1. GREENLAND GLACIERSARE: changing rapidly throughprocesses that are notfully understood; providing most of the icesheets increasedcontribution to sea levelrise.Helheim Glacier: ASTER satellite image

2. Why are glaciers important?observations show enhanced thinning, retreat, accelerationPritchard et al., 2009THICKNESS CHANGE: 2003-2007 (from ICESat)Joughin et al., 2010ICE VELOCITY and RETREAT:2000-2005 (InSAR) 3. Why are glaciers important?glacier acceleration accounts for nearly half of current mass losssurface mass balance(snowfall - surface ablation)At the current rate of accelerationin Greenland ice sheet loss, thesea level rise contribution will be34 cm by 2100.Rignot et al., 2011ice discharge(ice motion) 4. WHY DONT MY PREDICTIONSMATCH THE GRACE RESULTS?http://svs.gsfc.nasa.gov/vis/a030000/a030400/a030478/ 5. WHY DONT MY PREDICTIONSMATCH THE GRACE RESULTS?possible explanations: GRACE measurements have a big footprint. Mass lossestimates dont necessarily isolate processes that occuron a specific glacier. GRACE results dont give any indication into themechanism that is causing the mass change. The datasets dont all overlap the same time periods, soits hard to compare exactly! Can you think of other explanations? 6. What drives ice flow variability?Atmosphere: air temperature and precipitation changes caninfluence the amount of surface melting on the glacierCCLiVAR, 2013 (http://www.usclivar.org/meetings/griso-workshop)CLIVAR, 2012 7. mechanism: changes in the atmosphere leads to increased surfacewarming and meltingThe relationship between surface melting and ice flow is tricky to measure!Here we deployed instruments to estimate surface melt (weather station), lakedepth (pressure transducer), and ice flow speed (GPS).photJune 29, 2006instrument deploymentJuly 19, 2006instrument retrievalWhen we returned to collect our instruments, the lake had drained and thisblock of ice (the size of a car) was sitting on top of our instruments!Photos by: L. Stearns 8. mechanism: changes in the atmosphere leads to increased surfacewarming and meltingPhoto by: L. Stearns 9. What drives ice flow variability?Ocean: changes in ocean circulation, salinity, temperature, and tidescan influence the amount of melting a glacier experiencesCLiVAR, 2013 (http://www.usclivar.org/meetings/griso-workshop)CLIVAR, 2012 10. mechanism: changes in the ocean lead to increased submarinemelting 11. mechanism: changes in the ocean lead to increased submarinemeltingStraneo et al., 2010 12. mechanism: changes in the ocean lead to increased submarinemeltingHelheimGlacierStraneo et al., 2010 13. mechanism: changes in the ocean lead to increased submarinemelting 14. What drives ice flow variability?Glacier: changes in water at the base of the glacier, strength of theglacial margins, and conditions at the terminus of the glacier caninfluence meltingCLiVAR, 2013 (http://www.usclivar.org/meetings/griso-workshop)CLIVAR, 2012 15. mechanism: changes in the glacier lead to increased surface warmingand meltingZwally et al., 2002Nick Cobbing/Greenpeace 16. mechanism: changes in the glacierweakening of the ice mlange 17. mechanism: changes in the glacierweakening of the ice mlange1-Aug-2008; 1000-1530 UTC; 4 minutes between frames 18. CASE STUDY: HELHEIM GLACIERobservations: Helheim sped up substantially(1000 m/yr) between 2001-2009 Helheim thinned approximately 80meters between 2000-2011 SouthEast Greenland warmed over5C from 2001-2010 19. CASE STUDY: HELHEIM GLACIER 20. Why did Helheim Glacier lose so much mass between 2001 and 2010?Possible processes that lead to mass loss (blue) and the mechanisms thatinitiate these changes (red) are illustrated below.In this unit you investigated: surface warming and melting (which can increase the amount of water that gets to the bed of the glacier, causing acceleration); Ice dynamics (ice acceleration, which can be caused by any of themechanisms highlighted in red); Ice dynamics (glacier thinning, which can also be caused by any of the mechanisms highlighted in red). 21. Questions?Contact Leigh Stearnsstearns@ku.eduNick Cobbing/Greenpeace 22. ReferencesPritchard, Hamish D., et al. Extensive dynamic thinning on the margins of the Greenlandand Antarctic ice sheets." Nature 461.7266 (2009): 971-975.Joughin, Ian, et al. "Greenland flow variability from ice-sheet-wide velocity mapping.Journal of Glaciology 56.197 (2010): 415-430.Rignot, Eric, et al. "Acceleration of the contribution of the Greenland and Antarctic icesheets to sea level rise." Geophysical Research Letters 38.5 (2011).Straneo, Fiammetta, et al. "Rapid circulation of warm subtropical waters in a majorglacial fjord in East Greenland." Nature Geoscience 3.3 (2010): 182-186.Zwally, H. Jay, et al. "Surface melt-induced acceleration of Greenland ice-sheet flow." Science 297.5579 (2002): 218-222.