Influence of ice sheet and glacial erosion on passive margins of Greenland

The presence of Mesozoic and Cenozoic marine sediments at an altitude of 1.2 km near Scoresby Sund (central east Greenland) and Nuussuaq Peninsula (central west Greenland), and even up to 2 km in the Kangerdlugssuaq region (south-central east Greenland), illustrates significant uplifts of Greenland's margins. The magnitude of these uplifts somewhat contrasts with the absence of major tectonic activity along Greenland margins during the Cenozoic. In this study we test to which degree these vertical motions can be explained by glacial processes. We analyze the influence of the ice sheet loading in the central part of Greenland and the carving of the fjord systems on the evolution of the topography by numerically modeling these processes backward in time. In our experiments, we start with the modern topography and ice thickness and evaluate the pre-glacial topography calculating the flexural isostatic response to unloading the ice sheet. By restoring erosion backward in time and calculating the flexural isostatic effects, we estimate the influence of glacial carving (hereafter, the carving of the Earth surface by glacial-related erosion) and evaluate the pre-erosional topography of Greenland. Our analyses show that (1) the load of the ice sheet causes up to 850 m subsidence of the bedrock topography of the central part of Greenland. (2) The peripheral bulging caused by this ice loading has a negligible effect on amplitude of the uplifted Greenland margins. (3) Glacial carving and corresponding development of the large fjord system has a significant influence on vertical motion of passive margins of central (east and west) Greenland and can explain up to 1.2 km uplift. (4) The models show, however, that much of Greenland's topography is not caused by ice-related processes, and thus origin of these older mountain chains remains enigmatic. (5) Masses eroded from the regions of significant glacial erosion are larger than the recognized amount of sediments within adjacent off-shore basins, meaning that either the topography of those margins formed before breakup of Greenland or that sediments can be moved far away by the ocean. We also illustrate that our estimations are conservative because of low resolution of the DEMs used for calculations. Higher DEM resolution may increase effects of glacial carving by ~40%.