One of the most intriguing challenges in Antarctic Earth history is to understand the fundamental climate change from the past greenhouse world with no major polar ice caps to our present icehouse that is dominated by the vast ice sheets on the Antarctic continent. This change across a major climate threshold holds many clues that will help us understand the potential changes our world may undergo in future.

Geological evidence from rocks and fossils from the Antarctic continent and from marine oxygen isotopes that record changes in temperature, ice volume and water masses indicate that ice sheets built up on Antarctica from about Eocene/Oligocene (E/O) boundary times, approximately 34 million years ago. This is named the Oi-1 event in the marine oxygen isotope record and is represented by the appearance of several glacial deposits in the rock record. However, the actual pattern of climate cooling and the causes of glaciation are far from understood, and there are hints of the presence of ice in the Late Eocene. Indeed, it is possible that ice existed on Antarctica even during the Cretaceous (Miller et al., 2005; Tripati et al., 2005).

This chapter reviews our current understanding of the greenhouse-icehouse transition in Antarctica. It covers the interval of climate change from the warm greenhouse climates of the Early Eocene through to the first appearance of ice and the establishment of glacial conditions during the Oligocene. Several lines of evidence are presented for climate and environmental change: the sedimentary rock record on the continent provides clues to the nature of the cooling climate during the Eocene; latest

Eocene and Oligocene sediments recovered from marginal basins in drill cores contain the earliest undisputed glacial deposits; fossil plants and palynomorphs from both the continent and marginal basins have yielded information about cooling climates in the terrestrial realm; marine microfossils hold clues to ocean circulation and the significance of ocean gateways; the marine isotope record of the open oceans tells us about changes in deep ocean temperatures as the result of climate cooling and ice growth; and finally, the cause of cooling and the birth of the icehouse world is explored through computer modelling. The final section summarizes our current understanding of the greenhouse-icehouse transition in Antarctica.

0 0

Post a comment