Paleo Slide Set: Polar Ice Cores Extruding a core Scientists extrude the core from its barrel with the utmost care. Any butyl acetate on the core surface is carefully cleaned off before sawing the ice into 2 m sections. The cloudy layers clearly visible in this 6 m core section were formed when dust fell onto the ice sheet and was entrained in the ice. Photo Credits: Mark Twickler University of New Hampshire