Abstract: Insight into causes of ice sheet variability over a range of time scales is fundamental to our understanding of Earth system response to climate change. Furthermore, there is a need to constrain long-term commitments to future sea level rise and the potential for ice sheet 'recovery' if society is able to limit or reverse warming. It is well understood that fluctuations in the volume and extent of Antarctica's ice sheets (AIS) are primarily controlled by changes in global climate due to variation in incoming solar radiation due to orbital variations, surface reflectivity (albedo), and greenhouse gas concentrations. Regional changes in ocean circulation also have an effect. Furthermore, the AIS is sensitive to changes in topography over longer time periods. However, questions regarding the role that these different drivers have played in controlling ice sheet variability through time remain. Reconstructions of past ice sheet behaviour from the geological record offer a means to examine the influence of predictable orbital variations and to identify critical planetary thresholds that have affected ice sheet behaviour. These ice sheet reconstructions are often derived from far field records, which offer highly resolved, near continuous records over the past 34 million years. However, ice sheet proximal data are required to constrain interpretations based on far-field data.

Over forty years of scientific drilling and seismic data acquisition along the Antarctic margin provide a direct record of AIS variability. Drill cores recovered from the Ross Sea reveal a composite stratigraphy that spans the past 34 million years. Extensive marine seismic surveys across the region define stratigraphic packages that are linked to glacial processes and help constrain glacial history. Importantly, the location of this unique stratigraphic archive captures the evolution of ice sheets in both East and West Antarctica. We have established an integrated stratigraphy for the Ross Sea using new biostratigraphic data and revised core descriptions. This integrated framework offers a clear and coherent history of AIS variability and extent since the inception of isolated ice caps on the continental interior and mountains in the late Eocene. Whereas orbital forcing played an important role in AIS growth and retreat on glacial-interglacial timescales, proxy environmental data highlight fundamental thresholds in the climate system, across which the nature and behaviour of the AIS fundamentally changed. Importantly, these transitions suggest that the AIS is sensitive to relatively small changes in atmospheric CO₂ concentrations, similar to those projected for the coming decades. Collection of new geological data from regions that are most vulnerable to climate change are required to test and build on our current understanding of AIS sensitivity. Our community challenge is to identify, fund, and drill these locations soon!