How have glaciers caused the Caspian Sea to shrink and expand over time?

Over the past two million years, the advancement and retreat of glaciers across the Russian Plain have directly influenced the water levels of the Caspian Sea, causing it to alternately expand and shrink in successive phases known as the Baku, Khazar, and Khvalyn periods.1

These fluctuations are evidenced by peripheral terraces that mark the sea's former shorelines, as well as by patterns preserved in underlying sedimentary layers. While modern fluctuations in the Caspian are primarily driven by climate change affecting river influx, precipitation, and evaporation rates, the historical expansion and contraction of the sea were tied to these glacial cycles.12