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Following the tradition of modeling fluvial landscape evolution, a novel approach describing glacial erosion based on an empirical stream power law was proposed. This approach differs substantially from well-established process-based models applied to describe glacial erosion in mountain landscapes. Outstanding computational performance but a number of potential limitations compared to process-based models requires extensive testing to evaluate the applicability of this novel approach. In this study, we test the validity of the glacial stream power law and its implementation into a 2-D landform evolution model (OpenLEM) by benchmarking it against a state of the art surface process model based on the integrated second-order shallow-ice approximation (iSOSIA). Despite completely different approaches, OpenLEM and iSOSIA predict similar ice flow patterns and erosion rates for a wide range of climatic conditions without re-adjusting a set of calibrated parameters. This parameter set is valid for full glacial conditions where the entire precipitation is converted to ice but also for an altitude-dependent glacier mass balance as characteristic for most glaciated mountain ranges on Earth. In both models characteristic glacial features, such as overdeepenings, hanging valleys and steps at confluences emerge roughly at the same locations, resulting in a consistent altitude-dependent adjustment of channel slope and relief. Compared to iSOSIA, however, distinctly higher erosion rates occur in OpenLEM at valley flanks during the initial phase of the fluvial to glacial transition. This is mainly due to the simplified description of glacier width and ice surface in OpenLEM. In this respect, we found that the glacial stream power approach cannot replace process-based models such as iSOSIA but is complementary to them by addressing research questions that could not previously be answered due to a lack of computational efficiency. The implementation of the glacial stream power law is primarily suitable for large-scale simulations investigating the evolution of mountain topography in the interplay of tectonics and climate. As coupling glacial and fluvial erosion with sediment transport shows nearly the same computational efficiency as its purely fluvial counterpart, mountain-range-scale simulations at high spatial resolution are not exclusively restricted to the fluvial domain anymore, and a series of exciting research questions can be addressed by this novel approach.

Lateglacial (19.0–11.7 ka ago) paleo-temperature records in the Western European Alps document several short-term cooling episodes within the general post-Last Glacial Maximum warming trend, in phase with North Hemisphere climatic oscillations. Alpine paleo-precipitation reconstructions are instead rare, and further constraints are needed in order to assess whether Lateglacial cold periods were associated with a modified atmospheric circulation pattern over the European Alps. The Alpine paleoglacial record offers a quantitative framework to investigate Lateglacial paleoclimatic conditions and glacier sensitivity in response to both temperature and precipitation changes. Through the combination of 10Be surface-exposure dating of glacial landforms and deposits constraining ice front and surface, together with numerical glacier simulations (iSOSIA), our study aims to reconstruct in space and time the main Lateglacial ice stages and associated paleo-climatic conditions in three tributary valleys (Valpelline, Valsavarenche and Val di Cogne) located within the Dora Baltea catchment (north-western Italian Alps). Our dating-modelling approach reveals in all the three investigated sectors two distinct paleoglacier stages at ca. 13 and 11 ka, documenting respectively the ice configurations at the transition between the Oldest Dryas cold period and the Bølling-Allerød interstadial, and between the Younger Dryas cold period and the early Holocene warming. Numerical ice-simulation outcomes suggest a similar-to-today precipitation pattern during the two ice stages, with either same absolute or homogeneously decreased precipitation values over the Dora Baltea catchment, although a unique quantitative solution of paleo-precipitation magnitudes could not be constrained from our dataset. Using present-day precipitation pattern and magnitude, our results provide paleo-temperature offsets from present-day between −3.3 and −3.8 °C for the older glacial stage, and −2.7 to −3.2 °C for the younger glacial stage, coinciding with the upper range of paleo-temperature reconstructions from other paleoclimatic proxies. Finally, Alpine glaciers’ sensitivity to climate fluctuations differ significantly between the investigated catchments, with a much higher glacier sensitivity to changes in the Equilibrium Line Altitude in the northern (Valpelline) compared to the southern (Valsavarenche and Val di Cogne) tributaries, reflecting different topographic and/or climatic conditions between the three valleys.

Following the tradition of modeling fluvial landscape evolution, a novel approach describing glacial erosion based on an empirical stream power law was proposed. This approach differs substantially from well established process-based models applied to describe glacial erosion in mountain landscapes. Outstanding computational performance but a number of potential limitations compared to process-based models requires extensive testing to evaluate the applicability of this novel approach. In this study, we test the validity of the glacial stream power law and its implementation into a 2-D landform evolution model (OpenLEM) by benchmarking it against a state of the art surface process model based on the integrated second order shallow-ice approximation (iSOSIA). Despite completely different approaches, OpenLEM and iSOSIA predict similar ice flow patterns and erosion rates for a wide range of climatic conditions without re-adjusting a set of calibrated scaling parameters. This parameter set is valid for full glacial conditions where the entire precipitation is converted to ice but also for an altitude-dependent glacier mass balance as characteristic for most glaciated mountain ranges on Earth. In both models characteristic glacial features, such as overdeepenings, hanging valleys, and steps at confluences emerge roughly at the same locations resulting in a consistent altitude-dependent adjustment of channel slope and relief. Compared to iSOSIA, however, distinctly higher erosion rates occur in OpenLEM at valley flanks during the initial phase of the fluvial to glacial transition. This is mainly due to the simplified description of glacier width and ice surface in OpenLEM. In this respect, we found that the glacial stream power approach cannot replace process-based models such as iSOSIA, but is complementary to them by addressing research questions that could not previously be answered due to a lack of computational efficiency. The implementation of the glacial stream power law is primarily suitable for large-scale simulations investigating the evolution of mountain topography in the interplay of tectonics and climate. As coupling glacial and fluvial erosion with sediment transport shows nearly the same computationally efficiency as its purely fluvial counterpart, mountain range scale simulations at high spatial resolution are not exclusively restricted to the fluvial domain anymore and a series of exciting research questions can be attacked by this novel approach.

Glaciers and ice sheets fluctuate in response to climatic change and often record these changes by building ice-marginal (terminal and lateral) moraines. Therefore, glacial landscapes are a potentially valuable archive of terrestrial palaeoclimate change. Typically, a cooling climate causes glaciers to expand and warming causes glaciers to shrink. However, the influence of high-relief mountainous topography on glacier dynamics complicates this behaviour, such that ice-marginal moraines are not always a straightforward palaeoclimate indicator. We used a higher-order ice-flow model to simulate change in glacier erosion, extent, and thickness in the response to climatic change and the resulting formation and preservation of moraines in a synthetic mountain landscape. Our results show that the rate of palaeoclimatic change relative to the glacier’s response time determines the geometry, number and position of ice-marginal moraines. However, glaciers can build distinct moraines in the absence of climate change, and the distance from the glacial maximum may not represent the chronological order of moraine formation. While moraines can be preserved despite erosion during subsequent glaciations, moraine sequences frequently contain gaps that could be misinterpreted as representing more stable palaeoclimates. These results provide theoretical understanding for the interpretation of glacial landforms both in the field and from satellite data (e.g. digital terrain models) to understand Quaternary climate change.

Exposing the sensitivity of the Greenland Ice Sheet (GrIS) to Holocene climate changes is a key prerequisite for understanding the future response of the ice sheet to global warming. In this study, we present new information on the Holocene glacial history of the GrIS in Inglefield Land, north Greenland. We use 10Be and in-situ 14C exposure dating to constrain the timing of deglaciation in the area and radiocarbon dating of reworked molluscs and wood fragments to constrain when the ice sheet retreated behind its present-day extent. The 10Be ages are scattered ranging from c. 92.7 to 6.8 ka whereas the in-situ 14C ages range from c. 14.2 to 6.7 ka. Almost half of the apparent 10Be ages predate the Last Glacial Maximum and up to 89 % are to some degree affected by nuclide inheritance. Based on the few reliable 10Be ages, the in-situ 14C ages and existing radiocarbon ages from Inglefield Land, we find that the deglaciation along the coast commenced c. 8.6–8.3 cal. ka BP in the western part and c. 7.9 ka in the central part, following the opening of Nares Strait and arrival of warm waters. The ice margin reached its present-day position c. 8.2 ka at the Humboldt Glacier and c. 6.7 ka in the central part of Inglefield Land. Radiocarbon ages of reworked molluscs and wood fragments show that the ice margin was behind its present-day extent from c. 5.8 to 0.5 cal. ka BP. After 0.5 cal. ka BP, the ice advanced towards its Little Ice Age position. Our results emphasize that the slowly eroding and possibly cold-based ice in north Greenland makes it difficult to constrain the deglaciation history based on 10Be ages alone unless it is paired with in-situ 14C ages. Further, combining our findings with those of recently published studies reveals distinct differences between deglaciation patterns of northwest and north Greenland. Deglaciation of the land areas in northwest Greenland occurred earlier than in north Greenland and periods of restricted ice extent were longer, spanning middle and late Holocene. Overall, this highlights past ice sheet sensitivity towards Holocene climate changes in an area where little information was available just a few years ago.

Norway is famous for its deeply incised, steep-sided fjords, carved out by glacial erosion. The high relief of the fjords stands in contrast to the extensive areas of relatively low relief found between the fjords. The origin and development of these low-relief areas remain debated. The classical interpretation relates them to a Mesozoic peneplanation surface, uplifted to the current high elevation in the early Cenozoic (e.g. Nesje, 1994). The validity of this interpretation has, however, been repeatedly questioned in recent times (e.g. Nielsen et al. 2009, Steer et al. 2012). Recent studies point instead to a significant impact of glacial and periglacial erosion processes on the long-term development of the low-relief surfaces (Egholm et al. 2015). Here, we present a large new dataset of in-situ produced cosmogenic 10Be and 26Al in bedrock and boulders from the high, flat summit surfaces along a transect from the coast to the inner parts of Sognefjorden in Norway. Our results indicate substantial glacial modification of the sampled low-relief surfaces within the last 50 ka. Close to the coast, at an elevation of around 700 meters, the cosmogenic nuclide signal was reset around the Younger Dryas due to extensive glacial erosion. Regarding the higher surfaces further inland, our results indicate a maximum cosmogenic nuclide inheritance of 20-30 ka prior to the last deglaciation. We do not find any signs of exceptional longevity of the low-relief landscape. In contrast, our results indicate that the low-relief areas were continuously eroded by glacial and periglacial processes in the Quaternary. Nesje & Whillans. Erosion of Sognefjord, Norway. Geomorphology 9(1), 33-45, 1994. Nielsen et al. The evolution of western Scandinavian topography: a review of Neogene uplift versus the ICE (isostasy–climate–erosion) hypothesis. Journal of Geodynamics 47(2), 72-95, 2009. Steer et al. Bimodal Plio-Quaternary glacial erosion of fjords and low-relief surfaces in Scandinavia. Na- ture Geoscience 5(9), 635-639, 2012. Egholm et al. The periglacial engine of mountain erosion – Part 2: Modelling large-scale landscape evolu- tion. Earth Surface Dynamics 3(4), 463-482, 2015.

Studies of periglacial processes usually focus on small-scale, isolated phenomena, leaving less explored questions of how such processes shape vast areas of Earth’s surface. Here we use numerical surface process modelling to better understand how periglacial processes drive large-scale, long-term evolution of mountains in cold climates.We focus upon two periglacial processes: 1) production of regolith from bedrock via frost-weathering, and 2) transport of sediment via frost creep. First, we propose a mechanistic model that quantifies the influence of temperature and sediment cover on process rates. For an array of mean annual air temperature and sediment cover thickness, we integrate the heat equation through annual cycles and record the intervals when conditions are optimal for frost-weathering and frost creep. Second, we incorporate these results into a landscape evolution model to explore the long-term feedbacks among climate, weathering intensity, sediment transport and the evolution of mountain topography.Our results suggest that periglacial processes can produce effectively smooth topography at a rate that varies with climate. The observed smoothing closely simulates the morphology of high-elevation, low-relief summit surfaces known from many cold-region mountain ranges. Our model simulations also suggest that late- Cenozoic cooling has brought about variations in the intensity and spatial pattern of periglacial activity. Depending upon elevation, some summit surfaces experienced accelerated erosion, while erosion may have slowed on higher surfaces. The latter implies that areas considered inactive, or relict, today may simply be too cold, or too flat, to allow for efficient periglacial activity under current conditions. The periglacial origins of such surfaces possibly pre-date the advent of deep cooling in the Pleistocene.

In-situ cosmogenic nuclides demonstrate existence of landforms preserved under glacial ice in regions such as Northern Sweden (Fabel, 2002), Svalbard (Gjermundsen, 2015) and New England (Bierman, 2015). Elsewhere, the existence of relict landforms is inferred from landscape morphology. Low-relief mountain summits along Sognefjorden in Norway have in the past been used as a base for re-constructing a regional pre-Quaternary surface (Nesje, 1994). The underlying assumption of this approach is that Quaternary surface processes eroded the summits very little, and the reconstructed surface can then be used to determine the total Quaternary bedrock erosion between the summits. However, the amount of Quaternary erosion of these summit flats remains debated (e.g. Steer, 2012) Here, we present an extensive new dataset of in-situ produced cosmogenic 10Be and 26Al in bedrock and boulders from high and flat summits along a 200 km long transect from the coast to the inner parts of Sognefjorden. Our results indicate substantial glacial modification of the summits within the last 50 ka. Close to the coast, at an elevation of around 700 meters, the cosmogenic nuclide signal was reset around the Younger Dryas. Further inland, our results indicate very little cosmogenic nuclide inheritance prior to the last deglaciation. We do not find any signs of exceptional longevity of the low-relief landscape around Sognefjord. In contrast, our results indicate that the low-relief areas were continuously eroded by glacial and periglacial processes in the Quaternary, and that excluding recent erosion of the summits is likely to underestimate total Quaternary erosion. Bierman et al. Cold-based Laurentide ice covered New England’s highest summits during the Last Glacial Maximum. Geology 43(12), 1059-1062, 2015. Fabel et al. Landscape preservation under Fennoscandian ice sheets determined from in situ produced 10 Be and 26 Al. Earth and Planetary Science Letters 201(2), 397-406, 2002. Gjermundsen et al. Minimal erosion of Arctic alpine topography during late Quaternary glaciation. Nature Geoscience 8(10), 789-792, 2015. Nesje & Whillans. Erosion of Sognefjord, Norway. Geomorphology 9(1), 33-45, 1994. Steer et al. Bimodal Plio-Quaternary glacial erosion of fjords and low-relief surfaces in Scandinavia. Nature Geoscience 5(9), 635-639, 2012.

It is an ongoing debate whether the degree of chemical weathering in mountain regolith can be used to infer a pre-Quaternary formation history (e.g. Strømsøe and Paasche, 2011; Goodfellow 2012). Here we present a new dataset of in-situ produced cosmogenic 10Be and 26Al along with sediment analyses from five pit profiles dug through regolith mantle on the easternmost summits of Reinheimen Nationalpark in Norway. The study area only shows sporadic signs of glacial erosion, and could be classified as a relict non-glacial surface. We aim to use the residence time of regolith in this area to infer rates of landscape evolution of the mountain summit.ReferencesGoodfellow B W, 2012. A granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins. Quaternary Science Reviews, 57, 121- 135.Strømsøe J R, Paasche Ø, 2011. Weathering patterns in high-latitude regolith. Journal of Geophysical Research: Earth Surface, 116 (F3)