This thesis presents oxygen isotope values from Early Pliocene Ross Sea diatoms to gain insight into paleoclimate conditions. Diatoms are siliceous phytoplankton that can provide a comparable oxygen isotope record to benthic foraminifera but in high latitude regions where calcareous microfossils are poorly preserved. Samples were taken from the AND-1B drill core in the Ross Sea, dating to 13 million years ago. The diatoms were purified and their oxygen isotope compositions were measured. The results suggest ocean water isotope values around 10‰ lighter than present, pointing to a significant influx of glacial meltwater into a warmer, fresher Ross Sea during the early Pliocene. Interpreting the