Modelling alpine glacier geometry and subglacial erosion patterns in response to contrasting climatic forcing

Abstract

Climate exerts a primary control on glacier mass balance, driving changes in ice flux, which affects basal sliding and subglacial erosion. Although past glacier reconstructions have been widely used as paleo‐climate proxies, extracting quantitative temperature/precipitation data from paleo‐glaciers is still challenging. The iSOSIA ice model was used over a synthetic landscape to quantitatively investigate the non‐linear dependence of glacier geometry and ice dynamics on climate forcing, as well as to analyse how spatial patterns of subglacial erosion and erosion rates vary between the accumulation and ablation zones for different climatic settings. We performed 10 calibrated climatic scenarios with different combinations of temperature and precipitation rate in two separate sets of simulations [maintaining either same equilibrium line altitude (ELA) or same ice extent; SA and ST, respectively]. Our results reinforce the role of climate and the importance of ice flux in conditioning glacier geometry. In SA simulations, contrasting climatic scenarios showed a major influence on glacier length and thickness. In ST simulations, calibrated ELAs presented a variability of over 300 m in order to maintain similar ice extent, but showed reduced changes in glacier thickness. These results highlight the importance of ice flux to predict glacier geometry, when compared to the overall mass balance from an ELA estimate. Subglacial abrasion and quarrying showed notable differences between the accumulation and ablation zones for varying climatic forcing, with multimodal erosion distributions for increased precipitation/temperature, shifting erosion towards higher‐elevation tributaries and connecting erosion patches in the ablation zone. Such trends highlight the role of subglacial hydrology and ice‐bed contact (cavitation) in dictating patterns of subglacial erosion, while the depth of erosion relates closely to ice flux and climate inputs. Our results have potential implications for paleo‐climate reconstructions based on glacier geometry and provide insights on how subglacial erosion can help estimate paleo‐climatic conditions from paleo‐glacial records.

Forward modelling of the completeness and preservation of palaeoclimate signals recorded by ice‐marginal moraines

“…We used a glacial landscape evolution model that simulates the erosion, transport and deposition of sediment by glaciers using the higher-order equations for ice flow (Egholm et al, 2011(Egholm et al, , 2012 to investigate the impact of climate change on moraine building in a mountainous landscape. The glacier model used a synthetic fluvial topography to represent a 20 km  40 km domain with a 160 m  160 m grid spacing, as used in previous studies of glacial landscape evolution (Braedstrup et al, 2016;Magrani et al, 2021). Climate variables (e.g., air temperature, precipitation) were not explicitly defined F I G U R E 1 Cumulative length change from observational records for three Swiss glaciers with different dynamic response times during a period of overall recession showing how glacier size affects climatic filtering.…”

“…The magnitude of glacier length or volume change in response to climatic forcing is strongly influenced by the feedbacks between ice flow and high‐relief topography (Magrani et al, 2021; Pedersen & Egholm, 2013). Therefore, palaeoglacier reconstructions that do not consider these dynamic feedbacks may underestimate or overestimate the climatic forcing suggested by differences in length or volume change between individual glaciers (e.g., Boston et al, 2015; Ely et al, 2021).…”

Modeling large‐scale landform evolution with a stream power law for glacial erosion (OpenLEM v37): benchmarking experiments against a more process-based description of ice flow (iSOSIA v3.4.3)

“…3.1). The rates of ice production and melting along the glacier have a strong influence on landform evolution (Pedersen and Egholm, 2013;Seguinot et al, 2018;Lai and Anders, 2021;Magrani et al, 2022). However, the implementation in Open-LEM by Hergarten (2021a) did not pay much attention to a realistic description of these rates since focus was on the formulation and the implementation of the glacial stream power law.…”

Modelling large‐scale landform‐evolution with a stream‐power law for glacial erosion (OpenLEM v37): Benchmarking experiments against a more process-based description of ice flow (iSOSIA v3.4.3)

“…Hence, the benchmarking scenarios have to be designed carefully. For the first set of experiments, we use a synthetic initial topography that has already been used in a benchmark study of iSOSIA against the full-Stokes Elmer/Ice model (Braedstrup et al, 2016) as well as in studies on the impact of subglacial quarrying (Ugelvig et al, 2016), subglacial sediment transport (Ugelvig et al, 2018b), and contrasting climatic forcing (Magrani et al, 2022) on glacial erosion. This topography represents a synthetic mountain topography based on the detachment limited version of the stream-power incision law for fluvial conditions.…”

“…Since the model parameters of iSOSIA are related more closely to the involved processes than those of OpenLEM, we define parameter values for iSOSIA based on the experience from previous studies (Egholm et al, 2012;Pedersen and Egholm, 2013;Braedstrup et al, 2016;Ugelvig et al, 2016;Liebl et al, 2021;Magrani et al, 2022). The parameter values required in…”