Seismic reflection surveys at GHOST Ridge, Thwaites Glacier

Subglacial topography and the character of a glacier’s basal material have a controlling effect on ice flow and are therefore important to parameterise in ice sheet models. Seismic surveys provide a means to characterise basal materials through the estimation of the elastic parameters of the bed (for example, acoustic impedance and Poisson’s ratio). The subglacial topography of Thwaites glacier is oriented across flow, with a series of subglacial ridges running East to West across the glacier. The bed character in the vicinity of a subglacial ridge ~60km upstream of the grounding zone, named GHOST ridge, is of particular concern, as this ridge may be a future pinning point for the grounding zone as Thwaites retreats. We present measurements of basal conditions from an active seismic dataset acquired immediately upstream of GHOST Ridge. During the 2023-24 season a 14.4 km seismic line was shot with hot water drilled Pentolite sources. We observe varied bed topography within the 14km section, with areas of smooth bed topography interspersed with rougher areas, and crag-and-tail like features present. Bed reflectivities are consistent with a widespread subglacial dilatant till layer, with stiffer till on the stoss sides of basal topographic features, and the softest till on the lee sides of these features. We will also discuss preliminary results from amplitude-versus-offset analysis, which gives further constraint of basal elastic properties.