The timing and extent of early glaciations in Greenland and their co-evolution with the underlying landscape remain elusive. Here we use the concept of geophysical relief to estimate fjord erosion and the subsequent flexural isostatic response to erosional unloading in Northeast and North Greenland between Scoresby Sund (70°N) and Independence Fjord (82°N). The timing of erosion and isostatic uplift is constrained by marine sediments of late Pliocene–early Pleistocene age that are now exposed on land between ~24 m and 230 m above sea level. By determining the timing of fjord formation, we can establish the early history of the Greenland Ice Sheet. We find that the Independence Fjord system must have formed by glacial erosion at average rates of ~0.5–1 mm/yr since ca. 2.5 Ma in order to explain the current elevation of the marine Kap København Formation by erosion-induced isostatic uplift. In contrast, fjord formation in the outer parts of Scoresby Sund commenced before the Pleistocene, most likely in late Miocene, and continued throughout the Pleistocene by progressive inland fjord formation. Our results demonstrate that the inception of the Greenland Ice Sheet began in the central parts of Northeast Greenland before the Pleistocene and spread to North Greenland only at the onset of the Pleistocene.

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