EGU2020-871
https://doi.org/10.5194/egusphere-egu2020-871
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

The upper 2121 m at EastGRIP - Results from physical properties of NEGIS

Nicolas Stoll1, Ilka Weikusat1,2, Johanna Kerch1, Jan Eichler1, Wataru Shigeyama3,4, Tomoyuki Homma5, Daniela Jansen1, Steven Franke1, Ernst-Jan Kuiper1,6, David Wallis6, Julien Westhoff7, Tomotaka Saruya5, Sérgio Henrique Faria5,8,9, Sepp Kipfstuhl1, Kumiko Goto Azuma3,4, Nobuhiko Azuma5, and Dorthe Dahl-Jensen7
Nicolas Stoll et al.
  • 1Alfred Wegener Institute Helmholtz Centre for Polar- and Marine Research, Bremerhaven, Germany (nicolas.stoll@awi.de)
  • 2Department of Geosciences, Eberhard Karls University, Tübingen, Germany
  • 3Department of Polar Science, SOKENDAI | The Graduate University for Advanced Studies, Tokyo, Japan
  • 4National Institute of Polar Research, Tokyo, Japan
  • 5Nagaoka University of Technology, Nagaoka, Japan
  • 6Utrecht University, Utrecht, Netherlands
  • 7Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
  • 8Basque Centre for Climate Change (BC3), Bilbao, Spain
  • 9Ikerbasque Basque Foundation for Science, Spain

Here we present the ice microstructure and CPO (c-axes fabric) data from the upper 2121 m of the EastGRIP ice core, an on-going deep drilling project on the North East Greenland Ice Stream. Understanding ice flow behaviour of fast flowing ice streams is crucial for accurate projections of future global sea level rise, but is still poorly understood due to e.g. missing observational fabric data from ice streams.

The presented CPO patterns found at EastGRIP show (1) a rapid evolution of c-axes anisotropy compared to deep ice cores from less dynamic sites, (2) a CPO evolution towards a strong vertical girdle and (3) CPO patterns that have not previously been directly observed in ice. Furthermore, data regarding grain properties (e.g. grain size) and indications of dynamic recrystallization, already at shallow depths, are presented.

The ice CPO shows a clear evolution with depth. In the first measurements at 111 m depth a broad single maximum distribution is observed, which transforms into a crossed girdle CPO (196-294 m). With increasing depth, an evolution towards a vertical girdle c-axes distribution occurs. Below 1150 m the CPO evolves into a vertical girdle with a higher density of c-axes oriented horizontally, a novel CPO in ice. These CPO patterns indicate a depth-related change in deformation modes, from vertical compression to extensional deformation along flow.

Grain size values are similar to results from other Greenlandic deep ice cores. Grain size evolution is characterized by an increase until 500 m depth, a decrease until 1360 m depth and mainly constant values in the Glacial. These findings are accompanied by indications of an early onset of dynamic recrystallisation e.g. irregular grain shapes, protruding grains and island grains.

The presented high-resolution data enable, for the very first time, a detailed and data- based look into a fast-flowing ice stream and are an important step towards a better understanding of the rheology of ice and its flow behaviour.

How to cite: Stoll, N., Weikusat, I., Kerch, J., Eichler, J., Shigeyama, W., Homma, T., Jansen, D., Franke, S., Kuiper, E.-J., Wallis, D., Westhoff, J., Saruya, T., Faria, S. H., Kipfstuhl, S., Azuma, K. G., Azuma, N., and Dahl-Jensen, D.: The upper 2121 m at EastGRIP - Results from physical properties of NEGIS , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-871, https://doi.org/10.5194/egusphere-egu2020-871, 2020.

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