INTERPRETATION OF POLLEN DATA FROM SOUTHERN CHILE AND CLIMATE CHANGE AT THE LAST GLACIAL/INTERGLACIAL TRANSITIION

A number of high-quality pollen records have recently been published from southern Chile, with conflicting conclusions with respect to the timing and nature of climate change at the last glacial/interglacial transition. Bennett et al. (2000, Science 290, 325-328) found no evidence for climatic cooling during the Younger Dryas Chronozone at 45 degrees South. On the other hand, Moreno et al. (2001, Nature 409, 804-808) found cooling events at 41 degrees South that were nearly synchronous with climatic changes during the YDC in the North Atlantic.

Both papers rely heavily for their conclusions on the interpretation of pollen data, as percentages and accummulation rates. The range of taxa involved are similar and the dominant pollen types are the same in both regions. The different conclusions originate in differences of two aspects of interpretation.

1. Different interpretations of similar base data. Increases in tree pollen types can be interpreted as increasing warmth at the beginning of an interglacial or as occurrence at lower altitudes than today, indicating cooling.

2. The extent to which changes in pollen accummulation rates can (without simultaneous changes in pollen percentages) be used to infer climatic change rather than changing local sedimentary environments.

Both issues are fundamental to many pollen analytical questions. In this particular case, both are the key to understanding the nature of last glacial / interglacial climate change in southern Chile, with implications for the synchroneity of global climatic changes. This paper will raise and discuss these issues, with the aim of furthering understanding events in southern Chile, and hence attempting to resolve an issue of relevance to global climate change.