During Pleistocene glacial maxima, including the last glacial maximum, a thick floating ice shelf covered all or most of the deep Arctic Ocean. This conclusion is based on a preponderance of results from field and modeling studies. Of special importance are recent discoveries in the Arctic Ocean: the deep ice plowmarks on the submarine Yermak Plateau and Chukchi Borderland, and the evidence for sediment erosion and overconsolidation on the top of Lomonosov Ridge. In our view, they all are clear signatures of a former ice shelf that became grounded at these sites. While floating in the Arctic Ocean, the ice shelf would have exerted backpressure against any marine ice sheets that may have been grounded on circum-Arctic continental shelves, in particular against grounded ice streams, checking their instability, damping their surges, and deflecting their flow. At the close of glacial time, ice-shelf disintegration permitted ice-stream surges, making it possible for erratic-laden icebergs to reach the central Arctic. These features are those of an Arctic Ice Sheet that acted as a unified dynamic system, as the Antarctic Ice Sheet acts today. The Arctic Ice Sheet consisted of marine ice domes grounded on the continental shelf in the western Arctic and an ice shelf that spread across the Arctic Ocean basin and grounded against the continental shelf in the eastern Arctic. This grounding would dam Eurasian rivers flowing toward the Arctic. If the ice-dammed lakes then became frozen to the bed, marine ice domes would eventually form on the continental shelf of the eastern Arctic. However, there is evidence that these Eurasian marine ice domes formed and collapsed repeatedly between 24 ka and 12 ka, suggesting that these domes were highly unstable.