The geomorphology of the western Siberian Arctic coast represents a significant departure from the global trend of Holocene delta formation by major rivers. The Ob' and Yenisei Rivers in western Siberia drain into the Arctic Ocean via estuaries ∼900 and ∼500 km long, respectively. Eastern Siberian rivers such as the Lena, Indigirka, and Kolyma terminate at significant marine deltas. We show that this spatial variation in coastal geomorphology can be explained by the glacial isostatic adjustment of the region. The development and collapse of a peripheral bulge in western Siberia, associated with the glaciation and subsequent deglaciation of the Eurasian ice sheets, led to a distinct spatial variation in sea-level change that continues to this day. In particular, since the marked decrease in global-scale ice melting ca. 7 ka, our model predicts a sea-level rise at the mouth of the Ob' River of ∼14 m, compared to a rise of ∼6 m at the mouth of the Lena River, which ceased at 3 ka. We propose that the enhanced sea-level rise in the western Siberian Arctic associated with peripheral bulge subsidence has prevented the establishment of marine deltas at the mouths of the Ob' and Yenisei Rivers. We conclude that regional variations in relative sea-level change driven by glacial isostatic adjustment should be considered when interpreting large-scale coastal morphology and deltaic stratigraphy, which is normally assumed to correlate with eustatic fluctuations.