This dissertation documents both glacial-interglacial
and millennial-scale climatic oscillations from the
d18O and d13C composition of planktonic foraminifera
preserved in Southern Ocean deep-sea sediments.
Additionally, this work addresses the causes of such
oscillations through isotopic measurements of multiple
species of foraminifera that occupy different parts of the
water column, an approach that allows the role of
thermal, density, and nutrient stratification changes to
be examined. The methods are constrained by way of
modern observations (via plankton tow samples) of
foraminiferal abundances and geochemical
compositions.

The principal results of this work are threefold. Firstly,
the modern observations of depth habitat and isotopic
composition justify the application of the multi-species
approach in the realm of paleoceanography.
Globigerina bulloides and Neogloboquadrina
pachyderma (s.) are the most abundant species in the
upper part of the water column of the subantarctic
region, but regional hydrographic differences between
the northern and southern subantarctic suggest that
these species cannot be used interchangeably in the
fossil record. For example, G. bulloides d18O mimics
that of predicted calcite over a more limited range than
is the case for N. pachyderma d18O. In the northern
subantarctic where G. bulloides is unreliable, N.
pachyderma appears more abundant at deeper depths
and therefore less indicative of surface conditions. The
d18O gradient between these shallow dwelling
species and the relatively deep dwelling Globorotalia
truncatulinoides and Globorotalia inflata appears
consistent with Dd18O values predicted from water
column properties, thus demonstrating the potential of
the multi-species Dd18O approach for addressing
gradients in surface oceans of the past.

Secondly, results from multiple high resolution d18O
records from surficial species at different parts of the
subantarctic allow the Vostok ice core chronology to be
fixed, and taken together these records suggest similar
variations in the proxies for SST and atmospheric air
temperature. Together these records suggest changes
in ice accumulation rate, oceanic moisture source,
orbital sensitivity, and water column structure on the
millennial-scale over the past three climatic cycles.

Finally, the Dd18O approach is used to explicitly
address water column structure, and subantarctic
glacial terminations are suggested to proceed from
relatively less stratified to relatively more stratified.