From Greenhouse to Icehouse – The Eocene/Oligocene - UMass ...

310 J. E. Francis et al.
from the Ross Sea region and deposits of tidewater glacier origin in Prydz Bay
confirm the presence of ice at the continental shelf by the earliest Oligocene. This
matches the major Oi-1 oxygen isotope event in the marine record. On land,
vegetation was able to persist but the warmth-loving plants of the Eocene were
replaced by shrubby vegetation with the southern beech Nothofagus, mosses and
ferns, which survived in tundra-like conditions. Throughout the Oligocene,
glaciation waxed and waned until a major glacial phase in the Miocene.
Coupled climate–ice sheet modelling indicates that changing levels of atmospheric
CO2 controlled Antarctica’s climate. Factors such as mountain uplift,
vegetation changes and orbital forcing all played a part in cooling the polar
climate, but only when CO 2 levels reached critical thresholds was Antarctica
tipped into its icy glacial world.
8.1. Introduction
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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