Monthly Precipitation Reconstruction in Subtropical South America Using Seasonal Tree-Ring Oxygen Isotopes

The South American Summer Monsoon (SASM) is one of the most important climate systems in the tropical and subtropical regions of South America, and transports Atlantic moisture to the South American continent. However, there are few high-resolution tree ring based studies of the SASM due to the difficulty of crossdating and the lack of dependable moisture proxies based on tree-ring width. In this study, we use intra-annual tree-ring oxygen isotope (delta O-18(TR)) data (E.V.A 03w, E.V.Ar11e, E.V.Ar12e; the full name of sample code is Erval Velho - Araucaria) for crossdating, and to extract climate signals and reconstruct monthly precipitation. Our data are from Araucaria angustifolia in southern Brazil, and each annual tree-ring comprises four parts (parts 1, 2, 3, 4) during 1960-2016. The intra-annual delta O-18(TR) data show pronounced seasonal variations with a decreasing trend in the growing season. The intra-annual delta O-18(TR) data record variations in precipitation delta O-18 values, and the interannual delta O-18(TR) data record a precipitation amount. The delta O-18(TR) values of parts 1 and 2 of each ring show the strongest correlation with precipitation at the beginning of the SASM (i.e., December). delta O-18(TR) values of Part 3 have the strongest correlation with precipitation during January-February, and those of Part 4 are strongly correlated with precipitation during February-June. The seasonal delta O-18(TR) values can be used to reconstruct monthly precipitation in the growing season. Spatial correlations between monthly precipitation reconstruction and global sea surface temperatures reveal that EI Ni & ntilde;o-Southern Oscillation (ENSO) regulate seasonal precipitation and affect the delta O-18(TR) values in southern Brazil.