The phrase "interior of the ice sheet" refers to the part or area inside a large mass of ice, such as a glacier or polar ice sheet. It signifies the region that is further away from the edges or boundaries of the ice sheet. Full definition
Eventually, the floating ice shelf in front of the glaciers «broke up», which caused them to retreat onto land sloping downward from the grounding lines to the interior of the ice sheet. (sciencedaily.com)
«It was the biggest collapse of its kind up to that point, and it served to demonstrate how ice shelves regulate the movement of ice from the interior of the ice sheet to the ocean.» (scientificamerican.com)
«We believed this was a good time to look to the interior of the ice sheet. (sciencedaily.com)