MSGID: 1:317/3 64781f1f   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Ground beneath Thwaites Glacier mapped    
      
     Date:   
         May 31, 2023   
     Source:   
         British Antarctic Survey   
     Summary:   
         The ground beneath Antarctica's most vulnerable glacier has   
         now been mapped, helping scientists to better understand how   
         it is being affected by climate change. Analysis of the geology   
         below the Thwaites Glacier in West Antarctica shows there is less   
         sedimentary rock than expected -- a finding that could affect how   
         the ice slides and melts in the coming decades.   
      
      
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   FULL STORY   
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   The ground beneath Antarctica's most vulnerable glacier has been mapped   
   for the first time, helping scientists to better understand how it is   
   being affected by climate change. Analysis of the geology below the   
   Thwaites Glacier in West Antarctica shows there is less sedimentary   
   rock than expected -- a finding that could affect how the ice slides   
   and melts in the coming decades.   
      
   "Sediments allow faster flow, like sliding on mud," says Dr Tom Jordan,   
   a geophysicist with the British Antarctic Survey (BAS), who led the   
   study. "Now we have a map of where the slippery sediments are, we can   
   better predict how the glacier will behave in future as it retreats."   
   The distribution of sedimentary rocks beneath the Thwaites glacier is   
   included in a new map of the geology of the region produced by the BAS   
   researchers and published in the journal Science Advances. The findings   
   are important because the glacier, which is the size of Great Britain   
   or the US state of Florida, is one of the fastest changing ice-ocean   
   systems in Antarctica.   
      
   The Thwaites glacier's grounding zone -- the point where it meets the   
   seafloor -- has retreated 14 km since the late 1990s. Much of the ice   
   sheet is below sea level and susceptible to rapid, irreversible ice loss   
   that could raise global sea-level by over half a metre within centuries.   
      
   The new analysis is based on airborne surveys using aircraft equipped   
   with radar which can see through the ice to the rocks below, as well   
   as sensors which can map minute variations in gravity and magnetism   
   hundreds to thousands of metres below the ground and seabed on which   
   the glacier rests.   
      
   The researchers then use these multiple data sources to compile a 3D   
   picture of features, including the type and extent of different rocks.   
      
   Jordan says: "The integrated nature of the airborne surveys was one of the   
   keys to this research. Each sensor on the aircraft provided an important   
   but incomplete part of the picture, but by bringing them all together we   
   could provide the detailed map of the underlying geology."  In doing so,   
   the study effectively turns back the geological clock to examine what   
   happened when New Zealand was ripped away from Antarctica about 100   
   million years ago -- long before the Thwaites glacier was formed.   
      
   Because the base of Thwaites Glacier lies far below sea level, researchers   
   had expected that thick sediments would have been deposited there over the   
   subsequent millions of years Similar analysis has been done on some other   
   Antarctic glaciers, showing that these other systems were predominantly   
   underlain by thick sediments.   
      
   But the aircraft data suggests that only about a fifth of the ground   
   below the glacier is sedimentary rock. These lie in a series of basins   
   between 80 and 200 km long and about 30 km wide.   
      
   The rest is made up of other types of geological bodies, including granite   
   peaks and other hard rocks. The scientists think that these sedimentary   
   basins were once much larger, but they have been ground down to the   
   bedrock by movement of the glacier.   
      
   It's not yet clear how this new knowledge of the subglacial geology   
   will affect estimates of ice flow and loss from Thwaites and other   
   glaciers. The study does show that the geological landscape has a direct   
   control on the basal shear stress, which influences how fast ice can   
   flow into the ocean. Members of the research team will now carry out   
   more detailed studies of these processes.   
      
   Modellers may also be able to use the new data to make more reliable   
   projections of future ice loss.   
      
   Jordan says: "We hope that by showing the detailed geology, and how it   
   correlates with the basal friction, future models of glacial retreat   
   will have lower uncertainty, as the controls of the basal processes   
   will be better understood."  He adds: "No single scientific study   
   could ever match she scale and challenge of climate change. But it   
   is the incremental building of all the individual scientific studies   
   like this that allows us to understand and tackle that challenge."   
   Glaciologist Dr Sarah Thompson, co-author on the paper, said: "The   
   integrated approach used in this study has significant potential for   
   successful application elsewhere in Antarctica, enabling us to explore   
   other potentially vulnerable regions where current knowledge is sparse."   
       * RELATED_TOPICS   
             o Earth_&_Climate   
                   # Global_Warming # Snow_and_Avalanches # Ice_Ages   
                   # Oceanography # Climate # Geography # Geology #   
                   Environmental_Awareness   
       * RELATED_TERMS   
             o Ice_shelf o Glacier o Paleoclimatology o Antarctic_ice_sheet   
             o Temperature_record_of_the_past_1000_years o Antarctica o   
             Metamorphic_rock o Global_warming   
      
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   Story Source: Materials provided by British_Antarctic_Survey. Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Tom A. Jordan, Sarah Thompson, Bernd Kulessa, Fausto Ferraccioli.   
      
         Geological sketch map and implications for ice flow of Thwaites   
         Glacier, West Antarctica, from integrated aerogeophysical   
         observations. Science Advances, 2023; 9 (22) DOI:   
         10.1126/sciadv.adf2639   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230531145123.htm   
      
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