The last 25, 000 years of vegetation and climate history in NW Patagonia
by
Patricio I. Moreno
Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Chile

Northwest Patagonia is ideal for the study of interhemispheric linkages throughout the Quaternary because this region has insolation regimes in out-of-phase with northern mid-latitudes, is highly sensitive to variations in the southern westerlies, and is far removed from the direct influence of Northern Hemisphere ice sheets and deep water circulation.

A stacked palynological record encompassing the last 25,000 years was developed to examine the timing, rates, and direction of vegetation and climate change in NW Patagonia. The record shows extreme glacial climate between 25-17.7 ka (ka: 1000 cal yr BP), followed by the abrupt expansion of North Patagonian rainforest (NPR) taxa through successive warming events between 17.7-15.5 ka. Conditions approaching modern climate prevailed between 15.5-15 ka, followed by expansion of cold-resistant/hygrophilous NPR trees at 15 and 13.5 ka, and subsequent warming pulses at 12 and 10.2 ka. Extreme warm/dry conditions are evident between 10.2-7.8 ka, as indicated by the predominance of the warmth-loving, drought-resistant Valdivian trees Eucryphia cordifolia and Caldcluvia paniculata. Cold-resistant NPR trees re-expanded through a series of steps between 7.5-5.5 ka, and reached peak abundance between 5-3 ka. Eucryphia and Caldcluvia re-expanded at 5 ka establishing a vegetation mosaic with podocarps and Nothofagus that persists until today. Modern conditions started at 2 ka, following a warm/dry phase between 3-2 ka.

Rainforest vegetation changed at ecological timescales (≤100 years) in response to climate forcing at millennial timescales since the last termination. Moreover, the timing and mean time spacing of events fall in the range of millennial-scale changes in the North Atlantic region. Sub-millennial scale variability is also evident; El Niño years in NW Patagonia typically exhibit below-normal summer precipitation, hence the co-occurrence of thermophilous/drought-resistant Valdivian elements and cold-resistant/hygrophilous NPR trees since ~5 ka might represent a vegetation response to the onset of El Niño-like variability in the mid/late Holocene.

Acknowledgements: Fondecyt #1030766 and Iniciativa Científica Milenio P02-051

Date received: November 20, 2004