Geological Survey of Finland, Finland

The East Antarctic Ice Sheet (EAIS) behaviour in response to global temperature changes is under discussion today. Recent studies have shown that it has varied from a polythermal, dynamic condition to a predominantly cold stable state starting throughout its history. This presentation aims to give additional information of the glacial behavior of EAIS based on clay minerals occurrence and sediment physical properties since middle Miocene when the Earth's climate started cooling dramatically. We will present examples of use of spectral analysis related to sediment physical properties including magnetic susceptibility and gamma-ray attenuation porosity/density evaluation (GRAPE) and clay mineral distribution of Ocean Drilling Program Site 1165 on the continental rise, proximal to EAIS off the Prydz Bay. Site 1165 records the number and timing of late Neogene glacier ice expansions to the shelf edge, extending back to the earliest Miocene times (c.a. 22 Ma). This study examines existing data on the sediment column of Middle Miocene age (between 150-330 metres below sea floor) with comparison to Plio-Pleistocene record. By comparing clay mineral occurrence and physical properties with the general southern ocean oxygen isotope curves we aim to find more evidence on the dynamic behaviour of the East Antarctic Ice Sheet since Middle Miocene and see how sediment physical properties respond to growth and retreat of the EAIS. Increasing illite and decreasing smectite content supports the general cooling trend after middle Miocene thermal optimum. Illite is showing correlation with magnetic susceptibility and grape density. This supports the fact that illite is a typical product of physical weathering and glacial transport. In the Early Pliocene the content of smectite mineral tends to dominate the clay fraction frequently suggesting intervals of more open, warmer water than today. In the Middle Pliocene the increasing smectite and decreasing illite content suggest that the ice sheet at that time may have been more dynamic than in general during the Pleistocene.