Using records of large mammal populations in the Urals to decipher the timing and effects of global climate change.

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Current attempts to interpret the effects of global climate change hinge on the analysis of ice and sediment cores from places such as Greenland, Antarctica and the North Atlantic. However, while these records are very detailed and go back more than 750,000 years into the past, they are effectively a proxy record of the temperature of the sea surface in surrounding areas. Consequently, it is difficult to move from sea surface temperatures to an understanding of how land animals and plants are affected by the changes apparent in such records. Ancient DNA recovered from bones of large animals from the Late Pleistocene (c. 180-12,000 years ago) provides a completely new way to obtain detailed genetic records of how populations have changed through time (eg by becoming extinct, being replaced, or migrating elsewhere) as environmental conditions change. The Ural mountains happen to have an excellent set of caves at relatively high altitude, which contain thousands of well-preserved bones of the animals who occupied the area through the Late Pleistocene. We have shown that it is possible to extract DNA from these bones, and by carbon dating them it is possible to date the DNA sequences and work out when the population disruptions occur. By studying several different species (in this case horse, caribou, wolf and brown bear) we can survey broadly across the ecosystem and look for times when many species undergo major alteration in their genetic structure. This would suggest a major (ecosystem wide) event, and a prime candidate for the cause would be climate change. Our preliminary data suggests that major alterations can be seen at the same time in animal populations as far apart as Europe and Alaska/Canada, suggesting that planet-wide (or at least hemisphere-wide) events are responsible. While the animal DNA allows us to identify when things change, and to what extent populations move around or go extinct, it doesn't necessarily identify the cause of such agitation. To investigate this issue we will examine sediment (soil) samples from the same caves that the bones originate from. Recent work at Oxford have shown that soils contain DNA from animals and especially plants that occupied an area in the past, and can provide pictures of the range and type of vegetation at different times. Cave sediments are particularly useful for this form of study because they often have good stratigraphy (steady progression of younger to older soils down through the ground), and are preserved in a relatively intact state. By examining the vegetation records and comparing them to the animal populations, we should be able to identify what plant changes are occurring in periods of major upset, and perhaps why certain species are becoming extinct while others survive. We will then relate the changes in vegetation and animal populations to the physical ice and sediment records, to try and identify how signals in these records can be related to effects on the ground. It is already very interesting that several animal extinctions seem to relate to climatic fluctuations known as Heinrich events, when fresh water sheets on the Atlantic appear to alter current flows. It is possible that short sharp climatic alterations on land may not be readily apparent in the physical records, and it will be necessary to modify the way we interpret them. This information is critical for a better understanding of past climatic change, and in order to predict the future effects of current trends such as global warming.