1
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Chudley TR, Howat IM, King MD, Negrete A. Atlantic water intrusion triggers rapid retreat and regime change at previously stable Greenland glacier. Nat Commun 2023; 14:2151. [PMID: 37076489 PMCID: PMC10115864 DOI: 10.1038/s41467-023-37764-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Accepted: 03/30/2023] [Indexed: 04/21/2023] Open
Abstract
Ice discharge from Greenland's marine-terminating glaciers contributes to half of all mass loss from the ice sheet, with numerous mechanisms proposed to explain their retreat. Here, we examine K.I.V Steenstrups Nordre Bræ ('Steenstrup') in Southeast Greenland, which, between 2018 and 2021, retreated ~7 km, thinned ~20%, doubled in discharge, and accelerated ~300%. This rate of change is unprecedented amongst Greenland's glaciers and now places Steenstrup in the top 10% of glaciers by contribution to ice-sheet-wide discharge. In contrast to expected behaviour from a shallow, grounded tidewater glacier, Steenstrup was insensitive to high surface temperatures that destabilised many regional glaciers in 2016, appearing instead to respond to a >2 °C anomaly in deeper Atlantic water (AW) in 2018. By 2021, a rigid proglacial mélange had developed alongside notable seasonal variability. Steenstrup's behaviour highlights that even long-term stable glaciers with high sills are vulnerable to sudden and rapid retreat from warm AW intrusion.
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Affiliation(s)
- T R Chudley
- Byrd Polar and Climate Research Center, Ohio State University, Columbus, OH, USA.
- Department of Geography, Durham University, Durham, UK.
| | - I M Howat
- Byrd Polar and Climate Research Center, Ohio State University, Columbus, OH, USA
- School of Earth Sciences, Ohio State University, Columbus, OH, USA
| | - M D King
- Polar Science Center, University of Washington, Seattle, WA, USA
| | - A Negrete
- Byrd Polar and Climate Research Center, Ohio State University, Columbus, OH, USA
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2
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Khan SA, Bamber JL, Rignot E, Helm V, Aschwanden A, Holland DM, van den Broeke M, King M, Noël B, Truffer M, Humbert A, Colgan W, Vijay S, Kuipers Munneke P. Greenland Mass Trends From Airborne and Satellite Altimetry During 2011-2020. JOURNAL OF GEOPHYSICAL RESEARCH. EARTH SURFACE 2022; 127:e2021JF006505. [PMID: 35864950 PMCID: PMC9286656 DOI: 10.1029/2021jf006505] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 03/07/2022] [Accepted: 03/14/2022] [Indexed: 06/15/2023]
Abstract
We use satellite and airborne altimetry to estimate annual mass changes of the Greenland Ice Sheet. We estimate ice loss corresponding to a sea-level rise of 6.9 ± 0.4 mm from April 2011 to April 2020, with a highest annual ice loss rate of 1.4 mm/yr sea-level equivalent from April 2019 to April 2020. On a regional scale, our annual mass loss timeseries reveals 10-15 m/yr dynamic thickening at the terminus of Jakobshavn Isbræ from April 2016 to April 2018, followed by a return to dynamic thinning. We observe contrasting patterns of mass loss acceleration in different basins across the ice sheet and suggest that these spatiotemporal trends could be useful for calibrating and validating prognostic ice sheet models. In addition to resolving the spatial and temporal fingerprint of Greenland's recent ice loss, these mass loss grids are key for partitioning contemporary elastic vertical land motion from longer-term glacial isostatic adjustment (GIA) trends at GPS stations around the ice sheet. Our ice-loss product results in a significantly different GIA interpretation from a previous ice-loss product.
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Affiliation(s)
- Shfaqat A. Khan
- DTU SpaceTechnical University of DenmarkKongens LyngbyDenmark
| | - Jonathan L. Bamber
- Bristol Glaciology CentreUniversity of BristolBristolUK
- Department of Aerospace and GeodesyTechnical University MunichMunichGermany
| | - Eric Rignot
- Department of Earth System ScienceUniversity of California IrvineIrvineCAUSA
| | - Veit Helm
- Glaciology SectionAlfred Wegener InstituteBremerhavenGermany
| | | | - David M. Holland
- New York UniversityNew YorkNYUSA
- Center for Global Sea Level ChangeNew York UniversityAbu DhabiUAE
| | - Michiel van den Broeke
- Institute for Marine and Atmospheric Research UtrechtUtrecht UniversityUtrechtThe Netherlands
| | - Michalea King
- Applied Physics LaboratoryUniversity of WashingtonSeattleWAUSA
| | - Brice Noël
- Institute for Marine and Atmospheric Research UtrechtUtrecht UniversityUtrechtThe Netherlands
| | | | | | - William Colgan
- Department of Glaciology and ClimateGeological Survey of Denmark and GreenlandCopenhagenDenmark
| | - Saurabh Vijay
- Department of Civil EngineeringIndian Institute of Technology RoorkeeRoorkeeIndia
| | - Peter Kuipers Munneke
- Institute for Marine and Atmospheric Research UtrechtUtrecht UniversityUtrechtThe Netherlands
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3
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Uppermost crustal structure regulates the flow of the Greenland Ice Sheet. Nat Commun 2021; 12:7307. [PMID: 34911961 PMCID: PMC8674248 DOI: 10.1038/s41467-021-27537-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Accepted: 11/23/2021] [Indexed: 11/28/2022] Open
Abstract
The flow of the Greenland Ice Sheet is controlled by subglacial processes and conditions that depend on the geological provenance and temperature of the crust beneath it, neither of which are adequately known. Here we present a seismic velocity model of the uppermost 5 km of the Greenlandic crust. We show that slow velocities in the upper crust tend to be associated with major outlet glaciers along the ice-sheet margin, and elevated geothermal heat flux along the Iceland hotspot track inland. Outlet glaciers particularly susceptible to basal slip over deformable subglacial sediments include Jakobshavn, Helheim and Kangerdlussuaq, while geothermal warming and softening of basal ice may affect the onset of faster ice flow at Petermann Glacier and the Northeast Greenland Ice Stream. Interactions with the solid earth therefore control the past, present and future dynamics of the Greenland Ice Sheet and must be adequately explored and implemented in ice sheet models.
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4
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Fully Automated Detection of Supraglacial Lake Area for Northeast Greenland Using Sentinel-2 Time-Series. REMOTE SENSING 2021. [DOI: 10.3390/rs13020205] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The usability of multispectral satellite data for detecting and monitoring supraglacial meltwater ponds has been demonstrated for western Greenland. For a multitemporal analysis of large regions or entire Greenland, largely automated processing routines are required. Here, we present a sequence of algorithms that allow for an automated Sentinel-2 data search, download, processing, and generation of a consistent and dense melt pond area time-series based on open-source software. We test our approach for a ~82,000 km2 area at the 79 °N Glacier (Nioghalvfjerdsbrae) in northeast Greenland, covering the years 2016, 2017, 2018 and 2019. Our lake detection is based on the ratio of the blue and red visible bands using a minimum threshold. To remove false classification caused by the similar spectra of shadow and water on ice, we implement a shadow model to mask out topographically induced artifacts. We identified 880 individual lakes, traceable over 479 time-steps throughout 2016–2019, with an average size of 64,212 m2. Of the four years, 2019 had the most extensive lake area coverage with a maximum of 333 km2 and a maximum individual lake size of 30 km2. With 1.5 days average observation interval, our time-series allows for a comparison with climate data of daily resolution, enabling a better understanding of short-term climate-glacier feedbacks.
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5
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Khan SA, Bjørk AA, Bamber JL, Morlighem M, Bevis M, Kjær KH, Mouginot J, Løkkegaard A, Holland DM, Aschwanden A, Zhang B, Helm V, Korsgaard NJ, Colgan W, Larsen NK, Liu L, Hansen K, Barletta V, Dahl-Jensen TS, Søndergaard AS, Csatho BM, Sasgen I, Box J, Schenk T. Centennial response of Greenland's three largest outlet glaciers. Nat Commun 2020; 11:5718. [PMID: 33203883 PMCID: PMC7672108 DOI: 10.1038/s41467-020-19580-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 10/19/2020] [Indexed: 11/08/2022] Open
Abstract
The Greenland Ice Sheet is the largest land ice contributor to sea level rise. This will continue in the future but at an uncertain rate and observational estimates are limited to the last few decades. Understanding the long-term glacier response to external forcing is key to improving projections. Here we use historical photographs to calculate ice loss from 1880-2012 for Jakobshavn, Helheim, and Kangerlussuaq glacier. We estimate ice loss corresponding to a sea level rise of 8.1 ± 1.1 millimetres from these three glaciers. Projections of mass loss for these glaciers, using the worst-case scenario, Representative Concentration Pathways 8.5, suggest a sea level contribution of 9.1-14.9 mm by 2100. RCP8.5 implies an additional global temperature increase of 3.7 °C by 2100, approximately four times larger than that which has taken place since 1880. We infer that projections forced by RCP8.5 underestimate glacier mass loss which could exceed this worst-case scenario.
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Affiliation(s)
- Shfaqat A Khan
- DTU Space, Technical University of Denmark, Kongens Lyngby, Denmark.
| | | | | | - Mathieu Morlighem
- Department of Earth System Science, University of California, Irvine, USA
| | - Michael Bevis
- School of Earth Sciences, Ohio State University, Columbus, OH, USA
| | - Kurt H Kjær
- Globe Institute, University of Copenhagen, Copenhagen, Denmark
| | - Jérémie Mouginot
- Institut des Géosciences de l'Environnement, Université Grenoble Alpes, Grenoble, France
| | - Anja Løkkegaard
- DTU Space, Technical University of Denmark, Kongens Lyngby, Denmark
| | - David M Holland
- Center for global Sea Level Change, New York University Abu Dhabi, Abu Dhabi, UAE
| | | | - Bao Zhang
- School of Geodesy and Geomatics, Wuhan University, Wuhan, China
| | - Veit Helm
- Glaciology Section, Alfred Wegener Institute, Bremerhaven, Germany
| | | | - William Colgan
- Geological Survey of Denmark and Greenland, Copenhagen, Denmark
| | | | - Lin Liu
- Earth System Science Programme, The Chinese University of Hong Kong, Hong Kong, China
| | - Karina Hansen
- DTU Space, Technical University of Denmark, Kongens Lyngby, Denmark
| | | | | | | | - Beata M Csatho
- Department of Geology, University at Buffalo, Buffalo, NY, USA
| | - Ingo Sasgen
- Glaciology Section, Alfred Wegener Institute, Bremerhaven, Germany
| | - Jason Box
- Geological Survey of Denmark and Greenland, Copenhagen, Denmark
| | - Toni Schenk
- Department of Geology, University at Buffalo, Buffalo, NY, USA
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6
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Change Points Detected in Decadal and Seasonal Trends of Outlet Glacier Terminus Positions across West Greenland. REMOTE SENSING 2020. [DOI: 10.3390/rs12213651] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We investigated the change in terminus position between 1985 and 2015 of 17 marine-terminating glaciers that drain into Disko and Uummannaq Bays, West Greenland, by manually digitizing over 5000 individual frontal positions from over 1200 Landsat images. We find that 15 of 17 glacier termini retreated over the study period, with ~80% of this retreat occurring since 2000. Increased frequency of Landsat observations since 2000 allowed for further investigation of the seasonal variability in terminus position. We identified 10 actively retreating glaciers based on a significant positive relationship between glaciers with cumulative retreat >300 m since 2000 and their average annual amplitude (seasonal range) in terminus position. Finally, using the Detecting Breakpoints and Estimating Segments in Trend (DBEST) program, we investigated whether the 2000–2015 trends in terminus position were explained by the occurrence of change points (significant trend transitions). Based on the change point analysis, we found that nine of 10 glaciers identified as actively retreating also underwent two or three periods of change, during which their terminus positions were characterized by increases in cumulative retreat. Previous literature suggests potential relationships between our identified change dates with anomalous ocean conditions, such as low sea ice concentration and high sea surface temperatures, and our change durations with individual fjord geometry.
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7
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Synergistic Use of Single-Pass Interferometry and Radar Altimetry to Measure Mass Loss of NEGIS Outlet Glaciers between 2011 and 2014. REMOTE SENSING 2020. [DOI: 10.3390/rs12060996] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Mass balances of individual glaciers on ice sheets have been previously reported by forming a mass budget of discharged ice and modelled ice sheet surface mass balance or a complementary method which measures volume changes over the glaciated area that are subsequently converted to glacier mass change. On ice sheets, volume changes have been measured predominantly with radar and laser altimeters but InSAR DEM differencing has also been applied on smaller ice bodies. Here, we report for the first time on the synergistic use of volumetric measurements from the CryoSat-2 radar altimetry mission together with TanDEM-X DEM differencing and calculate the mass balance of the two major outlet glaciers of the Northeast Greenland Ice Stream: Zachariæ Isstrøm and Nioghalvfjerdsfjorden (79North). The glaciers lost 3.59 ± 1.15 G t a − 1 and 1.01 ± 0.95 G t a − 1 , respectively, between January 2011 and January 2014. Additionally, there has been substantial sub-aqueous mass loss on Zachariæ Isstrøm of more than 11 G t a − 1 . We attribute the mass changes on both glaciers to dynamic downwasting. The presented methodology now permits using TanDEM-X bistatic InSAR data in the context of geodetic mass balance investigations for large ice sheet outlet glaciers. In the future, this will allow monitoring the mass changes of dynamic outlet glaciers with high spatial resolution while the superior vertical accuracy of CryoSat-2 can be used for the vast accumulation zones in the ice sheet interior.
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8
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Mass balance of the Greenland Ice Sheet from 1992 to 2018. Nature 2019; 579:233-239. [DOI: 10.1038/s41586-019-1855-2] [Citation(s) in RCA: 257] [Impact Index Per Article: 51.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 11/25/2019] [Indexed: 01/13/2023]
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9
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Spatial and Temporal Variability of Glacier Surface
Velocities and Outlet Areas on James Ross Island,
Northern Antarctic Peninsula. GEOSCIENCES 2019. [DOI: 10.3390/geosciences9090374] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The northern Antarctic Peninsula was affected by a significant warming over the secondhalf of the 20th century and the collapse of several ice shelves. Local climate conditions on James RossIsland on the northeastern coast can differ strongly from the main part of the Antarctic Peninsula.This paper reports the spatial and temporal variability of glacier surface velocities and the area oftheir outlets throughout James Ross Island, and evaluates potential relationships with atmosphericand oceanic conditions. Velocity estimates were retrieved from intensity feature tracking of scenesfrom satellite synthetic aperture radar sensors TerraSAR-X and TanDEM-X between 2014 and 2018,which were validated against ground observations. Calving front positions back to 1945 were usedto calculate outlet area changes for the glaciers by using a common-box approach. The annualrecession rates of almost all investigated glacier calving fronts decelerated for the time periods2009–2014 and 2014–2018 in comparison to the period 1988–2009, but their velocity patterns differed.Analysis of atmospheric conditions failed to explain the different patterns in velocity and areachanges. We suggest a strong influence from local bathymetric conditions. Future investigations ofthe oceanic conditions would be necessary for a profound understanding of the super-position ofdifferent influencing factors.
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10
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Rapid iceberg calving following removal of tightly packed pro-glacial mélange. Nat Commun 2019; 10:3250. [PMID: 31324756 PMCID: PMC6642183 DOI: 10.1038/s41467-019-10908-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 06/05/2019] [Indexed: 11/23/2022] Open
Abstract
Iceberg calving is a major contributor to Greenland’s ice mass loss. Pro-glacial mélange (a mixture of sea ice, icebergs, and snow) may be tightly packed in the long, narrow fjords that front many marine-terminating glaciers and can reduce calving by buttressing. However, data limitations have hampered a quantitative understanding. We develop a new radar-based approach to estimate time-varying elevations near the mélange-glacier interface, generating a factor of three or more improvement in elevation precision. We apply the technique to Jakobshavn Isbræ, Greenland’s major outlet glacier. Over a one-month period in early summer 2016, the glacier experienced essentially no calving, and was buttressed by an unusually thick mélange wedge that increased in thickness towards the glacier front. The extent and thickness of the wedge gradually decreased, with large-scale calving starting once the mélange mass within 7 km of the glacier front had decreased by >40%. Observation systems are not sufficient to determine the relationship between mélange strength and calving frequency. Here the authors used the derivation of digital elevation models from radar interferometry data to study Jakobshavn Isbræ and show an inverse correlation between mélange thickness and calving rate.
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11
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Arctic Ocean Sea Level Record from the Complete Radar Altimetry Era: 1991–2018. REMOTE SENSING 2019. [DOI: 10.3390/rs11141672] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In recent years, there has been a large focus on the Arctic due to the rapid changes of the region. Arctic sea level determination is challenging due to the seasonal to permanent sea-ice cover, lack of regional coverage of satellites, satellite instruments ability to measure ice, insufficient geophysical models, residual orbit errors, challenging retracking of satellite altimeter data. We present the European Space Agency (ESA) Climate Change Initiative (CCI) Technical University of Denmark (DTU)/Technischen Universität München (TUM) sea level anomaly (SLA) record based on radar satellite altimetry data in the Arctic Ocean from the European Remote Sensing satellite number 1 (ERS-1) (1991) to CryoSat-2 (2018). We use updated geophysical corrections and a combination of altimeter data: Reprocessing of Altimeter Product for ERS (REAPER) (ERS-1), ALES+ retracker (ERS-2, Envisat), combination of Radar Altimetry Database System (RADS) and DTUs in-house retracker LARS (CryoSat-2). Furthermore, this study focuses on the transition between conventional and Synthetic Aperture Radar (SAR) altimeter data to make a smooth time series regarding the measurement method. We find a sea level rise of 1.54 mm/year from September 1991 to September 2018 with a 95% confidence interval from 1.16 to 1.81 mm/year. ERS-1 data is troublesome and when ignoring this satellite the SLA trend becomes 2.22 mm/year with a 95% confidence interval within 1.67–2.54 mm/year. Evaluating the SLA trends in 5 year intervals show a clear steepening of the SLA trend around 2004. The sea level anomaly record is validated against tide gauges and show good results. Additionally, the time series is split and evaluated in space and time.
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12
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Joughin I, Smith BE, Howat I. Greenland Ice Mapping Project: Ice Flow Velocity Variation at sub-monthly to decadal time scales. THE CRYOSPHERE 2018; 12:2211-2227. [PMID: 31007854 PMCID: PMC6469699 DOI: 10.5194/tc-12-2211-2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
We describe several new ice velocity maps produced by the Greenland Ice Mapping Project (GIMP) using Landsat 8 and Copernicus Sentinel 1A/B data. We then focus on several sites where we analyse these data in conjunction with earlier data from this project, which extend back to the year 2000. At Jakobshavn Isbrae and Koge Bugt, we find good agreement when comparing results from different sensors. In a change from recent behaviour, Jakobshavn Isbrae began slowing substantially in 2017, with a mid-summer peak that was even slower than some previous winter minimums. Over the last decade, we identify two major slowdown events at Koge Bugt that coincide with short-term advances of the terminus. We also examined populations of glaciers in northwest and southwest Greenland to produce a record of speedup since 2000. Collectively these glaciers continue to speed up, but there are regional differences in the timing of periods of peak speedup. In addition, we computed trends in winter flow speed for much of the southwest margin of the ice sheet and find little in the way of statistically significant change over the period covered by our data. Finally, although consistency of the data generally is good through time and across sensors, our analysis indicates substantial differences can arise in regions with high strain rates (e.g., shear margins) where sensor resolution can become a factor. For applications such as constraining model inversions, users should factor in the impact that the data's resolution has on their results.
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Affiliation(s)
- Ian Joughin
- Polar Science Center, Applied Physics Lab, University of Washington, 1013 NE 40th St., Seattle, WA 98105-6698, USA
| | - Ben E Smith
- Polar Science Center, Applied Physics Lab, University of Washington, 1013 NE 40th St., Seattle, WA 98105-6698, USA
| | - Ian Howat
- Byrd Polar and Climate Research Center, Ohio State University, 1090 Carmack Road, Columbus, OH 43210, USA
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13
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Millan R, Rignot E, Mouginot J, Wood M, Bjørk AA, Morlighem M. Vulnerability of Southeast Greenland Glaciers to Warm Atlantic Water From Operation IceBridge and Ocean Melting Greenland Data. GEOPHYSICAL RESEARCH LETTERS 2018; 45:2688-2696. [PMID: 29937604 PMCID: PMC5993238 DOI: 10.1002/2017gl076561] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 02/14/2018] [Accepted: 02/18/2018] [Indexed: 05/02/2023]
Abstract
We employ National Aeronautics and Space Administration (NASA)'s Operation IceBridge high-resolution airborne gravity from 2016, NASA's Ocean Melting Greenland bathymetry from 2015, ice thickness from Operation IceBridge from 2010 to 2015, and BedMachine v3 to analyze 20 major southeast Greenland glaciers. The results reveal glacial fjords several hundreds of meters deeper than previously thought; the full extent of the marine-based portions of the glaciers; deep troughs enabling warm, salty Atlantic Water (AW) to reach the glacier fronts and melt them from below; and few shallow sills that limit the access of AW. The new oceanographic and topographic data help to fully resolve the complex pattern of historical ice front positions from the 1930s to 2017: glaciers exposed to AW and resting on retrograde beds have retreated rapidly, while glaciers perched on shallow sills or standing in colder waters or with major sills in the fjords have remained stable.
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Affiliation(s)
- R. Millan
- Department Earth System ScienceUniversity of California IrvineIrvineCAUSA
| | - E. Rignot
- Department Earth System ScienceUniversity of California IrvineIrvineCAUSA
- Jet Propulsion LaboratoryCaltechPasadenaCAUSA
| | - J. Mouginot
- Department Earth System ScienceUniversity of California IrvineIrvineCAUSA
| | - M. Wood
- Department Earth System ScienceUniversity of California IrvineIrvineCAUSA
| | - A. A. Bjørk
- Centre for GeoGenetics, Natural History Museum of DenmarkUniversity of CopenhagenCopenhagenDenmark
| | - M. Morlighem
- Department Earth System ScienceUniversity of California IrvineIrvineCAUSA
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14
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Bamber JL, Tedstone AJ, King MD, Howat IM, Enderlin EM, van den Broeke MR, Noel B. Land Ice Freshwater Budget of the Arctic and North Atlantic Oceans: 1. Data, Methods, and Results. JOURNAL OF GEOPHYSICAL RESEARCH. OCEANS 2018; 123:1827-1837. [PMID: 29938150 PMCID: PMC5993240 DOI: 10.1002/2017jc013605] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Accepted: 02/15/2018] [Indexed: 06/02/2023]
Abstract
The freshwater budget of the Arctic and sub-polar North Atlantic Oceans has been changing due, primarily, to increased river runoff, declining sea ice and enhanced melting of Arctic land ice. Since the mid-1990s this latter component has experienced a pronounced increase. We use a combination of satellite observations of glacier flow speed and regional climate modeling to reconstruct the land ice freshwater flux from the Greenland ice sheet and Arctic glaciers and ice caps for the period 1958-2016. The cumulative freshwater flux anomaly exceeded 6,300 ± 316 km3 by 2016. This is roughly twice the estimate of a previous analysis that did not include glaciers and ice caps outside of Greenland and which extended only to 2010. From 2010 onward, the total freshwater flux is about 1,300 km3/yr, equivalent to 0.04 Sv, which is roughly 40% of the estimated total runoff to the Arctic for the same time period. Not all of this flux will reach areas of deep convection or Arctic and Sub-Arctic seas. We note, however, that the largest freshwater flux anomalies, grouped by ocean basin, are located in Baffin Bay and Davis Strait. The land ice freshwater flux displays a strong seasonal cycle with summer time values typically around five times larger than the annual mean. This will be important for understanding the impact of these fluxes on fjord circulation, stratification, and the biogeochemistry of, and nutrient delivery to, coastal waters.
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Affiliation(s)
- J. L. Bamber
- School of Geographical SciencesUniversity of BristolBristolUK
| | - A. J. Tedstone
- School of Geographical SciencesUniversity of BristolBristolUK
| | - M. D. King
- Byrd Polar Research CenterOhio State UniversityColumbusOHUSA
| | - I. M. Howat
- Byrd Polar Research CenterOhio State UniversityColumbusOHUSA
| | - E. M. Enderlin
- School of Earth and Climate SciencesUniversity of MaineOronoMEUSA
| | - M. R. van den Broeke
- Institute for Marine and Atmospheric ResearchUtrecht UniversityUtrechtNetherlands
| | - B. Noel
- Institute for Marine and Atmospheric ResearchUtrecht UniversityUtrechtNetherlands
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15
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Joughin I, Smith BE, Howat IM. A Complete Map of Greenland Ice Velocity Derived from Satellite Data Collected over 20 Years. THE JOURNAL OF GLACIOLOGY 2018; 64:1-11. [PMID: 31217636 PMCID: PMC6582972 DOI: 10.1017/jog.2017.73] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
While numerous maps of Greenland ice flow velocity exist, most have gaps in coverage and/or accuracy is limited. We processed a large volume of synthetic aperture radar (SAR) and Landsat 8 imagery collected between 1995 and 2015 to produce a nearly complete map of ice flow velocity for Greenland at a far greater accuracy than most prior products. We evaluated the accuracy of this map by comparing it with a variety of measured and estimated velocities. For the slow-moving interior of the ice sheet, where estimates are determined from interferometric phase, the errors are ~2 m a-1 or better. For coastal areas, where estimates are determined entirely from speckle- or feature-tracking methods, errors are 2-3 m a-1, which is in good agreement with the estimated formal errors. Especially for the slow-moving majority of the ice sheet, this map provides an important source of data for numerous types of glaciological studies.
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Affiliation(s)
- Ian Joughin
- Polar Science Center, Applied Physics Lab, University of Washington, 1013 NE 40th Streat, Seattle, WA 98105-6698, USA
| | - Ben E Smith
- Polar Science Center, Applied Physics Lab, University of Washington, 1013 NE 40th Streat, Seattle, WA 98105-6698, USA
| | - Ian M Howat
- Byrd Polar and Climate Research Center, Ohio State University, 1090 Carmack Road, Columbus, OH 43210, USA
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16
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King MD, Howat IM, Jeong S, Noh MJ, Wouters B, Noël B, van den Broeke MR. Seasonal to decadal variability in ice discharge from the Greenland Ice Sheet. THE CRYOSPHERE 2018; 12:3813-3825. [PMID: 31217911 PMCID: PMC6582977 DOI: 10.5194/tc-12-3813-2018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Rapid changes in thickness and velocity have been observed at many marine-terminating glaciers in Greenland, impacting the volume of ice they export, or discharge, from the ice sheet. While annual estimates of ice-sheet wide discharge have been previously derived, higher-resolution records are required to fully constrain the temporal response of these glaciers to various climatic and mechanical drivers that vary in sub-annual scales. Here we sample outlet glaciers wider than 1 km (N = 230) to derive the first continuous, ice-sheet wide record of total ice sheet discharge for the 2000-2016 period, resolving a seasonal variability of 6 %. The amplitude of seasonality varies spatially across the ice sheet from 5 % in the southeastern region to 9 % in the northwest region. We analyze seasonal to annual variability in the discharge time series with respect to both modelled meltwater runoff, obtained from RACMO2.3p2, and glacier front position changes over the same period. We find that year-to-year changes in total ice sheet discharge are related to annual front changes (r 2 = 0.59, p = 10-4) and that the annual magnitude of discharge is closely related to cumulative front position changes (r 2 = 0.79), which show a net retreat of > 400 km, or an average retreat of > 2 km at each surveyed glacier. Neither maximum seasonal runoff or annual runoff totals are correlated to annual discharge, which suggests that larger annual quantities of runoff do not relate to increased annual discharge. Discharge and runoff, however, follow similar patterns of seasonal variability with near-coincident periods of acceleration and seasonal maxima. These results suggest that changes in glacier front position drive secular trends in discharge, whereas the impact of runoff is likely limited to the summer months when observed seasonal variations are substantially controlled by the timing of meltwater input.
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Affiliation(s)
- Michalea D. King
- Byrd Polar and Climate Research Center, Columbus, USA
- School of Earth Sciences, Ohio State University, Columbus, USA
| | - Ian M. Howat
- Byrd Polar and Climate Research Center, Columbus, USA
- School of Earth Sciences, Ohio State University, Columbus, USA
| | - Seongsu Jeong
- Department of Earth System Science, University of California, Irvine
| | - Myoung J. Noh
- Byrd Polar and Climate Research Center, Columbus, USA
| | - Bert Wouters
- Institute for Marine and Atmospheric research Utrecht, Utrecht University, Utrecht, Netherlands
- Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, Netherlands
| | - Brice Noël
- Institute for Marine and Atmospheric research Utrecht, Utrecht University, Utrecht, Netherlands
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17
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Laidre KL, Moon T, Hauser DDW, McGovern R, Heide-Jørgensen MP, Dietz R, Hudson B. Use of glacial fronts by narwhals (Monodon monoceros) in West Greenland. Biol Lett 2017; 12:rsbl.2016.0457. [PMID: 27784729 DOI: 10.1098/rsbl.2016.0457] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2016] [Accepted: 10/06/2016] [Indexed: 11/12/2022] Open
Abstract
Glacial fronts are important summer habitat for narwhals (Monodon monoceros); however, no studies have quantified which glacial properties attract whales. We investigated the importance of glacial habitats using telemetry data from n = 15 whales tagged in September of 1993, 1994, 2006 and 2007 in Melville Bay, West Greenland. For 41 marine-terminating glaciers, we estimated (i) narwhal presence/absence, (ii) number of 24 h periods spent at glaciers and (iii) the fraction of narwhals that visited each glacier (at 5, 7 and 10 km) in autumn. We also compiled data on glacier width, ice thickness, ice velocity, front advance/retreat, area and extent of iceberg discharge, bathymetry, subglacial freshwater run-off and sediment flux. Narwhal use of glacial habitats expanded in the 2000s probably due to reduced summer fast ice and later autumn freeze-up. Using a generalized multivariate framework, glacier ice front thickness (vertical height in the water column) was a significant covariate in all models. A negative relationship with glacier velocity was included in several models and glacier front width was a significant predictor in the 2000s. Results suggest narwhals prefer glaciers with potential for higher ambient freshwater melt over glaciers with silt-laden discharge. This may represent a preference for summer freshwater habitat, similar to other Arctic monodontids.
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Affiliation(s)
- Kristin L Laidre
- Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA, USA
| | - Twila Moon
- Geographical Sciences and Bristol Glaciology Centre, University of Bristol, Bristol, UK
| | - Donna D W Hauser
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USA
| | - Richard McGovern
- Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA, USA
| | | | - Rune Dietz
- Department of Bioscience, Arctic Research Centre, Aarhus University, Roskilde, Denmark
| | - Ben Hudson
- Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA, USA
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18
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Drift-dependent changes in iceberg size-frequency distributions. Sci Rep 2017; 7:15991. [PMID: 29167443 PMCID: PMC5700179 DOI: 10.1038/s41598-017-14863-2] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 10/11/2017] [Indexed: 11/11/2022] Open
Abstract
Although the size-frequency distributions of icebergs can provide insight into how they disintegrate, our understanding of this process is incomplete. Fundamentally, there is a discrepancy between iceberg power-law size-frequency distributions observed at glacial calving fronts and lognormal size-frequency distributions observed globally within open waters that remains unexplained. Here we use passive seismic monitoring to examine mechanisms of iceberg disintegration as a function of drift. Our results indicate that the shift in the size-frequency distribution of iceberg sizes observed is a product of fracture-driven iceberg disintegration and dimensional reductions through melting. We suggest that changes in the characteristic size-frequency scaling of icebergs can be explained by the emergence of a dominant set of driving processes of iceberg degradation towards the open ocean. Consequently, the size-frequency distribution required to model iceberg distributions accurately must vary according to distance from the calving front.
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19
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Dyke LM, Andresen CS, Seidenkrantz MS, Hughes ALC, Hiemstra JF, Murray T, Bjørk AA, Sutherland DA, Vermassen F. Minimal Holocene retreat of large tidewater glaciers in Køge Bugt, southeast Greenland. Sci Rep 2017; 7:12330. [PMID: 28951548 PMCID: PMC5615072 DOI: 10.1038/s41598-017-12018-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 09/01/2017] [Indexed: 11/09/2022] Open
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.
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Affiliation(s)
- Laurence M Dyke
- Geological Survey of Denmark and Greenland, Department of Glaciology and Climate, Øster Voldgade 10, DK-1350, København K, Denmark.
| | - Camilla S Andresen
- Geological Survey of Denmark and Greenland, Department of Glaciology and Climate, Øster Voldgade 10, DK-1350, København K, Denmark
| | - Marit-Solveig Seidenkrantz
- Centre for Past Climate Studies, Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000, Aarhus C, Denmark
| | - Anna L C Hughes
- Department of Earth Science, University of Bergen and Bjerknes Centre for Climate Research, Allégaten 41, N-5007, Bergen, Norway
| | - John F Hiemstra
- Glaciology Group, Swansea University, Singleton Park, Swansea, SA2 8PP, UK
| | - Tavi Murray
- Glaciology Group, Swansea University, Singleton Park, Swansea, SA2 8PP, UK
| | - Anders A Bjørk
- Centre for GeoGenetics, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, DK-1350, København K, Denmark
| | - David A Sutherland
- Department of Geological Sciences, 1272 University of Oregon, Eugene, OR, 97403-1272, USA
| | - Flor Vermassen
- Geological Survey of Denmark and Greenland, Department of Glaciology and Climate, Øster Voldgade 10, DK-1350, København K, Denmark
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20
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Bendtsen J, Mortensen J, Lennert K, K Ehn J, Boone W, Galindo V, Hu YB, Dmitrenko IA, Kirillov SA, Kjeldsen KK, Kristoffersen Y, G Barber D, Rysgaard S. Sea ice breakup and marine melt of a retreating tidewater outlet glacier in northeast Greenland (81°N). Sci Rep 2017; 7:4941. [PMID: 28694490 PMCID: PMC5503942 DOI: 10.1038/s41598-017-05089-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 05/24/2017] [Indexed: 11/11/2022] Open
Abstract
Rising temperatures in the Arctic cause accelerated mass loss from the Greenland Ice Sheet and reduced sea ice cover. Tidewater outlet glaciers represent direct connections between glaciers and the ocean where melt rates at the ice-ocean interface are influenced by ocean temperature and circulation. However, few measurements exist near outlet glaciers from the northern coast towards the Arctic Ocean that has remained nearly permanently ice covered. Here we present hydrographic measurements along the terminus of a major retreating tidewater outlet glacier from Flade Isblink Ice Cap. We show that the region is characterized by a relatively large change of the seasonal freshwater content, corresponding to ~2 m of freshwater, and that solar heating during the short open water period results in surface layer temperatures above 1 °C. Observations of temperature and salinity supported that the outlet glacier is a floating ice shelf with near-glacial subsurface temperatures at the freezing point. Melting from the surface layer significantly influenced the ice foot morphology of the glacier terminus. Hence, melting of the tidewater outlet glacier was found to be critically dependent on the retreat of sea ice adjacent to the terminus and the duration of open water.
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Affiliation(s)
- Jørgen Bendtsen
- Arctic Research Centre, Aarhus University, 8000, Aarhus, Denmark. .,ClimateLab, Symbion Science Park, Fruebjergvej 3, 2100, Copenhagen O, Denmark.
| | - John Mortensen
- Greenland Climate Research Centre, Greenland Institute of Natural Resources, PO Box 570, 3900, Nuuk, Greenland
| | - Kunuk Lennert
- Greenland Climate Research Centre, Greenland Institute of Natural Resources, PO Box 570, 3900, Nuuk, Greenland
| | - Jens K Ehn
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Wieter Boone
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Virginie Galindo
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Yu-Bin Hu
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Igor A Dmitrenko
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Sergei A Kirillov
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Kristian K Kjeldsen
- Department of Earth Sciences, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada.,Centre for GeoGenetics, Natural History Museum, University of Copenhagen, Øster Voldgade 5-7, 1350, Copenhagen K, Denmark
| | | | - David G Barber
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Søren Rysgaard
- Arctic Research Centre, Aarhus University, 8000, Aarhus, Denmark.,Greenland Climate Research Centre, Greenland Institute of Natural Resources, PO Box 570, 3900, Nuuk, Greenland.,Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
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21
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Bendtsen J, Mortensen J, Lennert K, K Ehn J, Boone W, Galindo V, Hu YB, Dmitrenko IA, Kirillov SA, Kjeldsen KK, Kristoffersen Y, G Barber D, Rysgaard S. Sea ice breakup and marine melt of a retreating tidewater outlet glacier in northeast Greenland (81°N). Sci Rep 2017; 7:4941. [PMID: 28694490 DOI: 10.1038/s41598] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 05/24/2017] [Indexed: 05/25/2023] Open
Abstract
Rising temperatures in the Arctic cause accelerated mass loss from the Greenland Ice Sheet and reduced sea ice cover. Tidewater outlet glaciers represent direct connections between glaciers and the ocean where melt rates at the ice-ocean interface are influenced by ocean temperature and circulation. However, few measurements exist near outlet glaciers from the northern coast towards the Arctic Ocean that has remained nearly permanently ice covered. Here we present hydrographic measurements along the terminus of a major retreating tidewater outlet glacier from Flade Isblink Ice Cap. We show that the region is characterized by a relatively large change of the seasonal freshwater content, corresponding to ~2 m of freshwater, and that solar heating during the short open water period results in surface layer temperatures above 1 °C. Observations of temperature and salinity supported that the outlet glacier is a floating ice shelf with near-glacial subsurface temperatures at the freezing point. Melting from the surface layer significantly influenced the ice foot morphology of the glacier terminus. Hence, melting of the tidewater outlet glacier was found to be critically dependent on the retreat of sea ice adjacent to the terminus and the duration of open water.
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Affiliation(s)
- Jørgen Bendtsen
- Arctic Research Centre, Aarhus University, 8000, Aarhus, Denmark.
- ClimateLab, Symbion Science Park, Fruebjergvej 3, 2100, Copenhagen O, Denmark.
| | - John Mortensen
- Greenland Climate Research Centre, Greenland Institute of Natural Resources, PO Box 570, 3900, Nuuk, Greenland
| | - Kunuk Lennert
- Greenland Climate Research Centre, Greenland Institute of Natural Resources, PO Box 570, 3900, Nuuk, Greenland
| | - Jens K Ehn
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Wieter Boone
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Virginie Galindo
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Yu-Bin Hu
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Igor A Dmitrenko
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Sergei A Kirillov
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Kristian K Kjeldsen
- Department of Earth Sciences, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada
- Centre for GeoGenetics, Natural History Museum, University of Copenhagen, Øster Voldgade 5-7, 1350, Copenhagen K, Denmark
| | | | - David G Barber
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
| | - Søren Rysgaard
- Arctic Research Centre, Aarhus University, 8000, Aarhus, Denmark
- Greenland Climate Research Centre, Greenland Institute of Natural Resources, PO Box 570, 3900, Nuuk, Greenland
- Centre for Earth Observation Science, CHR Faculty of Environment, Earth, and Resources, University of Manitoba, 499 Wallace Building, Winnipeg, MB R3T 2N2, Canada
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22
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Price SF, Hoffman MJ, Bonin JA, Howat IM, Neumann T, Saba J, Tezaur I, Guerber J, Chambers DP, Evans KJ, Kennedy JH, Lenaerts J, Lipscomb WH, Perego M, Salinger AG, Tuminaro RS, van den Broeke MR, Nowicki SMJ. An ice sheet model validation framework for the Greenland ice sheet. GEOSCIENTIFIC MODEL DEVELOPMENT 2017; 10:255-270. [PMID: 29697704 PMCID: PMC5911937 DOI: 10.5194/gmd-10-255-2017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
We propose a new ice sheet model validation framework - the Cryospheric Model Comparison Tool (CmCt) - that takes advantage of ice sheet altimetry and gravimetry observations collected over the past several decades and is applied here to modeling of the Greenland ice sheet. We use realistic simulations performed with the Community Ice Sheet Model (CISM) along with two idealized, non-dynamic models to demonstrate the framework and its use. Dynamic simulations with CISM are forced from 1991 to 2013 using combinations of reanalysis-based surface mass balance and observations of outlet glacier flux change. We propose and demonstrate qualitative and quantitative metrics for use in evaluating the different model simulations against the observations. We find that the altimetry observations used here are largely ambiguous in terms of their ability to distinguish one simulation from another. Based on basin- and whole-ice-sheet scale metrics, we find that simulations using both idealized conceptual models and dynamic, numerical models provide an equally reasonable representation of the ice sheet surface (mean elevation differences of <1 m). This is likely due to their short period of record, biases inherent to digital elevation models used for model initial conditions, and biases resulting from firn dynamics, which are not explicitly accounted for in the models or observations. On the other hand, we find that the gravimetry observations used here are able to unambiguously distinguish between simulations of varying complexity, and along with the CmCt, can provide a quantitative score for assessing a particular model and/or simulation. The new framework demonstrates that our proposed metrics can distinguish relatively better from relatively worse simulations and that dynamic ice sheet models, when appropriately initialized and forced with the right boundary conditions, demonstrate predictive skill with respect to observed dynamic changes occurring on Greenland over the past few decades. An extensible design will allow for continued use of the CmCt as future altimetry, gravimetry, and other remotely sensed data become available for use in ice sheet model validation.
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Affiliation(s)
- Stephen F Price
- Los Alamos National Laboratory, MS B216, Los Alamos, NM 87545, USA
| | | | | | - Ian M Howat
- The Ohio State University, Columbus, OH 43210, USA
| | - Thomas Neumann
- NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
| | - Jack Saba
- NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- Science, Systems, and Applications, Inc., Lanham, Md 20706, USA
| | - Irina Tezaur
- Sandia National Laboratories, P.O. Box 969, MS 9159, Livermore, CA 94551, USA
| | - Jeffrey Guerber
- NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- Sigma Space Corp., Lanham, MD 20706, USA
| | - Don P Chambers
- University of South Florida, St. Petersburg, FL 33701, USA
| | | | - Joseph H Kennedy
- Oak Ridge National Laboratory, MS 6301, Oak Ridge, TN 37831, USA
| | | | | | - Mauro Perego
- Sandia National Laboratories, P.O. Box 5800, MS 1320, Albuquerque, NM 87185, USA
| | - Andrew G Salinger
- Sandia National Laboratories, P.O. Box 5800, MS 1320, Albuquerque, NM 87185, USA
| | - Raymond S Tuminaro
- Sandia National Laboratories, P.O. Box 5800, MS 1320, Albuquerque, NM 87185, USA
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23
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MacGregor JA, Colgan WT, Fahnestock MA, Morlighem M, Catania GA, Paden JD, Gogineni SP. Holocene deceleration of the Greenland Ice Sheet. Science 2016; 351:590-3. [PMID: 26912699 DOI: 10.1126/science.aab1702] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Accepted: 01/07/2016] [Indexed: 11/02/2022]
Abstract
Recent peripheral thinning of the Greenland Ice Sheet is partly offset by interior thickening and is overprinted on its poorly constrained Holocene evolution. On the basis of the ice sheet's radiostratigraphy, ice flow in its interior is slower now than the average speed over the past nine millennia. Generally higher Holocene accumulation rates relative to modern estimates can only partially explain this millennial-scale deceleration. The ice sheet's dynamic response to the decreasing proportion of softer ice from the last glacial period and the deglacial collapse of the ice bridge across Nares Strait also contributed to this pattern. Thus, recent interior thickening of the Greenland Ice Sheet is partly an ongoing dynamic response to the last deglaciation that is large enough to affect interpretation of its mass balance from altimetry.
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Affiliation(s)
- Joseph A MacGregor
- Institute for Geophysics, The University of Texas at Austin, Austin, TX 78758, USA.
| | - William T Colgan
- Geological Survey of Denmark and Greenland, Copenhagen DK-1350, Denmark
| | - Mark A Fahnestock
- Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775, USA
| | - Mathieu Morlighem
- Department of Earth System Science, University of California, Irvine, Irvine, CA 92697, USA
| | - Ginny A Catania
- Institute for Geophysics, The University of Texas at Austin, Austin, TX 78758, USA. Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, USA
| | - John D Paden
- Center for Remote Sensing of Ice Sheets, The University of Kansas, Lawrence, KS 66045, USA
| | - S Prasad Gogineni
- Center for Remote Sensing of Ice Sheets, The University of Kansas, Lawrence, KS 66045, USA
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24
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Joughin I, Smith BE, Howat IM, Moon T, Scambos TA. A SAR Record of Early 21 st Century Change in Greenland. THE JOURNAL OF GLACIOLOGY 2016; 62:62-71. [PMID: 31217635 PMCID: PMC6582974 DOI: 10.1017/jog.2016.10] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Glaciers in Greenland are changing rapidly. To better understand these changes, we have produced a series of seven synthetic-aperture-radar (SAR) backscatter mosaics for seven winters during the period from 2000 to 2013. Six of the mosaics were created using RADARSAT Fine-Beam data and the seventh used ALOS PALSAR Fine-Beam Single-Polarization data. The RADARSAT mosaics are radiometrically calibrated and capture changes in the backscatter coefficient related to melt and other events, particularly the strong melting in the summer of 2012. Comparison of features in the ascending-orbit ALOS mosaic and the descending-orbit RADARSAT mosaics indicate that in areas of smooth to moderate topography their locations are consistent to within a few 10s of meters. The locations of features identifiable in the RADARAT mosaics, which were collected with the same imaging parameters, generally agree to within better than the 20-m posting of the data. With such geometric accuracy, these data establish a record of change in Greenland for the early part of the 21st Century, thus providing a baseline that can be compared with new radar and optical data sets.
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Affiliation(s)
- Ian Joughin
- Polar Science Center, Applied Physics Lab, University of Washington, 1013 NE 40th Streat, Seattle, WA 98105-6698, USA
| | - Ben E Smith
- Polar Science Center, Applied Physics Lab, University of Washington, 1013 NE 40th Streat, Seattle, WA 98105-6698, USA
| | - Ian M Howat
- Byrd Polar and Climate Research Center, Ohio State University, 1090 Carmack Road, Columbus, OH 43210, USA
| | - Twila Moon
- Department of Geological Sciences, University of Oregon, 1272 University of Oregon, Eugene, OR 97403-1272, USA
| | - Ted A Scambos
- National Snow and Ice Data Center, University of Colorado, 1540 30 Street, Boulder, CO 80309-0449, USA
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25
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Abstract
The Greenland Ice Sheet is losing mass at an accelerating rate due to increased surface melt and flow acceleration in outlet glaciers. Quantifying future dynamic contributions to sea level requires accurate portrayal of outlet glaciers in ice sheet simulations, but to date poor knowledge of subglacial topography and limited model resolution have prevented reproduction of complex spatial patterns of outlet flow. Here we combine a high-resolution ice-sheet model coupled to uniformly applied models of subglacial hydrology and basal sliding, and a new subglacial topography data set to simulate the flow of the Greenland Ice Sheet. Flow patterns of many outlet glaciers are well captured, illustrating fundamental commonalities in outlet glacier flow and highlighting the importance of efforts to map subglacial topography. Success in reproducing present day flow patterns shows the potential for prognostic modelling of ice sheets without the need for spatially varying parameters with uncertain time evolution. Quantifying Greenland's future contribution to sea level requires accurate portrayal of its outlet glaciers in ice sheet simulations. Here, the authors show that outlet glacier flow can be captured if ice thickness is well constrained and vertical shearing as well as membrane stresses are included in the model.
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26
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Bradley JA, Anesio AM, Arndt S. Bridging the divide: a model-data approach to Polar and Alpine microbiology. FEMS Microbiol Ecol 2016; 92:fiw015. [PMID: 26832206 PMCID: PMC4765003 DOI: 10.1093/femsec/fiw015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/05/2016] [Indexed: 11/13/2022] Open
Abstract
Advances in microbial ecology in the cryosphere continue to be driven by empirical approaches including field sampling and laboratory-based analyses. Although mathematical models are commonly used to investigate the physical dynamics of Polar and Alpine regions, they are rarely applied in microbial studies. Yet integrating modelling approaches with ongoing observational and laboratory-based work is ideally suited to Polar and Alpine microbial ecosystems given their harsh environmental and biogeochemical characteristics, simple trophic structures, distinct seasonality, often difficult accessibility, geographical expansiveness and susceptibility to accelerated climate changes. In this opinion paper, we explain how mathematical modelling ideally complements field and laboratory-based analyses. We thus argue that mathematical modelling is a powerful tool for the investigation of these extreme environments and that fully integrated, interdisciplinary model-data approaches could help the Polar and Alpine microbiology community address some of the great research challenges of the 21st century (e.g. assessing global significance and response to climate change). However, a better integration of field and laboratory work with model design and calibration/validation, as well as a stronger focus on quantitative information is required to advance models that can be used to make predictions and upscale processes and fluxes beyond what can be captured by observations alone.
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Affiliation(s)
- James A Bradley
- Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, BS8 1SS, UK BRIDGE, School of Geographical Sciences, University of Bristol, BS8 1SS, UK
| | - Alexandre M Anesio
- Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol, BS8 1SS, UK
| | - Sandra Arndt
- BRIDGE, School of Geographical Sciences, University of Bristol, BS8 1SS, UK
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27
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The Sentinel-1 Mission: New Opportunities for Ice Sheet Observations. REMOTE SENSING 2015. [DOI: 10.3390/rs70709371] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Khan SA, Aschwanden A, Bjørk AA, Wahr J, Kjeldsen KK, Kjær KH. Greenland ice sheet mass balance: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2015; 78:046801. [PMID: 25811969 DOI: 10.1088/0034-4885/78/4/046801] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Over the past quarter of a century the Arctic has warmed more than any other region on Earth, causing a profound impact on the Greenland ice sheet (GrIS) and its contribution to the rise in global sea level. The loss of ice can be partitioned into processes related to surface mass balance and to ice discharge, which are forced by internal or external (atmospheric/oceanic/basal) fluctuations. Regardless of the measurement method, observations over the last two decades show an increase in ice loss rate, associated with speeding up of glaciers and enhanced melting. However, both ice discharge and melt-induced mass losses exhibit rapid short-term fluctuations that, when extrapolated into the future, could yield erroneous long-term trends. In this paper we review the GrIS mass loss over more than a century by combining satellite altimetry, airborne altimetry, interferometry, aerial photographs and gravimetry data sets together with modelling studies. We revisit the mass loss of different sectors and show that they manifest quite different sensitivities to atmospheric and oceanic forcing. In addition, we discuss recent progress in constructing coupled ice-ocean-atmosphere models required to project realistic future sea-level changes.
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Affiliation(s)
- Shfaqat A Khan
- DTU Space-National Space Institute, Technical University of Denmark, Department of Geodesy, Kgs. Lyngby, Denmark
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MacGregor JA, Fahnestock MA, Catania GA, Paden JD, Prasad Gogineni S, Young SK, Rybarski SC, Mabrey AN, Wagman BM, Morlighem M. Radiostratigraphy and age structure of the Greenland Ice Sheet. JOURNAL OF GEOPHYSICAL RESEARCH. EARTH SURFACE 2015; 120:212-241. [PMID: 26213664 PMCID: PMC4508962 DOI: 10.1002/2014jf003215] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Accepted: 01/14/2015] [Indexed: 05/25/2023]
Abstract
UNLABELLED Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet. KEY POINTS Phase information predicts reflection slope and simplifies reflection tracingReflections can be dated away from ice cores using a simple ice flow modelRadiostratigraphy is often disrupted near the onset of fast ice flow.
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Affiliation(s)
- Joseph A MacGregor
- Institute for Geophysics, The University of Texas at Austin Austin, Texas, USA
| | - Mark A Fahnestock
- Geophysical Institute, University of Alaska Fairbanks Fairbanks, Alaska, USA
| | - Ginny A Catania
- Institute for Geophysics, The University of Texas at Austin Austin, Texas, USA ; Department of Geological Sciences, University of Texas at Austin Austin, Texas, USA
| | - John D Paden
- Center for Remote Sensing of Ice Sheets, The University of Kansas Lawrence, Kansas, USA
| | - S Prasad Gogineni
- Center for Remote Sensing of Ice Sheets, The University of Kansas Lawrence, Kansas, USA
| | - S Keith Young
- Institute for Geophysics, The University of Texas at Austin Austin, Texas, USA ; Department of Geological Sciences, University of Texas at Austin Austin, Texas, USA
| | - Susan C Rybarski
- Institute for Geophysics, The University of Texas at Austin Austin, Texas, USA ; Department of Geological Sciences, University of Texas at Austin Austin, Texas, USA ; Now at Division of Hydrologic Sciences, Desert Research Institute Reno, Nevada, USA
| | - Alexandria N Mabrey
- Institute for Geophysics, The University of Texas at Austin Austin, Texas, USA ; Department of Geological Sciences, University of Texas at Austin Austin, Texas, USA
| | - Benjamin M Wagman
- Institute for Geophysics, The University of Texas at Austin Austin, Texas, USA ; Department of Geological Sciences, University of Texas at Austin Austin, Texas, USA
| | - Mathieu Morlighem
- Department of Earth System Science, University of California Irvine, California, USA
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Abstract
We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ⋅ y(-1), equivalent to 0.68 mm ⋅ y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers.
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Moon T, Joughin I, Smith B, van den Broeke MR, van de Berg WJ, Noël B, Usher M. Distinct patterns of seasonal Greenland glacier velocity. GEOPHYSICAL RESEARCH LETTERS 2014; 41:7209-7216. [PMID: 25821275 PMCID: PMC4373171 DOI: 10.1002/2014gl061836] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Accepted: 10/14/2014] [Indexed: 05/11/2023]
Abstract
UNLABELLED Predicting Greenland Ice Sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms. We present a 5 year record of seasonal velocity measurements for 55 marine-terminating glaciers distributed around the ice sheet margin, along with ice-front position and runoff data sets for each glacier. Among glaciers with substantial speed variations, we find three distinct seasonal velocity patterns. One pattern indicates relatively high glacier sensitivity to ice-front position. The other two patterns are more prevalent and appear to be meltwater controlled. These patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient, distributed hydrologic networks to efficient, channelized drainage, while others do not. The difference may be determined by meltwater availability, which in some regions may be influenced by perennial firn aquifers. Our results highlight the need to understand subglacial meltwater availability on an ice sheet-wide scale to predict future dynamic changes. KEY POINTS First multi-region seasonal velocity measurements show regional differencesSeasonal velocity fluctuations on most glaciers appear meltwater controlledSeasonal development of efficient subglacial drainage geographically divided.
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Affiliation(s)
- Twila Moon
- Earth and Space Sciences, University of Washington Seattle, Washington, USA ; Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA ; National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado-Boulder Boulder, Colorado, USA
| | - Ian Joughin
- Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA
| | - Ben Smith
- Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA
| | | | | | - Brice Noël
- Institute for Marine and Atmospheric Research, Utrecht University Utrecht, Netherlands
| | - Mika Usher
- Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA
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32
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Straneo F, Heimbach P. North Atlantic warming and the retreat of Greenland's outlet glaciers. Nature 2013; 504:36-43. [PMID: 24305146 DOI: 10.1038/nature12854] [Citation(s) in RCA: 283] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Accepted: 10/25/2013] [Indexed: 11/09/2022]
Abstract
Mass loss from the Greenland ice sheet quadrupled over the past two decades, contributing a quarter of the observed global sea-level rise. Increased submarine melting is thought to have triggered the retreat of Greenland's outlet glaciers, which is partly responsible for the ice loss. However, the chain of events and physical processes remain elusive. Recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes, multidecadal natural ocean variability and a long-term increase in the North Atlantic's upper ocean heat content since the 1950s all contributed to a warming of the subpolar North Atlantic. This led, in conjunction with increased runoff, to enhanced submarine glacier melting. Future climate projections raise the potential for continued increases in warming and ice-mass loss, with implications for sea level and climate.
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Affiliation(s)
- Fiammetta Straneo
- Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
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33
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Frezzotti M, Orombelli G. Glaciers and ice sheets: current status and trends. RENDICONTI LINCEI 2013. [DOI: 10.1007/s12210-013-0255-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Hanna E, Navarro FJ, Pattyn F, Domingues CM, Fettweis X, Ivins ER, Nicholls RJ, Ritz C, Smith B, Tulaczyk S, Whitehouse PL, Zwally HJ. Ice-sheet mass balance and climate change. Nature 2013; 498:51-9. [PMID: 23739423 DOI: 10.1038/nature12238] [Citation(s) in RCA: 221] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Accepted: 04/26/2013] [Indexed: 11/09/2022]
Abstract
Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain.
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Affiliation(s)
- Edward Hanna
- Department of Geography, University of Sheffield, Sheffield S10 2TN, UK.
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35
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Nick FM, Vieli A, Andersen ML, Joughin I, Payne A, Edwards TL, Pattyn F, van de Wal RSW. Future sea-level rise from Greenland's main outlet glaciers in a warming climate. Nature 2013; 497:235-8. [PMID: 23657350 DOI: 10.1038/nature12068] [Citation(s) in RCA: 221] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Accepted: 03/12/2013] [Indexed: 11/09/2022]
Abstract
Over the past decade, ice loss from the Greenland Ice Sheet increased as a result of both increased surface melting and ice discharge to the ocean. The latter is controlled by the acceleration of ice flow and subsequent thinning of fast-flowing marine-terminating outlet glaciers. Quantifying the future dynamic contribution of such glaciers to sea-level rise (SLR) remains a major challenge because outlet glacier dynamics are poorly understood. Here we present a glacier flow model that includes a fully dynamic treatment of marine termini. We use this model to simulate behaviour of four major marine-terminating outlet glaciers, which collectively drain about 22 per cent of the Greenland Ice Sheet. Using atmospheric and oceanic forcing from a mid-range future warming scenario that predicts warming by 2.8 degrees Celsius by 2100, we project a contribution of 19 to 30 millimetres to SLR from these glaciers by 2200. This contribution is largely (80 per cent) dynamic in origin and is caused by several episodic retreats past overdeepenings in outlet glacier troughs. After initial increases, however, dynamic losses from these four outlets remain relatively constant and contribute to SLR individually at rates of about 0.01 to 0.06 millimetres per year. These rates correspond to ice fluxes that are less than twice those of the late 1990s, well below previous upper bounds. For a more extreme future warming scenario (warming by 4.5 degrees Celsius by 2100), the projected losses increase by more than 50 per cent, producing a cumulative SLR of 29 to 49 millimetres by 2200.
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Affiliation(s)
- Faezeh M Nick
- Laboratoire de Glaciologie, Université Libre de Bruxelles, B-1050 Brussels, Belgium.
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Abstract
The ice sheets of Greenland and Antarctica are losing ice at accelerating rates, much of which is a response to oceanic forcing, especially of the floating ice shelves. Recent observations establish a clear correspondence between the increased delivery of oceanic heat to the ice-sheet margin and increased ice loss. In Antarctica, most of these processes are reasonably well understood but have not been rigorously quantified. In Greenland, an understanding of the processes by which warmer ocean temperatures drive the observed retreat remains elusive. Experiments designed to identify the relevant processes are confounded by the logistical difficulties of instrumenting ice-choked fjords with actively calving glaciers. For both ice sheets, multiple challenges remain before the fully coupled ice-ocean-atmosphere models needed for rigorous sea-level projection are available.
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Affiliation(s)
- Ian Joughin
- Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th, Seattle, WA 98105, USA.
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37
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Shepherd A, Ivins ER, A G, Barletta VR, Bentley MJ, Bettadpur S, Briggs KH, Bromwich DH, Forsberg R, Galin N, Horwath M, Jacobs S, Joughin I, King MA, Lenaerts JTM, Li J, Ligtenberg SRM, Luckman A, Luthcke SB, McMillan M, Meister R, Milne G, Mouginot J, Muir A, Nicolas JP, Paden J, Payne AJ, Pritchard H, Rignot E, Rott H, Sørensen LS, Scambos TA, Scheuchl B, Schrama EJO, Smith B, Sundal AV, van Angelen JH, van de Berg WJ, van den Broeke MR, Vaughan DG, Velicogna I, Wahr J, Whitehouse PL, Wingham DJ, Yi D, Young D, Zwally HJ. A Reconciled Estimate of Ice-Sheet Mass Balance. Science 2012. [DOI: 10.1126/science.1228102] [Citation(s) in RCA: 1100] [Impact Index Per Article: 91.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Andrew Shepherd
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
| | - Erik R. Ivins
- Jet Propulsion Laboratory, M/S 300-233, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
| | - Geruo A
- Department of Physics, University of Colorado, Boulder, CO 80309–0390, USA
| | - Valentina R. Barletta
- Geodynamics Department, Technical University of Denmark, DTU SPACE, National Space Institute, Elektrovej, Building 327, DK-2800 Kgs. Lyngby, Denmark
| | - Mike J. Bentley
- Department of Geography, Durham University, South Road, Durham DH1 3LE, UK
| | - Srinivas Bettadpur
- Center for Space Research, University of Texas at Austin, 3925 West Braker Lane, Suite 200, Austin, TX 78759–5321, USA
| | - Kate H. Briggs
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
| | - David H. Bromwich
- Polar Meteorology Group, Byrd Polar Research Center, and Atmospheric Sciences Program, Department of Geography, The Ohio State University, 1090 Carmack Road, Columbus, OH 43210, USA
| | - René Forsberg
- Geodynamics Department, Technical University of Denmark, DTU SPACE, National Space Institute, Elektrovej, Building 327, DK-2800 Kgs. Lyngby, Denmark
| | - Natalia Galin
- Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, London WC1E 6BT, UK
| | - Martin Horwath
- Institut für Astronomische und Physikalische Geodäsie, Technische Universität München, Arcisstraße 21, 80333 München, Germany
| | - Stan Jacobs
- Lamont-Doherty Earth Observatory (LDEO), 205 Oceanography, 61 Route 9W - Post Office Box 1000, Palisades, NY 10964, USA
| | - Ian Joughin
- Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, WA 98105–6698, USA
| | - Matt A. King
- School of Civil Engineering and Geosciences, Cassie Building, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
- School of Geography and Environmental Studies, University of Tasmania, Hobart 7001, Australia
| | - Jan T. M. Lenaerts
- Utrecht University, Institute for Marine and Atmospheric Research, Princetonplein 5, Utrecht, Netherlands
| | - Jilu Li
- Center for Remote Sensing of Ice Sheets, University of Kansas, Nichols Hall, 2335 Irving Hill Road, Lawrence, KS 66045, USA
| | - Stefan R. M. Ligtenberg
- Utrecht University, Institute for Marine and Atmospheric Research, Princetonplein 5, Utrecht, Netherlands
| | - Adrian Luckman
- Department of Geography, College of Science, Swansea University, Singleton Park, Swansea SA2 8PP, UK
| | - Scott B. Luthcke
- National Aeronautical and Space Administration (NASA) Goddard Space Flight Center, Planetary Geodynamics Laboratory, Greenbelt, MD 20771, USA
| | - Malcolm McMillan
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
| | - Rakia Meister
- Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, London WC1E 6BT, UK
| | - Glenn Milne
- Department of Earth Sciences, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Jeremie Mouginot
- Department of Earth System Science, University of California, 3226 Croul Hall, Irvine, CA 92697–3100, USA
| | - Alan Muir
- Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, London WC1E 6BT, UK
| | - Julien P. Nicolas
- Polar Meteorology Group, Byrd Polar Research Center, and Atmospheric Sciences Program, Department of Geography, The Ohio State University, 1090 Carmack Road, Columbus, OH 43210, USA
| | - John Paden
- Center for Remote Sensing of Ice Sheets, University of Kansas, Nichols Hall, 2335 Irving Hill Road, Lawrence, KS 66045, USA
| | - Antony J. Payne
- School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK
| | - Hamish Pritchard
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - Eric Rignot
- Jet Propulsion Laboratory, M/S 300-233, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
- Department of Earth System Science, University of California, 3226 Croul Hall, Irvine, CA 92697–3100, USA
| | - Helmut Rott
- Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria
| | - Louise Sandberg Sørensen
- Geodynamics Department, Technical University of Denmark, DTU SPACE, National Space Institute, Elektrovej, Building 327, DK-2800 Kgs. Lyngby, Denmark
| | - Ted A. Scambos
- National Snow and Ice Data Center, University of Colorado, Boulder, CO 80309, USA
| | - Bernd Scheuchl
- Department of Earth System Science, University of California, 3226 Croul Hall, Irvine, CA 92697–3100, USA
| | - Ernst J. O. Schrama
- Delft University of Technology, Faculty of Aerospace Engineering, Kluyverweg 1, 2629 HS Delft, Netherlands
| | - Ben Smith
- Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, WA 98105–6698, USA
| | - Aud V. Sundal
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK
| | - Jan H. van Angelen
- Utrecht University, Institute for Marine and Atmospheric Research, Princetonplein 5, Utrecht, Netherlands
| | - Willem J. van de Berg
- Utrecht University, Institute for Marine and Atmospheric Research, Princetonplein 5, Utrecht, Netherlands
| | - Michiel R. van den Broeke
- Utrecht University, Institute for Marine and Atmospheric Research, Princetonplein 5, Utrecht, Netherlands
| | - David G. Vaughan
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - Isabella Velicogna
- Jet Propulsion Laboratory, M/S 300-233, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
- Department of Earth System Science, University of California, 3226 Croul Hall, Irvine, CA 92697–3100, USA
| | - John Wahr
- Department of Physics, University of Colorado, Boulder, CO 80309–0390, USA
| | | | - Duncan J. Wingham
- Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, London WC1E 6BT, UK
| | - Donghui Yi
- SGT Incorporated, NASA Goddard Space Flight Center, Cryospheric Sciences Laboratory, Code 615 Greenbelt, MD 20771, USA
| | - Duncan Young
- Institute for Geophysics, University of Texas, Austin, TX 78759, USA
| | - H. Jay Zwally
- NASA Goddard Space Flight Center, Cryospheric Sciences Laboratory, Code 615 Greenbelt, MD 20771, USA
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Williams CR, Hindmarsh RCA, Arthern RJ. Frequency response of ice streams. Proc Math Phys Eng Sci 2012; 468:3285-3310. [PMID: 23197934 PMCID: PMC3509956 DOI: 10.1098/rspa.2012.0180] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Accepted: 06/01/2012] [Indexed: 11/14/2022] Open
Abstract
Changes at the grounding line of ice streams have consequences for inland ice dynamics and hence sea level. Despite substantial evidence documenting upstream propagation of frontal change, the mechanisms by which these changes are transmitted inland are not well understood. In this vein, the frequency response of an idealized ice stream to periodic forcing in the downstream strain rate is examined for basally and laterally resisted ice streams using a one-dimensional, linearized membrane stress approximation. This reveals two distinct behavioural branches, which we find to correspond to different mechanisms of upstream velocity and thickness propagation, depending on the forcing frequency. At low frequencies (centennial to millennial periods), slope and thickness covary hundreds of kilometres inland, and the shallow-ice approximation is sufficient to explain upstream propagation, which occurs through changes in grounding-line flow and geometry. At high frequencies (decadal to sub-decadal periods), penetration distances are tens of kilometres; while velocity adjusts rapidly to such forcing, thickness varies little and upstream propagation occurs through the direct transmission of membrane stresses. Propagation properties vary significantly between 29 Antarctic ice streams considered. A square-wave function in frontal stress is explored by summing frequency solutions, simulating some aspects of the dynamical response to sudden ice-shelf change.
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Affiliation(s)
- C. Rosie Williams
- British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK
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Joughin I, Smith BE, Howat IM, Floricioiu D, Alley RB, Truffer M, Fahnestock M. Seasonal to decadal scale variations in the surface velocity of Jakobshavn Isbrae, Greenland: Observation and model-based analysis. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011jf002110] [Citation(s) in RCA: 114] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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40
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Affiliation(s)
- Richard B. Alley
- Department of Geosciences, and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA
| | - Ian Joughin
- Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA 98105, USA
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A check on speeding glaciers. Nature 2012. [DOI: 10.1038/485150a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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