On the Special Rheological Properties of Ancient Microparticle-Laden Northern Hemisphere Ice as Derived from Bore-Hole and Core Measurements

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Abstract
In the Northern Hemisphere, ice layers which have high microparticle concentrations (in particular late Wisconsin) are “softer” than modern or Holocene ice. Such ice deforms more readily in bore-hole tilt and closure measurements. This enhancement in flow, which is shownnotto be related toc-axis concentration, has a maximum of three for late Wisconsin ice. The closure and tilt of a bore hole in the Agassiz Ice Cap, Ellesmere Island, drilled in 1977, has been followed every year since its drilling and the flow enhancement observed has been compared to the following quantities measured in the cores: concentration, δ(18O), crystal size,c-axis, Ca, Na, conductivity, and density. Flow enhancement of the ice age and bottom ice was found to be unrelated toc-axis concentration and density. Enhancement of flow is best related to microparticle (or Ca) concentration which in turn seems to be inversely related to crystal size. The latter relationship also seems to hold for the Devon Island Ice Cap and Greenland. In future, modellers of northern ice ages should use model ice that is three times softer than modern or Holocene ice.