Pliocene Record

The Pliocene Epoch (Chapter 10) is a critical time for understanding the nature of the Antarctic Ice Sheet as IPCC (2001, 2007) projections of global temperature rise suggest that we will reach Pliocene levels within the next hundred years (Fig. 1.2).

Indirect evidence, such as sea level changes and ocean floor sediments, suggests that ice volumes were subject to cyclical variability. It is believed that, since Northern Hemisphere ice sheets were not fully developed, sea level changes were driven by fluctuations of the Antarctic Ice Sheet. Many scientists believe that it was the relatively unstable West Antarctic Ice Sheet that was responsible for these changes, but the role of the much larger East Antarctic Ice Sheet remains controversial. Key to this argument is the timing of the transition of the East Antarctic Ice Sheet from a polythermal, dynamic condition to a predominantly cold-base and stable state. Two opposing and vigorously defended views prevail. The long-standing view is that the East Antarctic Ice Sheet became stable in mid-Miocene time; evidence of which is primarily from the longevity of the landscape and well-dated surfaces and ash deposits in the Dry Valleys region along the western border of the Ross Sea. Another controversial view is that terrestrial glacial deposits, known as the Sirius Group, scattered in a number of locations through the Transantarctic Mountains, indicate dynamic ice-sheet conditions as recently as Pliocene time; based on diatom biostratigraphy and preserved vegetation. The latter viewpoint is supported by work on deposits known as the Pagodroma Group along the western side of the Lambert Glacier-Amery Ice Shelf drainage system. Each argument is internally consistent and the biggest challenge is to reconcile the differing views. If the East Antarctic Ice Sheet was indeed subject to major fluctuations until Pliocene time then, taking into account IPCC projections, we have cause to be concerned about the possibility of the East Antarctic Ice Sheet reacting to climate change within the next few centuries.

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