geophys. Res. 108, 2182 (2003).

23. Kamb, B. Rheological nonlinearity and flow instability in the deforming bed

mechanism of ice stream motion. J. Geophys. Res. 96, 16585–16595 (1991).

24. Joughin, I., MacAyeal, D. R. & Tulaczyk, S. Basal shear stress of the Ross ice

streams from control method inversions. J. Geophys. Res. 109, B09405 (2004).

25. Sættem, J., Rise, L., Rokoengen, K. & By, T. Soil investigations, oﬀshore mid

Norway: a case study of glacial influence on geotechnical properties. Glob.

Planet. Change 12, 271–285 (1996).

26. Sættem, J., Rise, L. & Westgaard, D. A. Composition and properties of

glacigenic sediments in the southwestern Barents Sea. Mar. Geotechnol. 10,

229–255 (1992).

27. Wadham, J. L. et al. Potential methane reservoirs beneath Antarctica. Nature

488, 633–637 (2012).

28. Wallmann, K. et al. The global inventory of methane hydrate in marine

sediments: a theoretical approach. Energies 5, 2449–2498 (2012).

29. Uchida, T., Hondoh, T., Mae, S., Lipenkov, V. Y. & Duval, P. Air-hydrate crystals

in deep ice-core samples from Vostok Station, Antarctica. J. Glaciol. 40,

79–86 (1994).

30. Clark, C. D., Hughes, A. L. C., Greenwood, S. L., Jordan, C. & Sejrup, H. P.

Pattern and timing of retreat of the last British-Irish ice sheet. Quat. Sci. Rev.

44, 112–146 (2012).

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 m−1, 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

31. Smelror, M., Petrov, O., Larssen, G. B. & Werner, S. Geological History of the

Barents Sea (Norges geologiske undersøkelse, 2009).

32. Auriac, A. et al. Glacial isostatic adjustment associated with the Barents

Sea ice sheet: a modelling inter-comparison. Quat. Sci. Rev.

http://dx.doi.org/10.1016/j.quascirev.2016.02.011 (in the press).

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).

NATURE GEOSCIENCE |www.nature.com/naturegeoscience

The morphology of pockmarks on the north-east Antarctic Peninsula continental shelf

Article

May 2022
ANTARCT SCI

Glacial landforms reveal dynamic ice-sheet behaviour along the mid-Norwegian margin during the last glacial-deglacial cycle

Article

Jun 2022
QUATERNARY SCI REV

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.

A conceptual geological model for offshore wind sites in former ice stream settings: The Utsira Nord site, North Sea

Article

Full-text available

Apr 2022
J GEOL SOC LONDON

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.

A conceptual geological model for Utsira Nord offshore wind site in the Norwegian North Sea

Conference Paper

Full-text available

Jan 2021

Glacitectonic rafts and their role in the generation of Quaternary subglacial bedforms and deposits

Article

Full-text available

May 2021

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.

Glacier geoengineering to address sea-level rise: A geotechnical approach

Article

Full-text available

Dec 2020

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.

A conceptual model for glaciogenic reservoirs: From landsystems to reservoir architecture

Article

Dec 2019
MAR PETROL GEOL

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.

Gas Hydrate Potential in the Kara Sea

Chapter

Jan 2022

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.

European Ice Sheet Complex evolution during the Last Glacial Maximum (29–19 ka)

Chapter

Jan 2022

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.

Exceptions to bed-controlled ice sheet flow and retreat from glaciated continental margins worldwide

Article

Full-text available

Jan 2021

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.

A water-piracy hypothesis for the stagnation of Ice Stream C, Antarctica

Article

Jan 1994

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.

In search of ice-stream sticky spots

Article

Jan 1993

Richard B. Alley

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.

Air-hydrate crystals in deep ice-core samples from Vostok Station, Antarctica

Article

Jan 1994

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.

A water-piracy hypothesis for the stagnation of Ice Stream C, Antarctica

Article

Jan 1994

Clathrate hydrates of natural gases

Article

Jan 1990

E.D. Sloan

Glacial isostatic adjustment associated with the Barents Sea ice sheet: A modelling inter-comparison

Article

Jan 2015
QUATERNARY SCI REV

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.

Physical properties and rock physics models of sediment containing natural and laboratory-formed methane hydrate

Article

Aug 2004
AM MINERAL

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.

ATLAS: Geological History of the Barents Sea

Article

Jan 2009

Late Quaternary ice sheet history of northern Eurasia

Article

Jun 2004
QUATERNARY SCI REV

John Inge Svendsen

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.

Stagnation of Ice Stream C, West Antarctica by water piracy

Article

Feb 1997

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.