Timing and structure of vegetation, fire, and climate changes on the Pacific slope of northwestern Patagonia since the last glacial termination

Abstract

By virtue of its location in the southern mid-latitudes, northwestern Patagonia (40 degrees-44 degrees S) offers the opportunity to unravel the mechanisms involved in the initiation and propagation of paleoclimate signals of hemispheric and global significance. Of particular importance is deciphering the evolution of the Southern Westerly Winds (SWW) considering their influence at continental, zonal, hemispheric, and global scale. Here I present a multi-decadal record from Lago Proschle, a small closed-basin lake located on the Pacific slope of northwestern Patagonia, to examine the timing and structure of vegetation, fire, and climate change along a continuum since the onset of the Last Glacial Termination (T1). The record shows rapid glacier recession during T1, reaching the western Andean foothills in similar to 400 years or less. Nothofagus-dominated forests established between similar to 17.4-17 ka, followed by closed-canopy North Patagonian Rain Forests (NPRF) with shade-tolerant thermophilous trees between similar to 16.3-15.4 ka. These changes suggest an abrupt warming trend and an increase in precipitation at similar to 16.3 ka, associated with a northward shift of the SWW. Subsequent increases in cold-tolerant hygrophilous trees between similar to 15.4-12.8 ka imply a shift to cold, more humid conditions during the Antarctic Cold Reversal, suggesting stronger SWW influence. This was followed by stand-replacing fires brought by a sudden decline in summer precipitation at similar to 12.8 ka, associated with a millennial-scale southward shift of the SWW which was contemporaneous with the onset of the Younger Dryas. Dominance of thermophilous, summer-drought tolerant Valdivian rainforest trees and high fire activity ensued between similar to 10.3-7.8 ka, suggesting peak warmth and overall decline in annual precipitation associated with weakening of the SWW during the early Holocene. A multi-millennial cooling and wetting trend started at similar to 7.8 ka, brought by stronger SWW influence, followed by recurrent, centennial-scale variations in temperature and precipitation starting at similar to 6.4 ka. Deforestation, fire, and spread of non-native herbs by Chilean/European settlers began during the late 18th century. Abrupt vegetation changes in the Lago Proschle record were driven by rapid climate changes over the last 17,400 years amplified, in some instances, by fire disturbance.