Late Eocene Cooling

A variety of sources, particularly fossil plants, suggest that during the early Late Eocene, climates cooled but perhaps not to the extent of significant ice build-up. The Late Eocene sediment record in the Ross Sea region (McMurdo Erratics, magnetic and clay mineral record) and in the Prydz Bay area could be indicative of cold climates but the coastal/open marine shelf and fluvial-deltaic environments in these two areas, respectively, do not show signs of the presence of significant ice. By the latest Eocene, however, glacial deposits are apparent. Glacial deposits on Seymour Island, close to the E/O boundary, may indicate the presence of valley glaciers in that region, situated at about 65° South Palaeolatitude.

The ocean record, especially marine microfossils, provides information about the climate and currents in the oceans at critical times during this interval. South America and Australia were still not separated from Antarctica during the Early Eocene, so the Antarctic Circumpolar Current was unable to develop. Instead, warm equatorial currents may have fed warmth to the continent. Palaeoceanographic changes related to the deepening of the Tasmanian Gateway and the opening of the Drake Passage are still debated but do not seem to have been strictly related to Early Oligocene climate cooling and intensification of glaciation, so these oceanographic changes are not considered to be major drivers of polar cooling. Recent atmosphere-ocean modelling has also shown that changes in oceanography related to tectonic events were not likely to have driven the climate cooling that led to glaciation.

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