Manifestation of ice properties and dynamics in radar stratigraphy: Berkner Island ice saddle as a case study

Internal radar layers in ice sheets provide an indirect, but spatially-continuous record of ice flow and physical properties.Ground-based radar data recorded along the ridge of Berkner Island, Antarctica, reveals the presence of an isochrone arch in the vicinity of the saddle between the two domes (Thyssenhhe in the South and Reinwarthhhe in the North), upstream of McCarthy inlet to the East.The data show the isochrone arch between a two-way traveltime of about 0.3 us (30 m) to 5.2 us (~450 m), with an overall ice thickness of 11.2 us (950 m).At a depth of about 3.5 us (310 m) the isochrone arch changes its signature: it splits from a single bump to a double bump, with a separation of the anticlines of about 300 m.This oberservation has several implications.First, as isochrone arches were so far observed at ice domes and divides of zero along-divide flow, where deviatoric stresses are low (a "Raymond" bump), this should also be the case at the saddle point.Second, appearance of a double bumps are assumed to be an indicator of a strongly evolved crystal fabric at larger depth.Third, as the double bump appears at rather shallow depths (35% of the ice thickness) compared to other sites, thinning during the last millenia might have occured.The topography of a saddle is a very demanding three-dimensional composite scenario to test rheological assumptions.To analyse the influence of ice flow and fabric characteristics on internal layer architecture at the saddle, we employ a three-dimensional time-dependent anisotropic Full Stokes model that considers strain-induced fabric evolution.