Search

Landforms left behind by the last Scandinavian Ice Sheet (SIS) offer an opportunity to investigate controls governing ice sheet dynamics. Terrestrial sectors of the ice sheet have received considerable attention from landform and stratigraphic investigations. In contrast, despite its geographical importance, the Baltic Sea remains poorly constrained due to limitations in bathymetric data. Both ice-sheet-scale investigations and regional studies at the southern periphery of the SIS have considered the Baltic depression to be a preferential route for ice flux towards the southern ice margin throughout the last glaciation. During the deglaciation the Baltic depression hosted the extensive Baltic Ice Lake, which likely exerted a considerable control on ice dynamics. Here we investigate the Baltic depression using newly available bathymetric data and peripheral topographic data. These data reveal an extensive landform suite stretching from Denmark in the west to Estonia in the east and from the southern European coast to the Åland Sea, comprising an area of 0.3 million km 2. We use these landforms to reconstruct aspects of the ice dynamic history of the Baltic sector of the ice sheet. Landform evidence indicates a complex retreat pattern that changes from lobate ice margins with splaying lineations to parallel mega-scale glacial lineations (MSGLs) in the deeper depressions of the Baltic Basin. Ice margin still-stands on underlying geological structures indicate the likely importance of pinning points during deglaciation, resulting in a stepped retreat signal. Over the span of the study area we identify broad changes in the ice flow direction, ranging from SE–NW to N–S and then to NW–SE. MSGLs reveal distinct corridors of fast ice flow (ice streams) with widths of 30 km and up to 95 km in places, rather than the often-interpreted Baltic-wide (300 km) accelerated ice flow zone. These smaller ice streams are interpreted as having operated close behind the ice margin during late stages of deglaciation. Where previous ice-sheet-scale investigations inferred a single ice source, our mapping identifies flow and ice margin geometries from both Swedish and northern Bothnian sources. We anticipate that our landform mapping and interpretations may be used as a framework for more detailed empirical studies by identifying targets to acquire high-resolution bathymetry and sediment cores and also for comparison with numerical ice sheet modelling. [ABSTRACT FROM AUTHOR]

Subglacial meltwater landforms found on palaeo‐ice sheet beds allow the properties of meltwater drainage to be reconstructed, informing our understanding of modern‐day subglacial hydrological processes. In northern Canada and Fennoscandia, subglacial meltwater landforms are largely organized into continental‐scale networks of subglacial meltwater corridors (SMCs), interpreted as the relics of subglacial drainage systems undergoing variations in meltwater input, effective pressure and drainage efficiency. We review the current state of knowledge of bedforms (hummocks, ridges, murtoos, ribbed bedforms) and associated landforms (channels, eskers) described along SMCs and use selected high‐resolution DEMs in Canada and Fennoscandia to complete the bedform catalogue and categorize their characteristics, patterning and spatial distributions. We synthesize the diversity of bedform and formation processes occurring along subglacial drainage routes in a conceptual model invoking spatiotemporal changes in hydraulic connectivity, basal meltwater pressure and ice‐bed coupling, which influences the evolution of subglacial processes (bed deformation, erosion, deposition) along subglacial drainage systems. When the hydraulic capacity of the subglacial drainage system is overwhelmed glaciofluvial erosion and deposition will dominate in the SMC, resulting in tracts of hummocks and ridges arising from both fragmentation of underlying pre‐existing bedforms and downstream deposition of sediments in basal cavities and crevasses. Re‐coupling of ice with the bed, when meltwater supply decreases, facilitates deformation, transforming existing and producing new bedforms concomitant with the wider subglacial bedform imprint. We finally establish a range of future research perspectives to improve understanding of subglacial hydrology, geomorphic processes and bedform diversity along SMCs. These perspectives include the new acquisition of remote‐sensing and field‐based sedimentological and geomorphological data, a better connection between the interpreted subglacial drainage configurations down corridors and the mathematical treatments studying their stability, and the quantification of the scaling, distribution and evolution of the hydraulically connected drainage system beneath present‐day ice masses to test our bedform‐related conceptual model. [ABSTRACT FROM AUTHOR]

Supraglacial rivers and lakes are important for the routing and storage of surface meltwater during the summer melt season across the Greenland Ice Sheet (GrIS) but remain poorly mapped and quantified across the northern part of the ice sheet, which is rapidly losing mass. Here we produce, for the first time, a high-resolution record of the supraglacial drainage network (including both rivers and lakes) and its seasonal behaviour at Humboldt Glacier, a wide-outlet glacier draining a large melt-prone hydrologic catchment (13 488 km 2), spanning the period 2016 to 2020 using 10 m spatial resolution Sentinel-2 imagery. Our results reveal a perennially extensive yet interannually variable supraglacial network extending from an elevation of 200 m a.s.l. to a maximum of ∼ 1440 m a.s.l. recorded in 2020, with limited development of the network observed in the low-melt years of 2017 and 2018. The supraglacial drainage network is shown to cover an area ranging between 966 km 2 (2018) and 1566 km 2 (2019) at its maximum seasonal extent, with spatial coverage of up to 2685 km 2 recorded during the early phases of the melt season when a slush zone is most prominent. Up-glacier expansion and the development of an efficient supraglacial drainage network as surface runoff increases and the snowline retreats is clearly visible. Preconditioning of the ice surface following a high-melt year is also observed, with an extreme and long-lasting 2019 melt season and over-winter persistence of liquid lakes, followed by low snow accumulation the following spring, culminating in earlier widespread exposure of the supraglacial drainage network in 2020 compared to other years. This preconditioning is predicted to become more common with persistent warmer years into the future. Overall, this study provides evidence of a persistent, yet dynamic, supraglacial drainage network at this prominent northern GrIS outlet glacier and advances our understanding of such hydrologic processes, particularly under ongoing climatic warming and enhanced runoff. [ABSTRACT FROM AUTHOR]

Landforms left behind by the last Scandinavian Ice Sheet (SIS) offer an opportunity to investigate controls governing ice sheet dynamics. Terrestrial sectors of the ice sheet have received considerable attention by landform and stratigraphic investigations, but much less so for marine areas such as in the Baltic Sea. In contrast, despite its geographical importance, the Baltic Sea remain poorly constrained due to limitations in bathymetric data. The Baltic depression hosted the extensive Baltic Ice Lake, which likely exerted a considerable control on ice dynamics, providing an aqueous calving front that might have resulted in rapid collapse of this ice sheet sector. Both ice sheet scale investigations and regional studies at the southern periphery of the SIS have considered the Baltic depression as a preferential conduit for ice flux towards the southern ice margin throughout the last glaciation. Here we test this hypothesis using newly available bathymetric data and peripheral topographic data. For the first time, these data reveal an extensive landform suite stretching from Denmark in the west to Estonia in the east and from the southern European coast to the Aland Sea, comprising an area of 0.3 million km². We use these landforms to reconstruct the ice dynamic history of the Baltic sector of the SIS. Landform evidence indicates a complex retreat pattern that changes from lobate ice margins with splaying lineations to parallel MSGL in the deeper depressions of the Baltic Basin. Ice margin still-stands on underlying geological structures indicate the likely importance of pinning points during deglaciation resulting in a stepped retreat signal. Over the length of the study area we identify broad changes in ice flow geometry, ranging from SE-NW to N-S and then to NW-SE. Mega-scale glacial lineations reveal distinct corridors of fast ice flow (ice streams) with widths of 30 up to 95 km, rather that the often-interpreted Baltic-wide (300 km) accelerated ice flow zone. These smaller ice streams are interpreted to have operated during late stages of deglaciation. Where previous ice sheet-scale investigations inferred a single ice source, our mapping identifies flow and ice marginal geometries from both Swedish and north Bothnian sources. We anticipate our landform mapping and interpretations may be used as a framework for more detailed empirical studies by identifying targets to acquire high resolution bathymetry and sediment cores and also for comparison with numerical ice sheet modelling. [ABSTRACT FROM AUTHOR]

Hydrologically active subglacial lakes can drain large volumes of water and sediment along subglacial pathways, affecting the motion and mass balance of ice masses and impacting downstream sediment dynamics. To date, only eight active lakes have been reported beneath the Greenland Ice Sheet (GrIS), and thus the understanding of their spatial distribution and dynamic processes is still lacking. Here, using ICESat-2 (Ice, Cloud, and land Elevation Satellite-2) ATL11 data, we identify 18 active subglacial lakes, 16 of which have not been previously reported. Multi-temporal ArcticDEM (digital elevation model of the Arctic) strip maps were used to extend the time series to verify lakes and determine their drainage history. The identification of active subglacial lakes beneath the GrIS is complicated by the occurrence of supraglacial lakes, which also fill and drain and are hypothesized to be almost co-located. We therefore used the temporal pattern of ice-surface elevation change to discriminate subglacial lakes and utilized the ability of ICESat-2 to penetrate through surface water to correct the elevation provided by the ATL11 data. A significant localized elevation anomaly (-16.03 –10.30 m yr -1) was measured in all detected subglacial lakes after correction, revealing that six subglacial lakes are twinned with supraglacial lakes. The active subglacial lakes have large upstream hydrological catchments and are located near or below the equilibrium line. Lakes have a median area of 1.20 km 2 , and 12 lakes exhibited positive elevation-change rates during the ICESat-2 period. These observations illustrate the potential for combining ICESat-2 and the ArcticDEM to differentiate small subglacial lakes in the ablation zone and beneath supraglacial lakes. [ABSTRACT FROM AUTHOR]

We use a mathematical model to investigate the effect of basal topography and ice surface slope on transport and deposition of sediment within a water-filled subglacial channel. In our model, three zones of different behaviour occur. In the zone furthest upstream, variations in basal topography lead to sediment deposition under a wide range of conditions. In this first zone, even very small and gradually varying basal undulations (~5 m amplitude) can lead to the deposition of sediment within a modelled channel. Deposition is concentrated on the downstream gradient of subglacial ridges, and on the upstream gradient of subglacial troughs. The thickness and steepness of the ice sheet has a substantial impact on deposition rates, with shallow ice profiles strongly promoting both the magnitude and extent of sediment deposition. In a second zone, all sediment is transported downstream. Finally, a third zone close to the ice margin is characterised by high rates of sediment deposition. The existence of these zones has implications for esker formation and the dynamics of the subglacial environment. [ABSTRACT FROM AUTHOR]

Hydrologically active subglacial lakes can drain large volumes of water and sediment along subglacial pathways, a ffecting the motion and mass balance of ice masses, and impacting downstream sediment dynamics. Only seven active lakes have been reported beneath the Greenland Ice Sheet (GrIS) to date, and thus a systematic understanding of their spatial distri bution and dynamic processes is still lacking. Here, using the ICESat-2 ATL11 data, we identified 61 active subglacial lakes, 59 of which have not been previously reported. The identification of active subglacial lakes beneath the GrIS is complicated by the occurrence of supraglacial lakes, which also fill and drain, and are hypothesized to be almost co-located. However, the ability of ICESat-2 to penetrate through shallow surface water allowed us to correct the elevation provided by the ATL11 da ta. A significant localized elevation anomaly was still measured in all detected subglacial lakes after correction, revealing tha t 18 subglacial lakes are twinned with supraglacial lakes. The active subglacial lakes have large upstream hydrological catch ments and are located near or below the equilibrium line. These observations suggest that active subglacial lakes are widespr ead components of the subglacial drainage system and provide critical information for understanding their activity. [ABSTRACT FROM AUTHOR]