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Glaciers of southwestern Yukon (Canada) and southeastern Alaska (USA) are presently experiencing high rates of annual mass loss. These high melt rates have mainly been investigated with respect to regional temperature trends, but comparatively little is known about how climate variations regulate snow accumulation on these glaciers. This study examines the synoptic weather patterns and air flow trajectories associated with extreme snowfall events in the central St. Elias Mountains (Yukon). The analyses are based on data retrieved from an automated weather station (AWS) between 2003 and 2012, which provide the longest continuous records of surface meteorological data ever obtained from this remote region. The AWS data reveal that 47 extreme snowfall events (> 27 cm per 12 hours) occurred during this period, of which 79 % took place during the cold season months. Air flow trajectories associated with these events indicate that a vast majority had their origin in the North Pacific south of 50°N. Less frequent were air masses with a source in the Aleutian Arc/Bering Sea region and the Gulf of Alaska, and in a few rare cases precipitating air was traced to continental source regions in Western Canada and Alaska. Composite maps of sea-level pressure and upper-level winds associated with extreme snowfall events revealed a frequent synoptic pattern with a low-pressure area centered over the Kenai Peninsula (Alaska), which drives strong southerly winds over the Gulf of Alaska towards the St. Elias Mountains. This pattern is consistent with AWS data wind recordings during snow storms. The most typical synoptic configurations of the North Pacific low-pressure area during extreme snowfall events are either elongated, split, or single-centered, and these situations represent possible seasonal analogues for the different states of the Aleutian Low in the subarctic North Pacific. However, neither the geographical position or intensity of negative sea-level pressure anomalies, nor surface pressure gradients associated with extreme snowfall events are good predictors of the actual snowfall SWE amounts recorded in the central St. Elias Mountains. Estimated snowfall and total precipitation gradients with altitude were confirmed to be much steeper (by up to ~30 %) on the continental side (Yukon), than on the coastal side (Alaska) of the St. Elias Mountains, reflecting the strong orographic division between the continental and coastal marine climatic regimes. Finally, patterns of 500-mb geopotential height anomalies associated with extreme snowfall events at Divide were compared with those associated with unusually high accumulation years in an ice core from the nearby Eclipse Icefield. Results confirm previous findings that associate high snow accumulation winters in this region with the presence of a strong dipole pressure structure between western North America and the Aleutian Low region, a structure which resembles the positive phase of the Pacific North American atmospheric circulation pattern. / De höga smälthastigheter som uppmätts på glaciärer i S:t Eliasbergen (Yukon, Kanada) har främst undersökts utifrån regionala temperatureffekter, men hur storskaliga (synoptiska) klimatvariationer reglerar snöackumulation på dessa glaciärer är mindre känt. Denna analys belyser synoptiska mönster och rekonstruerade banor av luftmassor i samband med extrema snöfall i den centrala delen av S:tEliasbergen. De iakttagelser som gjorts i denna studie bygger på data som hämtas från automatiserade väderstationer (AWS) mellan 2003 och 2012, vilka ger den längst sammanhängande dokumentationen av markmeteorologisk data som någonsin erhållits från denna plats.AWS data avslöjar att 47 extrema snöfall (>27 cm per 12 timmar) inträffade på glaciären under denna period, varav 79 % ägde rum under den kalla årstiden. I samband med dessa snöfall visar det sig att en stor majoritet av luftmassebanorna hade en utgångspunkt i norra Stilla havet söder om 50°N. Mindre vanligt var att luftmassor utgick från Aleuterna/Berings hav och Alaskabukten, och i några sällsynta fall spårades luftmassorna till kontinentala utgångspunkter i västra Kanada och Alaska. Luftmassebanorna från norra Stilla havet visade främst syd-nordcykloniska luftflöden, medan luftmassorna från Aleuterna/Berings hav och Alaskabukten indikerade väst-öst cykloniska luftflöden. Sammansatta kartor indikerade ett likartat synoptiskt mönster av ett lågtryckscentrum över Kenaihalvön (Alaska) för dessa tre marina källområden. Lågtrycket drev starka sydliga cykloniska vindar över Alaskabukten mot S:tEliasbergen och detta vindmönster överensstämde med AWS data. De typiska synoptiska situationerna i samband med extrema snöfall kännetecknades antingen av ett långsträckt, ett delat eller ett litet lågtryckscentrum. Dessa kunde kopplas till olika möjliga tillstånd av det Aleutiska lågtrycket i norra Stilla havet. Studien kunde inte bekräfta att lågtryckscentrums geografiska placering, anomalier av havsnivåtryck eller tryckgradienten starkt reglerade de extrema snöfallmängderna uppmätta från AWS data på studieplatsen. De beräknade nederbördsgradienterna bekräftades vara brantare på den kontinentala sidan (Yukon) än på kustsidan (Alaska) av S:tElias-bergen, vilket återspeglade skillnader mellan den kontinentala och den kustnära marina klimatzonen. Slutligen jämfördes avvikande geopotentiella höjdmönster i samband med extrema snöfall med tidigare studieresultat av extrem snöackumulation i isborrkärnor från den intilliggande glaciären Eclipse. Resultaten indikerar att dessa mönster delvis korrelerade till tidigare resultat och bekräftar förekomsten av en liknande dipol-tryckstruktur mellan västra Nordamerika och Aleuterna.

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Palaeoglacier margins from the Zanskar Range of the north-western Indian Himalaya are reconstructed through geomorphological mapping and sedimentology. These are dated ilsing Optically Stimulated Luminescence (OSL) techniques on quartz extracted from related fluvioglacial and lacustrine deposits. A glaciated palaeosurface with broad, gentle slopes >280m above river level and high grade metamorphic erratics represents the oldest and most extensive glaciation, the Chandra Stage. This formed an ice-cap with its ice-shed to the south over the High Himalaya. A change from broad glacial troughs to narrow V -shaped gorges along with large subdued moraine ridges and drift/erratic limits defines an extensive valley glaciation, the Batal Stage, with its maximum close to -78.0±12.3ka BP (Oxygen Isotope Stage (OIS) 4). Distinct sets of moraine ridges represent a less extensive glaciation, the Kulti Stage, which is dated to shortly after the global Last Glacial Maximum (OIS 2) and a minor advance, the Sonapani, is represented by sharp crested moraine ridges < 2km from current ice bodies. The change in glacier extent and style from the Chandra Stage to the later glaciations may be related to uplift of more southerly ranges blocking monsoon precipitation and incision of the landscape such that ice reached lower altitudes over shorter horizontal distances. Batal and Kulti Stage Glacier Elevation Indexes (GEls) calculated for this and adjacent areas increase from south-west to the north-east, but decrease again towards the Indus valley, reflecting attenuation of the south-westerly monsoon and possible channelling of westerly depressions along the broad upper Indus valley. GEl values were depressed by ~500m during the Batal Stage and -300m during the Kulti Stage. Six new OSL age estimates from the Zanskar Range greatly improve the glacial chronology of the north-west Himalaya and reinforce the emerging asynchrony between this region and the Central and Eastern Himalaya, which experienced its maximum glaciation during OIS 2 rather than OIS 4. Improved glacier mass balance data, palaeoclimatic proxy data for the summer monsoon and particularly the winter westerlies, and numerical age estimates from Himalayan glaciers are required to explain this asynchronous maximum.

Glacier 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.

This thesis investigates the causes and patterns of glacier and ice shelf changes across Northern Ellesmere Island, including rapid recent changes to marine-terminating glaciers and the mass balance of the Milne Ice Shelf along Ellesmere Island’s northern coastline. The first part describes the change in the areal extent of 1773 glacier basins across northern Ellesmere Island between ~1999 and ~2015 that were measured from optical satellite imagery. The results show that the regional ice coverage decreased by 1705.3 km2 over the ~16-year period, a loss of ~5.9%. This indicates a marked acceleration compared to the 3.4% loss recorded by Sharp et al. (2014) between ~1960 and ~2000. Ice shelves had the greatest losses relative to their size, of ~42.4%. Glaciers feeding into ice shelves reduced in area by 4.7%, while tidewater glaciers reduced in area by 3.3%. Marine-terminating glaciers with floating ice tongues reduced in area by 4.9% and 19 of 27 ice tongues disintegrated, causing these glaciers to retreat to their grounding lines. Land-terminating glaciers lost 4.9% of their 1999 area, including the complete loss of three small ice caps (<1.5 km2). These changes indicate the high sensitivity of the ice cover of northern Ellesmere Island to recent climate warming, and that continued losses are likely to occur in the future. In particular, the ice masses most susceptible to further losses are marine-terminating glaciers with floating termini and small land-terminating ice caps at low elevations. To further investigate the forcings leading to the recent losses of floating ice tongues, the second part focuses on marine-terminating glacier changes in the Yelverton Bay region of northern Ellesmere Island since 1959. From 1959-2017, the total ice tongue area decreased by 49.07 km2, with the majority of this loss occurring from 2005-2009 (34.68 km2). The loss of ice tongues since 2005 occurred when open water replaced multi-year landfast sea ice and first-year sea ice in the regions adjacent to the ice tongues. These changes were accompanied by an increase in mean annual mid-depth (i.e., 100 and 200 m) ocean temperatures from -0.29°C from 1999-2005 to 0.67°C from 2006-2012. Despite the recent return of ocean temperatures to below pre-2006 levels, atmospheric summer temperatures have continued to rise (+0.15°C decade-1 between 1948 and 2016), with open water continuing to occur. This suggests that loss of buttressing from sea ice appears to be the primary control on ice tongue losses, with air and ocean warming important in weakening the sea ice and ice tongues, together with offshore wind events in some years. Based on current climate it is unlikely that ice tongues will reform in the future. To examine the stability of the remaining ice shelves, the Milne Ice Shelf was selected as a case study to analyse the processes and patterns of surface mass balance. In 2008 a mass balance network of eight stakes was established across the Milne Ice Shelf and over the past 10 years has revealed a mean annual surface mass balance of -0.33 ±0.04 m water equivalent yr-1. Comparison of this surface mass balance rate with past ice thickness change measurements made by Mortimer et al. (2012) indicate that recent thinning may be limited to the surface, and accelerating over time. Individual stake and snow measurements reveal a surface mass balance gradient, whereby ablation decreases with proximity to the seaward edge of the ice shelf. The ablation gradient is driven by the microclimatology recorded at three automatic weather stations installed along the ice shelf, which show that air temperature and solar radiation decreases towards the coastline, while snow accumulation increases. Climate analysis suggests that the entire Milne Ice Shelf is in a state of negative mass balance in years with >200 melting degree days (MDD), while the one net positive balance year (in 2013) occurred when MDD totals were 105 yr-1. Although the Milne Ice Shelf is the most stable remaining ice shelf along the northern coast of Ellesmere Island, the relationship between climate and mass balance, along with a recent increase in calving along its landward margins, indicate that it is out of equilibrium with current climate. Overall, the ice coverage across northern Ellesmere Island is shrinking. The land-terminating ice that formed under cooler climatic conditions of the past, particularly low-lying small ice caps, are out of equilibrium with current climatological conditions. In addition, recent changes in the ice tongues and ice shelves demonstrate that the northern coastline of Ellesmere Island is approaching a future where the permanent floating ice cover can no longer be sustained.

No description available.