Siberia covers the majority of Russia
The correct answer is REGION
The term is used in political geography to explains a particualr area with definable characteristics and not always limted to governments and boundaries. A region often has a similarity in terms of governance,climate,terrain and language.
You won't notice much at sea. Maybe a slight change in sea level.
Closer to the land though, water will draw away from the land maybe leaving the sea floor exposed. Then it will surge back in, flooding the land and inundating the coastal area.