Last occurrence datums of the diatoms Rouxia leventerae and Rouxia constricta: indicators for marine isotope stages 6 and 8 in Southern Ocean sediments

Diatom analysis of sediments recovered during ODP Leg 177 and RV Polarstern expeditions in the Atlantic sector of the Southern Ocean reveals that the abundance pattern and the stratigraphic distribution of the two recently described diatom taxa, Rouxia leventerae and Rouxia constricta, represent a new tool for dating sequences that have been deposited under Southern Ocean cold-water conditions. In sediments from the present Antarctic Zone (AZ) the last occurrence datums of R. leventerae and R. constricta can be placed into the upper portion of the marine isotope stage (MIS) 6 (∼0.14–0.13 Ma) and the lower portion of MIS 8 (∼0.3–0.28 Ma), respectively. This allows the identification of isotope stages in Pleistocene Southern Ocean sediments that are often characterized by the lack or discontinuous occurrences of calcareous microfossils. Occurrences of R. leventerae are restricted to glacial sediments deposited in the AZ, highlighting that this taxon is typically restricted to cold waters. In contrast, R. constricta occurs in glacial and interglacial sequences and displays a broader geographical distribution between the northern AZ and the Polar Front Zone.