Cryo IS, Pritchard et al 2009

Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets

How much do global ice losses contribute to sea level rise annually?

~1.8 mm yr⁻¹

What is dynamic thinning?

Ice loss caused by accelerated glacier flow and increased ice discharge rather than just surface melt

What methods are used to measure ice sheet change?

Surface mass balance (SMB), ice discharge measurements, satellite altimetry, and gravimetry

Where do measurement methods perform most poorly?

Where change is most rapid, especially steep, narrow outlet glaciers at ice sheet margins

Where is dynamic thinning most evident in Greenland?

SE and NW margins of the Greenland Ice Sheet

What unusual SMB pattern occurs in southern Greenland?

High-altitude areas show thickening, while margins thin strongly

How does thinning vary with flow speed in Greenland?

Fast-flowing ice thins at about twice the rate of nearby slow-flowing ice at the same altitude

How far inland can dynamic thinning penetrate in Greenland?

Deep into the ice sheet interior (e.g., up to ~77.6°N at Tracy Glacier)

What is the overall Greenland pattern of mass change?

Margins thin strongly while some interior high-elevation areas may thicken slightly

Which Greenland regions show strongest thinning?

Southeast (rapid thinning) and Northwest (continued thinning but less acceleration)

Where does thickening occur in Greenland?

Some southwest Greenland areas thicken at all elevations due to local dynamics

What is surge-type glacier behaviour?

Rare cases of dynamic thickening caused by temporary slowdown or redistribution of ice flow

Where is Antarctic thinning strongest?

Amundsen Sea Embayment in West Antarctica

Which glacier shows extreme thinning in Antarctica?

Smith Glacier, thinning at >9 m yr⁻¹

Which Antarctic ice shelves are linked to rapid thinning tributary glaciers?

Crosson and Dotson ice shelves

What is happening at Kamb Ice Stream?

Shutdown ~130 years ago led to reduced ice flow and local thickening

Why can some Antarctic ice streams thicken?

Reduced downstream flow causes ice to accumulate upstream of stagnant trunks

Which Antarctic ice shelf shows stable thickness due to snowfall?

Abbott Ice Shelf (~400 km coast) remains stable due to high snowfall

Which East Antarctic glacier shows significant thinning?

Totten Glacier

Where is thickening observed in West Antarctica?

Bellingshausen Sea coast slow-flowing ice caps (up to ~1 m yr⁻¹ thickening)

What is the key overall conclusion about GIS and AIS margins?

Both ice sheets show strong dynamic thinning at margins, with effects penetrating inland, especially where discharge and SMB losses combine