Why have sea levels changed?
Today, large glaciers and ice caps are restricted to Antarctica, Greenland, and some mountainous areas of the world. In the last ice age, however, huge ice sheets covered many areas of the Northern Hemisphere.
Twenty thousand years ago, the Laurentian Ice Sheet extended across the provinces of Atlantic Canada to the edge of the continental shelf in places (geographic change in the glacial period).
Glacio-isostasy
The weight of the ice sheet depressed the earths crust. At the same time, because so much water was contained in the ice sheets and glaciers, the ocean level was lower. Then, the ice retreated. In some parts of Atlantic Canada, far from the centre of the ice sheets, sea level rose. In other places, closer to the ice, the earths crust rebounded when the weight of the ice was removed, so that sea level dropped for a while. Eventually, the rising ocean level caught up with the rebounding crust, so sea level rose. The result: different histories of sea-level change in different places.