Its the anisotropy!
Blue ice areas (BIA) cover about 1% of the Antarctic ice sheet. They are characterized by a local enhanced ablation zone leaving bare ice (hence the name) in a distinct ablation zone. BIAs are confined to the coastal areas, usually close to nunataks. The distinct ablation zone has the coinciding feature that isochrones get vertically aligned, making BIAs an attractive source for easy accessible climate data from maritime influenced regions by simply scratching an ice core horizontally from the
surface. The huge drawback is, that - in comparison to the vertically drilled ice cores in the central regions of Antarctica - the dynamical evolution of the ice sheet is an even stronger determining input in order to interpret such horizontal ice cores. To that end, the well explored BIA at Scharffenbergbotnen, DML, East Antarctica was studied using Elmer/Ice. Being initially puzzled by a complete mismatch between computed and measured velocities with a standard Glen's flow law and by excluding all other possible reason, the authors came to the conclusion that the existence of a pronounced fabric at the glacier is the most likely explanation to correctly interpret the flow conditions at the BIA. Further, by studying the evolution of the age-depth horizons using a novel Semi-Lagrangian solver showed that the oldest ice is about the age of the Late GLacial Maximum (LGM) of about 15ka bp., leading to the conclusion that the BIA started to form after the LGM, when the surrounding ice sheet started to thin and the valley of Scharffenbergbotnen was decoupled from the main ice flow. The project behind this study was funded by the Finnish Academy.