Frontiers and Opportunities in Antarctic Geosciences * Certosa di Pontignano * 29-31 July 2004
Marine Palynomorphs: Studies From the Antarctic Margin
M. HANNAH, J. PREBBLE, C. STORKY
Antarctic Research Centre, School of Earth Sciences, Victoria University of Wellington, New Zealand
(Michael.hannah@vuw.ac.nz)
This poster outlines four studies of Marine palynomorphs from the Antarctic margin currently being carried out at Victoria
University. All are in various degrees of completeness. Each project is aimed at using marine palynomorphs to investigate
Late Cainozoic climate variation.
Project 1 – Long term climate changes in the Cape Roberts cores (Mike Hannah)
Building on the success of the Cape Roberts project, this study uses fluctuations in broad groups of marine palynomorphs to
help understand long term climate changes The complex assemblages recovered in the Cape Roberts core are similar to
assemblages recovered from the present day Arctic Sea floor (Mudie, 1992; Wrenn et al., 1998). Data from CRP 2/2A only
is presented here. Below about 300 mbsf the assemblages are dominated by the prasinophyte genus Cymatiosphaera and the
fusiform acritarch Leiofusa. The dinocyst assemblage in this interval is largely composed of autotrophs. Above 300 mbsf
the assemblages are dominated by the acritarch Leiosphaeridia and the dinocysts assemblage is now dominated by
heterotrophs. Comparison with Arctic material suggest that the older assemblages reflects a time of lowered salinity with a
complex, stratified water column with little ice present. The younger assemblage suggests a deterioration in climate, and
although there is still a strong fresh water signal, more ice is indicated.
Project 2 – Biotic response to climatic cycles (Joe Prebble)
In an attempt to understand the biotic response to the glacial cycles that have been documented in the Cape Roberts core
(Naish et al., 2001), both the marine and terrestrial assemblages from two cycles (cycle 11, CRP 2/2A and cycle 2 CRP 3)
have been investigated. Overall the samples yielded an average of 55 grains per gram of marine palynomorphs. The relative
abundance of some taxa change within the glacial cycles, notably Leiospheridia, Michrystridium and Cymatiosphaeridia in
CRP 3, and Tasmanties in CRP 2 but the cause of this is still unclear. Terrestrial palynomorphs are very sparse in the Cape
Roberts cores. An average of 1.6 grains per gram has been recovered from CRP 2, and 0.9 grains per gram from CRP 3. The
assemblages are dominated by Nothofagidites, bisaccate pollen, and assorted spores. The diversity of pollen in both cycles
is similar. However, CRP 2 cycle 11 has more taxa that are indicative of cooler climates (such as Tricolpiies sp. A and N.
lachlanae).
Project 3 – Glacial fluctuations in ODP 1165, Prydz Bay (Mike Hannah)
Palynomorph assemblages from drift sediments ranging in age from 22 to 8 Ma (Florindo et al., 2003) from ODP site 1165
were examined The assemblages recovered are similar in composition to those from the Cape Roberts core but they differ in
that many are dominated by reworked terrestrial palynomorphs. Almost all samples which contain little reworked material
are dominated by Leiospheres. This is interpreted as representing periods of advance (reworking dominant) and retreat
(Leiosphere dominant) of the Amery “ice sheet”. Four intervals of ice advance and three ice retreats can be recognised. The
final, and largest, advance started about 14.3 my ago and coincides with the well known mid Miocene shift in the 18O
curve associated with the establishment of persistent ice on the Antarctic continent.
Project 4 – Distribution of marine palynomorphs on the present day sea floor of Prydz Bay (Claire Storkey)
Using material supplied by Geoscience Australia we are looking at distribution of present day marine palynomorphs in
Prydz Bay in order to compare them with the ancient assemblages documented in Site 1165. Preliminary results suggest
today’s assemblages are different and more complex than those documented in Site 1165. The level of reworked material
today seems to be significantly lower than in the ancient assemblages.
REFERENCES
Florindo, F. et al., 2003. Magnetobiostratigraphic chronology abd palaeoenvironmental history of Cenozoic sequences from ODP sites 1165 and 1166,
Prydz Bay, Antarctica. Palaeogeography, Plaaeoclimatology, Palaeoecology, 198: 69-100.
Mudie, P.J., 1992. Circum-Arctic Quaternary and Neogene marine palynofloras: palaeoecology and staistical alnalysis. In: M.J. Head and J.H. Wrenn
(Editors), Neogene and Quaternary Dinoflagellate Cysts and Acritarchs. American Association of Stratigraphic Palynologists Foundation, Dallas, pp.
347-877.
Naish, T.R. et al., 2001. Orbitally Induced Oscillations in the East Antarctic Ice Sheet at the Oligocene/Miocene Boundary. Nature, 413: 719-723.
Wrenn, J.H., Hannah, M.J. and Raine, J., I., 1998. Diversity and Palaeoenvironmental significance of Late Cainozoic Marine palynomorphs from the CRP1 Core Ross Sea, Antarctica. Terra Antartica, 5(3): 553-570.