During the 2007 austral summer, the second project of the ANtarctic geological DRILLing (ANDRILL) Program recovered a 1138.54 m (3735.37 ft) core in the McMurdo Sound area (western Ross Sea) drilling through a floating sea-ice platform (~8.5 m [27.9 ft] thick) over ~380 m (~1247 ft) of water with a 98% recovery. The sedimentary record of the AND 2-2A drillcore spans the earliest Miocene to Pliocene, encompassing critical intervals in Earth's Neogene climate history.

This study describes the diatom biostratigraphy of the diatomite interval recovered at ~310 m (1017 ft) below seafloor and representative of the geologic time between 15.7

14.5 Ma. This microfossil assemblage provides a unique window into the middle Miocene, which is a stratigraphic interval never previously recovered from locations proximal to the Antarctic continent, and is considered to be one of the fundamental time intervals in the development of the modern Antarctic ice sheets. Denticulopsis maccollumii, Denticulopsis lauta, Nitzschia sp. 17 sensu Schrader (1976), Rhizosolenia spp., and Chaetoceros resting spores are among the species observed, indicating a productive, open-marine setting. This key paleoenvironmental information corroborates the overall results of the ANDRILL Southern McMurdo Sound (SMS) multidisciplinary project, which envisions warmer-than-present conditions in the McMurdo Sound region, and that the western Ross Sea resembled the modern climate of southwestern New Zealand and southern Alaska, a climatic regime quite different from the cold polar climate of Antarctica today.

This diatom record provides a high-resolution portrait of the middle Miocene climatic history of the Antarctic continent and will ultimately provide new data for glacial and climate models to help understand the behavior of the East Antarctic ice sheet in response to the current concern toward global warming.