ALBERT

Description: Oxygen isotope values from calcareous nannofossils in four cores spanning the Quaternary from DSDP Site 593 in Tasman Sea are compared with the delta18O signal of planktonic and benthic foraminifers from the same samples. The classic mid-late Quaternary isotope stages are exhibited with stage 12 particularly well developed. When delta18O values of nannofossils are adjusted for coccolithophore vital effects they indicate larger (by 1-6°C) surface to bottom paleotemperature gradients and greater (by 1-3°C) changes in mean sea-surface temperature between full glacial and interglacial conditions than do delta18O values from planktonic foraminifers. Along with the foraminifers, the nannofossils record a bimodal distribution of delta18O between the early and mid-late Quaternary, indicating a significant change in global ice budget. The delta13C of nannofossils also shows a bimodal distribution, but is opposite to that for the foraminifers. Nannofossil delta18O values record a shift of c. -0.8‰ at isotope stage 8 corresponding to a major reduction in abundance of the previously dominant gephyrocapsids. A shift in delta13C of c. -1.5‰ also occurs at stage 8, and a shift in delta13C of c. +1.2‰ at around stage 14. The delta18O shift in nannofossils is at least a Pacific-wide phenomenon; the delta13C shifts are possibly global. The delta13C signal of nannofossils exhibits an antipathetic relationship to that of benthic foraminifers back to isotope stage 18 but no significant correlation beyond this level to the base of the Quaternary. This is interpreted as reflecting local productivity dominating global influences on delta13C since stage 18 at DSDP Site 593. The difference between nannofossil and benthic foraminifer delta13C signals (Delta13C) tends to be maximum during glacial stages and minimum during interglacials throughout the section, showing a strong correlation with the nannofossil delta180 signal. The increased partitioning of 13C between surface and bottom waters during the glacial periods may indicate heightened productivity in surface waters in the southern Tasman Sea at these times.

Description: A moderate-resolution isotope stratigraphy (with an average of one sample per 17,500 yr.) derived from the benthic foraminifer Uvigerina (or Cibicides), the planktonic foraminifer Globigerina bulloides, and calcareous nannofossil concentrates is presented for the entire Quaternary (and latest Pliocene) section of mid-upper bathyal calcareous oozes from DSDP Site 593, western Challenger Plateau, south Tasman Sea. Superimposed on a trend of gradually increasing average delta18O values through the Pleistocene, reflecting the progressive buildup of polar ice sheets, is a record of highfrequency but generally low amplitude (0.5-1‰) isotope fluctuations in the early Quaternary (1.9-1.0 m.y.), followed by a greatly increased intensity (1.5-2.0 ‰) of glacial-interglacial fluctuations during the late Quaternary (〈 1.0 m.y.). The standard late Quaternary isotope stages 1 to 24 are mainly resolvable. Significant excursions in both delta18O and delta13C values at various times during the Quaternary are suggested to be due to periodic, fundamental changes in ocean circulation properties over the plateau. For example, intensified upwelling of Antarctic Intermediate Waters during several glacial periods is indicated by the convergence of benthic and planktonic foraminiferal delta18O data, and productivity variations may account for certain delta13C spikes in the record. With increasingly higher resolution analysis this core will provide a useful Quaternary isotope reference section for southern temperate waters in the southwest Pacific, centered on New Zealand.

Description: Oxygen and carbon isotope values from calcareous nannofossils in the mid-late Quaternary (Brunhes) interval of core from DSDP Site 594 off eastern South Island, New Zealand are compared with the delta18O and delta13C signal of planktic and benthic foraminifers from the same samples. Nannofossil delta18O values appear strongly affected by non-equilibrium fractionation, in agreement with previous in-vitro studies. The nannofossil delta18O and delta13C signals show a strong down-core cross-correlation and a significant positive linear correlation. This is interpreted as the result of kinetic isotope effects producing non-equilibrium fractionation of both 18O and 13C. A previously reported isotope stage 7/8 carbon-shift appears to be related mainly to a Pacific-wide reduction in the abundance of gephyrocapsids rather than to any significant change in the partitioning of carbon isotopes. The strong correlation between nannofossil delta18O and delta13C can also be interpreted as being influenced by increased productivity during glacial intervals and decreased productivity during interglacials in subantarctic waters.