The Terrestrial Fossil Record of Antarctic Climate

The terrestrial Neogene biota of Antarctica is poorly known with fossils coming only from exposures on the Beardmore Glacier and from boreholes in the Ross Sea region. This will soon change with the recent discoveries of Neogene fossil assemblages in the Dry Valleys (Ashworth, A. C., Lewis, A. R. and Marchant, D. M., personal communication, 2006). What is known so far is that the Neogene biota had a low diversity and was very different than the diverse forested habitats of the early Palaeogene. Evidently, tundra vegetation was present in the Transantarctic Mountains from the Oligocene until at least the Early Miocene and during that time it appears that there was a declining biodiversity (Askin and Raine, 2000; Raine and Askin, 2001). The final extinction of several vascular plants and animals with more complex life histories is assumed to be associated with the shift to the polar desert climate which prevails today in the interior of the continent. Whether or not this immediately followed the mid-Miocene climatic optimum or was as late as the mid-Pliocene is the most outstanding problem in Neogene climatic history in need of resolution.

The extinction implies that a climatic threshold was passed in which temperatures and available moisture were significantly reduced after the event than those which supported the tundra biota. The most parsimonious interpretation to explain the occurrence of the Neogene biota is that the organisms were descendents of the Gondwana biota that had existed on the continent for millions of years, long after the fragmentation of the continent. The conclusion that plants and animals continued to inhabit Antarctica for millions of years after the continent became isolated makes their extinction an especially significant event and supports the argument that it was associated with a major reorganization of the global climate system.

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