The Baltic Sea basin is geologically very young. Approximately 15.000 years ago, northern Europe was covered by an ice sheet of up to 3.000 m thickness. When the last ice age ended, the giant ice sheets melted, resulting in a gradual increase of the global sea level, and also for a liftup of the land masses, which were now released from the weight of the ice crust. As a consequence of these two simulataneous processes, the Baltic Sea region underwent rapid changes, from a giant glacier lake to the brackish sea with a small connection to the ocean we know now.

The geological stages of the Baltic Sea since the end of the last ice age are named after bottom-dwelling animals whose widespread occurrence in respective sediment layers could be related to characteristic stages in the recent history of the Baltic Sea basin.

Animated ice cover retreat

This is an animation of the ice cover retreat, starting with approximately 19.000 years before present. You can see how the Baltic Sea first was covered by a giant glacier and lake, then an open bay with a large connection to the Atlantic; as the land rose due reduced ice weight, the Baltic Sea was partly cut off from the ocean, until it reached its current shape as we know it now. The northern part of the Baltic Sea basin still rises a few mm per year, resulting in a gradual retreat of the sea shore. However, it is expected that global sea level rise in the next decades will overtake this uplift, resulting in rising sea levels also at the banks of the northern Baltic Sea.