957 results on '"Dahl-Jensen, Dorthe"'
Search Results
2. Crystal orientation fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream
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Gerber, Tamara Annina, Lilien, David A., Rathmann, Nicholas Mossor, Franke, Steven, Young, Tun Jan, Valero-Delgado, Fernando, Ershadi, M. Reza, Drews, Reinhard, Zeising, Ole, Humbert, Angelika, Stoll, Nicolas, Weikusat, Ilka, Grinsted, Aslak, Hvidberg, Christine Schøtt, Jansen, Daniela, Miller, Heinrich, Helm, Veit, Steinhage, Daniel, O’Neill, Charles, Paden, John, Gogineni, Siva Prasad, Dahl-Jensen, Dorthe, and Eisen, Olaf
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- 2023
- Full Text
- View/download PDF
3. New technique for high-precision, simultaneous measurements of CH4, N2O and CO2 concentrations; isotopic and elemental ratios of N-2, O-2 and Ar; and total air content in ice cores by wet extraction
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Oyabu, Ikumi, Kawamura, Kenji, Kitamura, Kyotaro, Dallmayr, Remi, Kitamura, Akihiro, Sawada, Chikako, Severinghaus, Jeffrey P, Beaudette, Ross, Orsi, Anais, Sugawara, Satoshi, Ishidoya, Shigeyuki, Dahl-Jensen, Dorthe, Goto-Azuma, Kumiko, Aoki, Shuji, and Nakazawa, Takakiyo
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Atmospheric Sciences ,Meteorology & Atmospheric Sciences - Abstract
Abstract. Air in polar ice cores provides unique information on past climatic and atmospheric changes. We developed a new method combining wet extraction, gaschromatography and mass spectrometry for high-precision, simultaneous measurements of eight air components (CH4, N2O andCO2 concentrations; δ15N, δ18O, δO2∕N2 and δAr∕N2; and total aircontent) from an ice-core sample of ∼ 60 g. The ice sample is evacuated for ∼ 2 h and melted under vacuum, and thereleased air is continuously transferred into a sample tube at 10 K within 10 min. The air is homogenized in the sample tubeovernight at room temperature and split into two aliquots for mass spectrometric and gas chromatographic measurements. Care is taken to minimize(1) contamination of greenhouse gases by using a long evacuation time, (2) consumption of oxygen during sample storage by a passivation treatment onsample tubes, and (3) fractionation of isotopic ratios with a long homogenization time for splitting. Precision is assessed by analyzing standardgases with artificial ice and duplicate measurements of the Dome Fuji and NEEM ice cores. The overall reproducibility (1 SD) of duplicate ice-coreanalyses are 3.2 ppb, 2.2 ppb and 2.9 ppm for CH4, N2O and CO2 concentrations;0.006 ‰, 0.011 ‰, 0.09 ‰ and 0.12 ‰ for δ15N, δ18O, δO2∕N2and δAr∕N2; and 0.63 mLSTP kg−1 for total air content, respectively. Our new method successfully combines thehigh-precision, small-sample and multiple-species measurements, with a wide range of applications for ice-core paleoenvironmental studies.
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- 2020
4. An 83 000-year-old ice core from Roosevelt Island, Ross Sea, Antarctica
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Lee, James E, Brook, Edward J, Bertler, Nancy AN, Buizert, Christo, Baisden, Troy, Blunier, Thomas, Ciobanu, V Gabriela, Conway, Howard, Dahl-Jensen, Dorthe, Fudge, Tyler J, Hindmarsh, Richard, Keller, Elizabeth D, Parrenin, Frederic, Severinghaus, Jeffrey P, Vallelonga, Paul, Waddington, Edwin D, and Winstrup, Mai
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Paleontology ,Physical Geography and Environmental Geoscience - Abstract
Abstract. In 2013 an ice core was recovered from Roosevelt Island, an ice dome between two submarine troughs carved by paleo-ice-streams in the Ross Sea, Antarctica. The ice core is part of the Roosevelt Island Climate Evolution (RICE) project and provides new information about the past configuration of the West Antarctic Ice Sheet (WAIS) and its retreat during the last deglaciation. In this work we present the RICE17 chronology, which establishes the depth–age relationship for the top 754 m of the 763 m core. RICE17 is a composite chronology combining annual layer interpretations for 0–343 m (Winstrup et al., 2019) with new estimates for gas and ice ages based on synchronization of CH4 and δ18Oatm records to corresponding records from the WAIS Divide ice core and by modeling of the gas age–ice age difference. Novel aspects of this work include the following: (1) an automated algorithm for multiproxy stratigraphic synchronization of high-resolution gas records; (2) synchronization using centennial-scale variations in methane for pre-anthropogenic time periods (60–720 m, 1971 CE to 30 ka), a strategy applicable for future ice cores; and (3) the observation of a continuous climate record back to ∼65 ka providing evidence that the Roosevelt Island Ice Dome was a constant feature throughout the last glacial period.
- Published
- 2020
5. New technique for high-precision, simultaneous measurements of CH4, N2O and CO2 concentrations, isotopic and elemental ratios of N2, O2 and Ar, and total air content in ice cores by wet extraction
- Author
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Oyabu, Ikumi, Kawamura, Kenji, Kitamura, Kyotaro, Dallmayr, Remi, Kitamura, Akihiro, Sawada, Chikako, Severinghaus, Jeffrey P, Beaudette, Ross, Sugawara, Satoshi, Ishidoya, Shigeyuki, Dahl-Jensen, Dorthe, Goto-Azuma, Kumiko, Aoki, Shuji, and Nakazawa, Takakiyo
- Abstract
Abstract. Air in polar ice cores provides various information on past climatic and atmospheric changes. We developed a new method combining wet extraction, gas chromatography and mass spectrometry, for high-precision, simultaneous measurements of eight air components (CH4, N2O and CO2 concentrations, δ15N, δ18O, δO2/N2, δAr/N2 and total air content) from an ice core sample of ~60 g. The ice sample is evacuated for ~2 hours and melted under vacuum, and the released air is continuously transferred into a sample tube at 10 K within 10 minutes. The air is homogenized in the sample tube overnight at room temperature, and split into two aliquots for mass spectrometric and gas chromatographic measurements. Cares are taken to minimize contamination of greenhouse gases with long evacuation time, consumption of oxygen during sample storage by passivation treatment on sample tubes, and fractionation of isotopic ratios with long homogenization time for splitting. Precisions are assessed by analysing standard gases with artificial ice, and by duplicate measurements of the Dome Fuji and NEEM ice cores. The overall reproducibility (one standard deviation) from duplicate ice-core analyses are 3.2 ppb, 2.2 ppb and 3.1 ppm for CH4, N2O and CO2 concentrations, 0.006, 0.010, 0.09 and 0.12 ‰ for δ15N, δ18O, δO2/N2 and δAr/N2, and 0.67 mlSTP kg-1 for total air content, respectively. Our new method successfully combines the high-precision, small-sample and multiple-species measurements, with a wide range of applications for ice-core paleoenvironmental studies.
- Published
- 2020
6. Accelerating ice flow at the onset of the Northeast Greenland Ice Stream
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Grinsted, Aslak, Hvidberg, Christine S., Lilien, David A., Rathmann, Nicholas M., Karlsson, Nanna B., Gerber, Tamara, Kjær, Helle Astrid, Vallelonga, Paul, and Dahl-Jensen, Dorthe
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- 2022
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7. A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century
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Christ, Andrew J., Bierman, Paul R., Schaefer, Joerg M., Dahl-Jensen, Dorthe, Steffensen, Jørgen P., Corbett, Lee B., Peteet, Dorothy M., Thomas, Elizabeth K., Steig, Eric J., Rittenour, Tammy M., Tison, Jean-Louis, Blard, Pierre-Henri, Perdrial, Nicolas, Dethier, David P., Lini, Andrea, Hidy, Alan J., Caffee, Marc W., and Southon, John
- Published
- 2021
8. High‐Resolution Ice‐Core Analyses Identify the Eldgjá Eruption and a Cluster of Icelandic and Trans‐Continental Tephras Between 936 and 943 CE.
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Hutchison, William, Gabriel, Imogen, Plunkett, Gill, Burke, Andrea, Sugden, Patrick, Innes, Helen, Davies, Siwan, Moreland, William M., Krüger, Kirstin, Wilson, Rob, Vinther, Bo M., Dahl‐Jensen, Dorthe, Freitag, Johannes, Oppenheimer, Clive, Chellman, Nathan J., Sigl, Michael, and McConnell, Joseph R.
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STRATOSPHERIC aerosols ,THOLEIITE ,VOLCANIC ash, tuff, etc. ,FLOOD basalts ,PUMICE ,VOLCANIC eruptions ,EXPLOSIVE volcanic eruptions - Abstract
The Eldgjá eruption is the largest basalt lava flood of the Common Era. It has been linked to a major ice‐core sulfur (S) spike in 939–940 CE and Northern Hemisphere summer cooling in 940 CE. Despite its magnitude and potential climate impacts, uncertainties remain concerning the eruption timeline, atmospheric dispersal of emitted volatiles, and coincident volcanism in Iceland and elsewhere. Here, we present a comprehensive analysis of Greenland ice‐cores from 936 to 943 CE, revealing a complex volatile record and cryptotephra with numerous geochemical populations. Transitional alkali basalt tephra matching Eldgjá are found in 939–940 CE, while tholeiitic basalt shards present in 936/937 CE and 940/941 CE are compatible with contemporaneous Icelandic eruptions from Grímsvötn and Bárðarbunga‐Veiðivötn systems (including V‐Sv tephra). We also find four silicic tephra populations, one of which we link to the Jala Pumice of Ceboruco (Mexico) at 941 ± 1 CE. Triple S isotopes, Δ33S, spanning 936–940 CE are indicative of upper tropospheric/lower stratospheric transport of aerosol sourced from the Icelandic fissure eruptions. However, anomalous Δ33S (down to −0.4‰) in 940–941 CE evidence stratospheric aerosol transport consistent with summer surface cooling revealed by tree‐ring reconstructions. Tephra associated with the anomalous Δ33S have a variety of compositions, complicating the attribution of climate cooling to Eldgjá alone. Nevertheless, our study confirms a major S emission from Eldgjá in 939–940 CE and implicates Eldgjá and a cluster of eruptions as triggers of summer cooling, severe winters, and privations in ∼940 CE. Plain Language Summary: The eruption of Eldgjá in the tenth century is the largest lava flood in the history of Iceland. Although Eldgjá emitted immense volumes of ash, lava, and gas, the exact timing and duration of this eruption, as well as its environmental and climatic impact remain unclear. Here, we provide a comprehensive chemical analysis of Greenland ice‐core records spanning the period 936–943 CE. We identify volcanic ash from at least three different Icelandic eruptions and confirm that there was a major ash and gas emission from Eldgjá in 939 CE. Using tree ring temperature estimates we find strong evidence for Northern Hemisphere climate cooling in the summer of 940 CE. However, the variety of volcanic ash identified in the ice‐cores shows that several Icelandic and Northern Hemisphere arc volcanoes were also erupting in this period. While Eldgjá remains the prime candidate, these additional eruptions complicate the attribution of reported climate and societal changes to Eldgjá alone. Ultimately, our study sheds new light on a cluster of volcanic eruptions between 936 and 943 CE and highlights the challenges of disentangling the individual contributions of multiple eruptions on the environment and climate. Key Points: New analyses of Greenland ice‐core records of volcanism between 936 and 943 CEIcelandic eruptions from Grímsvötn and Bárðarbunga‐Veiðivötn detected between 936 and 941 CE, and major Eldgjá emission in 939–940 CEVarious silicic eruptions identified, including the Jala Pumice (Mexico), providing new and valuable trans‐continental tephra isochrons [ABSTRACT FROM AUTHOR]
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- 2024
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9. An 83 000 year old ice core from Roosevelt Island, Ross Sea, Antarctica
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Lee, James E, Brook, Edward J, Bertler, Nancy AN, Buizert, Christo, Baisden, Troy, Blunier, Thomas, Ciobanu, V Gabriela, Conway, Howard, Dahl-Jensen, Dorthe, Fudge, Tyler J, Hindmarsh, Richard, Keller, Elizabeth D, Parrenin, Frédéric, Severinghaus, Jeffrey P, Vallelonga, Paul, Waddington, Edwin D, and Winstrup, Mai
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Climate Action - Abstract
Abstract. In 2013, an ice core was recovered from Roosevelt Island in the Ross Sea, Antarctica, as part of the Roosevelt Island Climate Evolution (RICE) project. Roosevelt Island is located between two submarine troughs carved by paleo-ice-streams. The RICE ice core provides new important information about the past configuration of the West Antarctic Ice Sheet and its retreat during the most recent deglaciation. In this work, we present the RICE17 chronology and discuss preliminary observations from the new records of methane, the isotopic composition of atmospheric molecular oxygen (δ18O-Oatm), the isotopic composition of atmospheric molecular nitrogen (δ15N-N2) and total air content (TAC). RICE17 is a composite chronology combining annual layer interpretations, gas synchronization, and firn modeling strategies in different sections of the core. An automated matching algorithm is developed for synchronizing the high-resolution section of the RICE gas records (60–720 m, 1971 CE to 30 ka) to corresponding records from the WAIS Divide ice core, while deeper sections are manually matched. Ice age for the top 343 m (2635 yr BP, before 1950 C.E.) is derived from annual layer interpretations and described in the accompanying paper by Winstrup et al. (2017). For deeper sections, the RICE17 ice age scale is based on the gas age constraints and the ice age-gas age offset estimated by a firn densification model. Novel aspects of this work include: 1) stratigraphic matching of centennial-scale variations in methane for pre-anthropogenic time periods, a strategy which will be applicable for developing precise chronologies for future ice cores, 2) the observation of centennial-scale variability in methane throughout the Holocene which suggests that similar variations during the late preindustrial period need not be anthropogenic, and 3) the observation of continuous climate records dating back to ∼ 65 ka which provide evidence that the Roosevelt Island Ice Dome was a constant feature throughout the last glacial period.
- Published
- 2018
10. The Ross Sea Dipole – temperature, snow accumulation and sea ice variability in the Ross Sea region, Antarctica, over the past 2700 years
- Author
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Bertler, Nancy AN, Conway, Howard, Dahl-Jensen, Dorthe, Emanuelsson, Daniel B, Winstrup, Mai, Vallelonga, Paul T, Lee, James E, Brook, Ed J, Severinghaus, Jeffrey P, Fudge, Taylor J, Keller, Elizabeth D, Baisden, W Troy, Hindmarsh, Richard CA, Neff, Peter D, Blunier, Thomas, Edwards, Ross, Mayewski, Paul A, Kipfstuhl, Sepp, Buizert, Christo, Canessa, Silvia, Dadic, Ruzica, Kjær, Helle A, Kurbatov, Andrei, Zhang, Dongqi, Waddington, Edwin D, Baccolo, Giovanni, Beers, Thomas, Brightley, Hannah J, Carter, Lionel, Clemens-Sewall, David, Ciobanu, Viorela G, Delmonte, Barbara, Eling, Lukas, Ellis, Aja, Ganesh, Shruthi, Golledge, Nicholas R, Haines, Skylar, Handley, Michael, Hawley, Robert L, Hogan, Chad M, Johnson, Katelyn M, Korotkikh, Elena, Lowry, Daniel P, Mandeno, Darcy, McKay, Robert M, Menking, James A, Naish, Timothy R, Noerling, Caroline, Ollive, Agathe, Orsi, Anaïs, Proemse, Bernadette C, Pyne, Alexander R, Pyne, Rebecca L, Renwick, James, Scherer, Reed P, Semper, Stefanie, Simonsen, Marius, Sneed, Sharon B, Steig, Eric J, Tuohy, Andrea, Venugopal, Abhijith Ulayottil, Valero-Delgado, Fernando, Venkatesh, Janani, Wang, Feitang, Wang, Shimeng, Winski, Dominic A, Winton, V Holly L, Whiteford, Arran, Xiao, Cunde, Yang, Jiao, and Zhang, Xin
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Earth Sciences ,Physical Geography and Environmental Geoscience ,Geology ,Climate Action ,Paleontology ,Climate change science - Abstract
Abstract. High-resolution, well-dated climate archives provide anopportunity to investigate the dynamic interactions of climate patternsrelevant for future projections. Here, we present data from a new, annuallydated ice core record from the eastern Ross Sea, named the Roosevelt IslandClimate Evolution (RICE) ice core. Comparison of this record with climatereanalysis data for the 1979–2012 interval shows that RICE reliably capturestemperature and snow precipitation variability in the region. Trends over thepast 2700 years in RICE are shown to be distinct from those in WestAntarctica and the western Ross Sea captured by other ice cores. For most ofthis interval, the eastern Ross Sea was warming (or showing isotopicenrichment for other reasons), with increased snow accumulation and perhapsdecreased sea ice concentration. However, West Antarctica cooled and thewestern Ross Sea showed no significant isotope temperature trend. Thispattern here is referred to as the Ross Sea Dipole. Notably, during theLittle Ice Age, West Antarctica and the western Ross Sea experienced colderthan average temperatures, while the eastern Ross Sea underwent a period ofwarming or increased isotopic enrichment. From the 17th century onwards, thisdipole relationship changed. All three regions show current warming, withsnow accumulation declining in West Antarctica and the eastern Ross Sea butincreasing in the western Ross Sea. We interpret this pattern as reflectingan increase in sea ice in the eastern Ross Sea with perhaps the establishmentof a modern Roosevelt Island polynya as a local moisture source for RICE.
- Published
- 2018
11. Advancing towards high-quality water isotope measurements in ice cores: a micro-destructive approach using Laser Ablation coupled with Cavity Ring Down Spectroscopy
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Malegiannaki, Eirini, primary, Zannoni, Daniele, additional, Bohleber, Pascal, additional, Stremtan, Ciprian, additional, Petteni, Agnese, additional, Stenni, Barbara, additional, Barbante, Carlo, additional, Dahl-Jensen, Dorthe, additional, and Gkinis, Vasileios, additional
- Published
- 2024
- Full Text
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12. Variation in recent annual snow deposition and seasonality of snow chemistry at the east Greenland ice core project (EGRIP) camp, Greenland
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Nakazawa, Fumio, Nagatsuka, Naoko, Hirabayashi, Motohiro, Goto-Azuma, Kumiko, Steffensen, Jørgen Peder, and Dahl-Jensen, Dorthe
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- 2021
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13. Temporal and spatial variabilities in surface mass balance at the EGRIP site, Greenland from 2009 to 2017
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Komuro, Yuki, Nakazawa, Fumio, Hirabayashi, Motohiro, Goto-Azuma, Kumiko, Nagatsuka, Naoko, Shigeyama, Wataru, Matoba, Sumito, Homma, Tomoyuki, Steffensen, Jørgen Peder, and Dahl-Jensen, Dorthe
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- 2021
- Full Text
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14. The Ross Sea Dipole – Temperature, Snow Accumulation and Sea Ice Variability in the Ross Sea Region, Antarctica, over the Past 2,700 Years
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Bertler, Nancy AN, Conway, Howard, Dahl-Jensen, Dorthe, Emanuelsson, Daniel B, Winstrup, Mai, Vallelonga, Paul T, Lee, James E, Brook, Ed J, Severinghaus, Jeffrey P, Fudge, Taylor J, Keller, Elizabeth D, Baisden, W Troy, Hindmarsh, Richard CA, Neff, Peter D, Blunier, Thomas, Edwards, Ross, Mayewski, Paul A, Kipfstuhl, Sepp, Buizert, Christo, Canessa, Silvia, Dadic, Ruzica, Kjær, Helle A, Kurbatov, Andrei, Zhang, Dongqi, Waddington, Ed D, Baccolo, Giovanni, Beers, Thomas, Brightley, Hannah J, Carter, Lionel, Clemens-Sewall, David, Ciobanu, Viorela G, Delmonte, Barbara, Eling, Lukas, Ellis, Aja A, Ganesh, Shruthi, Golledge, Nicholas R, Haines, Skylar A, Handley, Michael, Hawley, Robert L, Hogan, Chad M, Johnson, Katelyn M, Korotkikh, Elena, Lowry, Daniel P, Mandeno, Darcy, McKay, Robert M, Menking, James A, Naish, Timothy R, Noerling, Caroline, Ollive, Agathe, Orsi, Anaïs, Proemse, Bernadette C, Pyne, Alexander R, Pyne, Rebecca L, Renwick, James, Scherer, Reed P, Semper, Stefanie, Simonsen, Marius, Sneed, Sharon B, Steig, Eric J, Tuohy, Andrea, Venugopal, Abhijith Ulayottil, Valero-Delgado, Fernando, Venkatesh, Janani, Wang, Feitang, Wang, Shimeng, Winski, Dominic A, Winton, Victoria HL, Whiteford, Arran, Xiao, Cunde, Yang, Jiao, and Zhang, Xin
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Climate Action - Abstract
Abstract. High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually-dated ice core record from the eastern Ross Sea. Comparison of the Roosevelt Island Climate Evolution (RICE) ice core records with climate reanalysis data for the 1979–2012 calibration period shows that RICE records reliably capture temperature and snow precipitation variability of the region. RICE is compared with data from West Antarctica (West Antarctic Ice Sheet Divide Ice Core) and the western (Talos Dome) and eastern (Siple Dome) Ross Sea. For most of the past 2,700 years, the eastern Ross Sea was warming with perhaps increased snow accumulation and decreased sea ice extent. However, West Antarctica cooled whereas the western Ross Sea showed no significant temperature trend. From the 17th Century onwards, this relationship changes. All three regions now show signs of warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea, but increasing in the western Ross Sea. Analysis of decadal to centennial-scale climate variability superimposed on the longer term trend reveal that periods characterised by opposing temperature trends between the Eastern and Western Ross Sea have occurred since the 3rd Century but are masked by longer-term trends. This pattern here is referred to as the Ross Sea Dipole, caused by a sensitive response of the region to dynamic interactions of the Southern Annual Mode and tropical forcings.
- Published
- 2017
15. The recent warming trend in North Greenland
- Author
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Orsi, Anais J, Kawamura, Kenji, Masson‐Delmotte, Valerie, Fettweis, Xavier, Box, Jason E, Dahl‐Jensen, Dorthe, Clow, Gary D, Landais, Amaelle, and Severinghaus, Jeffrey P
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Climate Action ,Meteorology & Atmospheric Sciences - Published
- 2017
16. Shear margins in upper half of Northeast Greenland Ice Stream were established two millennia ago
- Author
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Ministerio de Ciencia, Innovación y Universidades (España), Jansen, Daniela [0000-0002-4412-5820], Franke, Steven [0000-0001-8462-4379], Binder, Tobias [0000-0002-9826-8835], Eichler, Jan [0000-0002-3239-9760], Eisen, Olaf [0000-0002-6380-962X], Hu, Yuanbang [0000-0002-8709-1165], Llorens, Maria-Gema [0000-0002-6148-2600], Miller, Heinrich [0000-0003-1015-2828], Paden, John [0000-0003-0775-6284], Stoll, Nicolas [0000-0002-3219-8395], Weikusat, Ilka [0000-0002-3023-6036], Bons, Paul D [0000-0002-6469-3526], Jansen, Daniela, Franke, Steven, Bauer, Catherine C, Binder, Tobias, Dahl-Jensen, Dorthe, Eichler, Jan, Eisen, Olaf, Hu, Yuanbang, Kerch, Johanna, Llorens, Maria-Gema, Miller, Heinrich, Neckel, Niklas, Paden, John, de Riese, Tamara, Sachau, Till, Stoll, Nicolas, Weikusat, Ilka, Wilhelms, Frank, Zhang, Yu, Bons, Paul D, Ministerio de Ciencia, Innovación y Universidades (España), Jansen, Daniela [0000-0002-4412-5820], Franke, Steven [0000-0001-8462-4379], Binder, Tobias [0000-0002-9826-8835], Eichler, Jan [0000-0002-3239-9760], Eisen, Olaf [0000-0002-6380-962X], Hu, Yuanbang [0000-0002-8709-1165], Llorens, Maria-Gema [0000-0002-6148-2600], Miller, Heinrich [0000-0003-1015-2828], Paden, John [0000-0003-0775-6284], Stoll, Nicolas [0000-0002-3219-8395], Weikusat, Ilka [0000-0002-3023-6036], Bons, Paul D [0000-0002-6469-3526], Jansen, Daniela, Franke, Steven, Bauer, Catherine C, Binder, Tobias, Dahl-Jensen, Dorthe, Eichler, Jan, Eisen, Olaf, Hu, Yuanbang, Kerch, Johanna, Llorens, Maria-Gema, Miller, Heinrich, Neckel, Niklas, Paden, John, de Riese, Tamara, Sachau, Till, Stoll, Nicolas, Weikusat, Ilka, Wilhelms, Frank, Zhang, Yu, and Bons, Paul D
- Abstract
Only a few localised ice streams drain most of the ice from the Greenland Ice Sheet. Thus, understanding ice stream behaviour and its temporal variability is crucially important to predict future sea-level change. The interior trunk of the 700 km-long North-East Greenland Ice Stream (NEGIS) is remarkable due to the lack of any clear bedrock channel to explain its presence. Here, we present a 3-dimensional analysis of the folding and advection of its stratigraphic horizons, which shows that the localised flow and shear margins in the upper NEGIS were fully developed only ca 2000 years ago. Our results contradict the assumption that the ice stream has been stable throughout the Holocene in its current form and show that upper NEGIS-type development of ice streaming, with distinct shear margins and no bed topography relationship, can be established on time scales of hundreds of years, which is a major challenge for realistic mass-balance and sea-level rise projections.
- Published
- 2024
17. Origin of silty basal ice in Greenland
- Author
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EGU General Assembly 2024 (14-19 April 2024: Vienna), Ardoin, Lisa, Tison, Jean-Louis, Bierman, P.R., Blard, Pierre-Henri, Dahl-Jensen, Dorthe, Vasileios, Gkinis, Catherine, Larose, Steffensen, Jørgen Peder, Röckmann, Thomas, Fripiat, François, EGU General Assembly 2024 (14-19 April 2024: Vienna), Ardoin, Lisa, Tison, Jean-Louis, Bierman, P.R., Blard, Pierre-Henri, Dahl-Jensen, Dorthe, Vasileios, Gkinis, Catherine, Larose, Steffensen, Jørgen Peder, Röckmann, Thomas, and Fripiat, François
- Abstract
info:eu-repo/semantics/nonPublished
- Published
- 2024
18. The Role of Near-Terminus Conditions in the Ice-Flow Speed of Upernavik Isstrøm in Northwest Greenland
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Voss, Kelsey, primary, Alley, Karen E., additional, Lilien, David A., additional, and Dahl-Jensen, Dorthe, additional
- Published
- 2023
- Full Text
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19. Simulating higher-order fabric structure in a coupled, anisotropic ice-flow model: application to Dome C
- Author
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Lilien, David A., primary, Rathmann, Nicholas M., additional, Hvidberg, Christine S., additional, Grinsted, Aslak, additional, Ershadi, M. Reza, additional, Drews, Reinhard, additional, and Dahl-Jensen, Dorthe, additional
- Published
- 2023
- Full Text
- View/download PDF
20. A 120,000-year long climate record from a NW-Greenland deep ice core at ultra-high resolution
- Author
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Gkinis, Vasileios, Vinther, Bo M., Popp, Trevor J., Quistgaard, Thea, Faber, Anne-Katrine, Holme, Christian T., Jensen, Camilla-Marie, Lanzky, Mika, Lütt, Anine-Maria, Mandrakis, Vasileios, Ørum, Niels-Ole, Pedersen, Anna-Sofie, Vaxevani, Nikol, Weng, Yongbiao, Capron, Emilie, Dahl-Jensen, Dorthe, Hörhold, Maria, Jones, Tyler R., Jouzel, Jean, Landais, Amaëlle, Masson-Delmotte, Valérie, Oerter, Hans, Rasmussen, Sune O., Steen-Larsen, Hans Christian, Steffensen, Jørgen-Peder, Sveinbjörnsdóttir, Árný-Erla, Svensson, Anders, Vaughn, Bruce, and White, James W. C.
- Published
- 2021
- Full Text
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21. Consistently dated records from the Greenland GRIP, GISP2 and NGRIP ice cores for the past 104 ka reveal regional millennial-scale δ18O gradients with possible Heinrich event imprint
- Author
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Seierstad, Inger K, Abbott, Peter M, Bigler, Matthias, Blunier, Thomas, Bourne, Anna J, Brook, Edward, Buchardt, Susanne L, Buizert, Christo, Clausen, Henrik B, Cook, Eliza, Dahl-Jensen, Dorthe, Davies, Siwan M, Guillevic, Myriam, Johnsen, Sigfús J, Pedersen, Desirée S, Popp, Trevor J, Rasmussen, Sune O, Severinghaus, Jeffrey P, Svensson, Anders, and Vinther, Bo M
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Climate Action ,Paleoclimate ,Greenland ice cores ,GICC05 chronology ,Tephra isochrons ,Regional climate ,Water isotopes ,Heinrich event ,Earth Sciences ,History and Archaeology ,Paleontology - Abstract
We present a synchronization of the NGRIP, GRIP and GISP2 ice cores onto a master chronology extending back to 104ka before present, providing a consistent chronological framework for these three Greenland records. The synchronization aligns distinct peaks in volcanic proxy records and other impurity records (chemo-stratigraphic matching) and assumes that these layers of elevated impurity content represent the same, instantaneous event in the past at all three sites. More than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash (tephra) tie-points. Using the reference horizons, we transfer the widely used Greenland ice-core chronology, GICC05modelext, to the two Summit cores, GRIP and GISP2. Furthermore, we provide gas chronologies for the Summit cores that are consistent with the GICC05modelext timescale by utilizing both existing and new gas data (CH4 concentration and δ15N of N2). We infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was ~10% greater at Summit compared to at NGRIP. The δ18O temperature-proxy records from NGRIP, GRIP, and GISP2 are generally very similar and display synchronous behaviour at climate transitions. The δ18O differences between Summit and NGRIP, however, changed slowly over the Last Glacial-Interglacial cycle and also underwent abrupt millennial-to-centennial-scale variations. We suggest that this observed latitudinal δ18O gradient in Greenland during the glacial period is the result of 1) relatively higher degree of precipitation with a Pacific signature at NGRIP, 2) increased summer bias in precipitation at Summit, and 3) enhanced Rayleigh distillation due to an increased source-to-site distance and a potentially larger source-to-site temperature gradient. We propose that these processes are governed by changes in the North American Ice Sheet (NAIS) volume and North Atlantic sea-ice extent and/or sea-surface temperatures (SST) on orbital timescales, and that changing sea-ice extent and SSTs are the driving mechanisms on shorter timescales. Finally, we observe that maxima in the Summit-NGRIP δ18O difference are roughly coincident with prominent Heinrich events. This suggests that the climatic reorganization that takes place during stadials with Heinrich events, possibly driven by a southward expansion of sea ice and low SSTs in the North Atlantic, are recorded in the ice-core records.
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- 2014
22. Greenland and Canadian Arctic ice temperature profiles database
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Løkkegaard, Anja, primary, Mankoff, Kenneth D., additional, Zdanowicz, Christian, additional, Clow, Gary D., additional, Lüthi, Martin P., additional, Doyle, Samuel H., additional, Thomsen, Henrik H., additional, Fisher, David, additional, Harper, Joel, additional, Aschwanden, Andy, additional, Vinther, Bo M., additional, Dahl-Jensen, Dorthe, additional, Zekollari, Harry, additional, Meierbachtol, Toby, additional, McDowell, Ian, additional, Humphrey, Neil, additional, Solgaard, Anne, additional, Karlsson, Nanna B., additional, Khan, Shfaqat A., additional, Hills, Benjamin, additional, Law, Robert, additional, Hubbard, Bryn, additional, Christoffersen, Poul, additional, Jacquemart, Mylène, additional, Seguinot, Julien, additional, Fausto, Robert S., additional, and Colgan, William T., additional
- Published
- 2023
- Full Text
- View/download PDF
23. Stagnant ice and age modelling in the Dome C region, Antarctica
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Chung, Ailsa, primary, Parrenin, Frédéric, additional, Steinhage, Daniel, additional, Mulvaney, Robert, additional, Martín, Carlos, additional, Cavitte, Marie G. P., additional, Lilien, David A., additional, Helm, Veit, additional, Taylor, Drew, additional, Gogineni, Prasad, additional, Ritz, Catherine, additional, Frezzotti, Massimo, additional, O'Neill, Charles, additional, Miller, Heinrich, additional, Dahl-Jensen, Dorthe, additional, and Eisen, Olaf, additional
- Published
- 2023
- Full Text
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24. Regional variations in mineralogy of dust in ice cores obtained from northeastern and northwestern Greenland over the past 100 years
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Nagatsuka, Naoko, primary, Goto-Azuma, Kumiko, additional, Fujita, Koji, additional, Komuro, Yuki, additional, Hirabayashi, Motohiro, additional, Ogata, Jun, additional, Fukuda, Kaori, additional, Ogawa-Tsukagawa, Yoshimi, additional, Kitamura, Kyotaro, additional, Yonekura, Ayaka, additional, Nakazawa, Fumio, additional, Onuma, Yukihiko, additional, Kurita, Naoyuki, additional, Rasmussen, Sune Olander, additional, Sinnl, Giulia, additional, Popp, Trevor James, additional, and Dahl-Jensen, Dorthe, additional
- Published
- 2023
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25. Dynamics of Crystal Formation in the Greenland NorthGRIP Ice Core
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Mathiesen, Joachim, Ferkinghoff-Borg, Jesper, Jensen, Mogens H., Levinsen, Mogens, Olesen, Poul, Dahl-Jensen, Dorthe, and Svensson, Anders
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Physics - Geophysics - Abstract
The North Greenland Ice Core Project (NorthGRIP) provides paleoclimatic information back to at about 120 kyr before present (Dahl-Jensen and others, 2002). Each year, precipitation on the ice sheet covers it with a new layer of snow, which gradually transforms into ice crystals as the layer sinks into the ice sheet. The size distribution of ice crystals has been measured at selected depths in the upper 880 m of the NorthGRIP ice core (Svensson and others, 2003b), which covers a time span of 5300 years. The distributions change with time toward a universal curve, indicating a common underlying physical process in the formation of crystals. We identify this process as an interplay between fragmentation of the crystals and diffusion of their grain boundaries. The process is described by a two-parameter differential equation to which we obtain the exact solution. The solution is in excellent agreement with the experimentally observed distributions., Comment: 10 pages, 4 figures (v2: moderate changes)
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- 2003
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26. Physical analysis of an Antarctic ice core—towards an integration of micro- and macrodynamics of polar ice
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Weikusat, Ilka, Jansen, Daniela, Binder, Tobias, Eichler, Jan, Faria, Sérgio H., Wilhelms, Frank, Kipfstuhl, Sepp, Sheldon, Simon, Miller, Heinrich, Dahl-Jensen, Dorthe, and Kleiner, Thomas
- Published
- 2017
27. Deglaciation of northwestern Greenland during Marine Isotope Stage 11
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Christ, Andrew J., primary, Rittenour, Tammy M., additional, Bierman, Paul R., additional, Keisling, Benjamin A., additional, Knutz, Paul C., additional, Thomsen, Tonny B., additional, Keulen, Nynke, additional, Fosdick, Julie C., additional, Hemming, Sidney R., additional, Tison, Jean-Louis, additional, Blard, Pierre-Henri, additional, Steffensen, Jørgen P., additional, Caffee, Marc W., additional, Corbett, Lee B., additional, Dahl-Jensen, Dorthe, additional, Dethier, David P., additional, Hidy, Alan J., additional, Perdrial, Nicolas, additional, Peteet, Dorothy M., additional, Steig, Eric J., additional, and Thomas, Elizabeth K., additional
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- 2023
- Full Text
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28. Chemical and visual characterisation of EGRIP glacial ice and cloudy bands within
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Stoll, Nicolas, primary, Westhoff, Julien, additional, Bohleber, Pascal, additional, Svensson, Anders, additional, Dahl-Jensen, Dorthe, additional, Barbante, Carlo, additional, and Weikusat, Ilka, additional
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- 2023
- Full Text
- View/download PDF
29. Modification of Pacific water in the northern Canadian Arctic
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Dmitrenko, Igor A., Kirillov, Sergei A., Rudels, Bert, Geilfus, Nicolas-Xavier, Ehn, Jens, Babb, David G., Lilien, David A., and Dahl-Jensen, Dorthe
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Global and Planetary Change ,Ocean Engineering ,Aquatic Science ,Oceanography ,Water Science and Technology - Published
- 2023
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30. Basal debris of the NEEM ice core, Greenland:a window into sub-ice-sheet geology, basal ice processes and ice-sheet oscillations
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Blard, Pierre-henri, Protin, Marie, Tison, Jean-louis, Fripiat, François, Dahl-jensen, Dorthe, Steffensen, Jørgen P., Mahaney, William C., Bierman, Paul R., Christ, Andrew J., Corbett, Lee B., Debaille, Vinciane, Rigaudier, Thomas, and Claeys, Philippe
- Published
- 2023
31. Basal debris of the NEEM ice core, Greenland: a window into sub-ice-sheet geology, basal ice processes and ice-sheet oscillations
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Blard, Pierre-Henri, Protin, Marie, Tison, Jean-Louis, Fripiat, François, Dahl-Jensen, Dorthe, Steffensen, Jørgen P., Mahaney, William C., Bierman, Paul R., Christ, Andrew J., Corbett, Lee B., Debaille, Vinciane, Rigaudier, Thomas, Claeys, Philippe, The ASTER team, Chemistry, Analytical, Environmental & Geo-Chemistry, and Earth System Sciences
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Ice core ,glacial sedimentology ,Basal ice - Abstract
We present new data from the debris-rich basal ice layers of the NEEM ice core (NW Greenland). Using mineralogical observations, SEM imagery, geochemical data from silicates (meteoric 10Be, εNd, 87Sr/86Sr) and organic material (C/N, δ13C), we characterize the source material, succession of previous glaciations and deglaciations and the paleoecological conditions during ice-free episodes. Meteoric 10Be data and grain features indicate that the ice sheet interacted with paleosols and eroded fresh bedrock, leading to mixing in these debris-rich ice layers. Our analysis also identifies four successive stages in NW Greenland: (1) initial preglacial conditions, (2) glacial advance 1, (3) glacial retreat and interglacial conditions and (4) glacial advance 2 (current ice-sheet development). C/N and δ13C data suggest that deglacial environments favored the development of tundra and taiga ecosystems. These two successive glacial fluctuations observed at NEEM are consistent with those identified from the Camp Century core basal sediments over the last 3 Ma. Further inland, GRIP and GISP2 summit sites have remained glaciated more continuously than the western margin, with less intense ice-substratum interactions than those observed at NEEM.
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- 2023
32. Dynamics throughout a complete surge of Iceberg Glacier on western Axel Heiberg Island, Canadian High Arctic
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Lauzon, Benoît, primary, Copland, Luke, additional, Van Wychen, Wesley, additional, Kochtitzky, William, additional, McNabb, Robert, additional, and Dahl-Jensen, Dorthe, additional
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- 2023
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33. Investigating two possible schemes of Laser Ablation – Cavity Ring Down Spectrometry for water isotope measurements on ice cores
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Malegiannaki, Eirini, primary, Gkinis, Vasileios, additional, Munk Wael Fassel, Simon Alexander, additional, Zannoni, Daniele, additional, Dreossi, Giuliano, additional, Stenni, Barbara, additional, Steen-Larsen, Hans Christian, additional, Bohleber, Pascal, additional, Barbante, Carlo, additional, and Dahl-Jensen, Dorthe, additional
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- 2023
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34. Reconstructing the Greenland ice sheet in past warm climates
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Hvidberg, Christine S., primary, Lauritzen, Mikkel, additional, Rathmann, Nicholas M., additional, Solgaard, Anne M., additional, and Dahl-Jensen, Dorthe, additional
- Published
- 2023
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- View/download PDF
35. Ice-core data used for the construction of the Greenland Ice-Core Chronology 2005 and 2021 (GICC05 and GICC21)
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Rasmussen, Sune Olander, primary, Dahl-Jensen, Dorthe, additional, Fischer, Hubertus, additional, Fuhrer, Katrin, additional, Hansen, Steffen Bo, additional, Hansson, Margareta, additional, Hvidberg, Christine Schøtt, additional, Jonsell, Ulf, additional, Kipfstuhl, Sepp, additional, Ruth, Urs, additional, Schwander, Jakob, additional, Siggaard-Andersen, Marie-Louise, additional, Sinnl, Giulia, additional, Steffensen, Jørgen Peder, additional, Svensson, Anders M., additional, and Vinther, Bo, additional
- Published
- 2023
- Full Text
- View/download PDF
36. Supplementary material to "Stagnant ice and age modelling in the Dome C region, Antarctica"
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Chung, Ailsa, primary, Parrenin, Frédéric, additional, Steinhage, Daniel, additional, Mulvaney, Robert, additional, Martín, Carlos, additional, Cavitte, Marie G. P., additional, Lilien, David A., additional, Helm, Veit, additional, Taylor, Drew, additional, Gogineni, Prasad, additional, Ritz, Catherine, additional, Frezzotti, Massimo, additional, O'Neill, Charles, additional, Miller, Heinrich, additional, Dahl-Jensen, Dorthe, additional, and Eisen, Olaf, additional
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- 2023
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37. Detection of ice core particles via deep neural networks
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Maffezzoli, Niccolò, primary, Cook, Eliza, additional, van der Bilt, Willem G. M., additional, Støren, Eivind N., additional, Festi, Daniela, additional, Muthreich, Florian, additional, Seddon, Alistair W. R., additional, Burgay, François, additional, Baccolo, Giovanni, additional, Mygind, Amalie R. F., additional, Petersen, Troels, additional, Spolaor, Andrea, additional, Vascon, Sebastiano, additional, Pelillo, Marcello, additional, Ferretti, Patrizia, additional, dos Reis, Rafael S., additional, Simões, Jefferson C., additional, Ronen, Yuval, additional, Delmonte, Barbara, additional, Viccaro, Marco, additional, Steffensen, Jørgen Peder, additional, Dahl-Jensen, Dorthe, additional, Nisancioglu, Kerim H., additional, and Barbante, Carlo, additional
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- 2023
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- View/download PDF
38. Examining the asynchronous behaviour of the Upernavik Isstrøm in northwest Greenland
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Marson, Juliana (Environment and Geography), Ehn, Jens (Environment and Geography), Alley, Karen, Dahl-Jensen, Dorthe, Voss, Kelsey, Marson, Juliana (Environment and Geography), Ehn, Jens (Environment and Geography), Alley, Karen, Dahl-Jensen, Dorthe, and Voss, Kelsey
- Abstract
The Upernavik Isstrøm, located in northwest Greenland, consists of five marine-terminating glaciers (referred to as U0 to U4, north to south) that have all been responding asynchronously to climate change. All five outlets share similar oceanic, atmospheric, and dynamic influences as they are geographically close, yet contrasting ice-flow behaviour was observed between outlets. This thesis presents a detailed analysis of the varying ice dynamics by updating the observational record of Upernavik’s outlets with recently derived satellite data, examining the role of floating ice tongues by evaluating a variety of proxies for floating ice, and modelling the drivers of ice-flow speed at the two fastest outlets, U1 and U2, with a recent flowline model, Icepack. We found recent patterns in floatation for U1 and U2 that indicated both outlets have new floating ice tongues that persisted through 2021. We evaluated four proxies of floating termini, including tabular iceberg calving, plume polynyas, hydrostatic elevation, and slope, and found only hydrostatic elevation and slope to be reliable proxies. While we initially hypothesized that floating ice tongues drove the acceleration of U1 and U2, our measured velocity data and modelled ice-flow sensitivity to changes in basal slipperiness, shear margin strength, thinning, and terminus retreat, showed ice-flow was realistically explained by changes in basal slipperiness. Icepack was capable of handling this complex case study and the simplified model provided great context regarding the forcings acting on Upernavik’s outlets. This strongly supports that U1 and U2 are seasonally and inter-annually controlled by subglacial hydrology. While the timing and magnitude of observed changes in thinning and retreat varies between outlets, all outlets displayed behaviour characteristic of glaciers controlled by meltwater availability at the bed. These results emphasize the importance of including subglacial hydrology in future studies of U
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- 2023
39. Ice-core data used for the construction of the Greenland Ice-Core Chronology 2005 and 2021 (GICC05 and GICC21)
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Rasmussen, Sune Olander, Dahl-Jensen, Dorthe, Fischer, Hubertus, Fuhrer, Katrin, Hansen, Steffen Bo, Hansson, Margareta, Hvidberg, Christine S., Jonsell, Ulf, Kipfstuhl, Sepp, Ruth, Urs, Schwander, Jakob, Siggaard-Andersen, Marie-Louise, Sinnl, Giulia, Steffensen, Jorgen Peder, Svensson, Anders M., Vinther, Bo M., Rasmussen, Sune Olander, Dahl-Jensen, Dorthe, Fischer, Hubertus, Fuhrer, Katrin, Hansen, Steffen Bo, Hansson, Margareta, Hvidberg, Christine S., Jonsell, Ulf, Kipfstuhl, Sepp, Ruth, Urs, Schwander, Jakob, Siggaard-Andersen, Marie-Louise, Sinnl, Giulia, Steffensen, Jorgen Peder, Svensson, Anders M., and Vinther, Bo M.
- Abstract
We here describe, document, and make available a wide range of data sets used for annual-layer identification in ice cores from DYE-3, GRIP, NGRIP, NEEM, and EGRIP. The data stem from detailed measurements performed both on the main deep cores and shallow cores over more than 40 years using many different setups developed by research groups in several countries and comprise both discrete measurements from cut ice samples and continuous-flow analysis data. The data series were used for counting annual layers 60 000 years back in time during the construction of the Greenland Ice-Core Chronology 2005 (GICC05) and/or the revised GICC21, which currently only reaches 3800 years back. Now that the underlying data are made available (listed in Table 1) we also release the individual annual-layer positions of the GICC05 timescale which are based on these data sets. We hope that the release of the data sets will stimulate further studies of the past climate taking advantage of these highly resolved data series covering a large part of the interior of the Greenland ice sheet.
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- 2023
- Full Text
- View/download PDF
40. Greenland and Canadian Arctic ice temperature profiles database
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Løkkegaard, Anja, Mankoff, Kenneth D., Zdanowicz, Christian, Clow, Gary D., Lüthi, Martin P., Doyle, Samuel H., Thomsen, Henrik H., Fisher, David, Harper, Joel, Aschwanden, Andy, Vinther, Bo M., Dahl-Jensen, Dorthe, Zekollari, Harry, Meierbachtol, Toby, McDowell, Ian, Humphrey, Neil, Solgaard, Anne, Karlsson, Nanna B., Khan, Shfaqat A., Hills, Benjamin, Law, Robert, Hubbard, Bryn, Christoffersen, Poul, Jacquemart, Mylène, Seguinot, Julien, Fausto, Robert S., Colgan, William T., Løkkegaard, Anja, Mankoff, Kenneth D., Zdanowicz, Christian, Clow, Gary D., Lüthi, Martin P., Doyle, Samuel H., Thomsen, Henrik H., Fisher, David, Harper, Joel, Aschwanden, Andy, Vinther, Bo M., Dahl-Jensen, Dorthe, Zekollari, Harry, Meierbachtol, Toby, McDowell, Ian, Humphrey, Neil, Solgaard, Anne, Karlsson, Nanna B., Khan, Shfaqat A., Hills, Benjamin, Law, Robert, Hubbard, Bryn, Christoffersen, Poul, Jacquemart, Mylène, Seguinot, Julien, Fausto, Robert S., and Colgan, William T.
- Abstract
Here, we present a compilation of 95 ice temperature profiles from 85 boreholes from the Greenland ice sheet and peripheral ice caps, as well as local ice caps in the Canadian Arctic. Profiles from only 31 boreholes (36 %) were previously available in open-access data repositories. The remaining 54 borehole profiles (64 %) are being made digitally available here for the first time. These newly available profiles, which are associated with pre-2010 boreholes, have been submitted by community members or digitized from published graphics and/or data tables. All 95 profiles are now made available in both absolute (meters) and normalized (0 to 1 ice thickness) depth scales and are accompanied by extensive metadata. These metadata include a transparent description of data provenance. The ice temperature profiles span 70 years, with the earliest profile being from 1950 at Camp VI, West Greenland. To highlight the value of this database in evaluating ice flow simulations, we compare the ice temperature profiles from the Greenland ice sheet with an ice flow simulation by the Parallel Ice Sheet Model (PISM). We find a cold bias in modeled near-surface ice temperatures within the ablation area, a warm bias in modeled basal ice temperatures at inland cold-bedded sites, and an apparent underestimation of deformational heating in high-strain settings. These biases provide process level insight on simulated ice temperatures.
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- 2023
- Full Text
- View/download PDF
41. Investigating the Radar Response of Englacial Debris Entrained Basal Ice Units in East Antarctica Using Electromagnetic Forward Modeling
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Franke, Steven, Gerber, Tamara, Warren, Craig, Jansen, Daniela, Eisen, Olaf, Dahl-Jensen, Dorthe, Franke, Steven, Gerber, Tamara, Warren, Craig, Jansen, Daniela, Eisen, Olaf, and Dahl-Jensen, Dorthe
- Abstract
Radio-echo sounding (RES) reveals patches of high backscatter in basal ice units, which represent distinct englacial features in the bottom parts of glaciers and ice sheets. Their material composition and physical properties are largely unknown due to their direct inaccessibility but could provide significant information on the physical state as well as on present and past processes at the ice-sheet base. Here, we investigate the material properties of basal ice units by comparing measured airborne radar data with synthetic radar responses generated using electromagnetic (EM) forward modeling. The observations were acquired at the onset of the Jutulstraumen Ice Stream in western Dronning Maud Land (DML) (East Antarctica) and show strong continuous near-basal reflections of up to 200-m thickness in the normally echo-free zone (EFZ). Based on our modeling, we suggest that these high-backscatter units are most likely composed of point reflectors with low dielectric properties, suggesting thick packages of englacial entrained debris. We further investigate the effects of entrained particle size, and concentration in combination with different dielectric properties, which provide useful information to constrain the material composition of radar-detected units of high backscatter. The capability and application of radar wave modeling in complex englacial environments is therefore a valuable tool to further constrain the composition of basal ice and the physical conditions at the ice base.
- Published
- 2023
42. Chemical and visual characterisation of EGRIP glacial ice and cloudy bands within
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Stoll, Nicolas, Westhoff, Julien, Bohleber, Pascal, Svensson, Anders, Dahl-jensen, Dorthe, Barbante, Carlo, Weikusat, Ilka, Stoll, Nicolas, Westhoff, Julien, Bohleber, Pascal, Svensson, Anders, Dahl-jensen, Dorthe, Barbante, Carlo, and Weikusat, Ilka
- Published
- 2023
43. New insights on Greenland ice sheet basal processes: modelling the evolution of a biological signature and diffusion processes
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Goldschmidt 2023 (9-14 July 2023: Lyon, France), Ardoin, Lisa, De Wit, Anne, Tison, Jean-Louis, Blunier, Thomas, Dahl-Jensen, Dorthe, Steffensen, Jørgen Peder, Fripiat, François, Goldschmidt 2023 (9-14 July 2023: Lyon, France), Ardoin, Lisa, De Wit, Anne, Tison, Jean-Louis, Blunier, Thomas, Dahl-Jensen, Dorthe, Steffensen, Jørgen Peder, and Fripiat, François
- Abstract
info:eu-repo/semantics/nonPublished
- Published
- 2023
44. Stagnant ice and age modelling in the Dome C region, Antarctica
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Chung, Ailsa, Parrenin, Frédéric, Steinhage, Daniel, Mulvaney, Robert, Martín, Carlos, Cavitte, Marie G. P., Lilien, David A., Helm, Veit, Taylor, Drew, Gogineni, Prasad, Ritz, Catherine, Frezzotti, Massimo, O'Neill, Charles, Miller, Heinrich, Dahl-Jensen, Dorthe, Eisen, Olaf, Chung, Ailsa, Parrenin, Frédéric, Steinhage, Daniel, Mulvaney, Robert, Martín, Carlos, Cavitte, Marie G. P., Lilien, David A., Helm, Veit, Taylor, Drew, Gogineni, Prasad, Ritz, Catherine, Frezzotti, Massimo, O'Neill, Charles, Miller, Heinrich, Dahl-Jensen, Dorthe, and Eisen, Olaf
- Abstract
The European Beyond EPICA project aims to extract a continuous ice core of up to 1.5 Ma, with a maximum age density of 20 kyr m−1 at Little Dome C (LDC). We present a 1D numerical model which calculates the age of the ice around Dome C. The model inverts for basal conditions and accounts either for melting or for a layer of stagnant ice above the bedrock. It is constrained by internal reflecting horizons traced in radargrams and dated using the EPICA Dome C (EDC) ice core age profile. We used three different radar datasets ranging from a 10 000 km2 airborne survey down to 5 km long ground-based radar transects over LDC. We find that stagnant ice exists in many places, including above the LDC relief where the new Beyond EPICA drill site (BELDC) is located. The modelled thickness of this layer of stagnant ice roughly corresponds to the thickness of the basal unit observed in one of the radar surveys and in the autonomous phase-sensitive radio-echo sounder (ApRES) dataset. At BELDC, the modelled stagnant ice thickness is 198±44 m and the modelled oldest age of ice is 1.45±0.16 Ma at a depth of 2494±30 m. This is very similar to all sites situated on the LDC relief, including that of the Million Year Ice Core project being conducted by the Australian Antarctic Division. The model was also applied to radar data in the area 10–15 km north of EDC (North Patch), where we find either a thin layer of stagnant ice (generally <60 m) or a negligible melt rate (<0.1 mm yr−1). The modelled maximum age at North Patch is over 2 Ma in most places, with ice at 1.5 Ma having a resolution of 9–12 kyr m−1, making it an exciting prospect for a future Oldest Ice drill site.
- Published
- 2023
45. Detection of ice core particles via deep neural networks
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Maffezzoli, N, Cook, E, van der Bilt, W, Støren, E, Festi, D, Muthreich, F, Seddon, A, Burgay, F, Baccolo, G, Mygind, A, Petersen, T, Spolaor, A, Vascon, S, Pelillo, M, Ferretti, P, dos Reis, R, Simões, J, Ronen, Y, Delmonte, B, Viccaro, M, Steffensen, J, Dahl-Jensen, D, Nisancioglu, K, Barbante, C, Maffezzoli, Niccolò, Cook, Eliza, van der Bilt, Willem G. M., Støren, Eivind N., Festi, Daniela, Muthreich, Florian, Seddon, Alistair W. R., Burgay, François, Baccolo, Giovanni, Mygind, Amalie R. F., Petersen, Troels, Spolaor, Andrea, Vascon, Sebastiano, Pelillo, Marcello, Ferretti, Patrizia, dos Reis, Rafael S., Simões, Jefferson C., Ronen, Yuval, Delmonte, Barbara, Viccaro, Marco, Steffensen, Jørgen Peder, Dahl-Jensen, Dorthe, Nisancioglu, Kerim H., Barbante, Carlo, Maffezzoli, N, Cook, E, van der Bilt, W, Støren, E, Festi, D, Muthreich, F, Seddon, A, Burgay, F, Baccolo, G, Mygind, A, Petersen, T, Spolaor, A, Vascon, S, Pelillo, M, Ferretti, P, dos Reis, R, Simões, J, Ronen, Y, Delmonte, B, Viccaro, M, Steffensen, J, Dahl-Jensen, D, Nisancioglu, K, Barbante, C, Maffezzoli, Niccolò, Cook, Eliza, van der Bilt, Willem G. M., Støren, Eivind N., Festi, Daniela, Muthreich, Florian, Seddon, Alistair W. R., Burgay, François, Baccolo, Giovanni, Mygind, Amalie R. F., Petersen, Troels, Spolaor, Andrea, Vascon, Sebastiano, Pelillo, Marcello, Ferretti, Patrizia, dos Reis, Rafael S., Simões, Jefferson C., Ronen, Yuval, Delmonte, Barbara, Viccaro, Marco, Steffensen, Jørgen Peder, Dahl-Jensen, Dorthe, Nisancioglu, Kerim H., and Barbante, Carlo
- Abstract
Insoluble particles in ice cores record signatures of past climate parameters like vegetation dynamics, volcanic activity, and aridity. For some of them, the analytical detection relies on intensive bench microscopy investigation and requires dedicated sample preparation steps. Both are laborious, require in-depth knowledge, and often restrict sampling strategies. To help overcome these limitations, we present a framework based on flow imaging microscopy coupled to a deep neural network for autonomous image classification of ice core particles. We train the network to classify seven commonly found classes, namely mineral dust, felsic and mafic (basaltic) volcanic ash grains (tephra), three species of pollen (Corylus avellana, Quercus robur, Quercus suber), and contamination particles that may be introduced onto the ice core surface during core handling operations. The trained network achieves 96.8ĝ€ ̄% classification accuracy at test time. We present the system's potential and its limitations with respect to the detection of mineral dust, pollen grains, and tephra shards, using both controlled materials and real ice core samples. The methodology requires little sample material, is non-destructive, fully reproducible, and does not require any sample preparation procedures. The presented framework can bolster research in the field by cutting down processing time, supporting human-operated microscopy, and further unlocking the paleoclimate potential of ice core records by providing the opportunity to identify an array of ice core particles. Suggestions for an improved system to be deployed within a continuous flow analysis workflow are also presented.
- Published
- 2023
46. Detection of ice core particles via deep neural networks
- Author
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Maffezzoli, Niccolo, Cook, Eliza, van der Bilt, Willem G. M., Storen, Eivind N., Festi, Daniela, Muthreich, Florian, Seddon, Alistair W. R., Burgay, Francois, Baccolo, Giovanni, Mygind, Amalie R. F., Petersen, Troels, Spolaor, Andrea, Vascon, Sebastiano, Pelillo, Marcello, Ferretti, Patrizia, dos Reis, Rafael S., Simoes, Jefferson C., Ronen, Yuval, Delmonte, Barbara, Viccaro, Marco, Steffensen, Jorgen Peder, Dahl-Jensen, Dorthe, Nisancioglu, Kerim H., Barbante, Carlo, Maffezzoli, Niccolo, Cook, Eliza, van der Bilt, Willem G. M., Storen, Eivind N., Festi, Daniela, Muthreich, Florian, Seddon, Alistair W. R., Burgay, Francois, Baccolo, Giovanni, Mygind, Amalie R. F., Petersen, Troels, Spolaor, Andrea, Vascon, Sebastiano, Pelillo, Marcello, Ferretti, Patrizia, dos Reis, Rafael S., Simoes, Jefferson C., Ronen, Yuval, Delmonte, Barbara, Viccaro, Marco, Steffensen, Jorgen Peder, Dahl-Jensen, Dorthe, Nisancioglu, Kerim H., and Barbante, Carlo
- Abstract
Insoluble particles in ice cores record signatures of past climate parameters like vegetation dynamics, volcanic activity, and aridity. For some of them, the analytical detection relies on intensive bench microscopy investigation and requires dedicated sample preparation steps. Both are laborious, require in-depth knowledge, and often restrict sampling strategies. To help overcome these limitations, we present a framework based on flow imaging microscopy coupled to a deep neural network for autonomous image classification of ice core particles. We train the network to classify seven commonly found classes, namely mineral dust, felsic and mafic (basaltic) volcanic ash grains (tephra), three species of pollen (Corylus avellana, Quercus robur, Quercus suber), and contamination particles that may be introduced onto the ice core surface during core handling operations. The trained network achieves 96.8 % classification accuracy at test time. We present the system's potential and its limitations with respect to the detection of mineral dust, pollen grains, and tephra shards, using both controlled materials and real ice core samples. The methodology requires little sample material, is non-destructive, fully reproducible, and does not require any sample preparation procedures. The presented framework can bolster research in the field by cutting down processing time, supporting human-operated microscopy, and further unlocking the paleoclimate potential of ice core records by providing the opportunity to identify an array of ice core particles. Suggestions for an improved system to be deployed within a continuous flow analysis workflow are also presented.
- Published
- 2023
47. Greenland and Canadian Arctic ice temperature profiles database
- Author
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Løkkegaard, Anja; https://orcid.org/0000-0002-1947-5773, Mankoff, Kenneth D; https://orcid.org/0000-0001-5453-2019, Zdanowicz, Christian; https://orcid.org/0000-0002-1045-5063, Clow, Gary D; https://orcid.org/0000-0002-2262-3853, Lüthi, Martin P; https://orcid.org/0000-0003-4419-8496, Doyle, Samuel H; https://orcid.org/0000-0002-0853-431X, Thomsen, Henrik H, Fisher, David, Harper, Joel; https://orcid.org/0000-0002-2151-8509, Aschwanden, Andy; https://orcid.org/0000-0001-8149-2315, Vinther, Bo M, Dahl-Jensen, Dorthe, Zekollari, Harry; https://orcid.org/0000-0002-7443-4034, Meierbachtol, Toby, McDowell, Ian; https://orcid.org/0000-0003-1285-724X, Humphrey, Neil, Solgaard, Anne; https://orcid.org/0000-0002-8693-620X, Karlsson, Nanna B; https://orcid.org/0000-0003-0423-8705, Khan, Shfaqat A; https://orcid.org/0000-0002-2689-8563, Hills, Benjamin; https://orcid.org/0000-0003-4490-7416, Law, Robert; https://orcid.org/0000-0003-0067-5537, Hubbard, Bryn; https://orcid.org/0000-0002-3565-3875, Christoffersen, Poul; https://orcid.org/0000-0003-2643-8724, Jacquemart, Mylène; https://orcid.org/0000-0003-2501-7645, Seguinot, Julien; https://orcid.org/0000-0002-5315-0761, Fausto, Robert S; https://orcid.org/0000-0003-1317-8185, Colgan, William T; https://orcid.org/0000-0001-6334-1660, Løkkegaard, Anja; https://orcid.org/0000-0002-1947-5773, Mankoff, Kenneth D; https://orcid.org/0000-0001-5453-2019, Zdanowicz, Christian; https://orcid.org/0000-0002-1045-5063, Clow, Gary D; https://orcid.org/0000-0002-2262-3853, Lüthi, Martin P; https://orcid.org/0000-0003-4419-8496, Doyle, Samuel H; https://orcid.org/0000-0002-0853-431X, Thomsen, Henrik H, Fisher, David, Harper, Joel; https://orcid.org/0000-0002-2151-8509, Aschwanden, Andy; https://orcid.org/0000-0001-8149-2315, Vinther, Bo M, Dahl-Jensen, Dorthe, Zekollari, Harry; https://orcid.org/0000-0002-7443-4034, Meierbachtol, Toby, McDowell, Ian; https://orcid.org/0000-0003-1285-724X, Humphrey, Neil, Solgaard, Anne; https://orcid.org/0000-0002-8693-620X, Karlsson, Nanna B; https://orcid.org/0000-0003-0423-8705, Khan, Shfaqat A; https://orcid.org/0000-0002-2689-8563, Hills, Benjamin; https://orcid.org/0000-0003-4490-7416, Law, Robert; https://orcid.org/0000-0003-0067-5537, Hubbard, Bryn; https://orcid.org/0000-0002-3565-3875, Christoffersen, Poul; https://orcid.org/0000-0003-2643-8724, Jacquemart, Mylène; https://orcid.org/0000-0003-2501-7645, Seguinot, Julien; https://orcid.org/0000-0002-5315-0761, Fausto, Robert S; https://orcid.org/0000-0003-1317-8185, and Colgan, William T; https://orcid.org/0000-0001-6334-1660
- Abstract
Here, we present a compilation of 95 ice temperature profiles from 85 boreholes from the Greenland ice sheet and peripheral ice caps, as well as local ice caps in the Canadian Arctic. Profiles from only 31 boreholes (36 %) were previously available in open-access data repositories. The remaining 54 borehole profiles (64 %) are being made digitally available here for the first time. These newly available profiles, which are associated with pre-2010 boreholes, have been submitted by community members or digitized from published graphics and/or data tables. All 95 profiles are now made available in both absolute (meters) and normalized (0 to 1 ice thickness) depth scales and are accompanied by extensive metadata. These metadata include a transparent description of data provenance. The ice temperature profiles span 70 years, with the earliest profile being from 1950 at Camp VI, West Greenland. To highlight the value of this database in evaluating ice flow simulations, we compare the ice temperature profiles from the Greenland ice sheet with an ice flow simulation by the Parallel Ice Sheet Model (PISM). We find a cold bias in modeled near-surface ice temperatures within the ablation area, a warm bias in modeled basal ice temperatures at inland cold-bedded sites, and an apparent underestimation of deformational heating in high-strain settings. These biases provide process level insight on simulated ice temperatures.
- Published
- 2023
48. Deglaciation of northwestern Greenland during Marine Isotope Stage 11
- Author
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Christ, Andrew J., Rittenour, Tammy M., Bierman, Paul R., Keisling, Benjamin A., Knutz, Paul C., Thomsen, Tonny B., Keulen, Nynke, Fosdick, Julie C., Hemming, Sidney R., Tison, Jean-louis, Blard, Pierre-henri, Steffensen, Jørgen P., Caffee, Marc W., Corbett, Lee B., Dahl-jensen, Dorthe, Dethier, David P., Hidy, Alan J., Perdrial, Nicolas, Peteet, Dorothy M., Steig, Eric J., Thomas, Elizabeth K., Christ, Andrew J., Rittenour, Tammy M., Bierman, Paul R., Keisling, Benjamin A., Knutz, Paul C., Thomsen, Tonny B., Keulen, Nynke, Fosdick, Julie C., Hemming, Sidney R., Tison, Jean-louis, Blard, Pierre-henri, Steffensen, Jørgen P., Caffee, Marc W., Corbett, Lee B., Dahl-jensen, Dorthe, Dethier, David P., Hidy, Alan J., Perdrial, Nicolas, Peteet, Dorothy M., Steig, Eric J., and Thomas, Elizabeth K.
- Published
- 2023
49. Dynamics throughout a complete surge of Iceberg Glacier on western Axel Heiberg Island, Canadian High Arctic
- Author
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Lauzon, Benoit, Copland, Luke, Van Wychen, Wesley, Kochtitzky, William, McNabb, Robert, Dahl-Jensen, Dorthe, Lauzon, Benoit, Copland, Luke, Van Wychen, Wesley, Kochtitzky, William, McNabb, Robert, and Dahl-Jensen, Dorthe
- Abstract
This study provides the first comprehensive reconstruction of the dynamics of Iceberg Glacier, located on western Axel Heiberg Island, and reveals detailed observations of a complete surge for the first time in the Canadian Arctic. Historical aerial photographs, declassified intelligence satellite photographs, optical satellite imagery and synthetic aperture radar data were used to quantify changes in terminus position, ice velocity and glacier thickness since the 1950s. A surge initiated at the terminus in 1981 and terminated in 2003, suggesting a 22-year active phase. High surface velocities, reaching -2300 m a(-1) in 1991, were accompanied by a maximum terminus advance of >7 km and a large transfer of mass down-glacier, causing significant median trunk-wide surface elevation changes attaining >3 +/- 1 m a(-1). We suggest that the retreat from a pinning point, flotation of the terminus, the removal of sea-ice from the ice front, and an increase in subglacial meltwater availability from relatively high air temperatures in 1981 likely contributed to surge initiation. The ensuing quiescent period has seen a continual decrease in surface flow rates to an average centreline velocity of 11.5 m a(-1) in 2020-21, a gradual steepening of the glacier surface and a > 2.5 km terminus retreat.
- Published
- 2023
50. Comparative carbon cycle dynamics of the present and last interglacial
- Author
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Brovkin, Victor, Brücher, Tim, Kleinen, Thomas, Zaehle, Sönke, Joos, Fortunat, Roth, Raphael, Spahni, Renato, Schmitt, Jochen, Fischer, Hubertus, Leuenberger, Markus, Stone, Emma J., Ridgwell, Andy, Chappellaz, Jérôme, Kehrwald, Natalie, Barbante, Carlo, Blunier, Thomas, and Dahl Jensen, Dorthe
- Published
- 2016
- Full Text
- View/download PDF
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