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  • 1
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    Relationship between Greenland Ice Sheet surface speed and modeled effective pressure (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 123 (2018): 2258-2278, doi:10.1029/2017JF004581.
    Description: We use a numerical subglacial hydrology model and remotely sensed observations of Greenland Ice Sheet surface motion to test whether the inverse relationship between effective pressure and regional melt season surface speeds observed at individual sites holds on a regional scale. The model is forced with daily surface runoff estimates for 2009 and 2010 across an ~8,000‐km2 region on the western margin. The overall subglacial drainage system morphology develops similarly in both years, with subglacial channel networks growing inland from the ice sheet margin and robust subglacial pathways forming over bedrock ridges. Modeled effective pressures are compared to contemporaneous regional surface speeds derived from TerraSAR‐X imagery to investigate spatial relationships. Our results show an inverse spatial relationship between effective pressure and ice speed in the mid‐melt season, when surface speeds are elevated, indicating that effective pressure is the dominant control on surface velocities in the mid‐melt season. By contrast, in the early and late melt seasons, when surface speeds are slower, effective pressure and surface speed have a positive relationship. Our results suggest that outside of the mid‐melt season, the influence of effective pressures on sliding speeds may be secondary to the influence of driving stress and spatially variable bed roughness.
    Description: National Aeronautics and Space Administration (NASA). Grant Number: NXX10AI30G National Science Foundation (NSF) American Geophysical Union Horton Research Grant; National Science Foundation Graduate Research Fellowship; National Science Foundation's Office of Polar Programs (NSF‐OPP) Grant Numbers: PLR‐1418256, ARC‐1023364, ARC‐0520077; Woods Hole Oceanographic Institution's Ocean and Climate Change Institute (OCCI)
    Description: 2019-03-27
    Keywords: Glaciology ; Greenland ; Subglacial hydrology ; Numerical modeling ; Ice dynamics
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Near-surface environmentally forced changes in the Ross Ice Shelf observed with ambient seismic noise (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 11,187-11,196, doi:10.1029/2018GL079665.
    Description: Continuous seismic observations across the Ross Ice Shelf reveal ubiquitous ambient resonances at frequencies 〉5 Hz. These firn‐trapped surface wave signals arise through wind and snow bedform interactions coupled with very low velocity structures. Progressive and long‐term spectral changes are associated with surface snow redistribution by wind and with a January 2016 regional melt event. Modeling demonstrates high spectral sensitivity to near‐surface (top several meters) elastic parameters. We propose that spectral peak changes arise from surface snow redistribution in wind events and to velocity drops reflecting snow lattice weakening near 0°C for the melt event. Percolation‐related refrozen layers and layer thinning may also contribute to long‐term spectral changes after the melt event. Single‐station observations are inverted for elastic structure for multiple stations across the ice shelf. High‐frequency ambient noise seismology presents opportunities for continuous assessment of near‐surface ice shelf or other firn environments.
    Description: NSF Office of Polar Programs Grant Number: PLR-1142518
    Description: 2019-04-16
    Keywords: Ross Ice Shelf ; Antarctica ; Firn ; Ambient noise ; Temporal monitoring ; Resonances
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  • 3
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    Seismicity on the western Greenland Ice Sheet : surface fracture in the vicinity of active moulins (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Earth Surface 120 (2015): 1082–1106, doi:10.1002/2014JF003398.
    Description: We analyzed geophone and GPS measurements collected within the ablation zone of the western Greenland Ice Sheet during a ~35 day period of the 2011 melt season to study changes in ice deformation before, during, and after a supraglacial lake drainage event. During rapid lake drainage, ice flow speeds increased to ~400% of winter values, and icequake activity peaked. At times 〉7 days after drainage, this seismicity developed variability over both diurnal and longer periods (~10 days), while coincident ice speeds fell to ~150% of winter values and showed nightly peaks in spatial variability. Approximately 95% of all detected seismicity in the lake basin and its immediate vicinity was triggered by fracture propagation within near-surface ice (〈330 m deep) that generated Rayleigh waves. Icequakes occurring before and during drainage frequently were collocated with the down flow (west) end of the primary hydrofracture through which the lake drained but shifted farther west and outside the lake basin after the drainage. We interpret these results to reveal vertical hydrofracture opening and local uplift during the drainage, followed by enhanced seismicity and ice flow on the downstream side of the lake basin. This region collocates with interferometric synthetic aperture radar-measured speedup in previous years and could reflect the migration path of the meltwater supplied to the bed by the lake. The diurnal seismic signal can be associated with nightly reductions in surface melt input that increase effective basal pressure and traction, thereby promoting elevated strain in the surficial ice.
    Description: Research by J. Carmichael was supported by a NASA NESSF Fellowship grant NNX08AU82H and NSF grant ANT-0424589. The fieldwork and additional analyses were supported by the National Science Foundation's Office of Polar Programs (NSF-OPP) through ARC-1023382, awarded to I. Joughin, and ARC-1023364, awarded to S. B. Das and M. D. Behn. Matt King is a recipient of an Australian Research Council Future Fellowship (project number FT110100207).
    Description: 2015-12-25
    Keywords: Western Greenland Ice Sheet ; Icequakes ; Statistical signal processing ; GPS ; Supraglacial lakes ; Seismic threshold monitoring
    Repository Name: Woods Hole Open Access Server
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  • 4
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    Large spatial variations in the flux balance along the front of a Greenland tidewater glacier. (2019)
    European Geosciences Union
    Details
    Publication Date: 2019-04-30
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wagner, T. J. W., Straneo, F., Richards, C. G., Slater, D. A., Stevens, L. A., Das, S. B., & Singh, H. Large spatial variations in the flux balance along the front of a Greenland tidewater glacier. Cryosphere, 13(3), (2019):911-925, doi:10.5194/tc-13-911-2019.
    Description: The frontal flux balance of a medium-sized tidewater glacier in western Greenland in the summer is assessed by quantifying the individual components (ice flux, retreat, calving, and submarine melting) through a combination of data and models. Ice flux and retreat are obtained from satellite data. Submarine melting is derived using a high-resolution ocean model informed by near-ice observations, and calving is estimated using a record of calving events along the ice front. All terms exhibit large spatial variability along the ∼5 km wide ice front. It is found that submarine melting accounts for much of the frontal ablation in small regions where two subglacial discharge plumes emerge at the ice front. Away from the subglacial plumes, the estimated melting accounts for a small fraction of frontal ablation. Glacier-wide, these estimates suggest that mass loss is largely controlled by calving. This result, however, is at odds with the limited presence of icebergs at this calving front – suggesting that melt rates in regions outside of the subglacial plumes may be underestimated. Finally, we argue that localized melt incisions into the glacier front can be significant drivers of calving. Our results suggest a complex interplay of melting and calving marked by high spatial variability along the glacier front.
    Description: We acknowledge support from the Woods Hole Oceanographic Institution Ocean and Climate Change Institute Arctic Research Initiative, and NSF OPP-1418256 and OPP-1743693, to Fiamma Straneo and Sarah B. Das. Till J. W. Wagner was further supported by NSF OPP award 1744835. Geospatial support for this work was provided by the Polar Geospatial Center under NSF OPP awards 1043681 and 1559691. DEMs provided by the Polar Geospatial Center under NSF OPP awards 1043681, 1559691, and 1542736. Donald A. Slater acknowledges the support of Scottish Alliance for Geoscience, Environment and Society early-career research exchange funding.
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages (2021)
    Nature Research
    Details
    Publication Date: 2022-05-27
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Lai, C.-Y., Stevens, L. A., Chase, D. L., Creyts, T. T., Behn, M. D., Das, S. B., & Stone, H. A. Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages. Nature Communications, 12(1), (2021): 3955, https://doi.org/10.1038/s41467-021-24186-6.
    Description: Surface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we infer drainage system transmissivity based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity (from 0.8 ± 0.3 mm3 to 215 ± 90.2 mm3) as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes driven by seasonal meltwater input.
    Description: C.-Y.L. and L.A.S thank Lamont-Doherty Earth Observatory for funding through the Lamont Postdoctoral Fellowships. D.L.C acknowledges support from the National Science Foundation (NSF) Graduate Research Fellowship. T.T.C. was supported by NSF’s Office of Polar Programs (NSF-OPP) through OPP-1643970, the National Aeronautics and Space Administration (NASA) through NNX16AJ95G, and a grant from the Vetlesen Foundation. S.B.D. and M.D.B. acknowledge funding from NSF-OPP and NASA’s Cryospheric Sciences Program through OPP-1838410, ARC-1023364, ARC-0520077, and NNX10AI30G. H.A.S. thanks the High Meadows Environmental Institute and the Carbon Mitigation Initiative at Princeton University. This publication was supported by the Princeton University Library Open Access Fund.
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  • 6
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    Linking glacially modified waters to catchment-scale subglacial discharge using autonomous underwater vehicle observations (2016)
    Copernicus Publications on behalf of the European Geosciences Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Cryosphere 10 (2016): 417-432, doi:10.5194/tc-10-417-2016.
    Description: Measurements of near-ice (〈  200 m) hydrography and near-terminus subglacial hydrology are lacking, due in large part to the difficulty in working at the margin of calving glaciers. Here we pair detailed hydrographic and bathymetric measurements collected with an autonomous underwater vehicle as close as 150 m from the ice–ocean interface of the Saqqarliup sermia–Sarqardleq Fjord system, West Greenland, with modeled and observed subglacial discharge locations and magnitudes. We find evidence of two main types of subsurface glacially modified water (GMW) with distinct properties and locations. The two GMW locations also align with modeled runoff discharged at separate locations along the grounded margin corresponding with two prominent subcatchments beneath Saqqarliup sermia. Thus, near-ice observations and subglacial discharge routing indicate that runoff from this glacier occurs primarily at two discrete locations and gives rise to two distinct glacially modified waters. Furthermore, we show that the location with the largest subglacial discharge is associated with the lighter, fresher glacially modified water mass. This is qualitatively consistent with results from an idealized plume model.
    Description: Support was provided by the National Science Foundation’s Office of Polar Programs (NSF-OPP) through PLR-1418256 to F. Straneo, S. B. Das and A. J. Plueddemann, PLR-1023364 to S. B. Das, and through the Woods Hole Oceanographic Institution Ocean and Climate Change Institute Arctic Research Initiative to F. Straneo, S. B. Das, and A. J. Plueddemann. L. A. Stevens was also supported by a National Science Foundation Graduate Research Fellowship. S. B. Das was also supported by the Woods Hole Oceanographic Institution James E. and Barbara V. Moltz Research Fellowship. M. Morlighem was supported by the National Aeronautics and Space Administration’s (NASA) Cryospheric Sciences Program through NNX15AD55G.
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Greenland Ice Sheet flow response to runoff variability (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 43 (2016): 11,295–11,303, doi:10.1002/2016GL070414.
    Description: We use observations of ice sheet surface motion from a Global Positioning System network operating from 2006 to 2014 around North Lake in west Greenland to investigate the dynamical response of the Greenland Ice Sheet's ablation area to interannual variability in surface melting. We find no statistically significant relationship between runoff season characteristics and ice flow velocities within a given year or season. Over the 7 year time series, annual velocities at North Lake decrease at an average rate of −0.9 ± 1.1 m yr−2, consistent with the negative trend in annual velocities observed in neighboring regions over recent decades. We find that net runoff integrated over several preceding years has a negative correlation with annual velocities, similar to findings from the two other available decadal records of ice velocity in western Greenland. However, we argue that this correlation is not necessarily evidence for a direct hydrologic mechanism acting on the timescale of multiple years but could be a statistical construct. Finally, we stress that neither the decadal slowdown trend nor the negative correlation between velocity and integrated runoff is predicted by current ice-sheet models, underscoring that these models do not yet capture all the relevant feedbacks between runoff and ice dynamics needed to predict long-term trends in ice sheet flow.
    Description: National Science Foundation's Office of Polar Programs Grant Number: NSF-OPP; National Aeronautics and Space Administration's (NASA) Cryospheric Sciences Program Grant Numbers: ARC-0520077, ARC-1023364, NNX10AI30G; National Science Foundation Graduate Research Fellowship Grant Numbers: ARC-0520382, ARC-1023382; American Geophysical Union Horton Research Grant. Grant Number: NNX10AI33G
    Description: 2017-05-12
    Keywords: Greenland Ice Sheet ; Ice flow ; Runoff
    Repository Name: Woods Hole Open Access Server
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  • 8
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    Large spatial variations in the flux balance along the front of a Greenland tidewater glacier (2019)
    European Geosciences Union
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wagner, T. J. W., Straneo, F., Richards, C. G., Slater, D. A., Stevens, L. A., Das, S. B., & Singh, H. Large spatial variations in the flux balance along the front of a greenland tidewater glacier. Cryosphere, 13(3), (2019):911-925, doi:10.5194/tc-13-911-2019.
    Description: The frontal flux balance of a medium-sized tidewater glacier in western Greenland in the summer is assessed by quantifying the individual components (ice flux, retreat, calving, and submarine melting) through a combination of data and models. Ice flux and retreat are obtained from satellite data. Submarine melting is derived using a high-resolution ocean model informed by near-ice observations, and calving is estimated using a record of calving events along the ice front. All terms exhibit large spatial variability along the ∼5 km wide ice front. It is found that submarine melting accounts for much of the frontal ablation in small regions where two subglacial discharge plumes emerge at the ice front. Away from the subglacial plumes, the estimated melting accounts for a small fraction of frontal ablation. Glacier-wide, these estimates suggest that mass loss is largely controlled by calving. This result, however, is at odds with the limited presence of icebergs at this calving front – suggesting that melt rates in regions outside of the subglacial plumes may be underestimated. Finally, we argue that localized melt incisions into the glacier front can be significant drivers of calving. Our results suggest a complex interplay of melting and calving marked by high spatial variability along the glacier front.
    Description: We acknowledge support from the Woods Hole Oceanographic Institution Ocean and Climate Change Institute Arctic Research Initiative, and NSF OPP-1418256 and OPP-1743693, to Fiamma Straneo and Sarah B. Das. Till J. W. Wagner was further supported by NSF OPP award 1744835. Geospatial support for this work was provided by the Polar Geospatial Center under NSF OPP awards 1043681 and 1559691. DEMs provided by the Polar Geospatial Center under NSF OPP awards 1043681, 1559691, and 1542736. Donald A. Slater acknowledges the support of Scottish Alliance for Geoscience, Environment and Society early-career research exchange funding.
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  • 9
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    Influence of meltwater on Greenland Ice Sheet dynamics (2017)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2017
    Description: Seasonal fluxes of meltwater control ice-flow processes across the Greenland Ice Sheet ablation zone and subglacial discharge at marine-terminating outlet glaciers. With the increase in annual ice sheet meltwater production observed over recent decades and predicted into future decades, understanding mechanisms driving the hourly to decadal impact of meltwater on ice flow is critical for predicting Greenland Ice Sheet dynamic mass loss. This thesis investigates a wide range of meltwater-driven processes using empirical and theoretical methods for a region of the western margin of the Greenland Ice Sheet. I begin with an examination of the seasonal and annual ice flow record for the region using in situ observations of ice flow from a network of Global Positioning System (GPS) stations. Annual velocities decrease over the seven-year time-series at a rate consistent with the negative trend in annual velocities observed in neighboring regions. Using observations from the same GPS network, I next determine the trigger mechanism for rapid drainage of a supraglacial lake. In three consecutive years, I find precursory basal slip and uplift in the lake basin generates tensile stresses that promote hydrofracture beneath the lake. As these precursors are likely associated with the introduction of meltwater to the bed through neighboring moulin systems, our results imply that lakes may be less able to drain in the less crevassed, interior regions of the ice sheet. Expanding spatial scales to the full ablation zone, I then use a numerical model of subglacial hydrology to test whether model-derived effective pressures exhibit the theorized inverse relationship with melt-season ice sheet surface velocities. Finally, I pair near-ice fjord hydrographic observations with modeled and observed subglacial discharge for the Saqqardliup sermia–Sarqardleq Fjord system. I find evidence of two types of glacially modified waters whose distinct properties and locations in the fjord align with subglacial discharge from two prominent subcatchments beneath Saqqardliup sermia. Continued observational and theoretical work reaching across discipline boundaries is required to further narrow our gap in understanding the forcing mechanisms and magnitude of Greenland Ice Sheet dynamic mass loss.
    Description: Provided by the National Science Foundation Graduate Research Fellowship Program; the National Science Foundation’s Office of Polar Programs through ARC- 0520077, ARC-1023364, PLR-1418256, and PLR-1023364; the National Aeronautics and Space Administration’s Cryospheric Science Program through NNX10AI30G; the Woods Hole Oceanographic Institution Ocean and Climate Change Institute Arctic Research Initiative; and the American Geophysical Union Horton Research Grant.
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 10
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    Erratum: Corrigendum: Greenland supraglacial lake drainages triggered by hydrologically induced basal slip (2015)
    Springer Nature
    Details
    Publication Date: 2015-07-01
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Springer Nature
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