Figure 2. Carbon dioxide concentrations (solid triangles; bar87 and jou93) in the Vostok ice core from Antarctica (Barnola et al., 1987; Jouzel et al., 1993) and eastern tropical Pacific (difference between the δ¹³C values of planktonic and benthic foraminifers (thick line; F [sha85]); Shackleton and Pisias, 1985), show that ocean productivity and atmospheric CO₂ tend to vary together. Time scale of Barnola et al. (1987) is adjusted to the one of Shackleton and Pisias (1985) by correlation of the deuterium signal in the ice with the oxygen-isotope signal in the sediment (from Berger et al., 1996).