Ice dynamics and glacial history from remote sensing of the Seno Skyring-Seno Otway-Strait of Magellan region, southernmost Patagonia

The glacial geomorphology of southernmost Patagonia records the advance and retreat of the Patagonian ice sheet over a number of glacial cycles. The well-preserved landform assemblages and sediments that have been left behind comprise one of the longest and most complete records of Quaternary glaciations in the world. Despite this, little is known about the pre-Last Glacial Maximum (LGM) ice sheet dynamics in a number of areas, particularly around the Strait of Magellan. This study has mapped in detail the glacial geomorphology of the Seno Skyring-Seno Otway-Strait of Magellan region from a combination of Landsat and ASTER satellite imagery and oblique and aerial photographs for the purposes of reconstructing the ice sheet dynamics. A wide variety of glacial landforms have been mapped, including glacial lineations, moraine ridges, meltwater channels, outwash plains and palaeo-shorelines. The most distinct features within the study area are highly elongate streamlined glacial lineations on the western side of the Strait of Magellan. A landsystems approach has been employed in order to decipher this group of lineations and three potentially plausible landsystems are evaluated: a palaeo-ice stream, a surging glacier, and an ice-marginal terrestrial landsystem. Based on the characteristic shape, dimensions and abrupt lateral margin of the flow-set, the lateral variation in lineation length and elongation ratios, and the presence of a potentially-deformable bed, these lineations are interpreted as being diagnostic of a terrestrial palaeo-ice stream. It is suggested that the initiation of ice streaming was caused by calving into one of two ice-dammed proglacial lakes. The lakes were located within the former Seno Skyring and Seno Otway ice lobes, which are well-defined by arcuate sequences of moraine ridges. The westernmost of the lakes, proglacial Lake Skyring, is delimited by a series of palaeo-shorelines surrounding the present-day lake Laguna Blanca. The size and orientation of meltwater channels and an outwash plain suggests that proglacial Lake Skyring drained eastwards towards the Strait of Magellan in an abrupt event. The ice sheet has been reconstructed at 10 time-steps, documenting stages of both advance and retreat. An attempt has been made to place this reconstruction within the framework of the wider glacial chronology of the region. From this, it is suggested that ice stream activity contributed to the rapid deglaciation of this sector of the ice sheet during the penultimate glaciation. Future work should focus on applying fieldwork to help validate the interpretations of this study. This should include dating of the landforms and sediments that have been mapped in order to improve the pre-LGM glacial chronology of this region, which is currently poorly-constrained

On the ice-sediment-landform associations of surging glaciers on Svalbard

PhDGlacier surges are amongst the most dynamic of glaciological phenomena, but their controlling mechanisms remain incompletely understood. Surging glaciers are characterised by cyclical flow instabilities and the rapid transfer of ice to the ablation area, typically resulting in significant mass loss. The High-Arctic archipelago of Svalbard is one of several regions in the northern hemisphere which contain a high-density of surge-type glaciers, variously estimated to be between 13-90% of the total glacier population across the islands. Developing a better understanding of which of these figures, if either, is most realistic is important in the context of glacier dynamics and related contributions of small glaciers and ice caps to sea level change in the immediate future. This study presents detailed assessments of the margins of several known surge-type glaciers in Svalbard in order to update and improve the existing framework by which they are identified, and to provide a foundation for future reassessments of the surge-type glacier population based on distinct ice-sediment-landform assemblages. A range of techniques is utilised, including geomorphological and structural glaciological mapping, sedimentological analysis, basal ice descriptions, and stable isotope analysis. This work provides further insight into diagnostic indicators of surge behaviour preserved in basal ice sequences; provides links between surge dynamics and basal ice sequences, the glaciological structure and the landform record; and investigates the structural and tectonic development of surge-type glaciers. Based on this, surge landsystems are proposed for: (1) small valley glaciers, (2) large land-terminating glaciers, and (3) large tidewater glaciers. It is suggested that these three landsystems, with some variability, broadly characterise the geomorphology of the vast majority of known Svalbard surge-type glaciers and, in conjunction with structural glaciological and basal ice investigations where relevant, may allow previously unknown surge-type glaciers to be identified in the field, from aerial photographs, and on sea floor imagery. This work adds to the existing repertoire of modern analogues and the breadth of surging glacier landsystems, and provides a holistic basis for assessing possible palaeo-surge behaviour within the Quaternary record.NERC algorithm PhD studentship (NE/I528050/1), a Queen Mary Postgraduate Research Fund award, an Arctic Field Grant award, and a QRA conference awar

Dendritic subglacial drainage systems in cold glaciers formed by cut-and-closure processes

The routing and storage of meltwater and the configuration of drainage systems in glaciers exert a profound influence on glacier behaviour. However, little is known about the hydrological systems of cold glaciers, which form a significant proportion of the total glacier population in the climate sensitive region of the High Arctic. Using glacio-speleological techniques, we obtained direct access to explore and survey three conduit systems and one moulin within the tongue area of Tellbreen, a small cold-based valley glacier in central Spitsbergen. More than 600 m of conduits were surveyed and mapped in plan, profile and cross-section view to analyse the configuration of the drainage system. The investigations revealed that cold-based glaciers can exhibit a dendritic drainage network with supra-, en- and subglacial components formed most likely by cut-and-closure processes as well as surface-to-bed drainage via moulins. Furthermore, we observed that water is stored within the glacier and released gradually via subglacial conduits during the winter months, forming a large and active icing in the proglacial area. The presence of supra-, en- and subglacial components, the surface-to-bed moulin and the dendritic subglacial drainage network suggest that existing models and understanding of the hydrology of cold glaciers needs to be re-evaluated, mostly concerning the different possible pathways and processes that form the hydrological system

Former dynamic behaviour of a cold-based valley glacier on Svalbard revealed by basal ice and structural glaciology investigations

H.L. was funded by a UK Natural Environment Research Council (NERC) PhD studentship (NE/I528050/1), the Queen Mary Postgraduate Research Fund, and an Arctic Field Grant from the Research Council of Norway. E.J.F. was funded by a NERC PhD studentship as part of the GAINS (Glacial Activity in Neoproterozoic Svalbard) grant (NE/H004963/1). K.N. was funded by an Arctic Field Grant, the Swiss Society for Speleology, and the travel grant commission of the Swiss Academy of Science.Large numbers of small valley glaciers on Svalbard were thicker and more extensive during the Little Ice Age (LIA), demonstrated by prominent ice-cored moraines up to several kilometres beyond present-day margins. The majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20th century and are now largely frozen to their beds, indicating they are likely to have undergone a thermal transition from a polythermal to a cold-based regime. We present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of Tellbreen, a small cold-based valley glacier in central Spitsbergen, based on its basal sequence and glaciological structures. Within the basal sequence, the underlying matrix-supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed, indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer. This is overlain by debris-poor dispersed facies ice, interpreted to have formed through strain-induced metamorphism of englacial ice. The sequential development of structures includes arcuate fracture traces, interpreted as shear planes formed in a compressive/transpressive stress regime; and fracture traces, interpreted as healed extensional crevasses. The formation of these sediment/ice facies and structures is indicative of dynamic, warm-based flow, most likely during the LIA when the glacier was significantly thicker.Publisher PDFPeer reviewe

Debris entrainment and landform genesis during tidewater glacier surges

Funded by: NERC. Grant Number: NE/I528050/1 GAINS (Glacial Activity in Neoproterozoic Svalbard). Grant Number: NE/H004963/1Peer reviewedPublisher PD