Abstract:
Currently, a debate exists regarding the extent of dynamism within the Neogene cryosphere of the Southern Hemisphere. Although Southern Ocean and Antarctic sediment records currently exist suggesting multiple warm intervals occurring between 3.1 Ma and 4.8 Ma, further verification is necessary to constrain the timing and magnitude of these events. Given future trends in global warming bear similarity to estimated climate conditions of the early Pliocene, our comprehension of Antarctica's role in climate change is clearly an important issue. Clarification of parameters affecting Southern Ocean hydrography, without the bias of feedback mechanisms, will refine modeling studies and enhance our ability to predict climate variation in the near future more accurately. New high-resolution diatom paleobiogeographical data recovered from Southern Ocean sediments not only have the potential to refine warm intervals, but also elucidate incongruous proxy records and expand the history of oceanographic factors influencing southern high-latitude thermohaline gradient variability and climate factors induced by such variation. Examination of new high-resolution (> or =10 cm sampling interval) silicoflagellate data from two coeval sites (64-66 degrees S latitude)--ODP Hole 1165B and two cores on the northern Gunnerus Ridge (PS1811-8 and PS1812-6)--constrains three intervals of significant warmth ( approximately 4.5-5.5 degrees C), occurring at approximately 3.7, approximately 4.3, and approximately 4.6-4.7 Ma. Synoptic comparison of these data with diatom microfossil assemblage data collected in this study and previously recorded Southern Ocean proxy data (e.g. calcareous nannofossils, delta (super 18) O, and terrigenous sediments) clearly reveals oceanographic factors other than sea-surface temperature influencing diatom paleobiogeography in Southern Hemisphere waters. Results of this research suggest that such non-corroboration amongst proxy records could potentially aid, rather than hamper, our understanding of their effects.