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How do ice ages cause sea levels to fall?

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Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters. — Marine ecosystem Zonation of the ocean. Note that in the littoral zone the water is at the high-tide mark.

During an ice age, global sea levels fall because water is transferred from the oceans to the continents, where it is sequestered on land in the form of massive ice sheets and glaciers.123

This process occurs because the ocean serves as the ultimate source of the water that forms glacial ice. As global temperatures drop, water evaporates from the sea and falls as snow over landmasses. When this snowfall exceeds the rate of melting, it accumulates and densifies into ice over long periods. Because this water remains trapped on land rather than returning to the sea, the total volume of water in the ocean basins decreases, leading to a drop in mean sea level.45612

At the peak of the most recent glacial stage approximately 18,000 years ago, this sequestration of water resulted in sea levels that were roughly 120 to 130 metres lower than they are today, exposing vast areas of the continental shelves as dry land.24