RECENT TRENDS IN TREE-RING RECORDS FROM HIGH-ELEVATION SITES IN THE ANDES OF NORTHERN PATAGONIA

A new set of tree-ring records from the Andes of northern Patagonist, Argentina (41 degrees S) was used to evaluate recent (i.e., fast 250 y ears) regional trends in tree growth at upper treeline. Fifteen tree-r ing chronologies from 1200 to 1750 m elevation were developed for Nath ofagus pumilio, the dominant subalpine species. Samples were collected along three elevational transects located along the steep west-to-eas t precipitation gradient from the main Cordillera (mean annual precipi tation > 4000 mm) to an eastern outlier of the Andes (mean annual prec ipitation > 2000 mm). Ring-width variation in higher elevation tree-ri ng records from the main Cordillera is mainly related to changes in te mperature and precipitation during spring and summer. However, the res ponse to climatic variation is also influenced by local site factors o f elevation and exposure. Based on the relationships between Nothofagu s growth and climate, we reconstructed changes in snow cover duration in late spring and variations in mean annual temperature since A.D. 17 50. Abrupt interannual changes in the mean annual temperature reconstr uction are associated with strong to very strong Fl Nino-Southern Osci llation events. At upper treeline, tree growth since 1977 has been ano malously high. A sharp rise in global average tropospheric temperature s has been recorded since the mid-1970s in response to an enhanced tro pical hydrologic cycle due to an increase in temperature of the tropic al Pacific. Temperatures in northern Patagonia have been anomalously h igh throughout the 1980s, which is consistent with positive temperatur e anomalies in the tropical Pacific and along the western coast of the Americas at ca. 40 degrees S latitude. Our 250-year temperature recon struction indicates that although the persistently high temperatures o f the 1980s are uncommon during this period, they are not unprecedente d. Tropical climatic episodes similar to that observed during the 1980 s may have occurred in the recent past under pre-industrial carbon dio xide levels.