Paleotopography, Late Neogene and Quaternary glaciations, and landscape evolution in the Norwegian region

The project focused on topography in the western Scandinavian region, especially concerned the effect of glacial activity on its recent evolution. The main goals of the project were therefore to provide new understanding of and constraints on 1) the origin and age of large-scale topography existing in the Norwegian region today, 2) the timing and extent of early glaciations in Scandinavia, and 3) the processes responsible for the formation of the characteristic Norwegian landscape morphology, with high-elevation low- relief surfaces and deeply carved fjords. We started from the present-day topography and moved backwards in time in order to reconstruct paleotopography. We did this in a quantitative way by considering contributions to surface change from 1) processes in the deep interior of the Earth that influence the topography from below, 2) the structure of the outer crust of the Earth that make up the topography, 3) the volume of material found offshore originating from the Norwegian region, and 4) surface processes such as glacial erosion, river incision, and avalanches that wear topography down on the surface. Our work has provided new understanding of and constraints on the origin and age of large-scale topography existing in the Norwegian region today. We have showed that most topography is compensated by the crustal structure, suggesting a topographic age related to ~400 million year old mountain building. In addition, we infer that dynamic uplift (~300 m) has rejuvenated existing topography locally in the coastal region of southern Norway within the last ~10 million years due to convection deep within the Earth. These results are in strong contrast to the prevalent views; that the high topography along the Scandinavian margin should represent remnants of a low-relief peneplain surface uplifted from sea level within the last ~20 million years. Our results show that topography must have been high since ~400 million years ago. We have also reconstructed topography back in time (55 million years) using a numerical inversion scheme in combination with a fluvial surface process model and offshore sediment volumes. This alternative, but supplemental approach has shown that several scenarios for long-term landscape evolution in the Norwegian region are consistent with the offshore sediment record. However, when considering also large-scale landscape configuration and the degree of incision in the landscape, we find it most likely that high topography has prevailed throughout the most recent ~55 million years. So using a very different approach, we find the same consistent result, that the topography in western Scandinavia cannot represent remnants of a peneplain uplifted within the last ~20 million years. The sediment flux that would result from the incision of this peneplain recently is simply inconsistent with the low rates of erosion that we can infer from offshore sediment volumes. Future work will use the different reconstructions of topography back in time in combination with paleoclimate estimates from global scale climate models, in order to investigate when glacial activity may have initiated in the Scandinavian region. Finally, this project is together with collaborators behind a new understanding of the processes responsible for the formation of the characteristic Norwegian landscape morphology, with high-elevation low-relief surfaces and deeply carved fjords. This new understanding suggests that ice sheets can both create very steep terrain and low-relief surfaces at the same time, depending on the appearance of the initial landscape Wide valleys will become deeper, eventually turning into fjords, while smaller valleys and ridges will be levelled out to form low-relief regions at high elevation. This work therefore suggests that the high-elevation surfaces are also a product of glacial erosion below ice sheets, formed recently after the introduction of glacial erosion in the Scandinavian region with in the latest few million years.

This project uses a multidisciplinary approach in order to increase the understanding of 1) the origin of large-scale topography in the Norwegian region, and 2) the origin of the characteristic Norwegian landscape, with high-elevation low-relief surfaces and deeply carved fjords. The project will provide quantitative constraints and insight on the recent evolution of Norwegian topography, which is highly debated and controversial. The project results will also provide insight into the timing of initial g laciations in Fennoscandia. The project undertakes first an inverse modelling approach in order to reconstruct paleotopography, considering mantle processes, crustal structure, eroded material, and surface processes in a quantitative way. The reconstructe d topography will then be used in a forward modelling approach to investigate how the characteristic present-day landscape may have originated. The objectives will be achieved using available constraints on offshore sediment volumes (erosion), estimates of dynamic topography (uplift) and paleoclimate, and available information on the crustal structure in combination with numerical surface process modelling that simulates glacial, periglacial, and fluvial activity, and calculations of flexural isostasy. T he proposed project integrates geodynamics, quantitative geomorphology, and climate science. It will advance these fields and produce information relevant for hydrocarbon exploration offshore Norway. The project gives the applicant the opportunity to stre ngthen her academic profile by 1) increasing her publication record, 2) engaging in popular science dissemination, and 3) enlarging her scientific and industrial network, thereby promoting the gender balance within earth sciences. The transfer of scienti fic knowledge and skills, expansion of international cooperation and development of new interdisciplinary methods associated with this project are highly beneficial for the ongoing excellence of Norwegian research.