What drives interannual variation in tree ring oxygen isotopes in the Amazon?

• Published in: Geophysical research letters 2016-11, Vol.43 (22), p.11,831-11,840
• Main Authors: Baker, J. C. A., Gloor, M., Spracklen, D. V., Arnold, S. R., Tindall, J. C., Clerici, S. J., Leng, M. J., Brienen, R. J. W.
• Format: Article
• Language: English
• Subjects: Air transport; Air transportation; Aircraft; Annual variations; Archives & records; Atmospheric circulation; Atmospheric precipitations; atmospheric transport; Bolivia; Circulation; Climate; Climate change; Climatology; dendrochronology; Isotope ratios; Isotopes; Local precipitation; Moisture; Oxygen; Oxygen atoms; Oxygen isotope ratio; Oxygen isotopes; Paleoclimate; Precipitation; Precipitation (meteorology); Rain; Rainfall; Rainout; Reconstruction; Recording; River basins; Satellite observation; Satellites; Signal processing; Trajectories; Travel; Tree rings; Trees; Tropical climate; Tropical climates; tropics; Water vapor; Water vapor transport; Water vapour; Weather; Weather station data; Weather stations; Wood
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL071507

Oxygen isotope ratios in tree rings (δ18OTR) from northern Bolivia record local precipitation δ18O and correlate strongly with Amazon basin‐wide rainfall. While this is encouraging evidence that δ18OTR can be used for paleoclimate reconstructions, it remains unclear whether variation in δ18OTR is truly driven by within‐basin processes, thus recording Amazon climate directly, or if the isotope signal may already be imprinted on incoming vapor, perhaps reflecting a pan‐tropical climate signal. We use atmospheric back trajectories combined with satellite observations of precipitation, together with water vapor transport analysis to show that δ18OTR in Bolivia are indeed controlled by basin‐intrinsic processes, with rainout over the basin the most important factor. Furthermore, interannual variation in basin‐wide precipitation and atmospheric circulation are both shown to affect δ18OTR. These findings suggest δ18OTR can be reliably used to reconstruct Amazon precipitation and have implications for the interpretation of other paleoproxy records from the Amazon basin. Plain Language Summary Developing a good understanding of past climate is important to understanding ongoing climate change. This can be challenging in regions such as Amazonia where weather station data are limited. Here, other means of reconstructing historical climate are needed. Tree rings are an example of a natural climate record, with each ring recording information about the environment during the period of its formation. To use tree ring characteristics as a proxy for past climate, it is important to understand exactly how climate influences the signal stored in the wood. In this study we look at the factors controlling the ratio of light and heavy oxygen atoms in tree rings from northern Bolivia, which have been shown to be a good indicator of rainfall over the whole Amazon basin. We used a model to reconstruct air transport pathways over the continent, and examine large‐scale moisture flow into, and out of, the basin. We show that the dominant factor controlling the tree ring oxygen signal is the amount of rain that falls during air travel. This result is important because it shows that oxygen isotope ratios in tree rings, and other natural archives, can be reliably used to reconstruct Amazon rainfall. Key Points The mechanisms driving interannual variation in oxygen isotopes in Amazon tree rings (δ18OTR) have previously not been fully understood We show that Amazon basin‐intrinsic proce