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| Open AccessConverging flow and anisotropy cause large-scale folding in Greenland's ice sheet
A range of mechanisms has been proposed for large-scale folding in polar ice sheets. Here, using new three-dimensional reconstructions of such folds in the onset region of the Greenland Petermann Glacier, the authors show that these formed due to flow convergence and the high mechanical anisotropy of ice.
- Paul D. Bons
- , Daniela Jansen
- & Ilka Weikusat
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| Open AccessBuried iceberg scours reveal reduced North Atlantic Current during the stage 12 deglacial
Reconstructing past ocean conditions, particularly current velocity, is difficult due to a lack of available proxies. Here, the authors present a set of well-preserved buried iceberg scours from the mid-Norwegian slope, from which they are able to infer North Atlantic current speeds during the third-last glacial.
- Andrew M. W. Newton
- , Mads Huuse
- & Simon H. Brocklehurst
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| Open AccessIce stream motion facilitated by a shallow-deforming and accreting bed
Ice streams are fundamental to ice sheet dynamics, but the mechanisms controlling their flow remain elusive. Here, the authors perform macro- and microscale analyses of mega-scale glacial lineations, which indicate a continuously accreting, shallow-deforming bed during ice stream flow.
- Matteo Spagnolo
- , Emrys Phillips
- & Izabela Szuman
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| Open AccessA potential hidden layer of meteorites below the ice surface of Antarctica
Collection data suggest the proportion of iron-based meteorites recovered from Antarctica is significantly lower than the rest of the world. Here, the authors propose a mechanism to explain this discrepancy, showing that iron meteorites heated by solar energy can move down through the ice, not to re-emerge.
- G. W. Evatt
- , M. J. Coughlan
- & I. D. Abrahams
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| Open AccessEvidence for link between modelled trends in Antarctic sea ice and underestimated westerly wind changes
Mechanisms responsible for the recent increase in Antarctic sea ice cover remain elusive. Here, the authors show that model underestimates of changes in wind-induced ocean circulation may contribute, in part, to the failure of CMIP5 models to accurately capture modern Antarctic sea ice trends.
- Ariaan Purich
- , Wenju Cai
- & Tim Cowan
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| Open AccessEvidence for the stability of the West Antarctic Ice Sheet divide for 1.4 million years
Predicting the West Antarctic Ice Sheet's response to future warming is hindered by a lack of historical evidence. Here, based on geomorphological evidence from and cosmogenic dating of Ellsworth Mountains' deposits, the authors show that at least a regional ice sheet survived Pleistocene interglacial cycles.
- Andrew S. Hein
- , John Woodward
- & David E. Sugden
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| Open AccessComplex Greenland outlet glacier flow captured
Quantifying Greenland's future contribution to sea level requires accurate portrayal of its outlet glaciers in ice sheet simulations. Here, the authors show that outlet glacier flow can be captured if ice thickness is well constrained and vertical shearing as well as membrane stresses are included in the model.
- Andy Aschwanden
- , Mark A. Fahnestock
- & Martin Truffer
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| Open AccessEvidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation
The development of pan-Arctic Ocean ice shelves during peak glacials was proposed in the 1970s, an idea that has been disputed due to lack of evidence. Here, the authors present geophysical mapping data supporting the presence of such an ice shelf during the peak of the penultimate glaciation ∼140–160 ka.
- Martin Jakobsson
- , Johan Nilsson
- & Igor Semiletov
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| Open AccessIce-sheet-driven methane storage and release in the Arctic
Methane release across the Arctic continental shelf has been attributed to modern dissociation of gas hydrate, accelerated by ocean warming. Here, the authors show that thermogenic methane was stored as subglacial gas hydrate during the last glaciation, and subsequently released following ice sheet retreat.
- Alexey Portnov
- , Sunil Vadakkepuliyambatta
- & Alun Hubbard
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Propagation style controls lava–snow interactions
How volcanoes and the cryosphere interact is of interest for understanding hazard mitigation at ice-clad volcanoes and for paleoclimate studies. Here, the authors provide quantitative details from an eruption in Kamchatka, demonstrating that two kinds of lava, ′a′a and pahoehoe, produced different snowpack responses.
- B. R. Edwards
- , A. Belousov
- & M. Belousova
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The emergence of modern sea ice cover in the Arctic Ocean
Reconstructing past sea ice coverage in the Arctic is important for future climate predictions. Here, the authors present a new sea ice record from the Eurasian sector of the Arctic Ocean and report that Arctic sea ice reached its modern winter maximum for the first time 2.6 million years ago.
- Jochen Knies
- , Patricia Cabedo-Sanz
- & Antoni Rosell-Melé
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Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning
The Antarctic ice sheets contribution to rising sea levels at the end of the last ice age remains a matter of debate. Here, the authors present a suite of ice-sheet modelling experiments and conclude that the retreating Antarctic ice sheet may have contributed as much as 0.7 m per century to meltwater pulse 1A.
- N. R. Golledge
- , L. Menviel
- & R. H. Levy
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Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed
The delivery of meltwater to the base of the Greenland Ice Sheet has been shown to regulate ice flow, yet the role of soft basal sediment is unknown. Here, the authors use a three-dimensional ice sheet model to assess the impact of seasonal meltwater delivery on subglacial sediment shear strength and ice flow.
- M. Bougamont
- , P. Christoffersen
- & S. P. Carter
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Sea-level variability over five glacial cycles
Detailed sea-level records beyond ~150,000 years ago are limited. Here, the authors present a radiometrically constrained sea-level record from the Red Sea, spanning five glacial cycles and examine sea-level rise rates and the effects of past global ice-volume changes on monsoon intensity.
- K. M. Grant
- , E. J. Rohling
- & F. Williams
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Weakening of the stratospheric polar vortex by Arctic sea-ice loss
The mechanism behind the severely cold winters experienced by the mid-latitudes of the Northern Hemisphere in recent years is not fully understood. Here, the authors combine observational analyses and model experiments to reveal a dynamic connection between Arctic sea-ice cover and the polar stratosphere.
- Baek-Min Kim
- , Seok-Woo Son
- & Jin-Ho Yoon
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| Open AccessA Cenozoic-style scenario for the end-Ordovician glaciation
Claims that the end-Ordovician Earth was characterized by giant ice sheets, yet paradoxically warm oceans and elevated CO2 levels are open to debate. Here, Ghienne et al. examine sedimentary records from low and high palaeolatitude settings and propose a revision of the mechanisms for end-Ordovician events.
- Jean-François Ghienne
- , André Desrochers
- & Jan Veizer
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| Open AccessIntensification of the meridional temperature gradient in the Great Barrier Reef following the Last Glacial Maximum
The Great Barrier Reef (GBR) is under threat from rising ocean temperatures, yet its response to past temperature change is poorly known. Felis et al. show that the GBR experienced a much steeper temperature gradient during the last deglaciation, suggesting it may be more resilient than previously thought.
- Thomas Felis
- , Helen V. McGregor
- & Jody M. Webster
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| Open AccessIce sheets as a significant source of highly reactive nanoparticulate iron to the oceans
Glacial meltwaters may help fertilize the iron-limited Polar Oceans, yet the contribution is poorly constrained. Hawkings et al.monitor iron fluxes during a full-melt season in Greenland, and propose that ice sheets provide highly reactive and potentially bioavailable iron, comparable with aeolian dust fluxes.
- Jon R. Hawkings
- , Jemma L. Wadham
- & Jon Telling
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Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay
Whether the origins of inner gorges were fluvial or subglacial has been debated for decades. Here, Jansen et al. present new evidence, in the form of a suite of cosmogenic nuclide exposure ages and a deglaciation map, which suggests a subglacial meltwater origin for inner gorges in northern Sweden.
- J.D. Jansen
- , A.T. Codilean
- & S. Xu
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| Open AccessSiple Dome ice reveals two modes of millennial CO2 change during the last ice age
Whether all rapid climate events during the last ice age impacted the global carbon cycle is not clearly understood. Ahn and Brook present a high-resolution record of atmospheric CO2 from Antarctica and suggest that only Greenland stadials associated with massive iceberg discharge influenced atmospheric CO2.
- Jinho Ahn
- & Edward J. Brook
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| Open AccessMarine ice regulates the future stability of a large Antarctic ice shelf
Signs of instability in the Antarctic Larsen C ice shelf have raised concerns that it might soon collapse like its northern neighbour Larsen B. Kulessa et al.combine an ice-shelf model with satellite and geophysical data to show that despite dynamic similarities, Larsen C is presently stabilized by marine ice.
- Bernd Kulessa
- , Daniela Jansen
- & Peter R. Sammonds
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| Open AccessEvidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age
The Atlantic Multidecadal Oscillation strongly influences Northern Hemisphere climate, yet its primary driver is poorly understood. Knudsen et al.analyse proxy records from the past ~450 years and show that external forcing has dominated control of the oscillation since the termination of the Little Ice Age.
- Mads Faurschou Knudsen
- , Bo Holm Jacobsen
- & Jesper Olsen
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Discovery of a novel methanogen prevalent in thawing permafrost
The microbes responsible for releasing the potent greenhouse gas methane from thawing permafrost remain largely unknown. Mondav and Woodcroft et al. investigate methane flux across a thaw gradient in Sweden and recover a near-complete genome of the dominant methanogen Candidatus ‘Methanoflorens stordalenmirensis’.
- Rhiannon Mondav
- , Ben J. Woodcroft
- & Gene W. Tyson
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Silicon isotopes indicate enhanced carbon export efficiency in the North Atlantic during deglaciation
The role of mesoscale processes in past carbon cycling in silica-limited regions such as the North Atlantic remains unclear. Hendry et al.show that changes in wind-driven upwelling during the last deglaciation resulted in enhanced silica utilization and carbon export efficiency compared with the present.
- Katharine R. Hendry
- , Laura F. Robinson
- & James D. Hays
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Rapid interhemispheric climate links via the Australasian monsoon during the last deglaciation
The global monsoon is considered to have provided an important interhemispheric climate link during deglaciation, but direct evidence is lacking. Here, climate evidence from speleothems suggests that rapid latitudinal displacements of the Australasian monsoon play a key role in deglacial warming.
- Linda K. Ayliffe
- , Michael K. Gagan
- & Bambang W. Suwargadi
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Observed thinning of Totten Glacier is linked to coastal polynya variability
Totten Glacier discharges the largest volume of ice in East Antarctica, but the mechanisms causing its recent thinning are relatively unknown. Khazendar et al.combine remote-sensing data with high-resolution ice–ocean modelling to link this recent thinning to reduced sea ice production in polynyas.
- A. Khazendar
- , M.P. Schodlok
- & M.R. van den Broeke
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Pink marine sediments reveal rapid ice melt and Arctic meltwater discharge during Dansgaard–Oeschger warmings
Meltwater pulses from Northern Hemisphere ice sheets are strongly implicated in past millennial-scale shifts in ocean circulation, yet direct evidence is sparse. Here, a 30,000-year glacial meltwater history for the Svalbard–Barents Sea ice sheet is reconstructed in a marine sediment core.
- Tine L. Rasmussen
- & Erik Thomsen
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Flow velocities of Alaskan glaciers
Alaskan mountain glaciers are losing ice and contribute to sea level rise, but contributions from specific ice-loss mechanisms are not known. Here, calving losses in Central Alaska are found to equal 36% of the net regional mass change each year and regional flux is dictated largely by snow accumulation rates.
- Evan W. Burgess
- , Richard R. Forster
- & Christopher F. Larsen
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| Open AccessPronounced interannual variability in tropical South Pacific temperatures during Heinrich Stadial 1
During the last glacial termination, the North Atlantic experienced a cold interval, but its impact on tropical climate variability is not clear. Here, a fossil Tahiti coral record shows that tropical sea surface temperature varied actively during this event, consistent with climate model simulations.
- Thomas Felis
- , Ute Merkel
- & Miriam Pfeiffer
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| Open AccessPotential regime shift in decreased sea ice production after the Mertz Glacier calving
The calving of the Mertz Glacier occurred in 2010 in East Antarctica, brought on by the re-positioning of a large iceberg. Using satellite data, this study shows a reduction in sea ice production following the calving, interpreted as a potential regime shift towards reduced sea ice production for the coming decades.
- T. Tamura
- , G.D. Williams
- & K.I. Ohshima
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Enhanced sea-ice export from the Arctic during the Younger Dryas
The Younger Dryas cold period is thought to have occurred mainly due to the release of fresh water into the North Atlantic from the glacial Lake Agassiz. Here, sedimentary and geochemical data from the central Arctic Ocean support the hypothesis of a northward route drainage event from Lake Agassiz during the Younger Dryas.
- Christelle Not
- & Claude Hillaire-Marcel
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Impact of the Mertz Glacier Tongue calving on dense water formation and export
Antarctic bottom water is important for the global climate system, but its main source in East Antarctica was altered recently because of calving of the Mertz Glacier Tongue. The authors model this event and find large changes in dense water exports from the region.
- Kazuya Kusahara
- , Hiroyasu Hasumi
- & Guy D. Williams