An ice sheet that extends over the sea and floats on the water. These range in thickness from a few hundred to over 1000 meters and are connected to land at coastal grounding lines and where they flow around islands. They calve icebergs at their seaward fronts and gain mass by flow from grounded ice sheets and glaciers and from new snow accumulation. Iceberg calving is the primary ablation process with melting providing a secondary mechanism. Ice shelves are key indicators of climate change since they respond much more rapidly than grounded ice sheets or glaciers to changes in climate. The continent of Antarctica is surrounded by ice shelves, with the largest being the Ross Ice Shelf, covering over 500,000 km².