49 results on '"Bjørk, Anders A."'
Search Results
2. Altimetry-based ice-marginal lake water level changes in Greenland
- Author
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Dømgaard, Mads, Kjeldsen, Kristian, How, Penny, and Bjørk, Anders
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- 2024
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3. Sediment discharge from Greenland’s marine-terminating glaciers is linked with surface melt
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Andresen, Camilla S., Karlsson, Nanna B., Straneo, Fiammetta, Schmidt, Sabine, Andersen, Thorbjørn J., Eidam, Emily F., Bjørk, Anders A., Dartiguemalle, Nicolas, Dyke, Laurence M., Vermassen, Flor, and Gundel, Ida E.
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- 2024
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4. Reply to: When did mammoths go extinct?
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Wang, Yucheng, Prohaska, Ana, Dong, Haoran, Alberti, Adriana, Alsos, Inger Greve, Beilman, David W., Bjørk, Anders A., Cao, Jialu, Cherezova, Anna A., Coissac, Eric, De Sanctis, Bianca, Denoeud, France, Dockter, Christoph, Durbin, Richard, Edwards, Mary E., Edwards, Neil R., Esdale, Julie, Fedorov, Grigory B., Fernandez-Guerra, Antonio, Froese, Duane G., Gusarova, Galina, Haile, James, Holden, Philip B., Kjeldsen, Kristian K., Kjær, Kurt H., Korneliussen, Thorfinn Sand, Lammers, Youri, Larsen, Nicolaj Krog, Macleod, Ruairidh, Mangerud, Jan, McColl, Hugh, Merkel, Marie Kristine Føreid, Money, Daniel, Möller, Per, Nogués-Bravo, David, Orlando, Ludovic, Owens, Hannah Lois, Pedersen, Mikkel Winther, Racimo, Fernando, Rahbek, Carsten, Rasic, Jeffrey T., Rouillard, Alexandra, Ruter, Anthony H., Skadhauge, Birgitte, Svendsen, John Inge, Tikhonov, Alexei, Vinner, Lasse, Wincker, Patrick, Xing, Yingchun, Zhang, Yubin, Meltzer, David J., and Willerslev, Eske
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- 2022
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5. Late Quaternary dynamics of Arctic biota from ancient environmental genomics
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Wang, Yucheng, Pedersen, Mikkel Winther, Alsos, Inger Greve, De Sanctis, Bianca, Racimo, Fernando, Prohaska, Ana, Coissac, Eric, Owens, Hannah Lois, Merkel, Marie Kristine Føreid, Fernandez-Guerra, Antonio, Rouillard, Alexandra, Lammers, Youri, Alberti, Adriana, Denoeud, France, Money, Daniel, Ruter, Anthony H., McColl, Hugh, Larsen, Nicolaj Krog, Cherezova, Anna A., Edwards, Mary E., Fedorov, Grigory B., Haile, James, Orlando, Ludovic, Vinner, Lasse, Korneliussen, Thorfinn Sand, Beilman, David W., Bjørk, Anders A., Cao, Jialu, Dockter, Christoph, Esdale, Julie, Gusarova, Galina, Kjeldsen, Kristian K., Mangerud, Jan, Rasic, Jeffrey T., Skadhauge, Birgitte, Svendsen, John Inge, Tikhonov, Alexei, Wincker, Patrick, Xing, Yingchun, Zhang, Yubin, Froese, Duane G., Rahbek, Carsten, Bravo, David Nogues, Holden, Philip B., Edwards, Neil R., Durbin, Richard, Meltzer, David J., Kjær, Kurt H., Möller, Per, and Willerslev, Eske
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- 2021
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6. Early aerial expedition photos reveal 85 years of glacier growth and stability in East Antarctica.
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Dømgaard, Mads, Schomacker, Anders, Isaksson, Elisabeth, Millan, Romain, Huiban, Flora, Dehecq, Amaury, Fleischer, Amanda, Moholdt, Geir, Andersen, Jonas K., and Bjørk, Anders A.
- Abstract
During the last few decades, several sectors in Antarctica have transitioned from glacial mass balance equilibrium to mass loss. In order to determine if recent trends exceed the scale of natural variability, long-term observations are vital. Here we explore the earliest, large-scale, aerial image archive of Antarctica to provide a unique record of 21 outlet glaciers along the coastline of East Antarctica since the 1930s. In Lützow-Holm Bay, our results reveal constant ice surface elevations since the 1930s, and indications of a weakening of local land-fast sea-ice conditions. Along the coastline of Kemp and Mac Robertson, and Ingrid Christensen Coast, we observe a long-term moderate thickening of the glaciers since 1937 and 1960 with periodic thinning and decadal variability. In all regions, the long-term changes in ice thickness correspond with the trends in snowfall since 1940. Our results demonstrate that the stability and growth in ice elevations observed in terrestrial basins over the past few decades are part of a trend spanning at least a century, and highlight the importance of understanding long-term changes when interpreting current dynamics.Pre-satellite era observations of Antarctic glaciers are rare. A unique record of aerial expedition images of East Antarctic outlet glaciers since the 1930s reveal long-term stability and moderate thickening. [ABSTRACT FROM AUTHOR]
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- 2024
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7. Rapidly changing glaciers, ocean and coastal environments, and their impact on human society in the Qaanaaq region, northwestern Greenland
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Sugiyama, Shin, Kanna, Naoya, Sakakibara, Daiki, Ando, Takuto, Asaji, Izumi, Kondo, Ken, Wang, Yefan, Fujishi, Yoshiki, Fukumoto, Shungo, Podolskiy, Evgeniy, Fukamachi, Yasushi, Takahashi, Minori, Matoba, Sumito, Iizuka, Yoshinori, Greve, Ralf, Furuya, Masato, Tateyama, Kazutaka, Watanabe, Tatsuya, Yamasaki, Shintaro, Yamaguchi, Atsushi, Nishizawa, Bungo, Matsuno, Kohei, Nomura, Daiki, Sakuragi, Yuta, Matsumura, Yoshimasa, Ohashi, Yoshihiko, Aoki, Teruo, Niwano, Masashi, Hayashi, Naotaka, Minowa, Masahiro, Jouvet, Guillaume, van Dongen, Eef, Bauder, Andreas, Funk, Martin, Bjørk, Anders Anker, and Oshima, Toku
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- 2021
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8. Evaluation of the Apple iPhone 12 Pro LiDAR for an Application in Geosciences
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Luetzenburg, Gregor, Kroon, Aart, and Bjørk, Anders A.
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- 2021
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9. Author Correction: Late Quaternary dynamics of Arctic biota from ancient environmental genomics
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Wang, Yucheng, Pedersen, Mikkel Winther, Alsos, Inger Greve, De Sanctis, Bianca, Racimo, Fernando, Prohaska, Ana, Coissac, Eric, Owens, Hannah Lois, Merkel, Marie Kristine Føreid, Fernandez-Guerra, Antonio, Rouillard, Alexandra, Lammers, Youri, Alberti, Adriana, Denoeud, France, Money, Daniel, Ruter, Anthony H., McColl, Hugh, Larsen, Nicolaj Krog, Cherezova, Anna A., Edwards, Mary E., Fedorov, Grigory B., Haile, James, Orlando, Ludovic, Vinner, Lasse, Korneliussen, Thorfinn Sand, Beilman, David W., Bjørk, Anders A., Cao, Jialu, Dockter, Christoph, Esdale, Julie, Gusarova, Galina, Kjeldsen, Kristian K., Mangerud, Jan, Rasic, Jeffrey T., Skadhauge, Birgitte, Svendsen, John Inge, Tikhonov, Alexei, Wincker, Patrick, Xing, Yingchun, Zhang, Yubin, Froese, Duane G., Rahbek, Carsten, Bravo, David Nogues, Holden, Philip B., Edwards, Neil R., Durbin, Richard, Meltzer, David J., Kjær, Kurt H., Möller, Per, and Willerslev, Eske
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- 2022
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10. Forty-six years of Greenland Ice Sheet mass balance from 1972 to 2018
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Mouginot, Jérémie, Rignot, Eric, Bjørk, Anders A., van den Broeke, Michiel, Millan, Romain, Morlighem, Mathieu, Noël, Brice, Scheuchl, Bernd, and Wood, Michael
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- 2019
11. Centennial response of Greenland’s three largest outlet glaciers
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Khan, Shfaqat A., Bjørk, Anders A., Bamber, Jonathan L., Morlighem, Mathieu, Bevis, Michael, Kjær, Kurt H., Mouginot, Jérémie, Løkkegaard, Anja, Holland, David M., Aschwanden, Andy, Zhang, Bao, Helm, Veit, Korsgaard, Niels J., Colgan, William, Larsen, Nicolaj K., Liu, Lin, Hansen, Karina, Barletta, Valentina, Dahl-Jensen, Trine S., Søndergaard, Anne Sofie, Csatho, Beata M., Sasgen, Ingo, Box, Jason, and Schenk, Toni
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- 2020
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12. Dataset supporting 'Ice shelf changes in North Greenland reveal dramatic signs of ongoing ice sheet instability'
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Millan, Romain, Jager, Eliot, Mouginot, Jeremie, Wood, Mike, Larsen, Signe, Mathiot, Pierre, Jourdain, Nicolas, and Bjørk, Anders
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greenland ,glaciology ,ice shelves - Abstract
This dataset accompanies the publication under review "Ice shelf changes in North Greenland reveal dramatic signs of ongoing ice sheet instability". It includes basal melt, discharge, calving, front position and grounding line data at the main ice shelves in North Greenland. This dataset also includes the codes used for the figures in the article. The version 1 should be used.
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- 2023
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13. Mass Loss of Glaciers and Ice Caps Across Greenland Since the Little Ice Age.
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Carrivick, Jonathan L., Boston, Clare M., Sutherland, Jenna L., Pearce, Danni, Armstrong, Hugo, Bjørk, Anders, Kjeldsen, Kristian K., Abermann, Jakob, Oien, Rachel P., Grimes, Michael, James, William H. M., and Smith, Mark W.
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LITTLE Ice Age ,MASS budget (Geophysics) ,ICE caps ,GLACIERS ,RUNOFF ,ICE sheets ,ABLATION (Glaciology) - Abstract
Glaciers and ice caps (GICs) are important contributors of meltwater runoff and to global sea level rise. However, knowledge of GIC mass changes is largely restricted to the last few decades. Here we show the extent of 5327 Greenland GICs during Little Ice Age (LIA) termination (1900) and reveal that they have fragmented into 5467 glaciers in 2001, losing at least 587 km3 from their ablation areas, equating to 499 Gt at a rate of 4.34 Gt yr−1. We estimate that the long‐term mean mass balance in glacier ablation areas has been at least −0.18 to −0.22 m w.e. yr−1 and note the rate between 2000 and 2019 has been three times that. Glaciers with ice‐marginal lakes formed since the LIA termination have had the fastest changing mass balance. Considerable spatial variability in glacier changes suggest compounding regional and local factors present challenges for understanding glacier evolution. Plain Language Summary: Glaciers and ice caps of Greenland peripheral to the ice sheet are important contributors of meltwater to the oceans and to global sea‐level rise. In this study we map the extent of 5467 glaciers during the Little Ice Age (LIA) termination c. 1900 and calculate that they have lost at least 587 km3. The rate of mass change of these glaciers between 2000 and 2019 was three times more negative than the long‐term average (of 4.34 Gt yr−1) since the LIA. Lake‐terminating glaciers now lose mass the fastest compared with land‐ or marine‐terminating glaciers. Considerable spatial variability in glacier responses suggests local factors are important and makes glacier evolution complex. Key Points: Total volume loss of at least 587 km3 since the Little Ice Age (LIA) termination, equating to 499 Gt and to 1.38 mm sea level equivalentGlacier mass balance from 2000 to 2019 is three times more negative than since the LIA but five times more negative in the North regionLake‐terminating glaciers have experienced the greatest change in rate of mass loss [ABSTRACT FROM AUTHOR]
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- 2023
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14. Greenland ice sheet climate disequilibrium and committed sea-level rise
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Box, Jason E., Hubbard, Alun, Bahr, David B., Colgan, William T., Fettweis, Xavier, Mankoff, Kenneth D., Wehrlé, Adrien, Noël, Brice, van den Broeke, Michiel R., Wouters, Bert, Bjørk, Anders A., Fausto, Robert S., Sub Dynamics Meteorology, Marine and Atmospheric Research, Sub Dynamics Meteorology, and Marine and Atmospheric Research
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Environmental Science (miscellaneous) ,Social Sciences (miscellaneous) - Abstract
Ice loss from the Greenland ice sheet is one of the largest sources of contemporary sea-level rise (SLR). While process-based models place timescales on Greenland’s deglaciation, their confidence is obscured by model shortcomings including imprecise atmospheric and oceanic couplings. Here, we present a complementary approach resolving ice sheet disequilibrium with climate constrained by satellite-derived bare-ice extent, tidewater sector ice flow discharge and surface mass balance data. We find that Greenland ice imbalance with the recent (2000–2019) climate commits at least 274 ± 68 mm SLR from 59 ± 15 × 103 km2 ice retreat, equivalent to 3.3 ± 0.9% volume loss, regardless of twenty-first-century climate pathways. This is a result of increasing mass turnover from precipitation, ice flow discharge and meltwater run-off. The high-melt year of 2012 applied in perpetuity yields an ice loss commitment of 782 ± 135 mm SLR, serving as an ominous prognosis for Greenland’s trajectory through a twenty-first century of warming.
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- 2022
15. Delta progradation in Greenland driven by increasing glacial mass loss
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Bendixen, Mette, Iversen, Lars Lønsmann, Bjørk, Anders Anker, Elberling, Bo, Westergaard-Nielsen, Andreas, Overeem, Irina, Barnhart, Katy R., Khan, Shfaqat Abbas, Box, Jason E., Abermann, Jakob, Langley, Kirsty, and Kroon, Aart
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- 2017
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16. Recent changes in drainage route and outburst magnitude of the Russell Glacier ice-dammed lake, West Greenland.
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Dømgaard, Mads, Kjeldsen, Kristian K., Huiban, Flora, Carrivick, Jonathan L., Khan, Shfaqat A., and Bjørk, Anders A.
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SUBGLACIAL lakes ,DRAINAGE ,GLACIERS ,GLACIAL lakes ,DIGITAL elevation models ,REMOTE-sensing images ,LAKES - Abstract
Glacial lake outburst floods (GLOFs) or jökulhlaups from ice-dammed lakes are frequent in Greenland and can influence local ice dynamics and bedrock motion, cause geomorphological changes, and pose flooding hazards. Multidecadal time series of lake drainage dates, volumes, and flood outlets are extremely rare. However, they are essential for determining the scale and frequency of future GLOFs, for identifying drainage mechanisms, and for mitigating downstream flood effects. In this study, we use high-resolution digital elevation models (DEMs) and orthophotos (0.1 × 0.1 m) generated from uncrewed-aerial-vehicle (UAV) field surveys, in combination with optical satellite imagery. This allows us to reconstruct robust lake volume changes associated with 14 GLOFs between 2007 and 2021 at Russell Glacier, West Greenland. As a result, this is one of the most comprehensive and longest records of ice-dammed lake drainages in Greenland to date. Importantly, we find a mean difference of ∼ 10 % between our lake drainage volumes when compared with estimates derived from a gauged hydrograph 27 km downstream. Due to thinning of the local ice dam, the potential maximum drainage volume in 2021 is ∼ 60 % smaller than that estimated to have drained in 2007. Our time series also reveals variations in the drainage dates ranging from late May to mid-September and drainage volumes ranging between 0.9 and 37.7 Mm 3. We attribute these fluctuations between short periods of relatively high and low drainage volumes to a weakening of the ice dam and an incomplete sealing of the englacial tunnel following the large GLOFs. This syphoning drainage mechanism is triggered by a reduction in englacial meltwater, likely driven by late-season drainage and sudden air temperature reductions, as well as annual variations in the glacial drainage system. Furthermore, we provide geomorphological evidence of an additional drainage route first observed following the 2021 GLOF, with a subglacial or englacial flow pathway, as well as supraglacial water flow across the ice margin. It seems probable that the new drainage route will become dominant in the future. This will drive changes in the downstream geomorphology and raise the risk of flooding-related hazards as the existing buffering outlet lakes will be bypassed. [ABSTRACT FROM AUTHOR]
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- 2023
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17. Accelerating Ice Loss From Peripheral Glaciers in North Greenland
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Khan, Shfaqat A., Colgan, William, Neumann, Thomas A., van den Broeke, Michiel R., Brunt, Kelly M., Noël, Brice, Bamber, Jonathan L., Hassan, Javed, Bjørk, Anders A., Sub Dynamics Meteorology, Marine and Atmospheric Research, Sub Dynamics Meteorology, and Marine and Atmospheric Research
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Icesat-2 ,Greenland ,Earth and Planetary Sciences(all) ,FIRN-DENSIFICATION ,satellite altimetry ,SHEET SURFACE ELEVATION ,RECONCILED ESTIMATE ,TIME ,Geophysics ,peripheral glacier ,sea level rise ,MASS-BALANCE ,BRIEF-COMMUNICATION ,MAP ,General Earth and Planetary Sciences ,GlobalMass ,CAPS ,ice mass loss - Abstract
In recent decades, Greenland's peripheral glaciers have experienced large-scale mass loss, resulting in a substantial contribution to sea level rise. While their total area of Greenland ice cover is relatively small (4%), their mass loss is disproportionally large compared to the Greenland ice sheet. Satellite altimetry from Ice, Cloud, and land Elevation Satellite (ICESat) and ICESat-2 shows that mass loss from Greenland's peripheral glaciers increased from 27.2±6.2Gt/yr (February 2003–October 2009) to 42.3±6.2Gt/yr (October 2018–December 2021). These relatively small glaciers now constitute 11±2% of Greenland's ice loss and contribute to global sea level rise. In the period October 2018–December 2021, mass loss increased by a factor of four for peripheral glaciers in North Greenland. While peripheral glacier mass loss is widespread, we also observe a complex regional pattern where increases in precipitation at high altitudes have partially counteracted increases in melt at low altitude.
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- 2022
18. An Early Pleistocene interglacial deposit at Pingorsuit, North‐West Greenland.
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Bennike, Ole, Colgan, William, Hedenäs, Lars, Heiri, Oliver, Lemdahl, Geoffrey, Wiberg‐Larsen, Peter, Ribeiro, Sofia, Pronzato, Roberto, Manconi, Renata, and Bjørk, Anders A.
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SPONGES (Invertebrates) ,PLEISTOCENE Epoch ,VASCULAR plants ,SEA level ,CADDISFLIES ,WETLANDS ,SHRUBS ,POTAMOGETON - Abstract
At the Pingorsuit Glacier in North‐West Greenland, an organic‐rich deposit that had recently emerged from the retreating ice cap was discovered at an elevation of 480 m above sea level. This paper reports on macrofossil analyses of a coarse detritus gyttja and peaty soil, which occurred beneath a thin cover of till and glacifluvial deposits. The sediments contained remains of vascular plants, mosses, beetles, caddisflies, midges, bryozoans, sponges and other invertebrates. The flora includes black spruce, tree birch, boreal shrubs and wetland and aquatic taxa, which shows that mires, lakes and ponds were present in the area. We describe a new extinct waterwort species Elatine odgaardii. The fossils were deposited in a boreal environment with a mean July air temperature that was at least 9 °C higher than at present. The fossil assemblages show strong similarities with others from Greenland that have been assigned an Early Pleistocene age, and we suggest a similar age for the sediments found at the margin of the Pingorsuit Glacier. At the Pingorsuit Glacier in North‐West Greenland, an organic‐rich deposit was discovered at an elevation of 480 m above sea level. The sediments contained remains of vascular plants, mosses, beetles, caddisflies, midges, bryozoans, sponges and other invertebrates. The fossils were deposited in a boreal environment with a mean July air temperature that was at least 9 °C higher than at present. [ABSTRACT FROM AUTHOR]
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- 2023
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19. TermPicks: a century of Greenland glacier terminus data for use in scientific and machine learning applications.
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Goliber, Sophie, Black, Taryn, Catania, Ginny, Lea, James M., Olsen, Helene, Cheng, Daniel, Bevan, Suzanne, Bjørk, Anders, Bunce, Charlie, Brough, Stephen, Carr, J. Rachel, Cowton, Tom, Gardner, Alex, Fahrner, Dominik, Hill, Emily, Joughin, Ian, Korsgaard, Niels J., Luckman, Adrian, Moon, Twila, and Murray, Tavi
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SCIENCE education ,SYNTHETIC apertures ,SYNTHETIC aperture radar ,GLACIERS ,GREENLAND ice ,MACHINE learning - Abstract
Marine-terminating outlet glacier terminus traces, mapped from satellite and aerial imagery, have been used extensively in understanding how outlet glaciers adjust to climate change variability over a range of timescales. Numerous studies have digitized termini manually, but this process is labor intensive, and no consistent approach exists. A lack of coordination leads to duplication of efforts, particularly for Greenland, which is a major scientific research focus. At the same time, machine learning techniques are rapidly making progress in their ability to automate accurate extraction of glacier termini, with promising developments across a number of optical and synthetic aperture radar (SAR) satellite sensors. These techniques rely on high-quality, manually digitized terminus traces to be used as training data for robust automatic traces. Here we present a database of manually digitized terminus traces for machine learning and scientific applications. These data have been collected, cleaned, assigned with appropriate metadata including image scenes, and compiled so they can be easily accessed by scientists. The TermPicks data set includes 39 060 individual terminus traces for 278 glaciers with a mean of 136 ± 190 and median of 93 of traces per glacier. Across all glaciers, 32 567 dates have been digitized, of which 4467 have traces from more than one author, and there is a duplication rate of 17 %. We find a median error of ∼ 100 m among manually traced termini. Most traces are obtained after 1999, when Landsat 7 was launched. We also provide an overview of an updated version of the Google Earth Engine Digitization Tool (GEEDiT), which has been developed specifically for future manual picking of the Greenland Ice Sheet. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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20. Spatial and temporal distribution of mass loss from the Greenland Ice Sheet since AD 1900
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Kjeldsen, Kristian K., Korsgaard, Niels J., Bjørk, Anders A., Khan, Shfaqat A., Box, Jason E., Funder, Svend, Larsen, Nicolaj K., Bamber, Jonathan L., Colgan, William, van den Broeke, Michiel, Siggaard-Andersen, Marie-Louise, Nuth, Christopher, Schomacker, Anders, Andresen, Camilla S., Willerslev, Eske, and Kjær, Kurt H.
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- 2015
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21. Late Quaternary dynamics of Arctic biota from ancient environmental genomics:[+ Correction]
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Wang, Yucheng, Pedersen, Mikkel Winther, Alsos, Inger Greve, De Sanctis, Bianca, Racimo, Fernando, Prohaska, Ana, Coissac, Eric, Owens, Hannah Lois, Merkel, Marie Kristine Føreid, Fernandez-Guerra, Antonio, Rouillard, Alexandra, Lammers, Youri, Alberti, Adriana, Denoeud, France, Money, Daniel, Ruter, Anthony H., McColl, Hugh, Larsen, Nicolaj Krog, Cherezova, Anna A., Edwards, Mary E., Fedorov, Grigory B., Haile, James, Orlando, Ludovic, Vinner, Lasse, Korneliussen, Thorfinn Sand, Beilman, David W., Bjørk, Anders A., Cao, Jialu, Dockter, Christoph, Esdale, Julie, Gusarova, Galina, Kjeldsen, Kristian K., Mangerud, Jan, Rasic, Jeffrey T., Skadhauge, Birgitte, Svendsen, John Inge, Tikhonov, Alexei, Wincker, Patrick, Xing, Yingchun, Zhang, Yubin, Froese, Duane G., Rahbek, Carsten, Nogues, David Bravo, Holden, Philip B., Edwards, Neil R., Durbin, Richard, Meltzer, David J., Kjær, Kurt H., Möller, Per, and Willerslev, Eske
- Abstract
During the last glacial–interglacial cycle, Arctic biotas experienced substantial climatic changes, yet the nature, extent and rate of their responses are not fully understood1–8. Here we report a large-scale environmental DNA metagenomic study of ancient plant and mammal communities, analysing 535 permafrost and lake sediment samples from across the Arctic spanning the past 50,000 years. Furthermore, we present 1,541 contemporary plant genome assemblies that were generated as reference sequences. Our study provides several insights into the long-term dynamics of the Arctic biota at the circumpolar and regional scales. Our key findings include: (1) a relatively homogeneous steppe–tundra flora dominated the Arctic during the Last Glacial Maximum, followed by regional divergence of vegetation during the Holocene epoch; (2) certain grazing animals consistently co-occurred in space and time; (3) humans appear to have been a minor factor in driving animal distributions; (4) higher effective precipitation, as well as an increase in the proportion of wetland plants, show negative effects on animal diversity; (5) the persistence of the steppe–tundra vegetation in northern Siberia enabled the late survival of several now-extinct megafauna species, including the woolly mammoth until 3.9 ± 0.2 thousand years ago (ka) and the woolly rhinoceros until 9.8 ± 0.2 ka; and (6) phylogenetic analysis of mammoth environmental DNA reveals a previously unsampled mitochondrial lineage. Our findings highlight the power of ancient environmental metagenomics analyses to advance understanding of population histories and long-term ecological dynamics.
- Published
- 2021
22. A national landslide inventory for Denmark.
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Luetzenburg, Gregor, Svennevig, Kristian, Bjørk, Anders A., Keiding, Marie, and Kroon, Aart
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LANDSLIDES ,SEDIMENT transport ,DIGITAL elevation models ,LAND cover ,QUALITY control - Abstract
Landslides are a frequent natural hazard occurring globally in regions with steep topography. Additionally, landslides play an important role in landscape evolution by transporting sediment downslope. Landslide inventory mapping is a common technique to assess the spatial distribution and extent of landslides in an area of interest. High-resolution digital elevation models (DEMs) have proven to be useful databases to map landslides in large areas across different land covers and topography. So far, Denmark had no national landslide inventory. Here, we create the first comprehensive national landslide inventory for Denmark derived from a 40 cm resolution DEM from 2015 supported by several 12.5 cm resolution orthophotos. The landslide inventory is created based on a manual expert-based mapping approach, and we implemented a quality control mechanism to assess the completeness of the inventory. Overall, we mapped 3202 landslide polygons in Denmark with a level of completeness of 87 %. The complete landslide inventory is freely available for download at 10.6084/m9.figshare.16965439.v2 (Svennevig and Luetzenburg, 2021) or as a web map (https://data.geus.dk/landskred/ , last access: 6 June 2022) for further investigations. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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23. Greenland Geothermal Heat Flow Database and Map (Version 1).
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Colgan, William, Wansing, Agnes, Mankoff, Kenneth, Lösing, Mareen, Hopper, John, Louden, Keith, Ebbing, Jörg, Christiansen, Flemming G., Ingeman-Nielsen, Thomas, Liljedahl, Lillemor Claesson, MacGregor, Joseph A., Hjartarson, Árni, Bernstein, Stefan, Karlsson, Nanna B., Fuchs, Sven, Hartikainen, Juha, Liakka, Johan, Fausto, Robert S., Dahl-Jensen, Dorthe, and Bjørk, Anders
- Subjects
ICE cores ,CALORIMETRY ,GREENLAND ice ,EARTH temperature ,FLOW measurement - Abstract
We compile and analyze all available geothermal heat flow measurements collected in and around Greenland into a new database of 419 sites and generate an accompanying spatial map. This database includes 290 sites previously reported by the International Heat Flow Commission (IHFC), for which we now standardize measurement and metadata quality. This database also includes 129 new sites, which have not been previously reported by the IHFC. These new sites consist of 88 offshore measurements and 41 onshore measurements, of which 24 are subglacial. We employ machine learning to synthesize these in situ measurements into a gridded geothermal heat flow model that is consistent across both continental and marine areas in and around Greenland. This model has a native horizontal resolution of 55 km. In comparison to five existing Greenland geothermal heat flow models, our model has the lowest mean geothermal heat flow for Greenland onshore areas. Our modeled heat flow in central North Greenland is highly sensitive to whether the NGRIP (North GReenland Ice core Project) elevated heat flow anomaly is included in the training dataset. Our model's most distinctive spatial feature is pronounced low geothermal heat flow (< 40 mW m -2) across the North Atlantic Craton of southern Greenland. Crucially, our model does not show an area of elevated heat flow that might be interpreted as remnant from the Icelandic plume track. Finally, we discuss the substantial influence of paleoclimatic and other corrections on geothermal heat flow measurements in Greenland. The in situ measurement database and gridded heat flow model, as well as other supporting materials, are freely available from the GEUS Dataverse (10.22008/FK2/F9P03L; Colgan and Wansing, 2021). [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
24. Mass balance of the Greenland Ice Sheet from 1992 to 2018
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Shepherd, Andrew, Ivins, Erik, Rignot, Eric, Smith, Ben, van den Broeke, Michiel, Velicogna, Isabella, Whitehouse, Pippa, Briggs, Kate, Joughin, Ian, Krinner, Gerhard, Nowicki, Sophie, Payne, Tony, Scambos, Ted, Schlegel, Nicole, Geruo, A., Agosta, Cécile, Ahlstrøm, Andreas, Babonis, Greg, Barletta, Valentina R., Bjørk, Anders A., Blazquez, Alejandro, Bonin, Jennifer, Colgan, William, Csatho, Beata, Cullather, Richard, Engdahl, Marcus E., Felikson, Denis, Fettweis, Xavier, Forsberg, Rene, Hogg, Anna E., Gallee, Hubert, Gardner, Alex, Gilbert, Lin, Gourmelen, Noel, Groh, Andreas, Gunter, Brian, Hanna, Edward, Harig, Christopher, Helm, Veit, Horvath, Alexander, Horwath, Martin, Khan, Shfaqat, Kjeldsen, Kristian K., Konrad, Hannes, Langen, Peter L., Lecavalier, Benoit, Loomis, Bryant, Luthcke, Scott, McMillan, Malcolm, Melini, Daniele, Mernild, Sebastian, Mohajerani, Yara, Moore, Philip, Mottram, Ruth, Mouginot, Jeremie, Moyano, Gorka, Muir, Alan, Nagler, Thomas, Nield, Grace, Nilsson, Johan, Noël, Brice, Otosaka, Ines, Pattle, Mark E., Peltier, W. Richard, Pie, Nadège, Rietbroek, Roelof, Rott, Helmut, Sørensen, Louise Sandberg, Sasgen, Ingo, Save, Himanshu, Scheuchl, Bernd, Schrama, Ernst, Schröder, Ludwig, Seo, Ki-Weon, Simonsen, Sebastian B., Slater, Thomas, Spada, Giorgio, Sutterley, Tyler, Talpe, Matthieu, Tarasov, Lev, Jan van de Berg, Willem, van der Wal, Wouter, van Wessem, Melchior, Vishwakarma, Bramha Dutt, Wiese, David, Wilton, David, Wagner, Thomas, Wouters, Bert, Wuite, Jan, Team, The IMBIE, Marine and Atmospheric Research, Sub Dynamics Meteorology, Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Andrew Shepherd, Erik Ivin, Eric Rignot, Ben Smith, Michiel van den Broeke, Isabella Velicogna, Pippa Whitehouse, Kate Brigg, Ian Joughin, Gerhard Krinner, Sophie Nowicki, Tony Payne, Ted Scambo, Nicole Schlegel, A Geruo, Cécile Agosta, Andreas Ahlstrøm, Greg Baboni, Valentina R. Barletta, Anders A. Bjørk, Alejandro Blazquez, Jennifer Bonin, William Colgan, Beata Csatho, Richard Cullather, Marcus E. Engdahl, Denis Felikson, Xavier Fettwei, Rene Forsberg, Anna E. Hogg, Hubert Gallee, Alex Gardner, Lin Gilbert, Noel Gourmelen, Andreas Groh, Brian Gunter, Edward Hanna, Christopher Harig, Veit Helm, Alexander Horvath, Martin Horwath, Shfaqat Khan, Kristian K. Kjeldsen, Hannes Konrad, Peter L. Langen, Benoit Lecavalier, Bryant Loomi, Scott Luthcke, Malcolm McMillan, Daniele Melini, Sebastian Mernild, Yara Mohajerani, Philip Moore, Ruth Mottram, Jeremie Mouginot, Gorka Moyano, Alan Muir, Thomas Nagler, Grace Nield, Johan Nilsson, Brice Noël, Ines Otosaka, Mark E. Pattle, W. Richard Peltier, Nadège Pie, Roelof Rietbroek, Helmut Rott, Louise Sandberg Sørensen, Ingo Sasgen, Himanshu Save, Bernd Scheuchl, Ernst Schrama, Ludwig Schröder, Ki-Weon Seo, Sebastian B. Simonsen, Thomas Slater, Giorgio Spada, Tyler Sutterley, Matthieu Talpe, Lev Tarasov, Willem Jan van de Berg, Wouter van der Wal, Melchior van Wessem, Bramha Dutt Vishwakarma, David Wiese, David Wilton, Thomas Wagner, Bert Wouter, Jan Wuite, Marine and Atmospheric Research, and Sub Dynamics Meteorology
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geography ,Multidisciplinary ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,Global warming ,Greenland ice sheet ,Climate change ,Glacier ,GLACIAL ISOSTATIC-ADJUSTMENT, RELATIVE SEA-LEVEL PETERMANN GLACIER, ELEVATION CHANGE, SURFACE, GRACE, CLIMATE, MODEL, ACCELERATION, ANTARCTICA ,010502 geochemistry & geophysics ,Atmospheric sciences ,01 natural sciences ,Glacier mass balance ,13. Climate action ,Taverne ,[SDE]Environmental Sciences ,SDG 13 - Climate Action ,Environmental science ,Climate model ,Ice sheet ,F840 Physical Geography ,Meltwater ,0105 earth and related environmental sciences - Abstract
ArticlePublished: 10 December 2019This is an unedited manuscript that has been accepted for publication. Nature Research are providing this early version of the manuscript as a service to our customers. The manuscript will undergo copyediting, typesetting and a proof review before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers apply.Mass balance of the Greenland Ice Sheet from 1992 to 2018The IMBIE TeamNature (2019)Cite this article6914 Accesses1410 AltmetricMetricsdetailsAbstractIn recent decades, the Greenland Ice Sheet has been a major contributor to global sea-level rise1,2, and it is expected to be so in the future3. Although increases in glacier flow4–6 and surface melting7–9 have been driven by oceanic10–12 and atmospheric13,14 warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite measurements of changes in the ice sheet’s volume, flow and gravitational potential to produce a reconciled estimate of its mass balance. Although the ice sheet was close to a state of balance in the 1990s, annual losses have risen since then, peaking at 335 ± 62 billion tonnes per year in 2011. In all, Greenland lost 3,800 ± 339 billion tonnes of ice between 1992 and 2018, causing the mean sea level to rise by 10.6 ± 0.9 millimetres. Using three regional climate models, we show that reduced surface mass balance has driven 1,971 ± 555 billion tonnes (52%) of the ice loss owing to increased meltwater runoff. The remaining 1,827 ± 538 billion tonnes (48%) of ice loss was due to increased glacier discharge, which rose from 41 ± 37 billion tonnes per year in the 1990s to 87 ± 25 billion tonnes per year since then. Between 2013 and 2017, the total rate of ice loss slowed to 217 ± 32 billion tonnes per year, on average, as atmospheric circulation favoured cooler conditions15 and as ocean temperatures fell at the terminus of Jakobshavn Isbræ16. Cumulative ice losses from Greenland as a whole have been close to the IPCC’s predicted rates for their high-end climate warming scenario17, which forecast an additional 50 to 120 millimetres of global sea-level rise by 2100 when compared to their central estimate.
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- 2020
25. Late glacial and Holocene glaciation history of North and Northeast Greenland.
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Larsen, Nicolaj K., Søndergaard, Anne Sofie, Levy, Laura B., Strunk, Astrid, Skov, Daniel S., Bjørk, Anders, Khan, Shfaqat A., and Olsen, Jesper
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LITTLE Ice Age ,GREENLAND ice ,LAST Glacial Maximum ,ICE sheets ,HOLOCENE Epoch - Abstract
Northeast Greenland is the place where the Greenland Ice Sheet (GrIS) experienced the largest areal changes since the Last Glacial Maximum. However, the age constraints of the last deglaciation are in some areas sparse. In this study, we use forty-seven new 10Be cosmogenic exposure ages to constrain the deglaciation of the present-day ice-free areas in Northeast Greenland. Our results show that the outer coast region was deglaciated between 12.8 ± 0.6 and 11.5 ± 0.2 ka and the region close to the present ice margin was deglaciated 2 to 4 ka later between 9.2 ± 0.3 to 8.6 ± 0.3 ka. By combining our new results with previously published data from North and Northeast Greenland, we find that the ice sheet advanced to the shelf edge between 26 and 20 cal. ka BP. The outer coast was deglaciated between 12.8 and 9.7 ka and the present ice extent was reached between 10.8 to 5.8 ka. The ice margin continued to retreat farther inland during the Middle Holocene before it readvanced toward its Little Ice Age position. The deglaciation was probably forced by a combination of increased atmospheric and ocean temperatures, but local topography also played an important role. These results add to the growing knowledge about the glaciation history of the GrIS and add useful constraints for future ice sheet models. [ABSTRACT FROM AUTHOR]
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- 2022
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26. A national landslide inventory of Denmark.
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Luetzenburg, Gregor, Svennevig, Kristian, Bjørk, Anders Anker, Keiding, Marie, and Kroon, Aart
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LANDSLIDES ,SEDIMENT transport ,DIGITAL elevation models ,LAND cover ,QUALITY control - Abstract
Landslides are a frequent natural hazard occurring globally in regions with steep topography. Additionally, landslides are playing an important role in landscape evolution by transporting sediment downslope. Landslide inventory mapping is a common technique to assess the spatial distribution and extend of landslides in an area of interest. High-resolution digital elevation models (DEMs) have proven to be useful databases to map landslides in large areas across different land covers and topography. So far, Denmark had no national landslide inventory. Here we create the first comprehensive national landslide inventory for Denmark derived from a 40 cm resolution DEM from 2015 supported by several 12.5 cm resolution orthophotos. The landslide inventory is created based on a manual expert-based mapping approach, and we implemented a quality control mechanism to assess the completeness of the inventory. Overall, we mapped 3202 landslide polygons in Denmark with a level of completeness of 87 %. The landslide inventory can act as a starting point for a more comprehensive hazard and risk reduction framework for Denmark. Furthermore, machine-learning algorithms can use the dataset as a training dataset to improve future automated mapping approaches. The complete landslide inventory is made freely available for download at https://doi.org/10.6084/m9.figshare.16965439.v1 (Svennevig and Luetzenburg, 2021) or as web map (https://data.geus.dk/landskred/) for further investigations. [ABSTRACT FROM AUTHOR]
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- 2021
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27. Temperature observations from northernmost Greenland, 2006-2010
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Schomacker, Anders, Larsen, Nicolaj K., Bjørk, Anders A., and Kjær, Kurt H.
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Surface temperature ,soil temperature ,North Greenland ,Moore Gletscher ,Bliss Bugt - Abstract
Air-, surface-, and subsurface temperatures were recorded by automatic weather stations in Bliss Bugt and Moore Gletscher, Johannes V. Jensen Land, North coast of Greenland from 2006-2010. The mean annual surface temperature is -12.1 ℃ in Bliss Bugt and -13.8 ℃ at Moore Gletscher. In 20 cm depth below the surface at Moore Gletscher, the mean annual temperature is -13.2 ℃ (2007-2008). High-amplitude fluctuations of the winter temperature at the surface and in 20 cm depth at Moore Gletscher indicate that the surface has little or no snow cover, possibly due to catabatic winds from the glacier. In contrast, in Bliss Bugt, c. 5 km to the north, the surface temperature series only shows lowamplitude variations during the winters. This indicates a significant snow cover in Bliss Bugt, persisting throughout the winter. The surface temperature series reveals that the surface is snow free from mid-late June to late August in Bliss Bugt.
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- 2017
28. Greenland Geothermal Heat Flow Database and Map (Version 1).
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Colgan, William, Wansing, Agnes, Mankoff, Kenneth, Lösing, Mareen, Hopper, John, Louden, Keith, Ebbing, Jörg, Christiansen, Flemming G., Ingeman-Nielsen, Thomas, Liljedahl, Lillemor Claesson, MacGregor, Joseph A., Hjartarson, Árni, Bernstein, Stefan, Karlsson, Nanna B., Fuchs, Sven, Hartikainen, Juha, Liakka, Johan, Fausto, Robert, Dahl-Jensen, Dorthe, and Bjørk, Anders
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CALORIMETRY ,FLOW measurement ,EARTH temperature ,DATABASES ,MACHINE learning ,GROUND source heat pump systems - Abstract
We compile, analyse and map all available geothermal heat flow measurements collected in and around Greenland into a new database of 419 sites and generate an accompanying spatial map. This database includes 290 sites previously reported by the International Heat Flow Commission (IHFC), for which we now standardize measurement and metadata quality. This database also includes 129 new sites, which have not been previously reported by the IHFC. These new sites consist of 88 offshore measurements and 41 onshore measurements, of which 24 are subglacial. We employ machine learning to synthesize these in situ measurements into a gridded geothermal heat flow model that is consistent across both continental and marine areas in and around Greenland. This model has a native horizontal resolution of 55 km. In comparison to five existing Greenland geothermal heat flow models, our model has the lowest mean geothermal heat flow for Greenland onshore areas (44 mW m
-2 ). Our model's most distinctive spatial feature is pronounced low geothermal heat flow (< 40 mW m-2 ) across the North Atlantic Craton of southern Greenland. Crucially, our model does not show an area of elevated heat flow that might be interpreted as remnant from the Icelandic Plume track. Finally, we discuss the substantial influence of paleoclimatic and other corrections on geothermal heat flow measurements in Greenland. The in-situ measurement database and gridded heat flow model, as well as other supporting materials, are freely available from the GEUS DataVerse (https://doi.org/10.22008/FK2/F9P03L; Colgan and Wansing, 2021). [ABSTRACT FROM AUTHOR]- Published
- 2021
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29. Estimating Ice Discharge at Greenland's Three Largest Outlet Glaciers Using Local Bedrock Uplift.
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Hansen, Karina, Truffer, Martin, Aschwanden, Andy, Mankoff, Kenneth, Bevis, Michael, Humbert, Angelika, Broeke, Michiel R., Noël, Brice, Bjørk, Anders, Colgan, William, Kjær, Kurt H., Adhikari, Surendra, Barletta, Valentina, and Khan, Shfaqat A.
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MELTWATER ,ALPINE glaciers ,GREENLAND ice ,GLOBAL Positioning System ,GLACIERS ,ICE sheets ,BEDROCK - Abstract
We present a novel method to estimate dynamic ice loss of Greenland's three largest outlet glaciers: Jakobshavn Isbræ, Kangerlussuaq Glacier, and Helheim Glacier. We use Global Navigation Satellite System (GNSS) stations attached to bedrock to measure elastic displacements of the solid Earth caused by dynamic thinning near the glacier terminus. When we compare our results with discharge, we find a time lag between glacier speedup/slowdown and onset of dynamic thinning/thickening. Our results show that dynamic thinning/thickening on Jakobshavn Isbræ occurs 0.87 ± 0.07 years before speedup/slowdown. This implies that using GNSS time series we are able to predict speedup/slowdown of Jakobshavn Isbræ by up to 10.4 months. For Kangerlussuaq Glacier the lag between thinning/thickening and speedup/slowdown is 0.37 ± 0.17 years (4.4 months). Our methodology and results could be important for studies that attempt to model and understand mechanisms controlling short‐term dynamic fluctuations of outlet glaciers in Greenland. Plain Language Summary: A wide range of sensors and methods have been used to study the changes of the Greenland Ice Sheet, including satellite gravimetry, altimetry, and the input‐output method. Here, we present a novel fourth method to estimate dynamic ice loss of Greenland's three largest outlet glaciers: Jakobshavn Isbræ, Kangerlussuaq Glacier, and Helheim Glacier. We use Global Navigation Satellite System (GNSS) stations attached to bedrock to measure rise of land masses caused by ongoing ice mass loss near the glacier terminus. When we compare our results with ice discharge, we find a time lag between glacier speedup/slowdown and onset of dynamic induced thinning/thickening. Our results show that dynamic thinning/thickening on Jakobshavn Isbræ occurs 0.87 ± 0.07 years before speedup/slowdown. This implies that using GNSS uplift time series we are able to predict ice flow speedup/slowdown of Jakobshavn Isbræ by up to 10 months. For Kangerlussuaq Glacier and Helheim Glacier the lag between thinning/thickening and speedup/slowdown is 0.37 ± 0.17 years (4.4 months) and 0.03 ± 0.16 years, respectively. Our methodology and results could be important for studies that attempt to model and understand mechanisms controlling short‐term dynamic fluctuations of outlet glaciers in Greenland. Key Points: A novel method to estimate dynamic ice loss of Greenland's three largest outlet glaciers, Jakobshavn, Kangerlussuaq, and Helheim glacierDynamic thinning/thickening occurs 0.87 ± 0.07 years before speedup/slowdown at Jakobshavn IsbræA similar time lag between change in uplift rate and flow speed change allows us to predict future ice discharge from past uplift [ABSTRACT FROM AUTHOR]
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- 2021
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30. Younger Dryas ice margin retreat in Greenland: new evidence from southwestern Greenland.
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Funder, Svend, Sørensen, Anita H. L., Larsen, Nicolaj K., Bjørk, Anders A., Briner, Jason P., Olsen, Jesper, Schomacker, Anders, Levy, Laura B., and Kjær, Kurt H.
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ICE shelves ,GREENLAND ice ,ICE ,GLACIAL landforms ,ICE sheets ,YOUNGER Dryas ,ICE cores - Abstract
To date the final stage in deglaciation of the Greenland shelf, when a contiguous ice sheet margin on the inner shelf transitioned to outlet glaciers in troughs with intervening ice-free areas, we generated cosmogenic 10 Be dates from bedrock knobs on six outlying islands along a stretch of 300 km of the southwestern Greenland coast. Despite 10 Be inheritance influencing some dates, the ages generally support a Greenland Ice Sheet (GrIS) margin that retreated off the inner shelf during the middle Younger Dryas (YD) period. Published 10 Be- and 14 C-dated records show that this history of the GrIS margin is seen in other parts of Greenland but with large variations in the extent and speed of retreat, sometimes even between neighbouring areas. Areas with a chronology extending into the Allerød period show no marked ice margin change at the Allerød–YD transition except in northernmost Greenland. In contrast, landforms on the shelf (moraines and grounding zone wedges) have been suggested to indicate YD readvances or long-lasting ice margin stillstands on the middle shelf. However, these features have been dated primarily by correlation with cold periods in the ice core temperature records. Ice margin retreat during the middle and late YD is explained by advection of warm subsurface water at the ice margin and by increased seasonality. Our results therefore point to the complexity of the climate–ice margin relation and to the urgent need for direct dating of the early deglaciation history of Greenland. [ABSTRACT FROM AUTHOR]
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- 2021
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31. Contrasting modes of deglaciation between fjords and inter‐fjord areas in eastern North Greenland.
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Larsen, Nicolaj K., Søndergaard, Anne Sofie, Levy, Laura B., Olsen, Jesper, Strunk, Astrid, Bjørk, Anders A., and Skov, Daniel
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GLACIAL melting ,FJORDS ,GREENLAND ice ,OCEAN temperature ,ICE sheets ,GLACIAL landforms - Abstract
Knowledge about the deglaciation history of the Greenland Ice Sheet (GrIS) is important to put the recent observations of ice loss into a longer‐term perspective. In southern Greenland, the deglaciation history is generally well constrained. In this study, we use 43 new 10Be surface exposure ages combined with existing minimum‐limiting 14C ages to constrain the deglaciation history of eastern North Greenland, including the three major fjord systems – Independence Fjord, Hagen Fjord and Danmark Fjord. The 10Be ages are generally scattered and many of the samples are significantly older than expected, with pre‐LGM ages being a result of inheritance from previous exposures. By using a Bayesian statistical approach to combine the new 10Be ages and existing 14C ages, we are able to constrain the deglaciation history. We find that the outer coast and deep fjords were rapidly deglaciated between ̃11 and 10 ka. Subsequently, the deglaciation progressed far inland up the fjords, probably as a result of increased summer surface temperatures and subsurface ocean temperatures during the Holocene Thermal Maximum. The rapid retreat of the Middle Holocene slowed when the ice sheet became land‐based in the central and southern part of the study area where the ice margin first reached its present extent by ̃6.7 ka. As the onset of Neoglacial ice advance had already commenced at ̃5 ka this limits the period when the ice margin could retreat farther inland and it probably remained within max. 30–40 km of its present extent. The contrasting behaviour between the fjords and inter‐fjord areas shows a clear topographic effect on the stability of the GrIS. These results inform how the GrIS may respond to a warmer climate in various topographic settings and may provide useful constraints for future ice‐sheet models. [ABSTRACT FROM AUTHOR]
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- 2020
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32. Ice-dammed lake drainage in west Greenland: Drainage pattern and implications on ice flow and bedrock motion
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Kjeldsen, Kristian Kjellerup, Khan, Shfaqat Abbas, Bjørk, Anders, Nielsen, Karina, and Mouginot, Jeremie
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Ice flow ,Greenland ,Ice-dammed lake ,SDG 13 - Climate Action ,Drainage pattern ,Bedrock motion - Abstract
Ice-dammed lakes drain frequently in Greenland, but the impacts of these events differ between sites. Here we study the quasi-cyclic behavior of the ~40 km2 Lake Tininnilik in west Greenland and its impact on ice flow and crustal deformation. Data reveal rapid drainage of 1.83 ± 0.17 km3 of water in less than 7 days in 2010, leading to a speedup of the damming glacier, and an instantaneous modeled elastic bedrock uplift of 18.6 ± 0.1 mm confirmed by an independent lakeside GPS record. Since ice-dammed lakes are common on Greenland, our results highlight the importance of including other sources of surface loading in addition to ice mass change, when assessing glacial isostatic adjustment or elastic rebound using geodetic data. Moreover, the results illustrates a linkage between subglacial discharge and ice surface velocity, important for assessing ice flux, and thus mass balance, in a future warming climate.
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- 2017
33. Younger Dryas ice-margin retreat in Greenland, new evidence from Southwest Greenland.
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Funder, Svend, Sørensen, Anita H. L., Larsen, Nicolaj K., Bjørk, Anders, Briner, Jason P., Olsen, Jesper, Schomacker, Anders, and Kjær, Kurt H.
- Abstract
Cosmogenic
10 Be dates from bedrock knobs on six outlying tiny islands along a stretch of 300 km of the Southwest Greenland coast, indicate that the Greenland Ice Sheet (GrIS) margin here was retreating on the inner shelf close to the coast during the Younger Dryas (YD) cold period. A survey of recently published10 Be and14 C-dated records show that this unexpected behaviour of the ice-margin has been seen also in other parts of Greenland, but with very large variations in extent and speed of retreat even between neighbouring areas. In contrast to this, landforms appearing in high resolution bathymetry surveys on the shelf, have recently been suggested to indicate YD readvance or long-lasting ice-margin still stand on mid shelf, far from the coast. However, these features have been dated primarily by correlation with cold periods in the ice core temperature records, and therefore cannot inform about the ice-margin/climate relation. Ice-margin retreat during a YD cooling has been explained by advection of warm subsurface water melting the ice-margin, and by increased seasonality of the climate with the temperature drop mainly in winter, with high impact on sea ice extent and duration, but little effect on glacier mass balance. This study therefore adds to the complexity of the climate/ice-margin relation, where local factors may for some time overrule or mute overall temperature change. It also points to the urgent need for climate-independent dating of the rich treasure trove of information coming from the shelf in these years. [ABSTRACT FROM AUTHOR]- Published
- 2020
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34. A Major Collapse of Kangerlussuaq Glacier's Ice Tongue Between 1932 and 1933 in East Greenland.
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Vermassen, Flor, Bjørk, Anders A., Sicre, Marie‐Alexandrine, Jaeger, John M., Wangner, David J., Kjeldsen, Kristian K., Siggaard‐Andersen, Marie‐Louise, Klein, Vincent, Mouginot, Jeremie, Kjær, Kurt H., and Andresen, Camilla S.
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- *
GLACIERS , *OCEAN temperature , *ALPINE glaciers , *HISTORICAL source material , *ATMOSPHERIC temperature - Abstract
In recent years, several large outlet glaciers in Greenland lost their floating ice tongue, yet little is known regarding their stability over a longer timescale. Here we compile historical documents to demonstrate a major ice tongue collapse of Kangerlussuaq Glacier between 1932 and 1933. This event resulted in a 9‐km retreat, exceeding any of the glacier's recent major retreat events. Sediment cores from the fjord are used to reconstruct sea surface temperatures and to investigate a potential sedimentological trace of the collapse. During the 1920s, local and regional sea surface temperatures and air temperatures increased rapidly, suggesting a climatic trigger for the collapse. Fjord bathymetry played an important role too, as the (partially) pinned ice tongue retreated off a submarine moraine during the event. This historical analogue of a glacier tongue collapse emphasizes the fragility of remaining ice tongues in North Greenland within a warming climate. Plain Language Summary: In the past two decades, multiple Greenlandic glaciers retreated because their floating part (="ice tongue") melted and broke off. While it is believed that such events are the result of a warming climate, not much is known about how often or when such events have occurred in the past. In this study, we compiled multiple historical sources to show that Kangerlussuaq Glacier, one of Greenland's largest glaciers, retreated drastically between 1932 and 1933. During this event the ice tongue collapsed, leading to a 9‐km retreat, which is more than during any of the glacier's recent retreat events. By studying fjord sediments we show that the ocean temperatures increased prior to the event, as did air temperatures. Thus, climatic warming likely triggered the collapse. While other glaciers had already started their retreat decades earlier, Kangerlussuaq Glacier had been stable until 1932, probably due to stabilizing effect of an underwater moraine. Overall, this study emphasizes that ice tongues are sensitive to climatic warming and highlights the precarious position of current ice tongues in Northern Greenland. Key Points: Historical evidence reveals a major collapse of Kangerlussuaq Glacier's ice tongue between 1932 and 1933The collapse was likely triggered by increasing air and ocean temperatures during the late 1920s/early 1930sCompared to other glaciers in Greenland this retreat event occurred relatively late, probably due to its pinning to a large submarine moraine [ABSTRACT FROM AUTHOR]
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- 2020
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35. Resolving Seasonal Ice Velocity of 45 Greenlandic Glaciers With Very High Temporal Details.
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Vijay, Saurabh, Khan, Shfaqat Abbas, Kusk, Anders, Solgaard, Anne M., Moon, Twila, and Bjørk, Anders Anker
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GLACIERS ,ICE sheets ,MELTWATER ,VELOCITY ,CRYOSPHERE - Abstract
Seasonal glacier ice velocities are important for understanding controlling mechanisms of ice flow. For many Greenlandic glaciers, however, these measurements are limited by low temporal resolution. We present seasonal ice velocity changes, melt season onset and extent, and ice front positions for 45 Greenlandic glaciers using 2015–2017 Sentinel‐1 synthetic aperture radar data. Seasonal velocity fluctuations of roughly half of the glaciers appear to be primarily controlled by surface melt‐induced changes in the subglacial hydrology. This includes (1) glaciers that speed up with the onset of surface melt and (2) glaciers with comparable late winter and early melt season velocities that show significant slowdown during most of the melt season and speedup during winter. In contrast, less than a quarter of the study glaciers show strong correspondence between seasonal ice speed and terminus changes. Our results pinpoint seasonal variations across Greenland, highlighting the variable influence of meltwater on year‐round ice velocities. Plain Language Summary: Many Greenlandic glaciers are marine‐terminating and seasonal fluctuations in the ice velocity influence ice discharge timing and magnitude. We used Sentinel‐1 satellite data to observe seasonal changes in ice velocities, ice front positions, and surface melt conditions for 45 Greenlandic glaciers during 2015–2017, capturing substantial temporal detail. Seasonal velocity variations of nearly half of the glaciers show the strongest correlation with surface melt changes, which seasonally alter the subglacial hydrology. In contrast, less than a quarter of the study glaciers show strong correspondence between seasonal ice velocities and seasonal advance and retreat of the glacier ice front. This study highlights the strong potential influence of surface meltwater on the ice velocities of many Greenlandic glaciers. Key Points: Sentinel‐1 radar data pinpoint seasonal ice velocity variations with high temporal detailsSurface melt‐induced changes in subglacial hydrology control seasonal ice flow of many glaciersSeasonal ice flow of ten of the sampled glaciers respond primarily to seasonal terminus changes [ABSTRACT FROM AUTHOR]
- Published
- 2019
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36. Greenland ice sheet mass balance assessed by PROMICE (1995-2015).
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Colgan, William, Mankoff, Kenneth D., Kjeldsen, Kristian K., Bjørk, Anders A., Box, Jason E., Simonsen, Sebastian B., Sørensen, Louise S., Khan, S. Abbas, Solgaard, Anne M., Forsberg, Rene, Skourup, Henriette, Stenseng, Lars, Kristensen, Steen S., Hvidegaard, Sine M., Citterio, Michele, Karlsson, Nanna, Fettweis, Xavier, Ahlstrøm, Andreas P., Andersen, Signe B., and van As, Dirk
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GREENLAND ice ,MASS budget (Geophysics) ,ICE sheets ,FINANCIAL statements ,MICROWAVE remote sensing - Published
- 2018
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37. Impact of External Forcing on Glacier Dynamics at Jakobshavn Isbræ during 1840-2012
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Ioana Stefania Muresan, Shfaqat Abbas Khan, Andy Aschwanden, Constantine Khroulev, Bjørk, Anders A., and Box, Jason E.
- Subjects
SDG 14 - Life Below Water - Abstract
Greenland's main outlet glaciers have more than doubled their contribution to global sea-level rise over the past decade through acceleration of ice discharge. One of the triggering mechanisms is a reduction in resistance (buttressing) at the marine based glacier front (i.e. through reduced thickness or retreat of the floating tongue of a glacier) caused by enhanced calving or a longer-term thinning due to a mass deficit of the ice sheet. Recent findings indicate the reduced buttressing at the marine terminus is responsible for the recent dynamic changes observed in Greenland, but the controlling processes and triggering mechanisms are still unclear. Furthermore, our current understanding is almost entirely based on observations from a short-term record spanning only from a year to a decade, and is characterized by short-term fluctuations and therefore not representative for longer-term trends of several decade time scales. Here, we study the mechanisms controlling dynamic changes at the terminus of Jakobshavn Isbræ over a period of 172 years. The recent glacier acceleration began in late 1990s but there is evidence for glacier retreat of comparable magnitude in 1930s, when a similarly warm period occurred. To control the acceleration and retreat based on observed front positions during 1840-2012, we use an ocean model modifier that implements forcing at the ocean boundary using melange back pressure offsets. The mean temperature anomaly in west Greenland, the North Atlantic oscillation (NAO) winter index and the Atlantic multidecadal oscillation (AMO) index anomalies for the period 1900-2012 sustain our modelling results. The modelled surface elevation changes near the front are considered and compared with observed surface elevation changes for the period 1880-2012. Furthermore, the modelled mass loss signal between 1997-2012 is validated based on ice mass change observations which we estimate using altimeter surveys from NASA's ATM flights during 1997-2012 supplemented with high-resolution Ice, Cloud and land Elevation Satellite (ICESat) data during 2003-2009 and Land, Vegetation and Ice Sensor (LVIS) data during 2007-2012. Our choice of ice sheet model comprises the Parallel Ice Sheet Model (PISM) and a continuous 172 years reconstruction of surface mass balance and its sub-components (Box, 2013).
- Published
- 2014
38. Instability of the Northeast Greenland Ice Stream over the last 45,000 years.
- Author
-
Strunk, Astrid, Skov, Daniel S., Larsen, Nicolaj K., Bjørk, Anders A., Levy, Laura B., Carlson, Anders E., Buizert, Christo, and Olsen, Jesper
- Subjects
ICE streams ,GREENLAND ice ,HOLOCENE Epoch ,GEOLOGY & climate - Abstract
The sensitivity of the Northeast Greenland Ice Stream (NEGIS) to prolonged warm periods is largely unknown and geological records documenting such long-term changes are needed to place current observations in perspective. Here we use cosmogenic surface exposure and radiocarbon ages to determine the magnitude of NEGIS margin fluctuations over the last 45 kyr (thousand years). We find that the NEGIS experienced slow early Holocene ice-margin retreat of 30-40ma
-1 , likely as a result of the buttressing effect of sea-ice or shelf-ice. The NEGIS was ~20-70 km behind its present ice-extent ~41-26 ka and ~7.8-1.2 ka; both periods of high orbital precession index and/or summer temperatures within the projected warming for the end of this century. We show that the NEGIS was smaller than present for approximately half of the last ~45 kyr and is susceptible to subtle changes in climate, which has implications for future stability of this ice stream. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
39. Ice-dammed lake drainage in west Greenland: Drainage pattern and implications on ice flow and bedrock motion.
- Author
-
Kjeldsen, Kristian K., Khan, Shfaqat A., Bjørk, Anders A., Nielsen, Karina, and Mouginot, Jeremie
- Published
- 2017
- Full Text
- View/download PDF
40. Greenland surface mass-balance observations from the ice-sheet ablation area and local glaciers.
- Author
-
MACHGUTH, HORST, THOMSEN, HENRIK H., WEIDICK, ANKER, AHLSTRØM, ANDREAS P., ABERMANN, JAKOB, ANDERSEN, MORTEN L., ANDERSEN, SIGNE B., BJØRK, ANDERS A., BOX, JASON E., BRAITHWAITE, ROGER J., BØGGILD, CARL E., CITTERIO, MICHELE, CLEMENT, POUL, COLGAN, WILLIAM, FAUSTO, ROBERT S., GLEIE, KARIN, GUBLER, STEFANIE, HASHOLT, BENT, HYNEK, BERNHARD, and KNUDSEN, NIELS T.
- Subjects
ICE sheets ,MASS budget (Geophysics) ,ABLATION (Glaciology) ,GLACIERS ,MELTING - Abstract
Glacier surface mass-balance measurements on Greenland started more than a century ago, but no compilation exists of the observations from the ablation area of the ice sheet and local glaciers. Such data could be used in the evaluation of modelled surface mass balance, or to document changes in glacier melt independently from model output. Here, we present a comprehensive database of Greenland glacier surface mass-balance observations from the ablation area of the ice sheet and local glaciers. The database spans the 123 a from 1892 to 2015, contains a total of ~3000 measurements from 46 sites, and is openly accessible through the PROMICE web portal (http://www.promice.dk). For each measurement we provide X, Y and Z coordinates, starting and ending dates as well as quality flags. We give sources for each entry and for all metadata. Two thirds of the data were collected from grey literature and unpublished archive documents. Roughly 60% of the measurements were performed by the Geological Survey of Denmark and Greenland (GEUS, previously GGU). The data cover all regions of Greenland except for the southernmost part of the east coast, but also emphasize the importance of long-term time series of which there are only two exceeding 20 a. We use the data to analyse uncertainties in point measurements of surface mass balance, as well as to estimate surface mass-balance profiles for most regions of Greenland. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
41. Holocene ice marginal fluctuations of the Qassimiut lobe in South Greenland.
- Author
-
Larsen, Nicolaj K., Find, Jesper, Kristensen, Anders, Bjørk, Anders A., Kjeldsen, Kristian K., Odgaard, Bent V., Olsen, Jesper, and Kjær, Kurt H.
- Published
- 2016
- Full Text
- View/download PDF
42. A Late Paleocene age for Greenland's Hiawatha impact structure.
- Author
-
Kenny, Gavin G., Hyde, William R., Storey, Michael, Garde, Adam A., Whitehouse, Martin J., Beck, Pierre, Johansson, Leif, Søndergaard, Anne Sofie, Bjørk, Anders A., MacGregor, Joseph A., Khan, Shfaqat A., Mouginot, Jérémie, Johnson, Brandon C., Silber, Elizabeth A., Wielandt, Daniel K. P., Kjær, Kurt H., and Larsen, Nicolaj K.
- Subjects
- *
IMPACT craters , *PALEOGENE , *GEOLOGICAL time scales , *EARTH system science , *PALEOCENE Epoch , *SECONDARY ion mass spectrometry - Abstract
The article offers information about the Late Paleocene age for Greenland's Hiawatha impact structure. It mentions that Hiawatha structure, located beneath Hiawatha Glacier in northwestern Greenland, has been proposed as an impact structure that may have formed after the Pleistocene inception of the Greenland Ice Sheet.
- Published
- 2022
- Full Text
- View/download PDF
43. The response of the southern Greenland ice sheet to the Holocene thermal maximum.
- Author
-
Larsen, Nicolaj K., Kjær, Kurt H., Lecavalier, Benoit, Bjørk, Anders A., Colding, Sune, Huybrechts, Philippe, Jakobsen, Karina E., Kjeldsen, Kristian K., Knudsen, Karen-Luise, Odgaard, Bent V., and Olsen, Jesper
- Subjects
- *
ICE sheets , *HOLOCENE paleoclimatology , *GEOLOGICAL time scales , *OCEANOGRAPHIC research - Abstract
To determine the long-term sensitivity of the Greenland ice sheet to a warmer climate, we explored how it responded to the Holocene thermal maximum (8-5 cal. kyr B.P.; calibrated to calendar years before present, i.e., A.D. 1950), when lake records show that local atmospheric temperatures in Greenland were 2-4 °C warmer than the present. Records from five new threshold lakes complemented with existing geological data from south of 70°N show that the ice margin was retracted behind its present-day extent in all sectors for a limited period between ca. 7 and 4 cal. kyr B.P. and in most sectors from ca. 1.5 to 1 cal. kyr B.P., in response to higher atmospheric and ocean temperatures. Ice sheet simulations constrained by observations show good correlation with the timing of minimum ice volume indicated by the threshold lake observations; the simulated volume reduction suggests a minimum contribution of 0.16 m sea-level equivalent from the entire Greenland ice sheet, with a centennial ice loss rate of as much as 100 Gt/yr for several millennia during the Holocene thermal maximum. Our results provide an estimate of the long-term rates of volume loss that can be expected in the future as regional air and ocean temperatures approach those reconstructed for the Holocene thermal maximum. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
44. A large impact crater beneath Hiawatha Glacier in northwest Greenland
- Author
-
Shfaqat Abbas Khan, Olaf Eisen, Tod E. Waight, Tobias Binder, Svend Funder, Joseph A. MacGregor, Michael Houmark-Nielsen, John Paden, Iain McDonald, Veit Helm, Henning Haack, Anders A. Bjørk, Mathieu Morlighem, Horst Machguth, Jeremie Mouginot, Eske Willerslev, Adam A. Garde, Mark Fahnestock, Christian Weikusat, Nicolaj K. Larsen, Kristian K. Kjeldsen, Kurt H. Kjær, Abteilung Klinische Sozialmedizin, Berufs- und Umweltdermatologie, Universität Heidelberg [Heidelberg], Centre for Star and Planet Formation (STARPLAN), Globe Institute, Faculty of Health and Medical Sciences, University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU)-Faculty of Health and Medical Sciences, University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU), Jodrell Bank Centre for Astrophysics (JBCA), University of Manchester [Manchester], Institut des Géosciences de l’Environnement (IGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut de Recherche pour le Développement (IRD)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), University of California [Irvine] (UCI), University of California, Center for Remote Sensing of Ice Sheets (CReSIS), University of Kansas [Lawrence] (KU), Section for GeoGenetics, Institute for Geophysics, University of Texas at Dallas [Richardson] (UT Dallas), Kjær, Kurt H [0000-0002-8871-5179], Larsen, Nicolaj K [0000-0002-0117-1106], Binder, Tobias [0000-0002-9826-8835], Bjørk, Anders A [0000-0002-4919-792X], Eisen, Olaf [0000-0002-6380-962X], Fahnestock, Mark A [0000-0002-5896-6858], Garde, Adam A [0000-0002-0410-3547], Haack, Henning [0000-0002-4618-3178], Helm, Veit [0000-0001-7788-9328], Kjeldsen, Kristian K [0000-0002-8557-5131], Khan, Shfaqat A [0000-0002-2689-8563], Machguth, Horst [0000-0001-5924-0998], McDonald, Iain [0000-0001-9066-7244], Morlighem, Mathieu [0000-0001-5219-1310], Mouginot, Jérémie [0000-0001-9155-5455], Paden, John D [0000-0003-0775-6284], Waight, Tod E [0000-0003-2601-1202], Weikusat, Christian [0000-0002-3812-6325], Willerslev, Eske [0000-0002-7081-6748], MacGregor, Joseph A [0000-0002-5517-2235], Apollo - University of Cambridge Repository, University of Zurich, Kjær, Kurt H, Universität Heidelberg [Heidelberg] = Heidelberg University, University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH)-Faculty of Health and Medical Sciences, University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), University of California [Irvine] (UC Irvine), and University of California (UC)
- Subjects
010506 paleontology ,010504 meteorology & atmospheric sciences ,[SDE.MCG]Environmental Sciences/Global Changes ,Greenland ice sheet ,010502 geochemistry & geophysics ,01 natural sciences ,Paleontology ,Impact crater ,Shocked quartz ,910 Geography & travel ,Foreland basin ,Holocene ,Research Articles ,0105 earth and related environmental sciences ,1000 Multidisciplinary ,geography ,Multidisciplinary ,geography.geographical_feature_category ,Bedrock ,SciAdv r-articles ,Glacier ,Geology ,Debris ,10122 Institute of Geography ,Geophysics ,[SDE]Environmental Sciences ,0406 Physical Geography and Environmental Geoscience ,Research Article - Abstract
Researchers present the first unambiguous discovery of a 31-km-wide impact crater buried beneath the Greenland Ice Sheet., We report the discovery of a large impact crater beneath Hiawatha Glacier in northwest Greenland. From airborne radar surveys, we identify a 31-kilometer-wide, circular bedrock depression beneath up to a kilometer of ice. This depression has an elevated rim that cross-cuts tributary subglacial channels and a subdued central uplift that appears to be actively eroding. From ground investigations of the deglaciated foreland, we identify overprinted structures within Precambrian bedrock along the ice margin that strike tangent to the subglacial rim. Glaciofluvial sediment from the largest river draining the crater contains shocked quartz and other impact-related grains. Geochemical analysis of this sediment indicates that the impactor was a fractionated iron asteroid, which must have been more than a kilometer wide to produce the identified crater. Radiostratigraphy of the ice in the crater shows that the Holocene ice is continuous and conformable, but all deeper and older ice appears to be debris rich or heavily disturbed. The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet.
- Published
- 2018
45. A large impact crater beneath Hiawatha Glacier in northwest Greenland.
- Author
-
Kjær KH, Larsen NK, Binder T, Bjørk AA, Eisen O, Fahnestock MA, Funder S, Garde AA, Haack H, Helm V, Houmark-Nielsen M, Kjeldsen KK, Khan SA, Machguth H, McDonald I, Morlighem M, Mouginot J, Paden JD, Waight TE, Weikusat C, Willerslev E, and MacGregor JA
- Abstract
We report the discovery of a large impact crater beneath Hiawatha Glacier in northwest Greenland. From airborne radar surveys, we identify a 31-kilometer-wide, circular bedrock depression beneath up to a kilometer of ice. This depression has an elevated rim that cross-cuts tributary subglacial channels and a subdued central uplift that appears to be actively eroding. From ground investigations of the deglaciated foreland, we identify overprinted structures within Precambrian bedrock along the ice margin that strike tangent to the subglacial rim. Glaciofluvial sediment from the largest river draining the crater contains shocked quartz and other impact-related grains. Geochemical analysis of this sediment indicates that the impactor was a fractionated iron asteroid, which must have been more than a kilometer wide to produce the identified crater. Radiostratigraphy of the ice in the crater shows that the Holocene ice is continuous and conformable, but all deeper and older ice appears to be debris rich or heavily disturbed. The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet.
- Published
- 2018
- Full Text
- View/download PDF
46. Instability of the Northeast Greenland Ice Stream over the last 45,000 years.
- Author
-
Larsen NK, Levy LB, Carlson AE, Buizert C, Olsen J, Strunk A, Bjørk AA, and Skov DS
- Abstract
The sensitivity of the Northeast Greenland Ice Stream (NEGIS) to prolonged warm periods is largely unknown and geological records documenting such long-term changes are needed to place current observations in perspective. Here we use cosmogenic surface exposure and radiocarbon ages to determine the magnitude of NEGIS margin fluctuations over the last 45 kyr (thousand years). We find that the NEGIS experienced slow early Holocene ice-margin retreat of 30-40 m a
-1 , likely as a result of the buttressing effect of sea-ice or shelf-ice. The NEGIS was ~20-70 km behind its present ice-extent ~41-26 ka and ~7.8-1.2 ka; both periods of high orbital precession index and/or summer temperatures within the projected warming for the end of this century. We show that the NEGIS was smaller than present for approximately half of the last ~45 kyr and is susceptible to subtle changes in climate, which has implications for future stability of this ice stream.- Published
- 2018
- Full Text
- View/download PDF
47. Minimal Holocene retreat of large tidewater glaciers in Køge Bugt, southeast Greenland.
- Author
-
Dyke LM, Andresen CS, Seidenkrantz MS, Hughes ALC, Hiemstra JF, Murray T, Bjørk AA, Sutherland DA, and Vermassen F
- Abstract
Køge Bugt, in southeast Greenland, hosts three of the largest glaciers of the Greenland Ice Sheet; these have been major contributors to ice loss in the last two decades. Despite its importance, the Holocene history of this area has not been investigated. We present a 9100 year sediment core record of glaciological and oceanographic changes from analysis of foraminiferal assemblages, the abundance of ice-rafted debris, and sortable silt grain size data. Results show that ice-rafted debris accumulated constantly throughout the core; this demonstrates that glaciers in Køge Bugt remained in tidewater settings throughout the last 9100 years. This observation constrains maximum Holocene glacier retreat here to less than 6 km from present-day positions. Retreat was minimal despite oceanic and climatic conditions during the early-Holocene that were at least as warm as the present-day. The limited Holocene retreat of glaciers in Køge Bugt was controlled by the subglacial topography of the area; the steeply sloping bed allowed glaciers here to stabilise during retreat. These findings underscore the need to account for individual glacier geometry when predicting future behaviour. We anticipate that glaciers in Køge Bugt will remain in stable configurations in the near-future, despite the predicted continuation of atmospheric and oceanic warming.
- Published
- 2017
- Full Text
- View/download PDF
48. Geodetic measurements reveal similarities between post-Last Glacial Maximum and present-day mass loss from the Greenland ice sheet.
- Author
-
Khan SA, Sasgen I, Bevis M, van Dam T, Bamber JL, Wahr J, Willis M, Kjær KH, Wouters B, Helm V, Csatho B, Fleming K, Bjørk AA, Aschwanden A, Knudsen P, and Munneke PK
- Abstract
Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year.
- Published
- 2016
- Full Text
- View/download PDF
49. Digital elevation model and orthophotographs of Greenland based on aerial photographs from 1978-1987.
- Author
-
Korsgaard NJ, Nuth C, Khan SA, Kjeldsen KK, Bjørk AA, Schomacker A, and Kjær KH
- Subjects
- Greenland, Models, Theoretical, Ice Cover, Reproducibility of Results
- Abstract
Digital Elevation Models (DEMs) play a prominent role in glaciological studies for the mass balance of glaciers and ice sheets. By providing a time snapshot of glacier geometry, DEMs are crucial for most glacier evolution modelling studies, but are also important for cryospheric modelling in general. We present a historical medium-resolution DEM and orthophotographs that consistently cover the entire surroundings and margins of the Greenland Ice Sheet 1978-1987. About 3,500 aerial photographs of Greenland are combined with field surveyed geodetic ground control to produce a 25 m gridded DEM and a 2 m black-and-white digital orthophotograph. Supporting data consist of a reliability mask and a photo footprint coverage with recording dates. Through one internal and two external validation tests, this DEM shows an accuracy better than 10 m horizontally and 6 m vertically while the precision is better than 4 m. This dataset proved successful for topographical mapping and geodetic mass balance. Other uses include control and calibration of remotely sensed data such as imagery or InSAR velocity maps.
- Published
- 2016
- Full Text
- View/download PDF
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