LATE PLEISTOCENE PALEOCEANOGRAPHY OF THE TASMAN SEA - IMPLICATIONS FOR THE DYNAMICS OF THE WARM POOL IN THE WESTERN PACIFIC

Quantitative analyses of planktonic foraminifera from 47 core-top samples (spatially distributed through the Tasman Sea) and cores RC12-113, E36-23, DSDP Sites 588, 591, 592, 593, and ODP Site 828A (from a N-S transect), supplemented with stable-isotope analyses indicate that three planktonic foraminiferal assemblages (defined by factor analysis on core-top material) correlate with three hydrographic modes defined on the basis of, sea-surface temperatures, temperature profiles, seasonal changes in temperature and mixed-layer depth. Similar assemblages were found in down-core material along the Tasman Sea transect that, combined with semi-quantitative analyses of foraminiferal assemblages (provinces), and the coiling ratio of Globorotalia truncatulinoides, allows reconstruction of the position of the Tasman Front (or the Subtropical Divergence) during the late Brunhes Chron. The results indicate that the Tasman Front migrated from its present position at similar to 30 degrees S to similar to 26 degrees S during the last glacial maximum. The northward migration of the Tasman Front may indicate a reduction in volume of the equatorial warm-pool and/or an increase in the strength of cool subtropical water masses. The late Pleistocene distribution of G. truncatulinoides left-coiling form appears to be related to the formation of Subantarctic Mode Water thermostads. This relationship may explain the evolutionary origin of this species in the Southwest Pacific at 2.4 Ma simultaneously with the onset of late Pliocene glaciations. The past position of the Subtropical Convergence is reconstructed by means of coiling directions in Neogloboquadrina pachyderma. The convergence apparently migrated slightly north of 43 degrees S (core E36-23) during glacial stages 6, 10, and 12.