Eemian Sea, former body of water that flooded much of northern Europe and essentially made an island of Scandinavia. This marine transgression occurred during the Eemian Interglacial Stage (130,000 to 115,000 years ago) of the Pleistocene Epoch (approximately 2.6 million to 11,700 years ago). The sea deposited a thick sequence of sediments containing fossils that indicate water temperatures at least as warm as those of the region today. Late in the history of the Eemian Sea, climatic conditions became colder, as indicated by a change to cooler water animals.