Gooey Ice beneath Greenland’s outlet glaciers

Gooey Icebeneath Greenland’s outlet glaciers …is this feedback important to ice flow? Kristin Poinar University of Washington The GCC! October 15, 2010

What’s happening in Greenland Kanger-dlugssuaq glacier tripled its speed 2000-2006 Jakobshavn Isbrae doubled its speed 1998-2005 Helheim glacier doubled its speed 2000-2005

What does it mean?? • Something is forcing these glaciers to accelerate. Smarter people are figuring out what, with good success • Unanswered question: Are the speedups self-sustaining?

What does it mean?? • Something is forcing these glaciers to accelerate. Smarter people are figuring out what, with good success • Unanswered question: Are the speedups self-sustaining? Why is it important to forecast Greenland’s outlet glacier speedups?

Sea level rise! It’s going to happen, so we need accurate predictions. My model will answer the question ARE THE SPEEDUPS SELF-SUSTAINING to understand which of these sea level rise projections is realistic

The gooey ice feedback* *technical term If you know how gooey your honey is and how hard you squeeze, you can predict how long it takes to come out (how fast honey deforms).

This is happening in Greenland! • The question is, how strong of a feedback is it? • Can self-warming gooey ice account for much of the recent speedups? • Will it keep Jakobshavn & the other glaciers moving, or even accelerating, at these rates?

Reality: Gooey temperate ice COLD ice (below melting point) Hard, brittle Ice flow  TEMPERATE ice (at melting point) Soft, gooey Includes liquid water 100 times more deformable than cold ice

Reality: Gooey temperate ice external forcing (e.g. ice tongue disintegrates) Ice speeds up More friction creates more heat Warmer ice deforms more easily Ice warms up, temperate ice layer grows COLD ice (below melting point) Hard, brittle Ice flow  TEMPERATE ice (at melting point) Soft, gooey Includes liquid water 100 times more deformable than cold ice

After one slide of reality… a model! • 2D implicit finite differences model • Predicts ice temperatures from divide to coast, including temperate ice gooeyness • Runtime • Equilibrate at pre-speedup speeds • Force with new speeds (2005) • Outputs • How much does temperate ice grow? • How much extra deformational velocity does it account for?

After one slide of nuts & bolts… Results! Ice flow 

Model validation – Two boreholes Temperature measurements exist for -Top 70% of ice (1500 meters) in the center of the Jakobshavn trough (!!!!) -100% of the ice thickness (800 meters) a few km north of the trough, where the ice is friendlier  Ice flow ocean BEDROCK TOPOGRAPHY

Model validation – Two boreholes Off-trough borehole Temperate ice thickness Observed: (31 ± 1) m Modeled: (33 ± 5) m (using parameters within a reasonable range) temperate ice

Model validation – Two boreholes Central trough borehole Temperate ice thickness Observed: ????? Modeled: (140 ± 20) m (using parameters within a reasonable range) temperate ice

Model output How much did the temperate ice thickness increase during Jakobshavn’s speedup, 1985-2005?

Model output How much did the temperate ice thickness increase during Jakobshavn’s speedup, 1985-2005? 18 meters at the borehole location a 15% increase Max increase 27 meters (a 22% increase) upstream of borehole Max decrease 10 meters (a 10% decrease) downstream of borehole

Model output How much did the temperate ice thickness increase during Jakobshavn’s speedup, 1985-2005? 18 meters at the borehole location a 15% increase Max increase 27 meters (a 22% increase) upstream of borehole Max decrease 10 meters (a 10% decrease) downstream of borehole SO? WHO CARES

Testing the feedback How much more deformation can the ice now sustain, with that extra 18 meters of gooey ice? Glen’s flow law!

Testing the feedback How much more deformation can the ice now sustain, with that extra 18 meters of gooey ice? Glen’s flow law! 2.0 m/yr … not much It took an extra 495 m/yr of speedup (8.3 m/yr of ice deformation + 487 m/yr of sliding) to produce that ice.

Feedback strength Kanger-dlugssuaq glacier tripled its speed 2000-2006 How much of the observed speedup is sustainable through the newly-created gooey temperate ice? Helheim glacier doubled its speed 2000-2005 Jakobshavn Isbrae doubled its speed 1998-2005

Translation to Sea level rise

Importance of gooey ice feedback • Increased gooeyness of warm, temperate ice can account for • 3.6% of the observed speedup on Jakobshavn since 1997 • 2.6% of the observed speedup on Helheim since 2000 • 0.4% of the observed speedup on Kangerdlugssuaq since 2000 • BUT the gooeyness will sustain its part of the fast motion, even if the external forcing is removed • Sea level rise in 2100 if velocities continue as is: (8.0 ± 1.6) mm • Sea level rise in 2100 if glaciers return to 1990s/2000 speed • WITH gooey ice feedback 3.70 ± 0.7 mm • WITHOUT gooey ice feedback 3.60 ± 0.7 mm

Conclusion: Is this feedback important? The gooey ice feedback isn’t going to drown us in melted Greenland ice (accounts for +0.1 mm additional sea level rise by year 2100, for the 16% of Greenland’s area tested) BUT it is significant enough that should be in ice sheet models (3% difference in ice speed)

Sea level rise! It’s going to happen, so we need accurate predictions. GREENLAND SLR in 2006: 0.5 mm/yr Jakobshavn, Helheim, Kangerdlugssuaq SLR in 2006: 0.08 mm/yr GREENLAND SLR projected in 2050: 1.5 mm/yr Jakobshavn, Helheim, Kangerdlugssuaq SLR projected in 2050: 0.24 mm/yr GREENLAND SLR projected in 2100: 2.6 mm/yr Jakobshavn, Helheim, Kangerdlugssuaq SLR projected in 2100: 0.42 mm/yr My model will answer the question ARE THE SPEEDUPS SELF-SUSTAINING to understand which of these sea level rise projections is realistic

Sea level rise! It’s going to happen, so we need accurate predictions. “Uncertainties about glacier basal conditions, ice deformation, and interactions with the surrounding ocean seriously limit the ability to make accurate projections” about sea level rise. My model will answer the question ARE THE SPEEDUPS SELF-SUSTAINING by better modeling the basal conditions, and doing its best to deal with ice flow uncertainties Intergovernmental Panel on Climate Change, 2007

Sea level rise! It’s going to happen, so we need accurate predictions. “Uncertainties about glacier basal conditions, ice deformation, and interactions with the surrounding ocean seriously limit the ability to make accurate projections” about sea level rise. My model will answer the question ARE THE SPEEDUPS SELF-SUSTAINING by better modeling the basal conditions, and doing its best to deal with ice flow uncertainties I smell a Feedback! Intergovernmental Panel on Climate Change, 2007

Gooey Ice beneath Greenland’s outlet glaciers