Past Summer Temperatures Inferred From Dendrochronological Records of Fitzroya cupressoides on the Eastern Slope of the Northern Patagonian Andes.

Abstract: Estimating summer temperature fluctuations over long timescales in southern South America is essential for better understanding the past climate variations in the Southern Hemisphere. Here we developed robust 212 year long basal area increment (BAI) and δ¹³C chronologies from living temperature‐sensitive Fitzroya cupressoides on the eastern slope of the northern Patagonian Andes (41°S). After removing the increasing trend from the growth records likely due to the CO₂ fertilization effect, we tested the potential to reconstruct past summer temperature variations using BAI and δ¹³C as predictors. The reconstruction based on δ¹³C records has the strongest predictive skills and explains as much as 62% of the total variance in instrumental summer temperature (n = 81, p < 0.001). The temperature signal recorded in tree‐ring growth is not substantially different to that present in δ¹³C and consequently does not provide additional information to improve the regression models. Our δ¹³C‐based reconstruction shows cold summer temperatures in the second part of the 19th century and in the mid‐20th century followed by a warmer period. Notably, the 20th and the early 21st centuries were warmer (+0.6°C) than the 19th century. Reconstructed summer temperature variations are modulated by low‐latitude (El Niño–Southern Oscillation) and high‐latitude (Southern Annular Mode) climate forcings. Our reconstruction based on δ¹³C agrees well with previous ring width based temperature reconstructions in the region and comparatively enhances the low‐frequency variations in the records. The present study provides the first reconstruction of summer temperature in South America south of 40°S for the period 1800–2011 entirely based on isotopic records. [ABSTRACT FROM AUTHOR]