The Cenozoic record of glaciations was the target of New Zealand’s CIROS-1 drillhole (CIROS = Cenozoic Investigations of the Ross Sea) in 1987. Established on the winter4 sea ice in McMurdo Sound, the drilling recovered 702 m of high quality core, extending the then known glacial record to the Eocene/Oligocene boundary at c. 34 Ma.