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  • Titill er á ensku Variations of southeast Vatnajökull, past, present and future
  • Breytingar á suðaustanverðum Vatnajökli, fortíð, nútíð og framtíð
  • Doktors
  • Útdráttur er á ensku

    The temperate outlet glaciers of SE-Vatnajökull are sensitive to climate change, and provide important climatic and glaciologic information through their recorded variations in mass balance and extent. They descend to the coast from an elevation of 1500–2100 m a.s.l., are located in one of the warmest and wettest area in Iceland and have among the highest mass turnover rates worldwide. The area was settled in the 9th century, and people have lived in close proximity to the glaciers, which has led to numerous contemporary written documents, also provided by the travelers and explorers of the 18th and 19th centuries. According to the unique local historical records, the outlet glaciers advanced in the latter half of the 17th century and extended far out on the lowlands in the mid-18th century. The glaciers were at their LIA terminal moraines around 1880–1890 and soon thereafter started retreating. The well-preserved glacial geomorphological features (including lateral moraines, trimlines and erratics) outlining the LIA maximum extent of the glaciers, have been mapped in this study. A reconstruction of the LIA glacier surface geometry was made, based on the geomorphological data, historical photographs, and information from the oldest reliable topographic maps of 1904. A LiDAR (laser scanning) digital elevation model (DEM) from 2010/2011 provided a reference topography for the reconstruction. From the elevation of the uppermost LIA lateral moraines, the equilibrium line altitude (ELA) was estimated to have been ~300 m lower during the LIA than around 2010. Various datasets on glacier extent and geometry since the end of the 19th century have been used to derive area and volume changes for the period 1890–2010. DEMs have been created from maps, aerial images, DGPS measurements and airborne surveys. In the period 1890–2010 the glacierized area shrunk by 164 km2, the outlet glaciers lowered by 150–270 m near the terminus and collectively lost 60±8 km3 of ice, equal to a global mean sea level rise of 0.15±0.02 mm. The bedrock topography of SE-Vatnajökull has previously been surveyed with radio echo sounding (RES) measurements, allowing relative volume change estimates, indicating that they have lost 15–50% of their LIA maximum volume. The geodetic mass balance has been estimated by subtracting the DEMs from each other. The most negative balance was observed between 2002 and 2010, when the glaciers lost on average –1.34±0.12 m w.e. a-1, which is among the highest rates of mass loss worldwide in the early 21st century. The variable dynamic response of the glaciers to similar climate forcing is related to their different hypsometry, bedrock topography, and the presence of proglacial lakes. The time series of area and volume changes of the entire post-LIA period created in this thesis provided an opportunity to evaluate the empirical volume-area scaling relation, indicating that ice volume may be underestimated by 50% if applying the commonly proposed constants of the power law. A vertically integrated Shallow Ice Approximation ice-flow model, coupled with a positive degree–day surface mass balance model, is used to simulate the evolution of the three outlet glaciers descending from the dome of Breiðabunga, constrained with the observed history of volume change. The degree–day model uses downscaled daily precipitation derived from an orographic precipitation model, that simulates well the observed pattern of winter mass balance variance. Simulations imply that the LIA maximum ice volume is reached with 1°C lower temperatures than the average of the 1980–2000 baseline period and a 20% decrease in annual precipitation, which is in line with meteorological data from nearby lowland stations. Applying a step change in temperature of +3°C, as predicted by some future scenarios will be reached by 2100, the model simulations indicate that the glaciers would loose 80–90% of their present volume.

  • Rannsóknasjóður Háskóla Íslands
    SVALI (Nordic Centre of Excellence)
  • 18.11.2014

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