Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 88

global average. Antarctica did not have an ice sheet, but may have had small
regions of alpine glaciation and a temperate climate that supported large areas of
forest-like vegetation including palms, ferns, and rainforest trees

...

. About 34
million years ago, at the end of the Eocene Period, a 'sudden' (in just 200,000
years) fall in global temperature of 3-4 C occurred. This cooling led to the
expansion of ice on Antarctica by up to 10 million km 3 , and a corresponding
fall in global sea level of up to 40m as ocean water was incorporated into the
continental ice sheet. The development of an ice sheet on Antarctica is one of the
most significant changes to Earth's climate known in the geological record. It
marks the abrupt end of the so-called 'greenhouse' world, and the beginning of
the 'icehouse' world'' (Naish).

The main evidence for cooling and sudden growth of ice on Antarctica comes
from isotope measurements on ocean sediments containing matter that was ice-
rafted from icebergs calving off the edges of the Antarctic ice sheet. Deep-sea
cores prior to 34 mybp contain plant pollen originating from the nearby Antarctic
continent indicating that lush temperate forests prevailed, whereas at later dates
they were replaced by colder climate tundra.
Kennett (1977) pointed out that the Antarctic continent had been in a
high-latitude position long before glaciation commenced there. However, con-
tinental glaciation developed only when the present day Southern Ocean
circulation system became established, as obstructing landmasses moved aside. He
described the historical evolution of continental drift:

65-55 mybp Australia and Antarctica were joined.

55 mybp Australia began to drift northward from Antarctica, forming

an ocean, although circum-Antarctic flow was blocked by the
continental South Tasman Rise and Tasmania.

55-38 mybp The Southern Ocean was relatively warm and Antarctica largely

non-glaciated.

38 mybp A shallow-water connection had developed between the southern

Indian and Pacific Oceans. Substantial Antarctic sea ice began to
form. This resulted in a rapid temperature drop in bottom waters
of about 5 C. Thermohaline oceanic circulation was initiated at
this time much like that of the present day.

39-22 mybp Gradual isolation of Antarctica from Australia and perhaps the

opening of the Drake Passage. Widespread glaciation probably
occurred throughout Antarctica, although no ice cap existed.

14-11 mybp The Antarctic ice cap formed. This occurred at about the time of

closure of the Australian-Indonesian deep-sea passage.

One theory is that the freezing of Antarctica was caused by a series of
movements in Earth's major tectonic plates, because the timing of ice sheet
growth in Antarctica coincided with sea-floor spreading that pushed Antarctica
away from Australia and South America. The opening of these ocean gateways