A WAIS Analog Found on Mars Polar Cap Weili Wang 1, Jun Li 1 and Jay Zwally 2 1. Raytheon ITSS, NASA/GSFC, Code 971, Greenbelt, MD 20771, USA. 2. Ocean and Ice Branch, NASA/GSFC, Code 971, Greenbelt, MD 20771, USA.

North Polar Cap South Polar Cap Mars X 5 km Meter X 5 km Meter (Surface topography) (Maximum thickness: ~ 3000 m at the dome)

(meter) Distance (x5 km) North Polar Cap on Mars Chasma Boreale Surface topography and flowlines

300 km AB Mars Polar Cap WAIS AB Theoretical (Vialov type) ice-sheet profile Grounding Line Inland Ice Ice Stream Ice Shelf Chasma Boreale

Ice-Stream Onset (After Bindschadler et al, 2001, The West Antarctic ice sheet ) The location of the transition between inland ice flow (corresponding to a convex-up shape profile) and ice-streaming flow (corresponding to a concave-up shape profile ).

WAIS Surface elevation (m) Surface slope Driving stress (bar) Onset Mars Polar Cap Surface elevation (m) Surface slope Driving stress (bar) Onset

Ice-Sheet Modelling A flowline model is applied to examine the basal/surface conditions required for maintaining this ice-stream type surface profile. Model Run I (warm bed) Inputs: Outputs: Flowline geometry Surface mass balance Basal temperature (at pressure melting point) Basal geothermal heat flux Distribution of temperature Distribution of velocity Model Run II (cold bed) Inputs: Outputs: Flowline geometry Surface temperature Basal geothermal heat flux Distribution of temperature Distribution of velocity Surface mass balance

Surface mass balance (accumulation rate + ablation/sublimation rate) Basal Melting Rate Emergence Velocity Ice-Sheet Modelling Continuity Equation { { :

Model Run I (warm bed) Distance (km) m/a ococ (m) Temperature Horizontal Velocity Vertical Velocity (m) Dynamic Velocity m/a (Glen’s flow law)

Distance (km) m/a ococ (m) Temperature Horizontal Velocity Vertical Velocity (m) m/a Dynamic Velocity Onset (Glen’s flow law) Model Run I (warm bed)

Model Run II (cold bed) Temperature Horizontal Velocity Vertical Velocity Surface mass balance Distance (km) m/a ococ (m/a) (m)

Temperature Horizontal Velocity Vertical Velocity Surface Mass Balance Distance (km) m/a ococ (m/a) (m) Model Run II (cold bed)

Distance (km) Surface Mass Balance Basal Temperature   C/m   C/m   C/m Surface Temperature Blue: x Red: x Green: x ( o C) (m/a) Model Run II (cold bed)

Summary: The surface topography determined by MOLA data shows an ice-stream type profile through the head of Chasma Boreale. “Onset” (the location of the transition between inland ice flow and ice-stream flow) is clearly detected. Modelling study indicates that basal melting may have been experienced over the bed of Chasma Boreale at various times in Mars’ history.