Figure 5. The cooling step observed between 3 and 2.5 Ma (as seen in the shift to more positive values of d18O) marks a change toward greater instability of climate, as seen in increased fluctuations of d18O values of planktonic foraminifers (Neogloboquadrina pachyderma and Globigerina bulloides) and benthic foraminifers (Cibicides spp.) sampled near the boundary between the South Atlantic and Southern Oceans (from Hodell and Venz, 1992).

Figure 5. The cooling step observed between 3 and 2.5 Ma (as seen in the shift to more positive values of δ¹⁸O) marks a change toward greater instability of climate, as seen in increased fluctuations of δ¹⁸O values of planktonic foraminifers (Neogloboquadrina pachyderma and Globigerina bulloides) and benthic foraminifers (Cibicides spp.) sampled near the boundary between the South Atlantic and Southern Oceans (from Hodell and Venz, 1992).