Køge Bugt: Evidence of a Greenland Firn Aquifer ...Cooperative Institute for Research in...
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Ryan Cassotto1, Michael J Willis1, Michael MacFerrin1, Clément Miège2, Michael Bevis3
1 Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO2 Rutgers University, New Brunswick, NJ
3 School of Earth Sciences, Ohio State University, Columbus, OH
Land Ice Working Group
National Center for Atmospheric Research
February 4, 2019
Køge Bugt: Evidence of a Greenland Firn Aquifer Influencing Tidewater Glacier Dynamics?
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
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Køge Central
Køge South
Køge North
Enderlin et al, 2014
Joughin et al, 2018
Data courtesy of NASA MEaSUREs
• 3 TWG systems • Køge North (Pamiagtik Glacier)• Køge Central (Køge Bugt Glacier)• Køge South (Havhestens Bugt Glacier)
• Køge Central (3rd) and Køge South (7th) highest discharge in Greenland (Enderlin et al, 2014)
• Small retreat for most of 20th century except for small re-advance between 1972 – 1981 (Bjørk et al, 2012)
• Minimal retreat during Holocene (Dyke et al, 2017); suggest physical setting controls response to external forcing.
• Submarine beds vulnerable to warm Atlantic Water (Millan et al, 2018)
Enderlin et al, 2014
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
3Moon et al, 2014
• 2003-09: experienced thinning-thickening-thinning pattern (Csatho et al, 2014)
• Køge South: • Seasonal speed variations triggered by melt, later sustained
by bed topography and ice dynamics. (Moon et al, 2014)
• Køge Central:• Lacks seasonal variability and a response to melt (Moon et al,
2014)
• Two major slowdown events occurred in recent years coincide with re-advance (Joughin et al, 2018)
• Large along-flow variability in sliding, suggesting a complex relationship with meltwater (Stearns & van der Veen, 2018)
Koge Central
Koge South
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• Surface Elevations (Ice Thicknesses)• Time-tagged ArcticDEM
• “What’s going on at Køge Central?”
• What roles, if any, do the ice mélange and the firn aquifer play in ice dynamics?
• Why do glaciers in the same fjord with similar bed and ice surface geometries exhibit such different flow characteristics?
• Speeds: 3 NASA derived datasets• MEaSUREs Radar (Joughin et al, 2011)
• MEaSUREs Optical (Howat, 2017)
• GoLIVE (Scambos et al, 2016)
• Terminus Positions• Landsats 1 & 5 (60-m)• Landsats 7 & 8 (15-m)• Sentinel-2 (10-m)
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Køge North: Stable• 1990 – 2000: Small ~1 km retreat
Køge Central: ~3 km retreat• 1972 – 1998: Advanced position, ~750-m variations • 1998 – 2003: Stable• 2003 – Present: Large (>1 km), multi-year variability
Køge South: ~1.2 km retreat• 1972 – 1992: Advanced position, ~500-m variations • 1992 – 2003: Stable• 2003 – Present: Increased annual variability
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
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4 yrs3 yrs 2 yrs
<=9 mos8 mos 9 mos
• Prolonged increase in speed followed by rapid slow down
• Slowdowns initiate in summer and occur over 6-9 months
• 2002 and 2012 slowdowns coincide with peak melt years (Steffen et al, 2004; Nghiem et al, 2012)
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Sep 2015 - Apr 2016 (7 months)1 winter: ~40 m elevation gain
Oct 2012 – Jun 2013 (8 months)1 winter: 60 m elevation gain
Csatho et al, 2014: “Thinning Thickening Thinning with abrupt termination of initial thinning”
Coincident speed reductions, terminus advance & ice thickening• 2003, 2007, 2013, 2016
Large scale dynamic thickening events
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Sep 2015 - Apr 2016 (7 months)1 winter: ~40 m elevation gain
Oct 2012 – Jun 2013 (8 months)1 winter: 60 m elevation gain
Csatho et al, 2014: “Thinning Thickening Thinning with abrupt termination of initial thinning”
Coincident speed reductions, terminus advance & ice thickening• 2003, 2007, 2013, 2016
Large scale dynamic thickening events
Recall, Køge Central:
• lacks any melt-induced seasonal changes in ice flow. (Moon et al, 2014)
• Large along-flow variability in sliding parameter; suggests complex relationship with melt
Q: What mechanism(s) are driving these changes?
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Miege et al, 2016
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• Perennial firn aquifer ~30 km upglacier (Forster et al, 2013)
Miége et al (in prep)
2012: FA levels lower (draining) glacier speeding up, thinning, and retreating
2013: FA levels higher (not draining and/or filling) --> glacier slowing, thickening, & advancing
2014: FA again lower (draining) glacier again accelerating, thinning, and retreating.
• 2013 • Water table increased 2 m• 4 km inland expansion
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Surface Melt
Firn Aquifer“Buffer”
Basal Hydrology(Meltwater)
Controlled, multi-year increase in ice speed, thinning and terminus retreat
Insufficient to incise large subglacial conduits
↑ Pw, ↓Pe, ↑ Sliding
Mode 1: Persistent discharge from firn aquifer facilitates prolonged periods of ice dynamics that promote mass loss
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Surface Melt
Firn Aquifer“Buffer”
Basal Hydrology(Meltwater)
Glacier slows, thickens and re-advances
Mode 2: Excessive melt inundates the hydrologic system, which incises large subglacial channels, decreases basal water pressure,
increases effective pressure, and slows the glacier
Incises large subglacial conduits↓ Pw, ↑Pe, ↓ Sliding
↑ Pw, ↓Pe, ↑ Sliding
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• Daily MODIS 250-m images
• Proglacial fjord typically ice free Jan – Mar
• EXCEPTIONS: 2007, 2013 & 2016 (years with a slower, thickening, and advancing terminus)
• This might suggest:• 1) an ice mélange influence• 2) low subglacial discharge (FA not draining?)
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Hydraulic Potential• Φ = 𝜌𝜌𝑤𝑤𝑔𝑔𝑍𝑍𝑏𝑏 + 𝜌𝜌𝑖𝑖𝑔𝑔𝐻𝐻𝑘𝑘𝑝𝑝
Køge Central
Køge South
Køge North
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Future Work• Simulate dynamic changes using an ice physics – basal hydrology coupled model; plan to use SHaKTI
• Collect additional in situ & satellite remote sensing data of firn aquifer variability (L-Band SAR, e.g. NiSAR?)
• Study regional climate models for patterns of melt, snow, precip, etc…
• Generate thermal SST record of fjord surface temperatures (winter ice mélange proxy)
• Investigate plume detection methods
15Køge Central
KøgeSouth
Køge NorthRemaining Questions• Do variations in the firn aquifer coincide with dynamic changes in 2003, 2007 and
2016?
• What mechanism(s) facilitate firn aquifer discharge/recharge?
• How does annual variability in surface melt affect firn aquifer?
• What is the buffering capacity of the firn aquifer?
• What role, if any, does ice mélange play in dynamic change at Køge Central?
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Summary• Three Køge Bugt tidewater glaciers exhibit very different flow characteristics
despite close proximity (<20 km apart) and similar bed and surface geometries
• Køge North: Slowest, stable and lacks significant dynamic change.
• Køge South: Moderate speeds, exhibits small scale seasonal variations in flow, ice thickness, and terminus location; sensitivity to melt (Moon et al, 2014).
• Køge Central: Fastest, lacks seasonal variability, but exhibits prolonged periods of accelerated flow, dynamic thinning and retreat. These multi-year processes abruptly lead to decelerated flow, ice thickening, and re-advance before returning to previous mode.
16Køge Central
KøgeSouth
Køge North
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Summary• Three Køge Bugt tidewater glaciers exhibit very different flow characteristics
despite close proximity (<20 km apart) and similar bed and surface geometries
• Køge North: Slowest, stable and lacks significant dynamic change.
• Køge South: Moderate speeds, exhibits small scale seasonal variations in flow, ice thickness, and terminus location; sensitivity to melt (Moon et al, 2014).
• Køge Central: Fastest, lacks seasonal variability, but exhibits prolonged periods of accelerated flow, dynamic thinning and retreat. These multi-year processes abruptly lead to decelerated flow, ice thickening, and re-advance before returning to previous mode.
17Køge Central
KøgeSouth
Køge North
• **Køge Central changes coincide with variations in the firn aquifer, first known evidence of firnaquifer influence on TWG dynamics**
• **Firn aquifer induced large scale changes in ice dynamics along Køge Bugt produced 3rd highest volume of ice dynamic losses in Greenland 2000 – 2012**
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
• Φ = 𝜌𝜌𝑤𝑤𝑔𝑔𝑍𝑍𝑏𝑏 + 𝜌𝜌𝑖𝑖𝑔𝑔𝐻𝐻𝑘𝑘𝑝𝑝Køge Central
Køge South
Køge North
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Cooperative Institute for Research in Environmental SciencesUNIVERSITY OF COLORADO BOULDER and NOAA
Hydraulic Potential• Φ = 𝜌𝜌𝑤𝑤𝑔𝑔𝑍𝑍𝑏𝑏 + 𝜌𝜌𝑖𝑖𝑔𝑔𝐻𝐻𝑘𝑘𝑝𝑝
Kp = 1Kp = 0.5Kp = 0.1
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Køge Central
Køge South
Similar bed profiles along lower 22 km:• 22 km (behind calving front): ~400 m ASL• 3 km: at sea level• 0 – 3 km: below sea level
Major Difference:• Køge Central: Retrograde bed behind calving front• Køge South: Prograde to the calving front
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+20-30 m Jul 2016 (1.5 yrs thickening)
+10-20 m May 2013 (winter thickening)
• Negligible change in surface elevation
• Some dynamic changes• Smaller in magnitude• Perhaps seasonal
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• 1.6 yrs: -12 m 29 Oct 2012
Surface elevation change from Mar 2011-12 m by 29 Oct 2012
Re-advance of terminus
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• 1.6 yrs: -12 m 29 Oct 2012
• 2.2 yrs: +46 m 30 Jun 2013
Surface elevation change from Mar 2011
Winter Thickening
+46 m by 30 Jun 2013
Re-advance of terminus
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• 1.6 yrs: -12 m 29 Oct 2012
• 2.2 yrs: +46 m 30 June 2013
• 2.6 yrs: +40 m 22 Oct 2013
Surface elevation change from Mar 2011
Winter Thickening
Summer Thinning
+40 m by 22 Oct 2013
Re-advance of terminus
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• 1.6 yrs: -12 m 29 Oct 2012
• 2.2 yrs: +46 m 30 June 2013
• 2.6 yrs: +40 m 22 Oct 2013
• 3.3 yrs: +17 m 4 Jul 2014
Surface elevation change from Mar 2011
Winter Thickening
Summer Thinning
Winter Thinning
+17 m by 4 Jul 2014
Re-advance of terminus
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• 1.6 yrs: -12 m 29 Oct 2012
• 2.2 yrs: +46 m 30 June 2013
• 2.6 yrs: +40 m 22 Oct 2013
• 3.3 yrs: +17 m 4 Jul 2014
• 4.5 yrs: +1 m 23 Sep 2015
Surface elevation change from Mar 2011
Winter Thickening
Summer Thinning
Winter Thinning
Multi-year Thinning
+1 m by 23 Sep 2015
Re-advance of terminus
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• 1.6 yrs: -12 m 29 Oct 2012
• 2.2 yrs: +46 m 30 June 2013
• 2.6 yrs: +40 m 22 Oct 2013
• 3.3 yrs: +17 m 4 Jul 2014
• 4.5 yrs: +1 m 23 Sep 2015
• 5.1 yrs: +44 m 12 Apr 2016
Winter Thickening
Summer Thinning
Winter Thinning
Multi-year Thinning
Winter Thickening
+44 m by 12 Apr 2016
Surface elevation change from Mar 2011
Re-advance of terminus
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• Multiple large-scale thickening events: Winters 2012 & 2016
• Thinning winter 2014
• Thickening summer 2016
• 1.6 yrs: -12 m 29 Oct 2012
• 2.2 yrs: +46 m 30 June 2013
• 2.6 yrs: +40 m 22 Oct 2013
• 3.3 yrs: +17 m 4 Jul 2014
• 4.5 yrs: +1 m 23 Sep 2015
• 5.1 yrs: +44 m 12 Apr 2016
• 5.5 yrs: +50 m 17 Sep 2016
Surface elevation change from Mar 2011
Winter Thickening
Summer Thinning
Winter Thinning
Multi-year Thinning
Winter Thickening
Summer Thickening
+50 m by 17 Sep 2016
Re-advance of terminus