In parts of West-Antarctica the ice stands to a depht of 2000 m on the bottom of the surrounding ocean. Central parts of Greenland and East-Antartica are submerged below sea level under the weight of their iceplates. The above figure shows this subglacial bed elevation. It has to be noted that the stored energy in the oceans by now due to the increasing temperatures is considerable and for the latest data on that subject see here the NOAA webpages.