Final answer:
The uplift in the Great Lakes and northern Baltic Sea region is primarily due to post-glacial rebound, a process that occurs following the melting of ice sheets and the subsequent rise of the underlying lithosphere.
Step-by-step explanation:
The crustal uplift in the Great Lakes and northern Baltic Sea over the last 10,000 years is mainly attributed to post-glacial rebound. This phenomenon occurs because as the massive weight of the glacial ice sheets is removed, the compressed lithosphere beneath begins to slowly rise or 'rebound'. This is not to be confused with marine regression, which is a geological process where areas of the seafloor previously submerged are exposed above sea level due to a decrease in sea level or a rise in regional land. Mantle upwelling is a process involving the ascent of hotter material within the Earth's mantle, but it is not the principal cause of uplift in this region. The concept of isostasy, akin to an iceberg melting in the ocean, helps explain how the Earth's lithosphere adjusts to changes in weight distribution.