Abstract
<p>The timing and extent of early glaciations in Greenland, and their co-evolution with the underlying landscape remain elusive. In this study, we explore the timing of fjord erosion in Northeast and North Greenland between Scoresby Sund (70°N) and Independence Fjord (82°N). By determining the timing of fjord formation, we can improve our understanding of the early history of the Greenland Ice Sheet in these regions.</p><p>We use the concept of geophysical relief to estimate fjord erosion and calculate the subsequent flexural isostatic response to erosional unloading. 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 and 230 m a.s.l.</p><p>We find that the northern Independence Fjord system must have formed by glacial erosion at average rates of ~0.5-1 mm/yr since ~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 southward Scoresby Sund commenced before the Pleistocene, most likely in late Miocene, and continued throughout the Pleistocene by fjord formation progressing inland. Our results suggest 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.  </p>
Highlights
Understanding the behavior and long-term stability of the Greenland Ice Sheet (GrIS) is key for predicting its future course
The timing of erosion and isostatic uplift is constrained by marine sediments of late Pliocene–early Pleistocene age that are exposed on land between ~24 m and 230 m above sea level
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
Summary
Understanding the behavior and long-term stability of the Greenland Ice Sheet (GrIS) is key for predicting its future course. Our understanding of the timing and extent of early glaciations and their influence on longterm landscape formation in Greenland remains fragmented. Provisional signs of glaciation in Northeast Greenland date back to the EoceneOligocene transition (Eldrett et al, 2007; Tripati et al, 2008; Bernard et al, 2016). Glaciation resumed from the mid-Miocene (14–11 Ma; Helland and Holmes, 1997; Thiede et al, 1998; Winkler et al, 2002; Berger and Jokat, 2008) and intensified markedly from the late Miocene (Larsen et al, 1994; Butt et al, 2001; St. John and Krissek, 2002; Pérez et al, 2018). For the Pleistocene, some studies suggest a persistent GrIS for the past several million years (Bierman et al, 2014, 2016), whereas others suggest that Greenland was deglaciated almost completely for extended periods during the second half of the Pleistocene (Schaefer et al, 2016)
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