This contains the dataset associated with the publication titled "Quantification of post-glacier bedrock surface erosion in the European Alps using 10Be and optically stimulated luminescence exposure dating" published in Earth Surface Dynamics (2022).
Abstract. The retreat of glaciers since the Last Glacial Maximum (LGM) in the European Alps has left an imprint on topography through glacial and non-glacial erosional processes. However, few methods are currently capable of resolving these mechanisms on Lateglacial to Holocene timescales. Quantifying the relative contributions of mountain erosion, during these different climate cycles, is useful for understanding long-term landscape evolution and the links between global climate and erosion. Here, we combine three Optically Stimulated Luminescence (OSL) exposure dating signals with 10Be surface exposure dating to constrain the post-glacier erosion rates of bedrock samples down a vertical transect adjacent to the Gorner glacier in Zermatt, Switzerland. The results reveal erosion rates on the order of 10-2 to 10-1 mm a-1, in general agreement with other studies in the region, as well as a strong negative correlation between erosion rates and elevation. Finally, at present glacial erosion is assumed to have a greater influence on landscapes, yet a global compilation of both glacial and non-glacial erosion rates in deglaciated environments shows that erosion rates during interglacial times could be equally important.
<p>The exhumation of bedrock is controlled by the interplay between tectonics, surface processes and climate. The highest exhumation rates of cm/yr are recorded in zones of highly active tectonic convergence such as the southern Alps of New Zealand or Himalayan syntaxes, where high rock uplift rates combine with very active surface processes. Here, we use a combination of different thermochronometric systems, and notably trapped-charge thermochronometery, to show that such rates also occur in the Hida Range, Japanese Alps. Our results imply that cm/yr rates of exhumation may be more common than previously thought.</p><p>The Hida Range is the most northern and most extensive of the Japanese Alps, and reaches elevations of up to 3000 m a.s.l. The Hida Range is thought to have uplifted in the last 3 Myr in response to E-W compression and magmatism. Our study focuses on samples from the Kurobe gorge, which is one of the steepest gorges in Japan. Previous work has shown that exhumation rates in this region are exceptionally high, as documented by the exposure of the ~0.8 Ma Kurobe granite (Ito et al., 2013) in the gorge. We combined 12 new zircon (U-Th/He) ages and 11 new OSL-thermochronometry ages together with existing thermochronometric data to investigate the late Pleistocene exhumation of this region.</p><p>We found that exhumation rates increased to ~10 mm/yr within the past 300 kyr, likely in response to river base-level fall that increased channel steepness due to climatically controlled eustatic changes. Our thermochronometry data allow the development of time-series of exhumation rate changes at the timescale of glacial-interglacial cycles and show a four-fold increase in baseline rates over the past ~65 kyr. This increase in exhumation rate is likely explained by knickpoint propagation due to a combination of very high precipitation rates, climatic change, sea-level fall, range-front faulting and moderate rock uplift. Our data show that in regions with horizontal convergence, coupling between climate, surface processes and tectonics can exert a significant effect on rates of exhumation.</p><p><strong>References</strong></p><p>Ito, H., Yamada, R., Tamura, A., Arai, S., Horie, K., Hokada T., 2013. Earth&#8217;s youngest exposed granite and its tectonic implications: the 10-0.8 Ma Kurobegawa Granite. Scientific Reports 3: 1306.</p><p>&#160;</p>
<p>As the climate warms, increases in glacier melt and altered glacier dynamics will result in changes to the dynamics of the Greenland Ice Sheet, impacting the sediment delivery in these rivers. In turn, examining the processes by which proglacial rivers transport sediment delivered by the ice sheet has important implications for the delivery of sediment to the oceans. Applying current knowledge of sediment transport from glacially-fed catchments in alpine regions is difficult, given several pronounced differences compared to glacially-fed catchments in the Arctic. These differences include elevated water discharge and reduced amplitude in diurnal variations of water discharge. Thus, it is imperative that we understand the differences in sediment dynamics between these two regions and evaluate the processes responsible for sediment transport between the ice sheet and ocean. To pursue this understanding, we installed seismic stations to measure bedload transport near the terminus of Russell Glacier during the summer of 2021.</p><p>&#160;</p><p>We convert the seismic signal from these stations to a bedload transport rate by evaluating several environmental variables, including the transported grain size and ground properties near the river. One station was close to the glacier, whilst the other is 1.5 km downstream. The distance between the stations allows us to evaluate the timing of proglacial sediment transport and deposition. Additionally, the operation of the instruments from early June through mid-August allows us to evaluate seasonal characteristics in sediment discharge. Lastly, we compare these results to the current knowledge of sediment transport from glacierized catchments in mountain regions.</p>
<p>The Japanese Alps uplifted throughout the Quaternary and reach elevations of up to 3,000 m today. However, understanding the interaction between rates of Earth surface processes, tectonics and climate is challenging, partly due to the difficulties of measuring changes in the rates of Earth surface processes at the timescale of glacial-interglacial cycles. In particular, the youth of the Japanese Alps has made measurement of their exhumation histories complicated. To help resolve this issue, we investigate the potential of ultra-low temperature thermochronometers based on the luminescence and electron spin resonance (ESR) of feldspar and quartz minerals, respectively. We focus on the Tateyama region in the Hida range, which was glaciated during the late Quaternary period. In total, eight samples were analyzed by luminescence and ESR thermochronometry. While most luminescence signals have already reached their upper dating limit, ESR signals do constrain exhumation rates.</p><p>We measured the ESR dose response and thermal decay properties of all samples, specifically targeting the Al and Ti centres. In general, thermal stability is higher for the Ti centre than the Al centre, resulting in ESR ages of between 0.5-0.9 Ma, although the natural intensity of the Ti centre is close to or above the upper dating limit. In contrast, the Al signal still grows with time and is suitable for determining finite exhumation rates. Initial inversions reveal rock cooling rates on the order of 80 &#176;C/Ma, which can be inverted to preliminarily rates of rock exhumation of <3 mm/a within the past 1 Ma. In the next step, we will relate these rates to the climatic (glacial) and tectonic history of the Tateyama region.</p>
Key Points: 10 • Ice flowing over a rough basal topography may spontaneously develop an inter-11 nal shear band on topographical highs. 12 • The shear strain rate localization and shear heating in the internal shear band is 13 amplified by a non-linear rheology. 14 • We identify two competing mechanisms that affect the energy balance near the 15 bedrock: vertical advective cooling and internal shear heating. Abstract 17 The dramatic acceleration of ice surface speed from upstream to downstream is a no-18 ticeable feature in many ice streams and glaciers. This speed-up is thought to be asso-19 ciated with a transition from internal, distributed deformation to highly localized defor-20 mation at the ice-bedrock interface, but the physical processes governing this transition 21 remain unclear. Here, we argue that basal topography amplifies the feedback between 22 shear heating and localization, leading to the spontaneous formation of an internal shear 23 band for a non-linear rheology. We model the thermo-mechanical ice flow over a simpli-24 fied basal topography using a high-resolution Stokes solver. To capture the interactions 25 between ice and rock, we implement an Immersed Boundary Method and use a level-set 26 approach to represent the free surface of the ice. Our results suggest that an internal shear 27 band can form on topographical highs, continuously heating the basal ice and may grad-28 ually enable a transition to basal sliding. This effect depends sensitively on rheology, with 29 the composite rheology by Goldsby and Kohlstedt (2001) amplifying shear heating no-30 tably. 31 Plain Language Summary 32 On its way towards the ocean, ice speeds up dramatically from less than one me-33 ter per year inland to up to a kilometer per year downstream. In this paper, we inves-34 tigate the physical processes controlling this speed-up. More specifically, we focus on the 35 role that the bedrock topography underneath the ice might play to facilitate this tran-36 sition. We use a two-dimensional numerical model to simulate the temperature distri-37 bution and deformation within a slab of ice flowing down a ramp over a simplified to-38 pography. We find that including basal topography could lead to the development of in-39 ternal shear band located on top of topographical highs. Around half of the total shear 40 deformation within the ice occurs within this band. We compare our model results to 41 borehole measurements from Greenland and find evidence that supports the existence 42 of a shear band. 43
<p>Late Miocene calc-alkaline intrusions in the back-arc of Southern Patagonia mark an eastward migration of the arc due to accelerated subduction velocity of the Nazca plate or slab flattening preceding active ridge subduction. Amongst these intrusions are the emblematic Torres del Paine (51&#176;S) and Fitz Roy (49&#176;S) plutonic complexes, crystalised at ca. 12.5 and ca. 16.5 Ma, respectively (Leuthold et al., 2012; Ram&#237;rez de Arellano et al., 2012). Both intrusions are located at the eastern boundary of the Southern Patagonian Icefield and form prominent peaks with steep slopes that are ~3 km higher in elevation than the surrounding low-relief foreland. Their exhumation has been proposed as a response to glacial erosion and associated glacial rebound since ca. 7 Ma (Fosdick et al., 2013), and/or by regional dynamic uplift between 14 and 6 Ma due to the northward migration of subducting spreading ridges (Guillaume et al., 2009). Here we present a new data set of apatite and zircon (U-Th)/He from both plutonic complexes, numerically modelled to unravel their late-Neogene to Quaternary thermal histories. Our results show three rapid cooling periods for the Fitz Roy intrusion: at ca. 9.5 Ma, at ca. 7.5 Ma, and since ca. 1 Ma. For Torres del Paine, inverse thermal modelling reveals short and rapid cooling at ca. 6.5 Ma followed by late-Quaternary final cooling. The 10 Ma cooling signal only evidenced in the northern plutonic complex (Fitz Roy) may represent an exhumation response to the northward migrating subduction of spreading ridge segments, causing localized dynamic uplift. Thus, the absence of exhumation signal before 6.5 Ma in the southern part (Torres del Paine) suggest that the spreading ridge subduction must have occurred before its 12.5 Ma emplacement. On the other hand, rapid cooling by similar magnitude in both plutonic complexes between ca. 7.5&#8211;6.5 Ma, likely reflects the onset of late-Cenozoic glaciations in Southern Patagonia. Finally, the late-stage Quaternary cooling signals differ between Torres del Paine and Fitz Roy, likely highlighting different exhumation responses (<em>i.e. </em>relief development vs. uniform exhumation) to mid-Pleistocene climate cooling. We thus identify and distinguish the causes of rapid exhumation periods in the Southern Patagonian Andes, and propose a first Late Miocene exhumation pulse due to subduction of spreading ridge dynamics, and two Late Cenozoic exhumation episodes due to regional climate changes that have shaped alpine landscapes in this region.</p><p>References:</p><p>Leuthold J., et al. 2012. Time resolved construction of a bimodal laccolith (Torres del Paine, Patagonia). EPSL.</p><p>Ram&#237;rez de Arellano C., et al. 2012. High precision U/Pb zircon dating of the Chalt&#233;n Plutonic Complex (Cerro Fitz Roy, Patagonia) and its relationship to arc migration in the southernmost Andes. Tectonics.</p><p>Fosdick J. C., et al. 2013. Retroarc deformation and exhumation near the end of the Andes, southern Patagonia. EPSL.</p><p>Guillaume B. 2009. Neogene uplift of central eastern Patagonia: Dynamic response to active spreading ridge subduction? Tectonics.</p>
<p>Our ability to quantify past climate conditions is crucial for understanding and predicting future climate scenarios as well as landscape evolution. One of the most drastic climatic changes in Earth&#8217;s history was the Last Glacial Maximum (LGM) where a significant area of the planet&#8217;s surface was covered in ice (Clark et al., 2009). However, most reconstructions of the Earth&#8217;s past climate rely on the use of climate proxies (e.g. Jones and Mann, 2004 for a review), which are particularly poorly preserved in terrestrial settings previously covered by ice- thus limiting the applicability of existing methods.</p><p>Here, we apply feldspar thermoluminescence (TL) surface paleothermometry (Biswas et al., 2018; 2020) to better constrain the temperature history of exposed bedrock surfaces since the Last Glacial Maximum to present day. The aim of this study is to contribute towards a more detailed understanding of glacial and interglacial temperature fluctuations across the Central and Western Alps. Feldspar TL paleothermometry is a recently developed technique that exploits the dependence of trapped charge on temperature (Biswas et al., 2018). The trapped charge is sourced from feldspar&#8217;s crystalline lattice. While a TL signal can be extracted between room temperature and 450&#176;C, traps sensitive to typical surface temperature variations (e.g.10&#176;C) are found between 200&#176;C and 250&#176;C (Biswas et al., 2020). As a result, five thermometers (200&#176;C to 250&#176;C in 10&#176;C intervals) can be used together as a multi-thermometer, and subsequently combined with a Bayesian inversion approach to constrain thermal histories over the last50 kyr (Biswas et al., 2020).</p><p>The temperature histories of bedrock samples collected down two vertical transects adjacent to the Gorner (Switzerland) and the Mer de Glace (France) glaciers, which have been exposed progressively since the LGM, will be presented. Preliminary results suggest a temperature difference of &#8764;10 &#176;C in both locations, which is promising and in agreement with past surface temperatures obtained from other studies.</p><p><strong>References</strong>:</p><p>Biswas, R.H., Herman, F., King, G.E., Braun, J., 2018. Thermoluminescence of feldspar as a multi-thermochronometer to constrain the temporal variation of rock exhumation in the recent past. Earth and Planetary Science Letters, 495, 56-68.</p><p>Biswas, R.H., Herman, F., King, G.E., Lehmann, B., Singhvi, A.K., 2020. Surface paleothermometry using low temperature thermoluminescence of feldspar. Climate of the Past, 16, 2075-2093.</p><p>Clark, P. U., Dyke, A. S., Shakun, J. D., Carlson, A. E., Clark, J., Wohlfarth, B., Mitrovica, J. X., Hostetler, S. W., and McCabe, A. M., 2009. The Last Glacial Maximum. Science, 325 (5941), 710-714.</p><p>Jones, P.D., Mann, M.E., 2004. Climate over past millennia. Reviews of Geophysics, 42, 2004.</p>
<p>During Late Quaternary time, the paleoclimate of the eastern Sahara was punctuated by multiple pluvial periods, then dramatically and cyclically transformed to hyperarid conditions, receiving less than 2 mm/yr of precipitation at present. Geologists, climate modelers, and archaeologists, therefore, have used various proxies to reconstruct past climates during that time, a crucial period for human habitation and migration. These reconstructions, however, lack the precipitation pattern during those pluvial periods, which represents a significant control on weighing the hypotheses of human migrations and occupations. Here we reconstruct the chronology and paleohydrology of a set of fossil rivers expressed by ridges in the modern landscape due to differential erosion. Our <sup>14</sup>C and Optically Stimulated Luminescence (OSL) ages of sediments preserved in these ancient rivers cluster within the last African Humid Period (AHP; ca. 14.8 &#8211; 5.5 ka BP) and hence support more significant fluvial activity during this distinct humid epoch. Based on median grain size (D<em><sub>50</sub></em>), paleochannel geometry, and drainage area, paleohydraulic reconstructions indicate that typical precipitation intensities of 55&#8211;80 mm/h occurred during sediment transport events. When combined with previous annual rainfall estimates, we find that such rainfall intensities were likely 3&#8211;4 times more frequent during the AHP. These climatic perturbations may have rendered some parts of the Nile River Valley inhospitable for occupation, driving humans to migrate away in the northwest and west of the Nile Valley between 10.2 and 7.2 ka BP.&#160;Ultimately, our results, along with the archeological data, tell a tale from the past of the dramatic climatic changes that our planet undergoes, demonstrating the critical role of climate in sustaining human populations.&#160;</p><p>&#160;</p>
<p>In mountain accretionary wedges, it is generally considered that the preservation of a topography in mechanical equilibrium is modulated by the activation of faults, sometimes internal to the prism, sometimes frontal. The folds of the Himalayan foothills correspond to the most frontal structures of the Himalayan prism. Understanding the timing of the initiation and the activity of these frontal folds can provide valuable information on the deformation sequences within the range (reactivation of the MCT, prograde sequences and transfer to frontal folds, ...) in response to tectonic and climatic forcing. Late Cenozoic climatic changes, including glaciations, might have impacted the denudation of the Himalayan range. The study of recent deformation rates is thus key for understanding lateral variations in deformation along the entire Himalayan arc, which will bring new constraints on the interactions between tectonics and surface processes at different scales time, as well as deepen our understanding of the seismic behaviour of the range.</p><p>&#160;</p><p>Here we quantify exhumation rates in the Himalayan foothills using luminescence thermochronometry, which is a recently developed very-low temperature thermochronometer applicable between tens of years and a few hundred kyr. In contrast to classical methods, it can resolve thermal histories from the upper few km of the Earth&#8217;s crust, allowing spatial variations in exhumation rates across the Himalayas to be deciphered on sub-Quaternary timescales. An extensive data set of more than 40 Siwalik rock samples, from Western Nepal to Eastern Bhutan, was measured to complement other thermochronometric data and understand the sub-Quaternary deformation on the Himalayan foreland.</p><p>&#160;</p><p>The results show along-strike variations in exhumation rates in the Himalayan foothills during the late Quaternary, with exhumation rates across the sub-Himalaya varying locally independently of precipitation trends and changes in the modern convergence rates. These along-strike variations may suggest that over the last 300 kyr, Himalayan shortening has not only been accommodated by the most frontal faults along the Himalayan range.</p>
