short time scale. Four differential GPS stations were installed in the lower ablation area of Storglaciären in Sweden for one week in August 2012. The position data over the period were then compared with the environment information including temperature, precipitation, known hydrology and topography.The instantaneous velocity results show 9 acceleration events in correlation to temperature and precipitation. The increase of the meltwater inputs drive increases of the motion supposedly through water pressures and basal sliding.Strain determination using the stations geometry showed that the lower part of the survey area had an extensive behavior when the upper part was showing compressive properties. A deformation event occurring the 14th of august shows an elongation deformation along the centerline from the front of the glacier resulting in a lateral compression on the upper part due to shear stress closer to the margin.It was proposed that the force driving the elongation is due to the increase of water pressure on the front of the glacier where the internal hydrological system pass from a complex multi-branched system to a channelized output. / Syftet med detta projekt var att studera sambandet mellan en glaciärs hydrologi och isrörelse under korta tidsperioder (minuter till timmar). I augusti 2012 installerades fyra differentiella GPS-stationer under en veckas tid i nedre ablationsområdet på Storglaciären i Sverige. Positionsdata under perioden jämfördes sedan med miljöinformation inklusive temperatur, nederbörd, avrinning från glaciären och topografi.De uppskattade hastighetsresultaten visar på 9 olika accelerationshändelser som relaterar till tempe-ratur och nederbörd. En ökad införsel av smältvatten driver upp vattentrycket vid glaciärens botten som minskar friktionsmotståndet och glaciären får ökad basal glidning.Isdeformationsberäkningar mellan DGPS-stationerna visar att den nedre delen av undersök-ningsområdet hade extensionell deformation i isrörelseriktningen medan den övre delen visade kompression vinkelrätt mot denna riktning. Deformationshändelsen den 14 augusti visar det motsatta med extensionell deformation längs mittlinjen från fronten av glaciären vilket resulterar i en lateral kompression i den övre delen av det undersökta området kanske orsakade av skjuvspänning vid marginalen.Det föreslås att utsträckningen av glaciären under dessa händelser är på grund av en ökning av vattentrycket i det område där det interna subglaciala hydrologiska systemet ändras från en komplex multigrenade system högre upp i ablationsområdet till ett kanaliserat system vid fronten.

Storglaciären is a sub-Arctic polythermal glacier in northern Sweden. Twenty years' monitoring of thecold surface layer found that it has lost one third of its total volume of cold ice with an average thinningrate of 0.80 ± 0.24 m·a-1 for the period of 1989-2009. This thesis presents the continuous investigationof the thermal structure evolution of Storglaciären using thermistor string measurements and a coupledenergy balance-snowpack model. The thickness dynamics of the cold surface layer is derived from boththe thermistor string measurement (2018-2019) and the simulation results (2009-2018).    The subsurface temperature evolution and the associated cold-temperate transition surface (CTS)dynamics are analyzed at both the thermistor scale and glacier scale. Point study involves installing athermistor string and extrapolating the measured subsurface temperature to the pressure melting pointisotherm depth. The simulated CTS depth changes at the study site was also used for comparison. Glacierscale study aims to simulate the spatial and temporal variations of the thickness of the cold surface layer.Meteorological data was collected from multiple automatic weather stations and the solid precipitationwas estimated from the winter mass balance survey. The model was utilized in the study of the coldsurface layer dynamics for the first time.    Both the point scale and glacier scale study suggest an overall thickening trend of the cold surfacelayer. The thermistor derived CTS depth exhibits a thickening rate of ~0.9 m·a-1 compared to the depthderived from ground penetrating radar survey in 2009. The influence of mass balance, melt andaccumulation are also examined by spatial correlation with CTS depth. / Storglaciären är en subarktisk polytermal glaciär i norra Sverige som har ett kallt ytskikt iablationsområdet. Tidigare studier av mäktigheten hos det kalla ytskiktet visar att Storglaciären harförlorat en tredjedel av sin totala volym av kall is med en genomsnittlig uttunningshastighet på 0,80 ±0,24 m · a-1 för perioden 1989-2009. Denna uppsats presenterar den fortsatta utvecklingen av det kallaytskiktet på Storglaciären under perioden 2009 till 2019 med hjälp av istemperaturmätningar och enytenergi balansmodell koppla till en och en termodynamisk modell för snö och is. Istemperaturensutveckling och djupet till övergången mellan kall och tempererad is (CTS) analyseras både på lokalskalavid en punkt och över hela glaciären. Punktstudien utnyttjar temperaturmätningar vid en termistorslingaför att uppskatta temperaturfördelningen i isen och djupet för övergången mellan kall och tempereradis. Resultaten används också för jämförelse med simulerade resultat. Den rumsliga studien använder enkopplad energibalans och en termodynamisk modell för snö och is för att simulera rumsliga ochtidsmässiga variationer av tjockleken på det kalla ytskiktet. Som ingångsdata till modellen användesmeteorologiska data från flera automatiska väder stationer och den nederbörden i fast form uppskattadesfrån massbalans mätningar som görs på glaciären. Det är fösta gången den här typen av modell användsför att studera det kalla ytskiktets dynamik.    Både på lokalskala och glaciärskala tyder på en övergripande förtjockningstrend av det kallaytskiktet. Uppskattningen av CTS djupet vid temperaturmätningar uppvisar en ökningshastighet av ~0,9 m · a-1 av det kalla skiktets tjocklek jämfört med markradar undersökningar i 2009. Påverkan ochrumslig korrelation mellan massbalans, smältning och ackumulation på CTS-djupet undersöks också.

Klimatförändringar har direkt påverkan på glaciärers tillväxt och avsmältning. Genom att studera glaciärers massbalans kan framtida riskbedömningar, för bland annat havsytans stigning, uppskattas. Skillnaden i glaciärens ackumulation och ablation ger den så kallade nettobalansen, som avslöjar om glaciären ökat eller minskat i massa under det gångna året. Storglaciären belägen i Tarfaladalen, öster om Kebnekaise, är en av världens mest välstuderade glaciärer. Här används den så kallade skandinaviska metoden för dokumentering av glaciärens massbalans. Metoden utgörs till stor del av manuella sonderingar i form av punktmätningar direkt på glaciärens yta. Då Storglaciären har upp mot 300 mätpunkter är inhämtningen av data både omfattande och tidskrävande. I detta kandidatarbete utfördes ett försök till optimering för den skandinaviska metoden på Storglaciären, med syftet att förhoppningsvis underlätta och effektivisera metoden. Punkter för mätdata avlägsnades för att undersöka om de resterande mätpunkterna gav ett godkänt värde för nettobalansen. För godkänt resultat av experimentet skall optimeringen ge ett representativt värde för storglaciärens nettobalans uppskattad med hela datamängden. Beräkningarna för nettobalansen är beroende av snöns densitet på glaciären, därav utfördes även densitetsmätningar i fält vid Tarfalas forskningsstation. Experimentet gav resultatet att metoden kan optimeras genom att var fjärde punkt för mätdata avlägsnades. Ytterligare studier kan dock utföras för att utforma mer specifika mönster för mätpunkter, som då skulle kunna ge ett ännu säkrare resultat för Storglaciärens nettobalans. / Climate changes has a direct impact on glaciers’ growth and melting. By studying the mass balance of glaciers, future risk assessments can be estimated by for example sea level rise. The difference between the glacier’s accumulation and ablation gives the net balance, which reveals if the glacier has increased or decreased in mass during the past year. Storglaciären, located in the Tarfala valley east of Kebnekaise, is one of the world's most studied glaciers. The Scandinavian method is used for documentations of the glacier’s mass balance. The method consists of manual probings at specific points on the glacier’s surface. Since Storglaciären has up to three hundred measurement points, the collection of the mass balance-data is both comprehensive and time consuming. For this bachelor project, an experiment was made to optimize the Scandinavian method at Storglaciären. The project was carried out with the aim of hopefully facilitating the method and to make it more efficient. Measurement points on the glacier were removed to investigate if the remaining points gave an approved value for the net balance. The requirement for the experiment to be approved is that the optimization shall provide a representative value for the net balance of Storglaciären, with all its measurement points included. The calculations for the net balance is dependent on the snow density on the glacier’s surface. Fieldwork at Tarfala research station was thereby carried out to collect data for the density on Storglaciären. The experiment gave the result that the Scandinavian method can be optimized. If every fourth measurement point on Storglaciären is removed, the glacier’s net balance is still representative. Further studies can be conducted to design specific patterns for removal of specific measurement points, which probably would provide even more accurate results for Storglaciären’s net balance.

<p>Polythermal glaciers, i.e. glaciers with a combination of ice at and below the freezing point, are widespread in arctic and subarctic environments. The polythermal structure has major implications for glacier hydrology, ice flow and glacial erosion. However, the interplay of factors governing its spatial and temporal variations such as net mass balance, ice advection and water content in the ice is poorly investigated and as yet not fully understood. This study deals with a thorough investigation of the polythermal regime on Storglaciären, northern Sweden, a small valley glacier with a cold surface layer in the ablation area. Extensive field work was performed including mapping of the cold surface layer using ground-penetrating radar, ice temperature measurements, mass balance and ice velocity measurements. Analyses of these data combined with numerical modelling were used specifically to investigate the spatial and temporal variability of the cold surface layer, the spatial distribution of the water content just below the cold surface layer transition, the effect of radar frequency on the detection of the surface layer, and the sensitivity of the cold surface layer to changes in forcing.</p><p>A comparison between direct temperature measurements in boreholes and ground-penetrating surveys shows that the radar-inferred cold-temperate transition depth is within ±1 m from the melting point of ice at frequencies above ~300 MHz. At frequencies below ~155 MHz, the accuracy degrades because of reduced scattering efficiency that occurs when the scatterers become much smaller compared to the wavelength. The mapped spatial pattern of the englacial cold-temperate transition boundary is complex. This pattern reflects the observed spatial variation in net loss of ice at the surface by ablation and vertical advection of ice, which is suggested to provide the predominant forcing of the cold surface layer thickness pattern. This is further supported by thermomechanical modeling of the cold surface layer, which indicates high sensitivity of the cold surface layer thickness to changes in vertical advection rates.</p><p>The water content is the least investigated quantity that is relevant for the thermal regime of glaciers, but also the most difficult to assess. Spatial variability of absolute water content in the temperate ice immediately below the cold surface layer on Storglaciären was determined by combining relative estimates of water content from ground-penetrating radar data with absolute determination from temperature measurements and the thermal boundary condition at the freezing front. These measurements indicate large-scale spatial variability in the water content, which seems to arise from variations in entrapment of water at the firn-ice transition. However, this variability cannot alone explain the spatial pattern in the thermal regime on Storglaciären.</p><p>Repeated surveys of the cold surface layer show a 22% average thinning of the cold surface layer on Storglaciären between 1989 and 2001. Transient thermomechanical modeling results suggest that the cold surface layer adapts to new equilibrium conditions in only a few decades after a perturbation in the forcing is introduced. An increased winter air temperature since mid-1980s seems to be the cause of the observed thinning of the cold surface layer. Over the last decades, mass balance measurements indicate that the glacier has been close to a steady state. The quasi-steady state situation is also reflected in the vertical advection, which shows no significant changes during the last decades. Increased winter temperatures at the ice surface would result in a slow-down of the formation of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold-temperate transition.</p>

Polythermal glaciers, i.e. glaciers with a combination of ice at and below the freezing point, are widespread in arctic and subarctic environments. The polythermal structure has major implications for glacier hydrology, ice flow and glacial erosion. However, the interplay of factors governing its spatial and temporal variations such as net mass balance, ice advection and water content in the ice is poorly investigated and as yet not fully understood. This study deals with a thorough investigation of the polythermal regime on Storglaciären, northern Sweden, a small valley glacier with a cold surface layer in the ablation area. Extensive field work was performed including mapping of the cold surface layer using ground-penetrating radar, ice temperature measurements, mass balance and ice velocity measurements. Analyses of these data combined with numerical modelling were used specifically to investigate the spatial and temporal variability of the cold surface layer, the spatial distribution of the water content just below the cold surface layer transition, the effect of radar frequency on the detection of the surface layer, and the sensitivity of the cold surface layer to changes in forcing. A comparison between direct temperature measurements in boreholes and ground-penetrating surveys shows that the radar-inferred cold-temperate transition depth is within ±1 m from the melting point of ice at frequencies above ~300 MHz. At frequencies below ~155 MHz, the accuracy degrades because of reduced scattering efficiency that occurs when the scatterers become much smaller compared to the wavelength. The mapped spatial pattern of the englacial cold-temperate transition boundary is complex. This pattern reflects the observed spatial variation in net loss of ice at the surface by ablation and vertical advection of ice, which is suggested to provide the predominant forcing of the cold surface layer thickness pattern. This is further supported by thermomechanical modeling of the cold surface layer, which indicates high sensitivity of the cold surface layer thickness to changes in vertical advection rates. The water content is the least investigated quantity that is relevant for the thermal regime of glaciers, but also the most difficult to assess. Spatial variability of absolute water content in the temperate ice immediately below the cold surface layer on Storglaciären was determined by combining relative estimates of water content from ground-penetrating radar data with absolute determination from temperature measurements and the thermal boundary condition at the freezing front. These measurements indicate large-scale spatial variability in the water content, which seems to arise from variations in entrapment of water at the firn-ice transition. However, this variability cannot alone explain the spatial pattern in the thermal regime on Storglaciären. Repeated surveys of the cold surface layer show a 22% average thinning of the cold surface layer on Storglaciären between 1989 and 2001. Transient thermomechanical modeling results suggest that the cold surface layer adapts to new equilibrium conditions in only a few decades after a perturbation in the forcing is introduced. An increased winter air temperature since mid-1980s seems to be the cause of the observed thinning of the cold surface layer. Over the last decades, mass balance measurements indicate that the glacier has been close to a steady state. The quasi-steady state situation is also reflected in the vertical advection, which shows no significant changes during the last decades. Increased winter temperatures at the ice surface would result in a slow-down of the formation of cold ice at the base of the cold surface layer and lead to a larger imbalance between net loss of ice at the surface and freezing of temperate ice at the cold-temperate transition.

Two Differential GPS (DGPS) stations were set up on Storglaciären in the upper and lower part of the ablation area to study short term variations of Storglaciären’s motion. The study period lasted from April to July 2009 and the DGPS logged data every second. Station 14, was situated over an overdeepening in the subglacial bedrock topography in the upper part of the ablation area, and was functioning the whole study period. Station 7, situated in the lower part of the ablation area, only lasted for nine days and only overlapped five days with station 14. There was a clear lag in ice motion between the two stations which indicates longitudinal coupling between the upper and the lower part of the ablation area. Station 14 pushed from up-glacier during the first acceleration event at the 24th of April and when the velocity decreased station 7 pulled from down-glacier.  The total movement of the DGPS station was 26 m during the study period. The velocity was well correlated to the external changes in temperature and precipitation. It appears to be eleven days lag in response time from April to middle of May, but after mid May the glacier responded directly to melt acts such as temperature changes and precipitation events. The delay most likely depended on the hydrological system was not entirely evolved during early spring. During the summer the system evolves which makes the glacier to respond directly to external changes. There were four major acceleration events during the study period and after the accelerations the velocity went back to the same low state as before. These cannot be interpreted as spring events as spring events should lead to an increase in the overall velocity. The temperature fluctuated during the whole study period which affects the melting rate and input and development of the hydrological system. To get a clear spring event a marked and substantial onset of melt season is needed. / Två differentiella bärvägs GPS (DGPS) stationer sattes upp på Storglaciären på den övre och lägre delen av ablations området för att studera korttidsvariationer i isflöde. Fältundersökningen pågick under april till juli 2009 och DGPS loggades varje sekund. Station 14 är placerad vid en överfördjupning i bottentopografin i den övre delen av ablationsområdet och var i gång under hela studien. Station 7 fungerade endast i nio dagar och är placerad vid den lägre delen av ablationsområdet samt överlappade under endast fem dagar med station 14. Det finns en tydlig fördröjning mellan de två stationerna i isrörelse vilket indikerar en longitudinell koppling mellan den övre och undre delen av ablationsområdet. Före den 24 april reagerade station 14 snabbare än station 7. Efter en kraftig acceleration vid station 14 den 24 april skedde det en förändring till att den nedre delen av ablationsområdet reagerade snabbare än den övre delen. Den totala förflyttningen av station 14 var 26 m under mätperioden. Hastigheten är korrelerad med externa förändringar i temperatur och nederbörd. Under april till mitten av maj var det en förändring i reaktionstid på elva dagar men den övergick under sommaren till att reagera direkt på förändringar i temperatur och nederbörd. Förskjutningen berodde troligtvis på att det hydrologiska systemet inte var tillräckligt utvecklat. Under sommaren utvecklas systemet vilket leder till att glaciären reagerar snabbare på externa förändringar. Det förekom fyra större accelerationshändelser under fältperioden. Efter de observerade accelerationerna gick hastigheten tillbaka till samma nivå. Dessa accelerationshändelser kan inte tolkas som våracceleration. En våracceleration innebär att den generella hastigheten hos glaciären ökar till en ny högre nivå. Detta kan bero på att temperaturen skiftade under hela fältperioden som styr smältning, isflöde och utveckling av det hydroligiska systemet. För att få en tydlig ”spring event” måste smältsäsongens nå en tydlig början och forstätta så kontinueligt.

The study in this thesis concerns Storglaciären, a very well known and studied glacier in northern Sweden. The glacier has been an object for research since the endof the 19th century. During the meltseason of 2012 25 dyetracing experiments were executed. These experiments were conducted to investigate the internal drainage system of Storglaciären in the lower ablation area. Similar studies were done in 1989 by Regine Hock and Roger Leb Hooke (1993). The outcome of the study in 2012 has been compared with their results to see if any changes in the drainage systemhave occurred. The results have also been compared to the results of Seaberg etal. (1988) from their experiments in 1984 and 1985. Studies of glacier behaviour are important since they have a large impact on the local and global environment. Moreover it has been observed that smaller glaciers (such as Storglaciären), that are easier to reach and to work on, have similar behaviour as bigger glaciers, making them good objects for research (Jansson, 1996). The experiments were conducted between the 6th and 24th of august and executed by first injecting dye into moulins on the glacier and then measuring the concentration of dye in the proglacial streams merging out from the front of Storglaciären. Rhodamine WT was used as dye. Storglaciären has three main pro-glacialstreams named Nordjåkk, Centerjåkk and Sydjåkk. Nordjåkk merges from the northside and the other two from the south side of the glacier front. Measurements were in the beginning taken in all of the streams but since no concentration was visible in Nordjåkk the focus was at the end of the fieldperiod only at Centerjåkk and Sydjåkk, which both had detectable dye concentrations. Both manual and automatical measurements were done. Breakthrough curves (concentration vs. time) were plotted for each experimentand for both Centerjåkk and Sydjåkk. From these curves calculations were donefollowing the methods in Willis et al. (2011). The main parameters calculatedwere: transit velocity, dispersivity and dye recovery. Breakthrough curves were also modelled for each experiment using the method in Willis et al. (1990). Overall the drainage system in the lower part of the ablation area of Storglaciärenhas not changed signicantly during the past 20 years. But the drainage systemseems to be divided into dierent parts using both a straight channel system and a distributed system. The distributed system of 2012 seems to be more homogeneous than in 1989 but whether the system is braided or consists of a linked cavity systemis hard to tell. Differences seen this year compared to previous investigations are that the transition from an early to a late season drainage system occurred later in the meltseason. The dominating subglacial stream in 2012 was Centerjåkk and not Sydjåkk as in previous investigations (Nordjåkk dominated north as before). The meltseason lasted only a few weeks in 2012 because of the cold conditions and low precipitation. This may have had a big inuence on the behaviour of the glacier.

<p>This thesis contributes to the understanding of glacier response to climate change by ice dynamical studies on Storglaciären, Sweden, and Bonnevie-Svendsenbreen, Kibergbreen and Plogbreen in Dronning Maud Land, Antarctica. Ice surface velocities, ice geometry and temperature information is fed through a force budget model to calculate ice mass outflux of these glacial systems via three-dimensional stress distributions for a flux-gate. </p><p>Field data were collected through repeated DGPS and GPR observations on Storglaciären between July 2000 to September 2001 and on Kibergbreen and Plobreen during the SWEDARP 2002/03 expedition to Antarctica. The work was strongly supported by remotely-sensed information.</p><p>The results from Storglaciären show a strength in the force budget model to discern both spatial and temporal variability in ice dynamical patterns. It highlights the influence of seasonality and bedrock topography upon glacier flow. A modeling experiment on Bonnevie-Svendsenbreen suggested that ice temperature increases substantially under conditions of high stress (≥0.4 MPa) due to strain-heating. This provides a positive feedback loop, increasing ice deformation, as long as it overcomes the advection of cool ice from the surface. These results explain, to some extent, the mechanism behind fast flowing ice streams. Mass flux caclulations from Bonnevie-Svendsenbreen suggest that the outflux given from force budget calculations can be used as a gauge for influx assuming steady state conditions. Plogbreen receives an influx of 0.48±0.1 km³ a^-1 and expedites a discharge volume of 0.55±0.05 km³ a^-1. This indicative negative mass balance is explained by a falling trend in upstream accumulation and the recent rise in global sea level, as it is likely to induce glacier acceleration due to a reduction in resistive forces at the site of the gate. This result is comparable with other Antarctic studies reporting negative mass balances, e.g. from WAIS, as caused by changes in the global atmospheric circulation pattern.</p>

This thesis contributes to the understanding of glacier response to climate change by ice dynamical studies on Storglaciären, Sweden, and Bonnevie-Svendsenbreen, Kibergbreen and Plogbreen in Dronning Maud Land, Antarctica. Ice surface velocities, ice geometry and temperature information is fed through a force budget model to calculate ice mass outflux of these glacial systems via three-dimensional stress distributions for a flux-gate. Field data were collected through repeated DGPS and GPR observations on Storglaciären between July 2000 to September 2001 and on Kibergbreen and Plobreen during the SWEDARP 2002/03 expedition to Antarctica. The work was strongly supported by remotely-sensed information. The results from Storglaciären show a strength in the force budget model to discern both spatial and temporal variability in ice dynamical patterns. It highlights the influence of seasonality and bedrock topography upon glacier flow. A modeling experiment on Bonnevie-Svendsenbreen suggested that ice temperature increases substantially under conditions of high stress (≥0.4 MPa) due to strain-heating. This provides a positive feedback loop, increasing ice deformation, as long as it overcomes the advection of cool ice from the surface. These results explain, to some extent, the mechanism behind fast flowing ice streams. Mass flux caclulations from Bonnevie-Svendsenbreen suggest that the outflux given from force budget calculations can be used as a gauge for influx assuming steady state conditions. Plogbreen receives an influx of 0.48±0.1 km3 a-1 and expedites a discharge volume of 0.55±0.05 km3 a-1. This indicative negative mass balance is explained by a falling trend in upstream accumulation and the recent rise in global sea level, as it is likely to induce glacier acceleration due to a reduction in resistive forces at the site of the gate. This result is comparable with other Antarctic studies reporting negative mass balances, e.g. from WAIS, as caused by changes in the global atmospheric circulation pattern.