The West Antarctic Ice Sheet (WAIS) is mostly grounded in broad, deep basins (down to 2.5 km below sea level) that are stretched between five crustal blocks. The geometry of the bedrock, being mostly below sea level, induces a fundamental instability in the WAIS through the possibility of runaway grounding line retreat. The crustal environment of the WAIS further influences the ice sheet’s fast flow through conditions at the ice-bedrock boundary. This study focuses on understanding the WAIS by examining the subglacial geology (such as volcanoes and sedimentary basins) at the icebedrock boundary and the continent’s deeper crustal structure- primarily using airborne gravity anomalies. The keystone of this study is a 2004-2005 aerogeophysical survey over one of the most negative mass balance glaciers on the continent: Thwaites Glacier (TG). The gravity anomalies derived from this dataset- as well as gravity-based modeling and spectral crustal boundary depth estimates- reveal a heterogeneous crustal environment beneath the glacier. The widespread Mesozoic rifting observed in the Ross Sea Embayment (RSE) of West Antarctica extends beneath TG, where the crust is ~27 km thick and cool. Adjacent to TG, spectrally-derived shallow Moho depths for the Marie Byrd Land (MBL) crustal block can be explained by thermal support from warm mantle. I assemble here new compilations of free-air and Bouguer gravity anomalies across West Antarctica (from both airborne and satellite datasets) and re-interpret the extents of West Antarctic crustal block and their boundaries with the rift system. Airy isostatic gravity anomalies reveal that TG is relatively sediment starved, in contrast to the sediment-rich RSE. TG’s fast flow velocities could be sustained in this sediment poor environment if higher heat flux in MBL was providing an ample source of subglacial melt water to the glacier. The isostatic anomalies also indicate that TG’s outlet rests on a bedrock sill that will impede future grounding line retreat (up to ~100 km) and temporarily stabilize the glacier. / text

No description available.

Herb- or shrub-chronology, a technique adapted from dendrochronology, is the study of the annual growth rings in roots of certain perennial dicotyledonous plants. The presence of annual growth increments in high-elevation plants is significant as it highlights the applicability of herbchronology for climatic, ecological and geomorphologic applications in alpine and other extra-arboreal regions. For alpine sites along the eastern crest of the Sierra Nevada range I present the first shrub-ring chronologies of the species Linanthus pungens (Torr.) J.M. Porter & L.A. Johnson. L. pungens individuals were collected at, and are especially ubiquitous at rock glacier sites in north-east trending glacial-cirque valleys. Rock glaciers are an increasingly recognized and studied feature on the alpine landscape, supporting floristically diverse plant populations, distinct thermal regimes decoupled from the external air and perennial water sources fed by interstitial ice. These landforms are expected to be refugia for alpine flora and fauna in some regions for projected warmer and drier climates. To evaluate plant growth on rock glaciers as compared to adjacent talus slopes in the central Sierra Nevada range of California, USA, a series of five cirque basins were selected as sites for paired rock glacier- talus slope vegetation comparisons. Vegetation cover, species richness, diversity measures and plant functional traits were recorded at ten sites (five rock glaciers, five talus slopes) along a 100-kilometer latitudinal span of the eastern slope of the Sierra Nevada range. Canonical correspondence analysis was used to evaluate general patterns in cover, diversity and functional traits for the 10 sites and inform subsequent statistical analyses. Both vegetation cover and species richness were significantly greater on rock glacier sites than on adjacent talus slopes even though mean slope values for the rock glacier sites were higher. Significantly, for the present study, rock glaciers support a higher number of the species Linanthus pungens, a climatically sensitive, long-lived alpine sub-shrub, showing that these periglacial landforms are not only floristically distinct but are also habitats containing natural climate archives useful to the field of herbchronology. L. pungens shrub-ring chronologies are determined to be distinct from Pinus albicaulis chronologies growing at the same five sets of sites in the Sierra Nevada study location. P. albicaulis (PIAL) tree-ring chronologies and L. pungens (LIPU) shrub-ring chronologies were constructed for four cirque basin sites. Comparisons were made between chronologies based on growth form (shrub or tree) and site, and on chronology response to average monthly temperature, total monthly precipitation and April 1 snowpack values. Chronologies are significantly more similar to other chronologies of the same growth form (PIAL-PIAL or LIPU-LIPU) than are same-site chronologies of different growth form (i.e. PIAL-LIPU chronologies) (p < 0.05). This holds true for comparisons based on Pearson’s correlation coefficients or Gleichläufigkeit (GLK) values. Growth response to monthly temperature and precipitation values is highly variable for same-site chronologies and also for same growth form chronologies. Topographical position and proximity to treeline was held constant at all sites so differences in climate-growth response within sites and within species may be attributed to factors that are unrealized in the sampling design. Based on composite climate anomaly maps, wide ring widths in PIAL chronologies occur after average winter and spring precipitation and with warm growing seasons while narrow PIAL rings fall after wet springs and with average summer temperatures. Years in which all LIPU rings are wide are found to occur during warm dry springs and growing seasons while years in which all LIPU rings are narrow occur in conjunction with wet winters and springs. Investigation into the longest and most replicated chronology at the Barney Lake (BL) site allowed a climate-growth comparison over a longer period of time (the BL chronology is 112 years in length with sufficient sample replication (EPS > 0.85) to capture a robust common signal from 1952 through 2007). Marker years in the BL chronology correspond to drought (wide rings) and persistent snowpack (narrow rings). Response function analysis indicates significant correlations with July minimum temperatures and the previous year's November precipitation. Increase in the radial growth of the taproot of L. pungens at BL has not decreased over the past century and is more highly correlated to temperature (positively) and snowpack and precipitation (negatively) during the latter half of the chronology period. Predictions of decreasing snowpack and warming temperatures for the alpine Sierra Nevada could indicate increased shrub growth over the next century and possible shrub range expansion if unprecedented drought does not prove to limit growth in the future. Work at BL and the other four alpine L. pungens chronology locations demonstrate a potential for additional research on climate-shrub growth interactions and in particular for investigations into climate controls on upper shrubline growth and movement in the Sierra Nevada range in California.

Accelerated glacial recession and downwasting of glaciers in the Bowser River Watershed of the northern British Columbia Coast Mountains have exposed subfossil wood remains and laterally contiguous wood mat layers. To develop an understanding of Holocene glacial fluctuations in this region, field investigations were conducted in 2005, 2006 and 2013 at Frank Mackie, Charlie, Salmon and Canoe glaciers. These wood remains represent periods of Holocene glacier advance, when glaciers expanded and overwhelmed downvalley forests. Dendroglaciology and radiocarbon analyses revealed five intervals of glacial expansion: (1) a mid-Holocene advance at 5.7-5.1 ka cal. yr BP; (2) an early Tiedemann advance at 3.6-3.4 ka cal. yr BP; (3) a late Tiedemann advance at 2.7-2.4 ka cal. yr BP; (4) a First Millennium AD Advance at 1.8-1.6 ka cal. yr BP; and, (5) three advances during the Little Ice Age at 0.9-0.7, 0.5 and 0.2-0.1 ka cal. yr BP. These results provide new evidence for mid-Holocene glacier activity in northern British Columbia, as well as supporting previous research that Holocene glacier advances were episodic and regionally synchronous. / Graduate / 0368

No description available.

According to climatic models there will be an increase in the amount of greenhouse gases which results in a warming of the earth where the change will be most prominent in the high latitudes. Glaciers mass balance is a good climate change indicator as the response is fast when climate is changing. Glacier mass balance, area of glaciers, elevation line altitude data for 13 glaciers in Scandinavia as well as North Atlantic oscillation (NAO), Arctic oscillation (AO) and sunspot data where gathered and a principle component analysis (PCA) where made. PCA is a multivariate statistical technique with the goal to extract important information and reduce the dimension of data. Three distinct groupings where found within the data set and was identified as extreme years of North Atlantic Oscillation and Arctic Oscillation and one glacier which had the largest area of the 13 glaciers. The PCA explained that all the variables in the data set is correlated with North Atlantic and Arctic Oscillation to about 40 % and we can conclude that there is a regional and local forcing within our data where the regional (NAO and AO) is of more importance for the variance and for the mass balance. / Enligt klimatmodeller kommer en ökning av växthusgaser i atmosfären leda till en ökning av temperaturen på jorden, den ökningen kommer främst att ske på höga latituder. Glaciärer är bra indikation på förändrat klimat på grund av deras korta responstid när klimatet ändrar sig. För tillfället finns det ca 1900 glaciärer utspridda i de Skandinaviska bergen. Eftersom Skandinavien är så avlångt är det en skillnad i meterologiska och klimatiska förhållanden, både i en nord-syd riktning men även i en öst-väst riktning med kontinentala glaciärer i öst och mer marina i väst. Klimat och glaciärdata för 13 olika glaciärer i Skandinavien, 5 från Sverige och 8 ifrån Norge har samlats in och en statistisk analys, principle component analysis (PCA) har gjorts för att se vad som påverkar massbalansen för glaciärerna. De klimat parametrar som har undersökts är Nordatlantsika oscillationen (NAO), Arktiska oscillationen (AO) och solfläckar tillsammans med massbalans, equilibrium line altitude (ELA) och area för glaciärerna. Tre grupperingar har hittats som kan kopplas till olika klimatvariabler och PCA visar extremår för NAO och AO samt en glaciär som har den största arean. PCA analysen visade att alla variabler korrelerade till NAO och AO med omkring 40 % och vi kan dra slutsatsen att det finns en drivande regional och lokal kraft inom vårat dataset där NAO och AO är viktigast för massbalansen.

Tidewater glaciers form a significant drainage catchment of glacierised areas, directly transporting meltwater from the terrestrial to the marine environment. Surface melt of glaciers in the Arctic is increasing in response to warmer atmospheric temperatures, whilst tidewater glaciers are also exposed to warmer ocean temperatures, stimulating submarine melt. Increased freshwater discharge not only freshens fjord waters, but also plays a key role in glacimarine sedimentary processes, transporting sediment to glacial fjords. Despite this, the temporal evolution of meltwater production, storage and release from tidewater glacier systems at seasonal and interannual time scales is poorly understood. This leaves large uncertainties in the predictions for future sea level rise, ocean circulation and the impacts on the marine ecosystem. This study focuses on Kronebreen, a tidewater glacier which flows into the head of Kongsfjorden, north west Svalbard. Surface melt produces freshwater runoff, which is discharged from the grounding line as a buoyant, sediment laden plume, which spreads laterally across the surface water. This supraglacial melt is the dominant freshwater source, contributing an order of magnitude more freshwater to Kongsfjorden, than direct submarine melting of the ice face. Calibration of MODIS band 1 satellite imagery with in situ measurements of Total Suspended Solids and spectral reflectance, provides a method to quantify meltwater and sediment discharge. Plume extent has been determined for each cloud free day, from June to September, 2002 - 2013. Analysis of plume extent with atmospheric temperature and modeled surface runoff, gives a source to sea insight to meltwater production, storage and discharge. The extent of the plume changes in response to meltwater; larger plumes form when discharge increases. These results reveal that meltwater discharge into Kongsfjorden lags atmospheric temperature, the primary driver of meltwater production, by over a week during June and July. This is reduced to only 1 - 2 days in August and September, indicating a decline in meltwater storage as the ablation season progresses, and the development of more efficient glacial drainage. Sediment plumes respond to meltwater production, making them a valuable tool for quantifying meltwater discharge from a tidewater glacier. Insights to glacier hydrology can also be obtained when surface processes are also considered. This furthers the understanding of tidewater glacier hydrology, which is valuable for improving the accuracy of sea level rise predictions.

Meltwater accumulated on the Greenland Ice Sheet drains to glacier beds, discharging into fjords hundreds of meters below sea level. The injection of meltwater at depth generates an upwelling plume that entrains warm ocean water as it rises along the terminus, increasing submarine melt and driving a fjord-scale exchange flow. However, due to sparse ocean-glacier observations, we lack a process understanding of how plumes control fjord circulation and submarine melt. Combining numerical modeling, theory, and observations, this dissertation investigates near-glacier plume dynamics, the influence of glacier depth on plume structure and submarine melt, and the role of fjord-glacier geometry on circulation in tidewater glacier fjords. In Chapter II, I use buoyant plume theory and a nonhydrostatic, three-dimensional ocean–ice model to investigate the sensitivity of plume dynamics to subglacial discharge, turbulent diffusivity, and conduit geometry. Large discharges result in plumes with positive temperature and salinity anomalies in the upper water column. Fjord circulation is sensitive to conduit geometry; distributed subglacial discharge results in a stronger return flow of warm water toward the terminus. In Chapter III, I use buoyant plume theory, initialized with realistic ranges of subglacial discharge, glacier depth, and ocean stratification, to investigate how plume structure and submarine melt vary during summer months in 12 Greenland fjords. Grounding line depth is a primary control on plume-induced submarine melt: deep glaciers produce warm, salty subsurface plumes that undercut termini, and shallow glaciers produce cold, fresh surface-confined plumes that can overcut. Finally, in Chapter IV, I use regional-scale numerical ocean simulations to systematically evaluate how fjord circulation forced by subglacial plumes, tides, and wind stress depends on fjord width, glacier depth, and sill height. Glaciers grounded below sill depth can draw shelf waters over a shallow sill and into fjord basins with seasonal subglacial discharge; this process is independent of external shelf forcing. These results underscore the first-order effect that subglacial discharge and fjord-glacier geometry have in controlling fjord circulation and, thus, ocean heat flux to the ice. This dissertation includes previously published and co-authored material.

Groups of closely spaced minor moraines allow for observations of moraine formation and ice-marginal fluctuations on short timescales, helping to better understand glacier retreat and predict its geomorphological effects. Some minor moraines can be classified as annual moraines given sufficient chronological control, which implies a seasonal climatic driver of ice-marginal fluctuations. This leads to moraines being utilised as very specific, short-term records of glacier fluctuations and climate change. This research is common in lowland, maritime settings, but remains sparse in high-mountain settings. This study presents the detailed geomorphological and sedimentological results of minor moraines at two high-mountain settings in the European Alps. Geomorphological investigations included mapping and measurements through field observations and remotely-sensed imagery. Detailed sedimentological investigations followed excavation of moraines and include multiple scales of observation and measurements to support interpretations of sediment transport and deposition. Additionally, ground-penetrating radar data were collected in one foreland. Minor moraines at Schwarzensteinkees, Austria, formed as push or combined push and freeze-on moraines in two groups between approximately 1850 and 1930. The existence of a former proglacial lake appears to have exerted a strong control on moraine formation. Modern minor moraines at Silvrettagletscher, Switzerland, exist primarily on reverse bedrock slopes and have formed since approximately 1850 through push, freeze-on, and controlled moraine mechanisms. The presence of these bedrock slopes, and in some areas englacial debris septa, appear to exert the primary controls on moraine formation. The foreland of Gornergletscher, Switzerland, has been revisited using aerial imagery to assess if moraines are still forming annually, and this has been confirmed. These findings show a range of mechanisms responsible for moraine formation, which are then compared to previously published research on minor moraines to elucidate any common drivers of minor and annual moraine formation globally. This includes a global database of forelands where minor moraines have been studied, created as part of this research and presented as a table and Google Earth file, both easily accessible and freely available online, for use by other researchers when exploring similar topics.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 174-184).