Foraminifera from Deep Sea Drilling Project Site 270, Ross Sea, Antarctica, are used to trace an early phase of glaciation during the late Oligocene–early Miocene. The central Ross Sea underwent significant bathymetric and oceanographic evolution with the inception of glaciomarine sedimentation, resulting in the sequential development of four contrasting foraminiferal populations (assemblage zones). Gradual climatic change in the Ross Sector during latest Paleogene-early Neogene time culminated in major ice build-up by the late early Miocene. Conclusions derived from our microfaunal studies reaffirm climatic and oceanographic trends interpreted from oxygen-isotope data for sub-Antarctic deep sea sites north of the Ross. Sea. Intensification of glaciation within the Ross Sea area may be responsible for the increase in production of Antarctic Bottom Water and associated development of widespread early Neogene deep-sea hiatuses reported from lower latitude regions.