Center for Remote Sensing of Ice Sheets (CReSIS) Scholarly Workshttps://hdl.handle.net/1808/222352024-03-28T20:40:59Z2024-03-28T20:40:59ZCrystal orientation fabric anisotropy causes directional hardening of the Northeast Greenland Ice StreamGerber, Tamara AnninaLilien, David A.Rathmann, Nicholas MossorFranke, StevenYoung, Tun JanValero-Delgado, FernandoErshadi, M. RezaDrews, ReinhardZeising, OleHumbert, AngelikaStoll, NicolasWeikusat, IlkaGrinsted, AslakHvidberg, Christine SchøttJansen, DanielaMiller, HeinrichHelm, VeitSteinhage, DanielO’Neill, CharlesPaden, JohnGogineni, Siva PrasadDahl-Jensen, DortheEisen, Olafhttps://hdl.handle.net/1808/343442023-06-14T06:06:46Z2023-05-08T00:00:00ZCrystal orientation fabric anisotropy causes directional hardening of the Northeast Greenland Ice Stream
Gerber, Tamara Annina; Lilien, David A.; Rathmann, Nicholas Mossor; Franke, Steven; Young, Tun Jan; Valero-Delgado, Fernando; Ershadi, M. Reza; Drews, Reinhard; Zeising, Ole; Humbert, Angelika; Stoll, Nicolas; Weikusat, Ilka; Grinsted, Aslak; Hvidberg, Christine Schøtt; Jansen, Daniela; Miller, Heinrich; Helm, Veit; Steinhage, Daniel; O’Neill, Charles; Paden, John; Gogineni, Siva Prasad; Dahl-Jensen, Dorthe; Eisen, Olaf
The dynamic mass loss of ice sheets constitutes one of the biggest uncertainties in projections of ice-sheet evolution. One central, understudied aspect of ice flow is how the bulk orientation of the crystal orientation fabric translates to the mechanical anisotropy of ice. Here we show the spatial distribution of the depth-averaged horizontal anisotropy and corresponding directional flow-enhancement factors covering a large area of the Northeast Greenland Ice Stream onset. Our results are based on airborne and ground-based radar surveys, ice-core observations, and numerical ice-flow modelling. They show a strong spatial variability of the horizontal anisotropy and a rapid crystal reorganisation on the order of hundreds of years coinciding with the ice-stream geometry. Compared to isotropic ice, parts of the ice stream are found to be more than one order of magnitude harder for along-flow extension/compression while the shear margins are potentially softened by a factor of two for horizontal-shear deformation.
2023-05-08T00:00:00ZHeterogeneous melting near the Thwaites Glacier grounding lineSchmidt, B. E.Washam, P.Davis, P. E. D.Nicholls, K. W.Holland, D. M.Lawrence, J. D.Riverman, K. L.Smith, J. A.Spears, A.Dichek, D. J. G.Mullen, A. D.Clyne, E.Yeager, B.Anker, P.Meister, M. R.Hurwitz, B. C.Quartini, E. S.Bryson, F. E.Basinski-Ferris, A.Thomas, C.Wake, J.Vaughan, D. G.Anandakrishnan, S.Rignot, E.Paden, J.Makinson, K.https://hdl.handle.net/1808/340922023-04-12T06:06:07Z2023-02-15T00:00:00ZHeterogeneous melting near the Thwaites Glacier grounding line
Schmidt, B. E.; Washam, P.; Davis, P. E. D.; Nicholls, K. W.; Holland, D. M.; Lawrence, J. D.; Riverman, K. L.; Smith, J. A.; Spears, A.; Dichek, D. J. G.; Mullen, A. D.; Clyne, E.; Yeager, B.; Anker, P.; Meister, M. R.; Hurwitz, B. C.; Quartini, E. S.; Bryson, F. E.; Basinski-Ferris, A.; Thomas, C.; Wake, J.; Vaughan, D. G.; Anandakrishnan, S.; Rignot, E.; Paden, J.; Makinson, K.
Thwaites Glacier represents 15% of the ice discharge from the West Antarctic Ice Sheet and influences a wider catchment1,2,3. Because it is grounded below sea level4,5, Thwaites Glacier is thought to be susceptible to runaway retreat triggered at the grounding line (GL) at which the glacier reaches the ocean6,7. Recent ice-flow acceleration2,8 and retreat of the ice front8,9,10 and GL11,12 indicate that ice loss will continue. The relative impacts of mechanisms underlying recent retreat are however uncertain. Here we show sustained GL retreat from at least 2011 to 2020 and resolve mechanisms of ice-shelf melt at the submetre scale. Our conclusions are based on observations of the Thwaites Eastern Ice Shelf (TEIS) from an underwater vehicle, extending from the GL to 3 km oceanward and from the ice–ocean interface to the sea floor. These observations show a rough ice base above a sea floor sloping upward towards the GL and an ocean cavity in which the warmest water exceeds 2 °C above freezing. Data closest to the ice base show that enhanced melting occurs along sloped surfaces that initiate near the GL and evolve into steep-sided terraces. This pronounced melting along steep ice faces, including in crevasses, produces stratification that suppresses melt along flat interfaces. These data imply that slope-dependent melting sculpts the ice base and acts as an important response to ocean warming.
2023-02-15T00:00:00ZMeasuring Height Change Around the Periphery of the Greenland Ice Sheet With Radar AltimetryGray, LaurenceBurgess, DavidCopland, LukeLangley, KirstyGogineni, PrasadPaden, JohnLeuschen, Carlvan As, DirkFausto, RobertJoughin, IanSmith, Benhttps://hdl.handle.net/1808/311082021-01-13T09:00:55Z2019-06-11T00:00:00ZMeasuring Height Change Around the Periphery of the Greenland Ice Sheet With Radar Altimetry
Gray, Laurence; Burgess, David; Copland, Luke; Langley, Kirsty; Gogineni, Prasad; Paden, John; Leuschen, Carl; van As, Dirk; Fausto, Robert; Joughin, Ian; Smith, Ben
Ice loss measurements around the periphery of the Greenland Ice Sheet can provide key information on the response to climate change. Here we use the excellent spatial and temporal coverage provided by the European Space Agency (ESA) CryoSat satellite, together with NASA airborne Operation IceBridge and automatic weather station data, to study the influence of changing conditions on the bias between the height estimated by the satellite radar altimeter and the ice sheet surface. Surface and near-surface conditions on the ice sheet periphery change with season and geographic position in a way that affects the returned altimeter waveform and can therefore affect the estimate of the surface height derived from the waveform. Notwithstanding the possibility of a varying bias between the derived and real surface, for the lower accumulation regions in the western and northern ice sheet periphery (<∼1 m snow accumulation yearly) we show that the CryoSat altimeter can measure height change throughout the year, including that associated with ice dynamics, summer melt and winter accumulation. Further, over the 9-year CryoSat lifetime it is also possible to relate height change to change in speed of large outlet glaciers, for example, there is significant height loss upstream of two branches of the Upernavik glacier in NW Greenland that increased in speed during this time, but much less height loss over a third branch that slowed in the same time period. In contrast to the west and north, winter snow accumulation in the south-east periphery can be 2–3 m and the average altimeter height for this area can decrease by up to 2 m during the fall and winter when the change in the surface elevation is much smaller. We show that vertical downward movement of the dense layer from the last summer melt, coupled with overlying dry snow, is responsible for the anomalous altimeter height change. However, it is still possible to estimate year-to-year height change measurements in this area by using data from the late-summer to early fall when surface returns dominate the altimeter signal.
This work is licensed under a Creative Commons Attribution 4.0 International License.
2019-06-11T00:00:00ZCReSIS airborne radars and platforms for ice and snow soundingArnold, Emily J.Leuschen, CarlRodriguez-Morales, FernandoLi, JiluPaden, JohnHale, RichardKeshmiri, Shawnhttps://hdl.handle.net/1808/309912021-02-26T23:07:02Z2019-11-19T00:00:00ZCReSIS airborne radars and platforms for ice and snow sounding
Arnold, Emily J.; Leuschen, Carl; Rodriguez-Morales, Fernando; Li, Jilu; Paden, John; Hale, Richard; Keshmiri, Shawn
This paper provides an update and overview of the Center for Remote Sensing of Ice Sheets (CReSIS) radars and platforms, including representative results from these systems. CReSIS radar systems operate over a frequency range of 14–38 GHz. Each radar system's specific frequency band is driven by the required depth of signal penetration, measurement resolution, allocated frequency spectra, and antenna operating frequencies (often influenced by aircraft integration). We also highlight recent system advancements and future work, including (1) increasing system bandwidth; (2) miniaturizing radar hardware; and (3) increasing sensitivity. For platform development, we are developing smaller, easier to operate and less expensive unmanned aerial systems. Next-generation platforms will further expand accessibility to scientists with vertical takeoff and landing capabilities.
This work is licensed under a Creative Commons Attribution 4.0 International License.
2019-11-19T00:00:00Z