Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)

1. Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica) M. Guglielmin 1 and H.M. French 2 1 Department of Structural and Functional Biology of Insubria University, Via J.H. Dunant, 3, 21100, Varese, Italy; E-mail: mauro.guglielmin@uninsubria.it 2Departments of Geography and Earth Sciences, University of Ottawa, Ottawa, Ontario KIN 6N5, Canada. E-mail: hughfrench@rogers.com

2. Why is it important to study ground ice in a continent that is almost completely covered by glaciers ice? 1) Nature and distribution of ground-ice in Antarctica and its relationship with present and past climates is poor. 2) Ground ice may be older than 8 million years and might preserve information about paleoclimatic conditions. 3) The amount and the type of ground ice can influence the evolution of landscape and the terrestrial ecosystem. This paper contributes to knowledge about the distribution of the ground ice. We use isotopic data to characterise the different surface and subsurface ice bodies present in the Northern Foothills region of Northern Victoria Land. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

3. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

4. Permafrost and climate conditions The climate is cold and arid. The mean annual air temperature at Terra Nova Bay is -14.7ºC. The region receives less than 200mm precipitation (water equivalent) per year.   Permafrost is continuous. Its thickness is estimated to be several hundred meters. Permafrost conditions have been monitored at Boulder Clay since December 1996. The thermally-defined active layer typically reaches 18-30 cm. The mean annual ground surface temperature (MAGST) is around –16°C, with an amplitude of more than 48 °C. The depth of zero annual amplitude is approximately 11.0 m. The temperature at that depth approximates –15 º C. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

5. SURFACE ICE is widespread Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

6. ICE – BONDED PERMAFROST OR DRY PERMAFROST ? Surface indicators suggest ICE-BONDED PERMAFROST Differential frost heaving is limited to small and isolated features such as Debris-Island and Non-sorted circles Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

7. ICE – BONDED PERMAFROST OR DRY PERMAFROST ? Surface indicators suggest ICE-BONDED PERMAFROST Frost- Fissure polygons are high-centered and ice-wedges are small or non existent Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

8. For comparison, in the High Arctic, high and low-centered Ice-wedge polygons and Sorted circles indicate ice-rich permafrost conditions. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

9. INTERSTITIAL ICE This exists especially in beach material near sea level Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

10. BURIED GLACIER ICE Buried Glacier ice: (1) Amorphous Glacier, Antarctica (2) Eureka, Ellesmere Island, Canadian High Arctic. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

11. GROUND (SUBSURFACE) ICE A. Injection ice Frost Mound on Enigma Lake Clear ice with vertically aligned bubble trains, indicative of rapid freezing of free water Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

12. GROUND (SUBSURFACE) ICE Icing blister, snow covered at Edmonson Point Icing blister at Boulder Clay Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

13. GROUND (SUBSURFACE) ICE B. Ice-Wedge ice. Usually found on Older Drift terrain at higher elevations than the ice-free terrain consinsting of Younger Drift. Not widespread. Wedges are small in comparison to northern polar regions Ice vein found in Older Drift at M. Browning (photo M.G.) Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

14. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

15. DISCUSSION • Dry Permafrost does not exist in Northern Victoria Land because it is more humid than Southern Victoria Land Dry Valleys. • Geomorphic evidence indicates relatively low ground-ice contents: • Limited occurence, and size, of ice-wedges, and widespread occurrence of sand wedges. • 2) A few poorly-defined, non-sorted circles (‘debris islands’) suggest differential frost heaveis limited to poorly-drained areas. • 3) Absence of obvious evidence of thermokarst. • 4) Frost-fissure polygons lack the bordering ridges that result from the thermal expansion associated with ice-rich sediments. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

16. DISCUSSION (continued) To date, attention has focussed (a) the ice within debris-covered mounds, and (b) the nature of buried glacier ice. The ice found within the frost mounds shows crystallography typical of intrusive ice. The isotopic δ18O composition is similar to buried glacier ice, being typically in the range of -28 to -31‰. Ice lies along a line with a slope much lower than the GMWL and of buried glacier ice samples. The highly negative isotopic values and the lower slope of the δD- δ18O line of the frost mound ice are thought to reflect a combination of intrusion and segregation ice that formed at variable depth within the perennially lake-ice cover. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

17. DISCUSSION As might be expected, icing-blister ice is more similar in isotopic composition to both pond ice and to snow being in the range of -22 to -25‰. Icing blister ice lies along a line almost parallel to the GMWL but with δ18O values more negative (i.e. the line is above the GMWL). This may be indicative of open system freezing with low evaporation plus possibly, the addition of ground water with more negative values. Buried glacier ice is characterised by an absence of foliations and/or debris layers, reflecting the cold-based nature of Antarctic ice sheet, and unlike buried glacier ice from Northern Canada. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

18. CONCLUSIONS Dry permafrost does not occur in the areas of Northern Victoria Land covered in this report. If we exclude buried glacier ice, the amount of traditionally-defined ground ice is small. The ice contained within small debris-covered mounds is problematic even if crystallography and isotopic composition suggest a combination of intrusive and segregated ice. Considering the relationship between δ18O and δD values, icing blister ice appears related to a freezing process associated with injection in a open system. Guglielmin and French “Ground ice in the Northern Foothills (Northern Victoria Land, Antarctica)”

19. ACKOWLEDGEMENTS Research was conducted under the auspices of the Italian Antarctic Research program (PNRA) (Project 2a.13, Professor F. Dramis, University of Rome 3) during the first period of the 1998/1999 expedition. Field logistics were supplied by the PNRA station at Terra Nova Bay. Leave by HMF from the University of Ottawa to participate in the 1998/1999 expedition is gratefully acknowledged. Special thanks to M. Filipazzi (Milano Bicocca University) for his technical assistance in the laboratory.