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

• Published in: Journal of geophysical research. Biogeosciences Vol. 128; no. 12
• Main Authors: Liu, Sainan, Xu, Chenxi, Fontana, Cláudia, An, Wenling, Tomazello‐Filho, Mario, Zhao, Qingyu, Zhao, Yaru, Liu, Yucheng, Guo, Zhengtang
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-12-2023
• Subjects: Annual; Annual precipitation; Araucaria angustifolia; Climate; Climate system; Correlation; El Nino; El Nino phenomena; Global temperatures; Growing season; Isotopes; Moisture; Monsoons; Monthly; Oxygen; Oxygen isotopes; Precipitation; precipitation oxygen isotopes; Rainy season; Reconstruction; Sea surface; Sea surface temperature; Seasonal variation; Seasonal variations; South American summer monsoon; Southern Oscillation; Summer; Surface temperature; Tree rings; Trees; tree‐ring α‐cellulose oxygen isotopes; Wet season; South America; Brazil
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2023JG007490

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 (δ18OTR) 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 δ18OTR data show pronounced seasonal variations with a decreasing trend in the growing season. The intra‐annual δ18OTR data record variations in precipitation δ18O values, and the interannual δ18OTR data record a precipitation amount. The δ18OTR values of parts 1 and 2 of each ring show the strongest correlation with precipitation at the beginning of the SASM (i.e., December). δ18OTR 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 δ18OTR 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 Niño‐Southern Oscillation (ENSO) regulate seasonal precipitation and affect the δ18OTR values in southern Brazil.
Plain Language Summary
The South American summer monsoon (SASM) is an important climate system in South America. However, knowledge of past SASM variations based on tree rings is limited due to the difficulty of crossdating and the weak climatic signal expressed in tree‐ring widths. In this study, we measured the intra‐annual oxygen isotope of Araucaria angustifolia southern Brazil to help crossdating and extracting climate signal. Our intra‐annual tree‐ring oxygen isotopes record shows obvious seasonal variations, which can be used for crossdating. It also provides a record of monthly precipitation in rainy season, and thus it can be used to precipitation reconstruction.
Key Points
Seasonal tree ring δ18O is controlled by precipitation δ18O and amount
Intra‐annual δ18OTR helps to crossdate and reconstruct monthly precipitation
EI Niño‐Southern Oscillation affects tree‐ring oxygen isotope in southern Brazil