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This study assesses the response on ice dynamics of Petermann Glacier, a major outlet glacier in northern Greenland, to the 2012 and a possible future calving event. So far Petermann Glacier has been believed to be dynamically stable as another large calving event in 2010 had no significant impact on flow velocity or grounding line retreat. By analyzing a time series of remotely sensed surface velocities, we find an average acceleration of 10% between winter 2011/2012 and winter 2016/2017. This increase in surface velocity is not linear but can be separated into two parts, starting in 2012 and 2016 respectively. By conducting modeling experiments, we show that the first speedup can be directly connected to the 2012 calving event, while the second speedup is not captured. However, on recent remote sensing imagery newly developing fractures are clearly visible ∼12 km upstream from the terminus, propagating from the eastern fjord wall to the center of the ice tongue, indicating a possible future calving event. By including these fracture zones as a new terminus position in the modeling domain, we are able to reproduce the second speedup, suggesting that surface velocities remain on the 2016/2017 level after the anticipated calving event. This indicates that, from a dynamical point of view, the terminus region has already detached from the main ice tongue. Based on remote sensing data, Petermann Glacier sped up after the calving event in 2012Speedup is caused by a reduction in buttressingFurther retreat into the fjord likely causes glacier acceleration

Melt ponds forming on Arctic sea ice in summer significantly reduce the surface albedo and impact the heat and mass balance of the sea ice. Therefore, their areal coverage, which can undergo rapid change, is crucial to monitor. We present a revised method to extract melt pond fraction (MPF) from Sentinel‐2 satellite imagery, which is evaluated by MPF products from higher‐resolution satellite and helicopter‐borne imagery. The analysis of melt pond evolution during the MOSAiC campaign in summer 2020, shows a split of the Central Observatory (CO) into a level ice and a highly deformed ice part, the latter of which exhibits exceptional early melt pond formation compared to the vicinity. Average CO MPFs are 17% before and 23% after the major drainage. Arctic‐wide analysis of MPF for years 2017–2021 shows a consistent seasonal cycle in all regions and years. In the Arctic summer, puddles of surface melt water, called melt ponds, form on the sea ice. These melt ponds reduce the ability of the surface to reflect the sunlight. Instead, they absorb more solar energy and pave the way into the ocean beneath where the energy is also absorbed. Thus, it is important to know where these melt ponds develop and what fraction of the surface they cover. To investigate this, we present a classification algorithm that is used to extract the areal fraction of melt ponds from satellite measurements. The special focus of this study is the MOSAiC campaign in summer 2020, where the research vessel Polarstern drifted with an ice floe for 1 year. We can see a separation of this floe into two parts. One of them shows melt pond formation much earlier than the other. This is because of different ice age and surface properties. Additionally, we use the classification algorithm to analyze the differences of melt pond fraction between different dates and regions in the Arctic. Algorithm to extract melt pond and open water areas from Sentinel‐2 imagery with maximum uncertainty of 6%Exceptional early melt pond formation on MOSAiC Central Observatory, summer 2020, compared to broader vicinityHigh spatial and temporal variability of melt pond fraction on local and regional scales Algorithm to extract melt pond and open water areas from Sentinel‐2 imagery with maximum uncertainty of 6% Exceptional early melt pond formation on MOSAiC Central Observatory, summer 2020, compared to broader vicinity High spatial and temporal variability of melt pond fraction on local and regional scales

Migration of subglacial water underneath thick Antarctic ice is difficult to observe directly but is known to influence ice flow dynamics. Here, we analyze a 6‐year time series of displacement maps from differential Sentinel‐1 SAR interferometry (DInSAR) in the upstream region of Jutulstraumen Glacier. Our results reveal short‐term (between 12 days and 1 year) interconnected subsidence‐ and uplift events of the ice surface, which we interpret as a pressure response to the drainage and filling of subglacial lakes. This indicates an episodic cascade‐like water transport with longer quiescent phases in a dynamically stable glacial setting. Abrupt events appear in the DInSAR time series and are confirmed by ICESat‐2 altimetry. The events can be traced for a 1‐year period along a ∼175 km flow path. We are able to observe the migration of subglacial water with unprecedented spatial and temporal resolution, providing a new observational baseline to further develop subglacial hydrological models. Subglacial lakes and the movement of subglacial water play an important role in the way how ice flows in the Antarctic Ice Sheet. The drainage and filling of subglacial lakes is reflected in subsidence and uplift at the ice surface, which can be monitored by satellite based elevation measurements. In this study, we detect these elevation changes of the ice surface at the onset of Dronning Maud Land’s largest glacier (Jutulstraumen Glacier, Antarctica). We register a number of connected events which show us where and when subglacial water moves downstream. We find that the water flows similarly to a self‐tipping swimming pool bucket: water beneath the ice is localized and abruptly moves from one place to another after some time has passed. Using airborne radar‐sounding techniques, we find that the water flows along preferential flowpaths in the subglacial system. These are the first confirmed subglacial water movements in central Dronning Maud Land, an area where no subglacial water flow has been observed previously. The episodic nature of water flow is a new observation that will help us to understand how the subglacial water forms its own pluming system beneath these large glaciers. Sentinel‐1 DInSAR estimates reveal a ∼175 km flow path of a cascade‐like chain of subglacial water propagation over a 1‐year periodHigh‐resolution ultra‐wideband radar data show no characteristic lake bed reflections and suggests water transport via a local trough systemWe find evidence of highly dynamic water transport in a static glacial stetting providing a benchmark dataset to improve modeling results Sentinel‐1 DInSAR estimates reveal a ∼175 km flow path of a cascade‐like chain of subglacial water propagation over a 1‐year period High‐resolution ultra‐wideband radar data show no characteristic lake bed reflections and suggests water transport via a local trough system We find evidence of highly dynamic water transport in a static glacial stetting providing a benchmark dataset to improve modeling results

The ice stream geometry and large ice surface velocities at the onset region of the Northeast Greenland Ice Stream (NEGIS) are not yet well reproduced by ice sheet models. The quantification of basal sliding and a parametrization of basal conditions remains a major gap. In this study, we assess the basal conditions of the onset region of the NEGIS in a systematic analysis of airborne ultra‐wideband radar data. We evaluate basal roughness and basal return echoes in the context of the current ice stream geometry and ice surface velocity. We observe a change from a smooth to a rougher bed where the ice stream widens, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. In the upstream region, the excess ice mass flux through the shear margins is evacuated by ice flow acceleration and along‐flow stretching of the ice. At the downstream part, the generally rougher bed topography correlates with a decrease in flow acceleration and lateral variations in ice surface velocity. Together with basal water routing pathways, this hints to two different zones in this part of the NEGIS: the upstream region collecting water, with a reduced basal traction, and downstream, where the ice stream is slowing down and is widening on a rougher bed, with a distribution of basal water toward the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology. The Northeast Greenland Ice Stream (NEGIS) transports a large amount of ice mass from the interior of the Greenland Ice Sheet (GrIS) toward the ocean. The extent and geometry of the NEGIS are difficult to reproduce in current ice sheet models because many boundary conditions, such as the properties of the ice base, are not well known. In this study, we present new characteristics of the ice base from the onset region of the NEGIS derived by airborne radio‐echo sounding data. Our data yield a smooth and increasingly lubricated bed in the upstream part of our survey area, which enables the ice to accelerate. Our results confirm the hypothesis that the position of the ice stream boundaries are coupled to the subglacial hydrology system. Basal roughness at the onset of the NEGIS hints to a geomorphic anisotropy and a change in the geomorphological regimeBasal water is funneled into the ice stream upstream and redistributed toward the shear margins further downstreamA smooth and progressively lubricated bed reduces basal traction and favors the acceleration of the NEGIS at its onset Basal roughness at the onset of the NEGIS hints to a geomorphic anisotropy and a change in the geomorphological regime Basal water is funneled into the ice stream upstream and redistributed toward the shear margins further downstream A smooth and progressively lubricated bed reduces basal traction and favors the acceleration of the NEGIS at its onset