Figure 175-2. Carbon dioxide concentrations in the Vostok ice core from Antarctica (Barnola et al., 1987), compared with a productivity-related carbon isotope signal from the eastern tropical Pacific (difference between the ¶13C values of planktonic and benthic foraminifera; Shackleton et al., 1983), show that ocean productivity and atmospheric CO2 tend to vary together. Time scale of Barnola et al. is adjusted to the one of Shackleton et al. by correlation of the deuterium signal in the ice with the oxygen isotope signal in the sediment (from Berger et al., 1989).