The imperfect direct record of Antarctic glaciation has led
to the delayed recognition of the initiation of a continentsized ice sheet. Early studies interpreted initiation in the
middle Miocene (ca 15 Ma). Most current studies place the
first ice sheet in the earliest Oligocene (33.55 Ma), but there
is physical evidence for glaciation in the Eocene. Though
there are inherent limitations in sea-level and deep-sea isotope records, both place constraints on the size and extent
of Late Cretaceous to Cenozoic Antarctic ice sheets. Sealevel records argue that small- to medium-size (typically
10-12 × 106
km3
) ephemeral ice sheets occurred during the
greenhouse world of the Late Cretaceous to middle Eocene.
Deep-sea δ 18O records show increases associated with
many of these greenhouse sea-level falls, consistent with
their attribution to ice-sheet growth. Global cooling began
in the middle Eocene and culminated with the major earliest Oligocene (33.55 Ma) growth of a large (25 × 106
km3
)
Antarctic ice sheet that caused a 55-70 m eustatic fall and
a 1‰ δ
18O increase. This large ice sheet became a driver of
climate change, not just a response to it, causing increased
latitudinal thermal gradients and a spinning up of the oceans
that, in turn, caused a dramatic reorganization of ocean circulation and chemistry.
