Reconstructing the Englacial Stratigraphy of the Greenland Ice Sheet

Briefly explained the stratigraphy of an ice sheet depends not only on accumulation rates and patterns, but also on the ice dynamics. This coupling between layer thickness and ice flow vastly complicates the reconstruction of the precipitation rates. These rates are therefore relatively poorly constrained, even for the last glacial cycle. A large amount of dated stratigraphy data obtained by air-borne ice penetrating radar during the Nata Operation IceBridge exists, however, holding the information on the accumulation fields. This project aims at deploying and advancing inverse modelling techniques for evaluating the fields from the radiostratigraphy. In essence this means that the model parameters, in this case the surface mass balance, are adjusted until the (measured) ice stratigraphy data is reproduced by the model as required by the data uncertainties. The problem will be approached by using the isochronal tracing scheme ELSA (Englacial Layer Simulation Architecture) in combination the non-steady 3D thermomechanical ice model Yelmo, together explicitly simulating the ice layers. This combined model will be forced with different realistic precomputed surface mass balance patterns, simulated using BESSI (the BErgen Snow Simulator). Thereby the sensitivity of the stratigraphy on the different patterns and accumulation rates can be determined. In turn this allows for the reconstruction of past mass balance fields from the measured stratigraphy. At the current stage, a linearized model between mass balance and layer thickness will be used for the inversion process, building upon the methodology of Alexios Theofilopoulos.