8th International Nannoplankton Association Conference


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Claire Findlay:
Calcareous nannoplankton from the Australian sector of the Southern Ocean: Implications of paleoceanography

This study documents the distribution of calcareous nannoplankton in the waters and surface-sediments of the Australian sector of the Southern Ocean, and applies the information to core-samples from this region to infer past changes in the ocean between 41S and 64S. The preservation of calcite plates produced by these phytoplankton are preserved in pelagic sediments and are useful in palaeoceanography.

Water-column samples show that calcareous nannoplankton can be separated into five distinct assemblages associated with properties of the water mass, i.e. temperature, salinity, light and nutrients. In general, the abundance and diversity of nannoplankton decrease poleward from subtropical to polar waters.

The surface-sediments show an abundance and diversity of calcareous nannoplankton different from living assemblages in the water-column. Surface-sediments are dominated by a single assemblage, including C. pelagicus, a species not found in water-column samples. The absence of C. pelagicus suggests a recent extinction in the Southern Ocean. Of 45 surface-sediment samples, only eight were identified as younger than 73ka BP based on currently recognised biostratigraphy, indicating erosion and disturbance of sediments in the region. Preferential preservation of larger, more-robust species of nannoplankton in the surface-sediments suggests that chemical dissolution of calcite is significant.

Calcareous nannoplankton biostratigraphy from a 5.1m core (GC07: 45S, 146E; 3307m water-depth), coupled with 14C dates, oxygen isotope ratios and %CaCO3 data show that the core spans the interval of about 129ky (from the beginning of the last interglacial) to Late Holocene. Changes in fossil assemblages with time are related to glacial and interglacial intervals, suggesting that the nannoplankton are useful as palaeoclimatic indicators. A change from dominance of Gephyrocapsa mullerae to dominance of Emiliania huxleyi occurred at about 11ka BP, suggesting that the commonly-used date for this reversal (73ka BP) is not applicable for the sub-Antarctic. The presence of Miocene and Pliocene species in the core-samples indicates that reworking of sediments is common in the region.


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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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