Radar attenuation and temperature within the Greenland Ice Sheet

Joseph A MacGregor; Jilu Li; John D Paden; Ginny A Catania; Gary D. Clow; Mark A Fahnestock; Prasad S. Gogineni; Robert E. Grimm; Mathieu Morlighem; Soumyaroop Nandi; Helene Seroussi; David E Stillman

doi:10.1002/2014jf003418

USGS · 70148418

Radar attenuation and temperature within the Greenland Ice Sheet

Joseph A MacGregor·Jilu Li·John D Paden·Ginny A Catania·Gary D. Clow·Mark A Fahnestock·Prasad S. Gogineni·Robert E. Grimm·Mathieu Morlighem·Soumyaroop Nandi·Helene Seroussi·David E Stillman

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Abstract

The flow of ice is temperature-dependent, but direct measurements of englacial temperature are sparse. The dielectric attenuation of radio waves through ice is also temperature-dependent, and radar sounding of ice sheets is sensitive to this attenuation. Here we estimate depth-averaged radar-attenuation rates within the Greenland Ice Sheet from airborne radar-sounding data and its associated radiostratigraphy. Using existing empirical relationships between temperature, chemistry, and radar attenuation, we then infer the depth-averaged englacial temperature. The dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry. Where radar transects intersect boreholes, radar-inferred temperature is consistently higher than that measured directly. We attribute this discrepancy to the poorly recognized frequency dependence of the radar-attenuation rate and correct for this effect empirically, resulting in a robust relationship between radar-inferred and borehole-measured depth-averaged temperature. Radar-inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice-sheet model, particularly in southern Greenland. This pattern suggests that past changes in surface boundary conditions (temperature and accumulation rate) affect the ice sheet's present temperature structure over a much larger area than previously recognized. This radar-inferred temperature structure provides a new constraint for thermomechanical models of the Greenland Ice Sheet.

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Journal of Geophysical Research F: Earth Surface Article

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BibTeX RIS

Joseph A MacGregor, Jilu Li, John D Paden, Ginny A Catania, Gary D. Clow, Mark A Fahnestock, Prasad S. Gogineni, Robert E. Grimm, Mathieu Morlighem, Soumyaroop Nandi, Helene Seroussi, David E Stillman. 2015. Radar attenuation and temperature within the Greenland Ice Sheet. https://doi.org/10.1002/2014jf003418

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