Iceberg Calving and Meltwater Drainage at the Ice-Cliff ...
Transcript of Iceberg Calving and Meltwater Drainage at the Ice-Cliff ...
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Iceberg Calving and Meltwater Drainage at the Ice-Cliff Terminus of Helheim Glacier, Greenland
Photo: NASA
Sierra MeltonRichard Alley
Sridhar AnandakrishnanByron Parizek
Penn State Geosciences
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Introduction Methods Results Discussion Conclusion
Helheim
NASA JPL
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Introduction Methods Results Discussion Conclusion
Marine-terminating glaciers
Glacier
Fjord
Image: NASA
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Introduction Methods Results Discussion Conclusion
Marine-terminating glaciers lose ice through…
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Iceberg calving Melting
Modified from www.AntarcticGlaciers.org, Jacob BendleModified from Parizek et al., 2019
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Introduction Methods Results Discussion Conclusion
Calving: Not all icebergs are created equal
NontabularIcebergs
Tabular Icebergs
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Sentinel-2, 7 May 2016, Helheim
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Introduction Methods Results Discussion Conclusion
Nontabular iceberg calving at Helheim Glacier
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Time-lapse footage, James et al., 12 July 2010
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icebergs
fjord
Modified from www.AntarcticGlaciers.org, Jacob Bendle
glacier
Meltwater: Glacial hydrology
surface meltwater lake
7Introduction Methods Results Discussion Conclusion
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Subglacial hydrologyHigh water supply: Channelized network(Röthlisberger, 1972)
Surface meltwater drains to bed
fjord
Modified from www.AntarcticGlaciers.org, Jacob Bendle
glacier
8Introduction Methods Results Discussion Conclusion
Meltwater: Glacial hydrology
icebergs
surface meltwater lake
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Surface meltwater drains to bed
fjord
Modified from www.AntarcticGlaciers.org, Jacob Bendle
glacier
9Introduction Methods Results Discussion Conclusion
Meltwater: Glacial hydrology
icebergs
surface meltwater lake
Meltwater plumeBuoyant freshwater rises toward surface, stopping after reaching neutral density
Subglacial hydrologyHigh water supply: Channelized network(Röthlisberger, 1972)
Hypothesis: Plume appearance indicates that the subglacial water system is channelized to a grounded glacial front
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Introduction Methods Results Discussion Conclusion
Drone footage from Sridhar Anandakrishnan, summer 2019
Buoyant meltwater plume at Helheim Glacier
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Introduction Methods Results Discussion Conclusion
Greenland’s 5th largest glacier (Enderlin et al., 2014)
Flows up to >25 m/day: Fastest-flowing glacier in East Greenland (Rignot et al., 2004)
Helheim Glacier, Greenland
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Introduction Methods Results Discussion Conclusion
What is Helheim’s calving behavior?
How does meltwater drain?
How are calving and meltwater drainage related?
Satellite Imagery Time-Lapse Imagery
Extreme Ice Survey
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2011-2019
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Introduction Methods Results Discussion Conclusion
Satellite Imagery
1NIR: Near-Infrared 2SWIR: Short-wave Infrared3CAVIS: Clouds, Aerosols, Water Vapor, Ice, & Snow
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Meltwater plume observationIntroduction Methods Results Discussion Conclusion
07-18-2017 06:00
Plume at center terminusFractures south of plume
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Introduction Methods Results Discussion Conclusion
07-18-2017 09:00
Plume disappeared
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Introduction Methods Results Discussion Conclusion
07-18-2017 12:00
Large nontabular calving a few hours after plume disappeared
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Introduction Methods Results Discussion Conclusion 17
Plume consistently appeared at central terminus
WorldView-1 (©2012 Maxar Technologies, Inc.), 24 June 2012
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Introduction Methods Results Discussion Conclusion 18
Sentinel-2 band 2, 8 September 2019
Digitized terminus positions from satellite imagery
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Introduction Methods Results Discussion Conclusion
Meltwater pooling on glacier surface
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QuickBird (© 2011 MaxarTechnologies, inc.), 24 Aug 2011
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Introduction Methods Results Discussion Conclusion
Calculated water surface area with NDWIice
NDWIice method developed by Yang & Smith (2013)
𝑁𝐷𝑊𝐼𝑖𝑐𝑒 =𝐵𝐿𝑈𝐸 − 𝑅𝐸𝐷
𝐵𝐿𝑈𝐸 + 𝑅𝐸𝐷True-color Sentinel-2
imagery from 23 July 2017
Normalized Difference Water Index for Ice
Classified into “water” and “no water” pixels
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Introduction Methods Results Discussion Conclusion 21
Time-series: Plume
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Introduction Methods Results Discussion Conclusion 22
Time-series: Plume, calving
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Introduction Methods Results Discussion Conclusion
Time-series: Plume, calving, terminus position
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Introduction Methods Results Discussion Conclusion
Time-series: Plume, calving, terminus position, & surface water
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Introduction Methods Results Discussion Conclusion
Terminus position: Advance and retreat
Most advanced – 10 Mar 2011 (defined as zero)Most retreated – 8 Sep 2019 (5.6 km behind)
Relatively stable terminus position 2011-2016 despite ~3-4 km seasonal fluctuations
Retreated ~1.5 km beyond previous retreats in 2017 & 2019
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Introduction Methods Results Discussion Conclusion 26
Calving and plumes
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Introduction Methods Results Discussion Conclusion
Ceased calving when plume was visible
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One exception: 16 April 2017
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Introduction Methods Results Discussion Conclusion
Ceased calving when plume was visible, except…
16 April 2017
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WV-2 (©2017 Maxar Technologies, Inc.)
Landsat-8
Tabular iceberg
Plume
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Introduction Methods Results Discussion Conclusion
Why did calving (generally) not occur while a plume was visible?
Supports our hypothesis thatplume appearance indicates a grounded glacial front and channelized subglacial water system
Basal crevasses could be unable to form at a completely grounded glacial front, inhibiting full-thickness calving
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Modified from Murray et al. (2015)
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Introduction Methods Results Discussion Conclusion 30
Sentinel-2, 7 May 2016
Subglacial flow pathways coincide with plume locations
Meltwater drainage: Subglacial flow pathways
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Meltwater drainage: Timing
Lake & crevasses: Downglacier filling & drainage progression
Plumes:Appear after subglacial system reconfigures into channelized network
Visible while surface crevasses are filled
Introduction Methods Results Discussion Conclusion 31
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Introduction Methods Results Discussion Conclusion
Seasonal sequence driven by evolving hydrology
Lake drainage & large release of meltwater into the subglacial system
Channelized subglacial drainage system
Buoyant plume discharges from grounded terminus Calving ceases
Ungrounding of terminus:Plume dispersion and disappearance
Calving resumes
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Introduction Methods Results Discussion Conclusion
Background Image: NASA
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Link between meltwater drainage and iceberg calving, the two major ways in which marine-terminating glaciers lose ice
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• Huge thank you to my advisors/committee: Sridhar Anandakrishnan, Richard Alley, and Byron Parizek
• Funding from a National Science Foundation Graduate Research Fellowship and the Heising-Simons Foundation
• Michael Shahin, Leigh Stearns, the Cold Regions Research and Engineering Laboratory (CRREL), Laura Kehrl, and Ian Joughin
• Cathleen Torres Parisian and the Polar Geospatial Center
• Nouf Waleed Alsaad, Luke Trusel, the Penn State Ice and Climate Exploration research team, and the Penn State Geosciences Department
Acknowledgements
Background Image: NASA 34
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Thank you!
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@SierraMelting