The late Quaternary calcareous nannoplankton assemblages from three cores from the Tasman Sea

Abstract

The composition of the late Quaternary calcareous nannoplankton in three deep-sea cores RC12-113, Z-2108 and GC-3, located along a N-S transect at three different latitudes (25°, 33°, 44°S) in the Tasman Sea, has been investigated. The shift in floral dominance from small Gephyrocapsa to small placoliths (labelled here “Small Placolith”), and then to Emiliania huxleyi is recognized at stage 5 and stage 4, respectively, in cores RC12-113 and Z-2108. However, the occurrence of small Gephyrocapsa and Small Placolith displays a seesaw relationship in core GC-3 which is located today just north of the Subtropical Convergence, east of Tasmania. Gephyrocapsa muellerae and Coccolithus pelagicus increase their abundance geographically southwards and stratigraphically during glacial periods, whereas the percentage abundances of Florisphaera profunda and Umbilicosphaera sibogae demonstrate reverse patterns. The relationships between the percentage abundance of each nannoplankton species and the δ18O record for three cores are discussed in detail. A transfer function for estimating past sea-surface temperatures (= TN) is attempted here; it is based on core-top data from the Tasman Sea and provides a good relationship between some calcareous nannoplankton assemblages and modern mean summer sea-surface temperatures. The TN value shows a good correspondence with the δ18O record in all three cores. Core GC-3 is much affected by CaCO3 dissolution in comparison with cores RC12-113 and Z-2108. The calcareous nannoplankton dissolution patterns recognized in the three cores do not show a systematic correspondence with the δ18O record. Of interest, however, is the good preservation peaks that are recognized in all three cores at the transitions from glacial to interglacial events.