Ice-flow modeling results to assist the interpretation of millennial-scale ice cores recovered at the high-Alpine ice drilling site Colle Gnifetti, Swiss/Italian Alps

Ice-flow modeling studies were conducted to assist the interpretation of millennial-scale ice cores recovered at the high-Alpine drilling site Colle Gnifetti, Swiss/Italian Alps. Backwards trajectories starting from the borehole sites at different depths are calculated in order to estimate ice-core catchment areas. The position of source points identified on the glacier surface is provided in the Swiss coordinate system (LV03) and in the UTM system. The uncertainty of the position of the source points is about 10% of the distance from the corresponding drill site. The ice-flow model also provides ice-core chronologies with an uncertainty of about 20%. Apart from the KCI core, the other four model chronologies are well in agreement with experimental results. Inclination angles of the boreholes KCC and KCI were measured in September 2016 (i.e. 3 and 11 years after drilling, respectively) to validate the modeled velocity field. The measurements were performed twice: downwards (from the top to the bottom of the borehole) and upwards. The uncertainty of the measurements is 1.9° and is estimated considering the diameter of the borehole and the size of the inclinometer probe. The uncertainty of the measurements is dominated by the potentially wrong (i.e. non-parallel to the borehole walls) positioning of the inclinometer probe inside the borehole. The quantity "Q orientation" indicates whether the inclinometer probe was likely correctly aligned with the borehole walls (Q orientation=1) or not (Q orientation=0).