Search

Glaciers expel sediment as they melt, in addition to ice and water. As a result, changing glacier dynamics and melt produce changes to glacier erosion and sediment discharge, which can impact the landscape surrounding retreating glaciers, as well as communities and ecosystems downstream. Currently, numerical models that transport subglacial sediment on sub-hourly to decadal scales are one-dimensional, usually along a glacier's flow line. Such models have proven useful in describing the formation of glacial landforms, the impact of sediment transport on glacier dynamics, and the interactions among climate, glacier dynamics, and erosion. However, these models omit the two-dimensional spatial distribution of sediment and its impact on sediment connectivity – the movement of sediment between its detachment in source areas and its deposition in sinks. Here, we present a numerical model that fulfills a need for predictive frameworks that describe subglacial sediment discharge in two spatial dimensions (x and y) over time. SUGSET_2D evolves a two-dimensional subglacial till layer in response to bedrock erosion and changing sediment transport conditions. Numerical experiments performed using an idealized alpine glacier illustrate the heterogeneity in sediment transport and bedrock erosion below the glacier. An increase in sediment discharge follows increased glacier melt, as has been documented in field observations and other numerical experiments. We also apply the model to a real alpine glacier, Griesgletscher in the Swiss Alps, where we compare outputs with annual measurements of sediment discharge. SUGSET_2D accurately reproduces the general quantities of sediment discharge and the year-to-year sediment discharge pattern measured at the glacier terminus. The model's ability to match the measured data depends on the tunable sediment grain size parameter, which controls subglacial sediment transport capacity. Smaller grain sizes allow sediment transport to occur in regions of the bed with reduced water flow and channel size, effectively increasing sediment connectivity into the main channels. The model provides the essential components of modeling subglacial sediment discharge on seasonal to decadal timescales and reveals the importance of including spatial heterogeneities in water discharge and sediment transport in both the x and y dimensions in evaluating sediment discharge. [ABSTRACT FROM AUTHOR]

The western European Alps are characterised by deeply incised valleys, however the timing of their formation and the impact of Quaternary glaciation on rates of erosion remains disputed. This is mainly due to a lack of geochronological methods that cover the timespan of 10³-106 years. Electron spin resonance (ESR) thermochronometry using both the Al and Ti centres in quartz has high potential to fill this temporal gap because of its low closure temperature (<100 °C), potentially allowing changes in erosion rates to be related to glacial advance and retreat. We took surface rock samples for ESR and OSL-thermochronometry from two elevation transects in the Rhône valley, Switzerland near to the towns of Sion and Visp. Before applying the ESR thermochronometry method, a series of ESR protocol validation experiments were conducted using the Sion samples. A single aliquot regenerative additive measurement protocol was used that involves an annealing step at 400°C following the measurement of the natural signal. The suitability of this protocol was tested by using preheat plateau, dose recovery and recycling ratio tests, as well as through comparison with single aliquot additive dose response. To estimate the thermal kinetic parameters, both isochronal and isothermal decay experiments were performed. OSL-thermochronometry measurements were done following Bouscary and King (2022)[1]. The preheat plateau experiment showed that 170°C is the appropriate preheat temperature whilst sensitivity changes are not significant. ESR thermochronometric ages of seven samples from Sion range between 240 kyr and 650 kyr, while Ti centre ESR signals of samples from Visp are saturated. Although the lithology of the two sites is similar, the D0 values of samples from Visp are 2-3 times smaller than those measured at Sion. The frequency factors were >8 orders of magnitude smaller for the isochronal experiment relative to the isothermal experiment, with the latter experiment yielding the most plausible parameters. For most samples the Al-centre has higher thermal stability than the Ti-centre, although the thermal stability of the different samples investigated is highly variable (e.g., s ranges from 7.5*109 - 4.5*1012 s-1 and Et from 1.3-2 eV for the Ti-centre). Preliminary inversion of the Sion ESR data yield consistent cooling histories, with the exception of the valley bottom sample that suggests more rapid rock cooling. These data show that the low closure temperatures of the Al and Ti signals in quartz allow the Late Quaternary exhumation of the Alpine valleys to be resolved. In contrast, first luminescence measurements on the samples from Sion yielded saturated values (e.g., D0 values of the IR50 signals are between 130 and 200 Gy), demonstrating the additional potential of ESR-thermochronometry in these kinds of settings. [ABSTRACT FROM AUTHOR]

Understanding the interactions between Earth surface processes, tectonics and climate in mountain regions is challenging, partly due to the difficulties of measuring changes in the rates of Earth surface processes at the timescale of glacial-interglacial cycles. The Japanese Alps uplifted throughout the Quaternary and now reach elevations of up to 3,000 m. In particular, the young age 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 of feldspar minerals and electron spin resonance (ESR) of quartz minerals, in combination with inverse modelling to derive rock cooling rates and exhumation rates histories at 104-106 years timescales. We focus on the Tateyama region in the Hida range of the Japanese Alps. In total, 19 new samples were analyzed by luminescence and ESR thermochronometry. While most luminescence signals (IR50, IR100, IR150, IR225) have already reached saturation, ESR signals (Al and Ti centres) still grow with dose and are suitable for determining finite exhumation rates in the Tateyama region. We used the ESR single aliquot regenerative additive (SARA) dose protocol for dose evaluation including protocol optimization (i.e., preheat-plateau test). We checked for sensitivity changes due to the high-temperature annealing step within the SARA procedure using SARA vs. single aliquot additive dose response, repeated dose points (i.e., recycling ratio) and dose recovery of an artificially zeroed sample. Thermal stabilities of the ESR signals were analysed by using isothermal decay experiments and simulations of the isothermal decay using the experimentally constrained kinetic parameters. Our experiments showed insignificant sensitivity changes during measurements, resulting in Al and Ti ages of between 0.3-0.9 Ma and 0.5-1.1 Ma, respectively. In general, thermal stability is lower for the Al centre compared to that of the Ti centre but simulations yielded sufficient thermal stability over Quaternary timescales for both ESR centres. Inversions of the ESR data reveal rock cooling rates on the order of 30-80 °C/Ma, allowing us to resolve erosion rates on the order of few mm/a. Thus, preliminary erosion rates of <1 mm/a within the past 1 Ma could be inferred. [ABSTRACT FROM AUTHOR]