Late Holocene Stabilization of Conway Ice Ridge

Abstract. Marine ice sheets are low-pass filters of climate variability that take centuries to millenia to adjust to interior and near-terminus changes in mass balance. Constraining these long-term changes from satellite altimetry and velocity observations that span only the last 40 years is challenging. Here, we take a different approach, synthesizing different data sources to infer changes in the configurations of van der Veen and Mercer Ice Streams on the Siple Coast over the past 3000 years. Englacial radar data from Conway Ice Ridge reveal smooth, surface conformal layers overlying disrupted stratigraphy that suggest the van der Veen Ice Stream was 40 km wider over 3000 years ago. Englacial layer dating indicates that the ice stream narrowed to its present configuration between ~3000 and ~1000 years ago. Similarly disrupted stratigraphy and buried crevasses suggest that ice flowing from Mercer to Whillans Ice Stream across the northwestern tip of the ridge slowed shortly after van der Veen narrowed. Using an ice-flow model capable of simulating shear-margin migration, we evaluate whether small changes in ice thickness can lead to large changes in shear-margin location. Our results suggest that the tip of Conway Ice Ridge is sensitive to ice thickness change, and that when the basal strength at the tip of the ridge increases with the ice thickness above flotation, the ice-stream shear margin locations can change quickly.