Specialeforsvar af Jacob Sievers – Niels Bohr Institute - University of Copenhagen

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Niels Bohr Institute > Calendar > 2010 > Specialeforsvar af Jac...

Specialeforsvar af Jacob Sievers

abstract:

Due to the recent increasing interest in global warming and its implications, an understanding of the highly climate-sensitive past patterns of snow accumulation across glaciers and ice sheets such as Greenland, has become essential. The Greenland ice sheet represents a formidable climate archive describing many key factors of past climates. Within the ice sheet internal isochronous layers, constituting layers of past deposition, can be detected by radio-echo sounding techniques. This type of data describes the past flow of the ice sheet and can be directly linked to the accumulation above which feeds the flow. The interpretation of radio-echo sounding data however, is tedious and is therefore typically only carried out for single flightlines, thus only providing insight into two dimensions of an actual three-dimensional problem. During this study 25 isochronous layers, which are dated from their depths at NGRIP, have been analyzed in a large number of interconnected aerial radio-echo sounding datasets across the NW Greenland ice sheet to form 25 large isochronous surfaces. A simple two-dimensional and three-dimensional flow model for the Greenland ice sheet has been developed to infer accumulation rates for a number of past periods down to, and including, 7496 yrs before present day, across the expansive surfaces. To determine the correct past accumulation patterns, an inverse Monte Carlo method, in the form of a combined simulated annealing and Metropolis-Hastings approach, is applied to the simple models.