Stable isotopic analyses of bulk carbonates recovered from Ontong Java Plateau during Ocean Drilling Program (ODP) Leg 192 (Holes 1183A and 1186A) show an ~0.5 per mil increase in d18O values from the upper Campanian/lower Maastrichtian to the upper Maastrichtian. This shift is consistent with widespread evidence for cooling at this time. Similar shifts were found at other localities on Ontong Java Plateau (Deep Sea Drilling Project [DSDP] Sites 288 and 289 and ODP Site 807) and at DSDP Site 317 on Manihiki Plateau. These data extend evidence for Maastrichtian cooling into the southwestern tropical and subtropical Pacific. The record of apparent cooling survives despite a significant diagenetic overprint at all sites. Comparing average Maastrichtian d18O values among sites suggests that diagenesis caused d18O to first be shifted toward higher values and then back toward lower values as burial depth increased. Carbon isotopes at the six sites show no apparent primary shifts, but at four sites, the Cretaceous/Tertiary boundary interval coincides with a negative excursion attributed to alteration of sediments near the boundary.

Sediment depth is given in mbsf. External precision is <0.03 per mil for d13C and <0.05 per mil for d18O (1 sigma). For nannofossil datums and depths of holes 30-288A and 30-289 see Andrews, Packham, et al. (1975, doi:10.2973/dsdp.proc.30.1975), for Hole 33-317A see Schlanger, Jackson, et al. (1976, doi:10.2973/dsdp.proc.33.1976), for Hole 130-807C see Mao and Wise (1993, doi:10.2973/odp.proc.sr.130.054.1993), and for holes 192-1183A and 192-1186A see Bergen (2004, doi:10.1144/GSL.SP.2004.229.01.08).