Consiglio Nazionale delle Ricerche, Italy

Regarding Kerguelen Plateau region of the Southern Ocean during the middle Miocene (14.8-11.8 Ma), abundance fluctuations of several planktonic foraminiferal taxa, stable oxygen isotope and Mg/Ca ratios have been integrated as a multi-proxy approach to reach a better understanding of the growth modality and fluctuations of the East Antarctic Ice Sheet (EAIS) during this period. A 7 degrees C decrease in Sea Surface Temperature (SST), an abrupt turnover in the planktonic foraminiferal assemblage, a 1.5% shift towards heavier delta (super 18) O values (Mi3 event) and a related shift towards heavier seawater delta (super 18) O values between 13.9 and 13.7 Ma, are interpreted to reflect rapid surface water cooling and EAIS expansion. Hole 747A data suggest a major change in the variability of the climate system fostered by EAIS expansion between 13.9 and 13.7 Ma. Ice sheet fluctuations were greater during the interval 14.8-13.9 Ma compared with those from 13.7 to 11.8 Ma, whereas the latter interval was characterized by a more stable EAIS. In our opinion, the middle Miocene ice sheet expansion in Antarctica represents a first step towards the development of the modern permanent ice sheet.