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Living and fossil calcareous nannoplankton from the Australian sector of the Southern Ocean: Implications for Paleoceanography

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Findlay, CS (1998) Living and fossil calcareous nannoplankton from the Australian sector of the Southern Ocean: Implications for Paleoceanography. PhD thesis, University of Tasmania.

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Abstract

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 the region to
infer past changes in the ocean between 41 os and 64°S. The preservation
of calcite plates produced by these phytoplankton are preserved in pelagic
sediments and are useful in paleoceanography.
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 a1recent extinction in the Southern Ocean. Of 45
surface sediment s~mples, only eight were identified as younger than 73
ka 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 biost~atigraphy from a 5.1-metre core (GC07;
45°S; 146°E; 3307m water depth), coupled with 14C dates, oxygen isotope
ratios and %CaC03 data show that the core spans the interval of about 129
ky (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 paleoclimatic indicators. A change from dominance by Gephyrocapsa muellerae to
dominance by Emiliania huxleyi occurred at about 11 ka BP, suggesting
that the commonly used date for this reversal (73 ka 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 commori in the
region.

Item Type: Thesis (PhD)
Keywords: Findlay, C
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Date Deposited: 19 Mar 2014 03:29
Last Modified: 15 Sep 2017 01:06
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