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Improved synchronization of deep ice-core records by geophysical methods

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Citation:
Eisen, O. , Wihelms, F. , Steinhage, D. and Schwander, J. (2005): Improved synchronization of deep ice-core records by geophysical methods , EGU General Assembly, Vienna, Austria. .
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Abstract:

We present a new combination of existing methods to identifythe origin of internal layers in an ice sheet by unprecedented accuracy.Most continuous internal reflection horizons observed by radio-echo soundingare known to form isochrones and can be followed over large distances.With an ice core at either end of the profile, the reflection horizons presenttime markers that are used to synchronize the ice-core records. Using electricalproperties along an ice core as input to a numerical model which simulates thepropagation of electromagnetic waves in the ice we reproduce the reflectioncharacteristics of a radar profile near the ice core. The depth of origin ofreflections are identified by removing individual peaks in conductivity in theinput record, thus also removing the corresponding reflections in the syntheticradargram. A pilot study at the EPICA drilling site in Dronning Maud Land,Antarctica, shows that it is possible to locate the origin of internal reflectionswith an accuracy of 0.5 m in a depth of 2000 m and more. Our approach imposeslittle constrains on the input records, making it applicable to a number ofdrilling sites, and has several advantages over usual methods where merelyreflector traveltimes (respective depths) and ice-core profiles are compared.Both, dielectric profiling and electrical conductivity measurements can be usedas electrical model input. As we use pronounced series of reflections to calibratethe traveltime-depth relation, only a coarse density record is required. Inaddition, as we do not require explicite electromagnetic wave speeds, systematicphysical errors in the ice-core or radio-echo sounding data have no effect onthe final result. Application of this method to deep-drilling locations inAntarctica connected by radio-echo sounding will improve their relativesynchronization and will help to answer the question of phase relations ofclimate changes observed in the ice-core records at different locations.

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