Effects of surface topography and wind on reflection horizons in ice sheets

Abstract

Radar horizons within the great ice sheets of Antarctica are distorted by greater snow deposition on windward than on leeward slopes. In West Antarctica, this effect can change horizon depth by tens of meters but still leave the horizons surface-conformable and continuous for hundreds of kilometers. When viewed on a scale of tens of kilometers, the additional effect of ice speed makes horizons appear falsely recumbent and suggests false historical changes in ice speed. In large regions of the high East Antarctica plateau, deposition occurs only on windward slopes to form prograding bedding sequences up to tens of kilometers long and hundreds of meters thick. Beneath the leeward slopes, long-term metamorphism transforms the bedded strata into unconformable and unstratified pseudolayers that grow with burial, merge with others, form concatenated layers more than 70 km long and over 100 m thick, and generally account for all major englacial horizons. For the largest sequences, the bed topography controls the surface topography and in large part, the way accumulation is distributed on the high plateaus.