INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
Regional differences in South American monsoon precipitation inferred from the growth and isotopic composition of tropical trees
BALLANTYNE, A.P.; BAKER, P.A.; CHAMBERS, J.Q.; VILLALBA, R.; ARGOLLO, J.
AMER METEOROLOGICAL SOC
Año: 2011 vol. 15 p. 1 - 35
The authors present results on the relationship between tree-ring proxies and regional precipitation for several sites in tropical South America. The responsiveness of oxygen isotopes (d18O) and seasonal growth as precipitation proxies was first validated by high-resolution sampling of a Tachigali myrmecophila from Manaus, Brazil (3.18S, 60.08W). Monthly growth of Tachigalispp. was significantly correlated with monthly precipitation. Intra-annual measurements of cellulose d18O in Tachigali spp. were also significantly correlated with monthly precipitation at a lag of approximately one month. The annual ring widths of two tropical tree taxa, Cedrela odorata growing in the Amazon (12.68S, 69.28W) and Polylepis tarapacana growing in the Altiplano (22.08S, 66.08W), were validated using bomb-derived radiocarbon 14C. Estimated dates were within two to three years of bomb-inferred 14C dates, indicating that these species exhibit annualrings but uncertainties in our chronologies remain. A multiproxy record spanning 180 years from Cedrela spp. showed a significant negative relationship between cellulose d18O and January precipitation. A 150-yr record obtained from Polylepis spp. also showed a significant negative relationship between d18O and March precipitation, whereas annual ring width showed a significant positive correlation with December precipitation. These proxies were combined in a multivariate framework to reconstruct past precipitation, revealing a significant increase inmonsoon precipitation at the Amazon site since 1890 and a significant decrease in monsoon precipitation at the Altiplano since 1880. Proxy time series also showed spatial and temporal coherence with precipitation variability due to El Niño forcing, suggesting that oxygen isotopes and ring widths in tropical trees may be important diagnostics for identifying regional differences in the response of the tropical hydrologic cycle to anthropogenic warming.