MAMMAMIA – Multi-scAle-Multi-Method Analysis of Mechanisms causing Ice Acceleration

• Alexander, Andreas; Piermattei, Livia; Assmy, Philipp Kurt Wolf; Popp, Andrea; Zhao, Ken & Parra, Nicolas Valiente [Vis alle 20 forfattere av denne artikkelen] (2026). The Impact of Subglacial Drainage System Evolution and Glacier Lake Outburst on Arctic Fjord Macronutrient Dynamics. Journal of Geophysical Research (JGR): Biogeosciences. ISSN 2169-8953. 131(7). doi: 10.1029/2023jg007969. Fulltekst i vitenarkiv Vis sammendrag

  Global warming is amplified in the Arctic, accelerating glacier melt and freshwater runoff. At tidewater glaciers, runoff typically enters fjords at depth and generates buoyancy‐driven circulation that enhances glacier‐ocean exchanges of energy and matter, influencing macronutrient delivery and marine primary production. However, most studies lack the temporal resolution to capture low‐frequency, high‐magnitude events, leaving their impacts poorly understood. Here, we combine glacier observations with high‐frequency fjord and glacier‐lake sampling to examine the 2021 glacier lake outburst flood (GLOF) from Lake Setevatnet into Kongsfjorden (Svalbard). We show how evolving subglacial conditions before and during the GLOF shaped macronutrient supply to the inner fjord through both direct runoff and entrainment of bottom waters. Early in summer, nutrient delivery was dominated by direct runoff, supplying nitrate (NO 3 − ) and silicate via an inefficient drainage system. As the melt increased, an efficient system formed, generating a subglacial plume and initiating buoyancy‐driven circulation that entrained nutrient‐rich deep water. Despite high NO 3 − lake concentrations, the flood barely affected fjord NO 3 − levels. Instead, it produced a seasonal maximum in nitrite (NO 2 − ). Comparisons with conservative mixing estimates and nitrogen budget analyses reveal a non‐conservative nutrient signal. Although sedimentary sources cannot be excluded, the timing and spatial pattern of the NO 2 − anomaly suggest subglacial modification during floodwater transit. These findings indicate that Kongsfjorden functions as a summer nitrogen sink, partly shaped by subglacial transformations. Overall, nutrient delivery from tidewater glaciers depends not only on runoff volume but also on the subglacial drainage system characteristics, which evolve during high‐magnitude events such as GLOFs.

• Schuler, Thomas Vikhamar; Benestad, Rasmus; Isaksen, Ketil; Kierulf, Halfdan Pascal; Kohler, Jack & Moholdt, Geir [Vis alle 7 forfattere av denne artikkelen] (2025). Svalbard's 2024 record summer: An early view of Arctic glacier meltdown? Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 122(34). doi: 10.1073/pnas.2503806122. Fulltekst i vitenarkiv Vis sammendrag

  A record-breaking melt season affected the Arctic glaciers of Svalbard in summer 2024 by a substantial margin. Across the entire archipelago, glacier melting corresponded to an anomaly of up to four SD and exceeded any previous observation. The pan-Svalbard mass loss in summer 2024 amounts to ~61.7 ± 11.1 Gt and corresponds to 1% of the total ice volume on Svalbard and is comparable to that of the Greenland ice sheet (55 ± 35 Gt), which occupies an area about 50 times larger. Altogether, Svalbard and other glacier regions surrounding the Barents Sea lost 102.1 ± 22.9 Gt of ice in a single year and contributed 0.27 ± 0.06 mm (of which 0.16 mm alone is due to Svalbard) to global sea-level, putting the circum-Barents region among the strongest contributors to global sea-level rise in 2024. Most of the 2024 glacier melt occurred during a 6-wk period of persistent atmospheric circulation pattern causing record-high air temperatures, an event with an extremely low recurrence interval under current climate conditions. However, future climate projections suggest that such temperature levels will become increasingly commonplace by the end of the 21st century, potentially even surpassing those of 2024. Svalbard’s summer of 2024 serves as a forecast for future glacier meltdown in the Arctic, offering a glimpse into conditions 70 y ahead.

• Nanni, Ugo; Bouchayer, Coline Lili Mathy; Åkesson, Henning; Lefeuvre, Pierre-Marie; Mannerfelt, Erik Schytt & Köhler, Andreas [Vis alle 12 forfattere av denne artikkelen] (2025). Observed positive feedback between surface ablation and crevasse formation drives glacier acceleration and potential surge. Nature Communications. 16(1). doi: 10.1038/s41467-025-66349-9. Fulltekst i vitenarkiv Vis sammendrag

  Sudden glacier acceleration and instability, e.g. surges, strongly influence glacier ice loss. However, lack of in-situ observations of the involved processes hampers our ability to understand, quantify and model such a role. We present an analysis of the initiation of a surge (Kongsvegen glacier, Svalbard), focusing on the interplay between climatic and glacier-specific drivers. We integrate two decades of in-situ observations (GNSS, borehole and surface seismometers) with runoff simulations, and remotely sensed surface-elevation changes. We show that initial glacier thinning led to localized acceleration and crevassing. Then, we show that stronger surface melt enabled meltwater to reach the glacier bed. This input promotes high basal water pressure and glacier sliding, and in turn further surface crevassing. Our observations suggest that this positive feedback leads to the expansion of the initially localized instability. Our findings highlight mechanisms that could trigger glacier instabilities under a warming atmosphere beyond the High Arctic.

• Cao, Wenxue; Aalstad, Kristoffer; Schmidt, Louise Steffensen; Westermann, Sebastian & Schuler, Thomas (2025). Bayesian data assimilation on an Arctic glacier: learning from large ensemble twin experiments. Journal of Glaciology. ISSN 0022-1430. 71, s. 1–17. doi: 10.1017/jog.2025.10101. Fulltekst i vitenarkiv Vis sammendrag

  Numerical modeling is crucial for quantifying the evolution of cryospheric processes. At the same time, uncertainties hamper process understanding and predictive accuracy. Here, we suggest improving glacier surface mass balance simulations for the Kongsvegen glacier in Svalbard through the application of Bayesian data assimilation techniques in a set of large ensemble twin experiments. Noisy synthetic observations of albedo and snow depth, generated using the multilayer CryoGrid community model with a full energy balance, are assimilated using two ensemble-based data assimilation schemes: the particle batch smoother and the ensemble smoother. A comprehensive evaluation exercise demonstrates that the joint assimilation of albedo and snow depth improves the simulation skill by up to 86% relative to the prior in specific glacier regions. The particle batch smoother excels in representing albedo dynamics, while the ensemble smoother is marginally more effective for snow depth under low snowfall conditions in the ablation area. By combining the strengths of both observations, the joint assimilation achieves improved surface mass balance simulations across different glacier zones using either assimilation scheme. This work underscores the potential of ensemble-based data assimilation methods for refining glacier models by offering a robust framework to enhance predictive accuracy and reduce uncertainties in cryospheric simulations. Further advances in glacier data assimilation research with both synthetic and real observations will be critical to better understanding the fate and role of Arctic glaciers in a changing climate.

• Thøgersen, Kjetil; Gilbert, Adrien; Bouchayer, Coline Lili Mathy & Schuler, Thomas Vikhamar (2024). Glacier Surges Controlled by the Close Interplay Between Subglacial Friction and Drainage. Journal of Geophysical Research (JGR): Earth Surface. ISSN 2169-9003. 129(10). doi: 10.1029/2023JF007441. Fulltekst i vitenarkiv Vis sammendrag

  The flow of glaciers and ice sheets is largely influenced by friction at the ice-bed interface that can trigger rapid changes in glacier motion ranging from seasonal velocity variations to cyclic surge instabilities or even devastating glacier collapse. This wide range of transient glacier dynamics is currently not captured by models, and its implications for long-term glacier evolution are uncertain. This highlights the need of developing improved descriptions for processes that occur at the glacier bed. Here, we present a model that describes the evolution of basal friction inspired by a “rate and state” approach, coupled to models of subglacial drainage and glacier flow, and investigate how these couplings affect the dynamics of glaciers. We show that a wide range of sliding behavior results from a feedback loop between subglacial drainage efficiency and friction which depends on the evolution of a frictional state that can be interpreted as the degree of cavitation or till porosity for hard and soft beds, respectively. In our simulations, we find that glaciers are susceptible to surging if they exhibit a transition to velocity weakening friction associated with a poor sensitivity of the drainage capacity to the frictional state. This potential materializes if the local topography and mass balance create the conditions for high water pressure to build up in an area sufficiently large to exceed a critical length. We advocate accounting for feedback loops between friction and drainage as a promising avenue for better understanding dynamical instabilities of glaciers and ice sheets.

• Bouchayer, Coline Lili Mathy; Nanni, Ugo; Lefeuvre, Pierre-Marie; Hulth, John; Schmidt, Louise Steffensen & Kohler, Jack [Vis alle 8 forfattere av denne artikkelen] (2024). Multi-scale variations of hydro-mechanical conditions at the base of the surge-type glacier Kongsvegen, Svalbard. The Cryosphere. ISSN 1994-0416. 18(6), s. 2939–2968. doi: 10.5194/tc-18-2939-2024. Fulltekst i vitenarkiv Vis sammendrag

  The flow of glaciers is largely controlled by changes at the ice–bed interface, where basal slip and sediment deformation drive basal glacier motion. Determining subglacial conditions and their responses to hydraulic forcing remains challenging due to the difficulty of accessing the glacier bed. Here, we monitor the interplay between surface runoff and hydro-mechanical conditions at the base of the Kongsvegen glacier in Svalbard. From July 2021 to August 2022, we measured both subglacial water pressure and till strength. Additionally, we derived median values of subglacial hydraulic gradient and radius of channelized subglacial drainage system from seismic power, recorded at the glacier surface. To characterize the variations in the subglacial conditions caused by changes in surface runoff, we investigate the variations of the following hydro-mechanical properties: measured water pressure, measured sediment ploughing forces, and derived hydraulic gradient and radius, over seasonal, multi-day, and diurnal time

• Bouchayer, Coline Lili Mathy; Aiken, John Mark; Thøgersen, Kjetil; Renard, Francois & Schuler, Thomas (2022). A Machine learning framework to automate the classification of surge-type glaciers in Svalbard. Journal of Geophysical Research (JGR): Earth Surface. ISSN 2169-9003. 127(7). doi: 10.1029/2022JF006597. Fulltekst i vitenarkiv Vis sammendrag

  Surge-type glaciers are present in many cold environments in the world. These glaciers experience a dramatic increase in velocity over short time periods, the surge, followed by an extended period of slow movement, the quiescence. This study aims at understanding why only few glaciers exhibit a transient behavior. We develop a machine learning framework to classify surge-type glaciers, based on their location, exposure, geometry, climatic mass balance and runoff. We apply this approach to the Svalbard archipelago, a region with a relatively homogeneous climate. We compare the performance of logistic regression, random forest, and extreme gradient boosting (XGBoost) machine learning models that we apply to a newly combined database of glaciers in Svalbard. Based on the most accurate model, XGBoost, we compute surge probabilities along glacier centerlines and quantify the relative importance of several controlling features. Results show that the surface and bed slopes, ice thickness, glacier width, climatic mass balance, and runoff along glacier centerlines are the most significant features explaining surge probability for glaciers in Svalbard. A thicker and wider glacier with a low surface slope has a higher probability to be classified as surge-type, which is in good agreement with the existing theories of surging. Finally, we build a probability map of surge-type glaciers in Svalbard. The framework shows robustness on classifying surge-type glaciers that were not previously classified as such in existing inventories but have been observed surging. Our methodology could be extended to classify surge-type glaciers in other areas of the world.

• Gilbert, Adrien; Gimbert, Florent; Thøgersen, Kjetil; Schuler, Thomas & Kääb, Andreas (2022). A Consistent Framework for Coupling Basal Friction With Subglacial Hydrology on Hard-Bedded Glaciers. Geophysical Research Letters. ISSN 0094-8276. 49(13). doi: 10.1029/2021GL097507. Fulltekst i vitenarkiv Vis sammendrag

  Below hard-bedded glaciers, both basal friction and distributed subglacial drainage are thought to be controlled by a network of cavities. Previous coupled hydro-mechanical models, however, describe cavity-driven friction and hydraulic transmissivity independently, resulting in a physically inconsistent cavity evolution between the two components of the models. Here, we overcome this issue by describing the hydro-mechanical system using a common cavity-evolution description, that governs both transient friction and hydraulic transmissivity. We show that our coupling approach is superior to previous formulations in explaining a unique observation record of glacier sliding speed from the French Alps. We find that, at multi-day to multi-decadal timescales, sliding speed can be expressed as a direct function of basal shear stress and water discharge, without accounting for water pressure, which simply adjusts to maintain the cavitation ratio needed to accommodate the water supply.

• Piho, Laura; Alexander, Andreas & Kruusmaa, Maarja (2022). Topology and spatial-pressure-distribution reconstruction of an englacial channel. The Cryosphere. ISSN 1994-0416. 16(9), s. 3669–3683. doi: 10.5194/tc-16-3669-2022. Fulltekst i vitenarkiv Vis sammendrag

  Information about glacier hydrology is important for understanding glacier and ice sheet dynamics. However, our knowledge about water pathways and pressure remains limited, as in situ observations are sparse and methods for direct area-wide observations are limited due to the extreme and hard-to-access nature of the environment. In this paper, we present a method that allows for in situ data collection in englacial channels using sensing drifters. Furthermore, we demonstrate a model that takes the collected data and reconstructs the planar subsurface water flow paths providing spatial reference to the continuous water pressure measurements. We showcase this method by reconstructing the 2D topology and the water pressure distribution of a free-flowing englacial channel in Austre Brøggerbreen (Svalbard). The approach uses inertial measurements from submersible sensing drifters and reconstructs the water flow path between given start and end coordinates. Validation of the method was done on a separate supraglacial channel, showing an average error of 3.9 m and the total channel length error of 29 m (6.5 %). At the englacial channel, the average error is 12.1 m; the length error is 107 m (11.6 %); and the water pressure standard deviation is 3.4 hPa (0.3 %). Our method allows for mapping of subsurface water flow paths and spatially referencing the pressure distribution within. Further, our method would be extendable to the reconstruction of other, previously underexplored subsurface fluid flow paths such as pipelines or karst caves.

• Piho, Laura; Alexander, Andreas & Kruusmaa, Maarja (2022). Topology and spatial-pressure-distribution reconstruction of an englacial channel. The Cryosphere. ISSN 1994-0416. doi: 10.5194/tc-16-3669-2022. Fulltekst i vitenarkiv
• Scholzen, Chloé Elisabeth; Schuler, Thomas Vikhamar & Gilbert, Adrien (2021). Sensitivity of subglacial drainage to water supply distribution at the Kongsfjord basin, Svalbard. The Cryosphere. ISSN 1994-0416. 15(6), s. 2719–2738. doi: 10.5194/tc-15-2719-2021. Fulltekst i vitenarkiv Vis sammendrag

  By regulating the amount, the timing, and the location of meltwater supply to the glacier bed, supraglacial hydrology potentially exerts a major control on the evolution of the subglacial drainage system, which in turn modulates ice velocity. Yet the configuration of the supraglacial hydrological system has received only little attention in numerical models of subglacial hydrology so far. Here we apply the two-dimensional subglacial hydrology model GlaDS (Glacier Drainage System model) to a Svalbard glacier basin with the aim of investigating how the spatial distribution of meltwater recharge affects the characteristics of the basal drainage system. We design four experiments with various degrees of complexity in the way that meltwater is delivered to the subglacial drainage model. Our results show significant differences between experiments in the early summer transition from distributed to channelized drainage, with discrete recharge at moulins favouring channelization at higher elevations and driving overall lower water pressures. Otherwise, we find that water input configuration only poorly influences subglacial hydrology, which instead is controlled primarily by subglacial topography. All experiments fail to develop channels of sufficient efficiency to substantially reduce summertime water pressures, which we attribute to small surface gradients and short melt seasons. The findings of our study are potentially applicable to most Svalbard tidewater glaciers with similar topography and low meltwater recharge. The absence of efficient channelization implies that the dynamics of tidewater glaciers in the Svalbard archipelago may be sensitive to future long-term trends in meltwater supply.

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