(Table 1) Subsidence and calcite accumulation for South Pacific DSDP drill sites

Patterns of crustal subsidence in the southeast Pacific Ocean reflect the complex tectonic history of that region. A plot of the depth-time history of calcite accumulation recorded at DSDP sites beneath the oligotrophic subtropical gyre allows us to define the Neogene history of the calcite compensation depth (CCD) and the lysocline. The CCD shoaled from 4200 to 3700 m between 24 and 20 Ma and then deepened to near the present depth of 4100 m by 5 Ma. The lysocline became distinctly separate from the CCD between 20 and 17 Ma. By 14 Ma, the lysocline rose to 600 m above the CCD, where it has remained until the present. We interpret these data to reflect an increase in the volume of Antarctic Bottom Water beginning at 18 or 19 Ma and reaching a steady-state condition by 14 Ma, the time of rapid ice build-up in Antarctica.