This work is supported by the National Science Foundation’s Transforming Undergraduate Education in STEM program within the Directorate for Education and Human Resources (DUE ). G REENLAND G LACIER C HANGES Unit 3: Part 4

G REENLAND GLACIERS ARE : Changing rapidly through processes that are not fully understood Providing most of the ice sheet’s increased contribution to sea level rise Helheim Glacier: ASTER satellite image

WHY DON’T MY PREDICTIONS MATCH THE GRACE RESULTS? Modified from

WHY DON’T MY PREDICTIONS MATCH THE GRACE RESULTS? Possible explanations: GRACE measurements have a big footprint. Mass loss estimates do not necessarily isolate processes that occur on a specific glacier. GRACE results do not give any indication into the mechanism that is causing the mass change. The data sets do not all overlap the same time periods, so it is hard to compare exactly! Can you think of other explanations?

What drives ice flow variability? Many factors influence ice flow, including the geometry of the glacier (width, ice thickness, bed topography), the bed conditions (hard bedrock, soft sediment, amount of water), ocean conditions (amount of submarine melt at the terminus) and atmosphere conditions (amount of meltwater that can get to the glacier bed).

Mechanism 1: Changes in the atmosphere lead to increased surface warming and melting The relationship between surface melting and ice flow is tricky to measure! Here we deployed instruments to estimate surface melt (weather station), lake depth (pressure transducer), and ice flow speed (GPS). When we returned to collect our instruments, the lake had drained and this block of ice (the size of a car) was sitting on top of our instruments! June 29, 2006 instrument deployment July 19, 2006 instrument retrieval Photo by: L. Stearns

Mechanism 1: Changes in the atmosphere lead to increased surface warming and melting Photo by: L. Stearns

Mechanism 2: Changes in the ocean lead to increased submarine melting

Modified from Straneo et al., 2010

CASE STUDY: HELHEIM GLACIER Helheim sped up substantially (1000 m/yr) between 2001–2009 Helheim thinned approximately 80 meters between 2000–2011 Southeast Greenland warmed over 5°C from 2001–2010 Observations:

Why did Helheim Glacier lose so much mass between 2001 and 2010? Possible processes that lead to mass loss (blue) and the mechanisms that initiate 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 warmer oceans melting the terminus of the glacier, or warmer atmosphere causing more water to reach the glacier bed).