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

By: Jessica Baker – PhD Student at Leeds University @JessTreeBaker http://www.geog.leeds.ac.uk/people/j.baker

Developing a good understanding of past climate is vital when trying to interpret ongoing, and predict future, climate changes. This can be challenging in regions such as Amazonia where weather station data are particularly 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.

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Tree rings in Cedrela montana (Meliaceae). Tree rings can record information about the amount of rainfall which occurs as moisture is transported across the Amazon basin from the Atlantic.

 

In a recent study published in  Geophysical Research Letters we looked 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.

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Clouds passing over the Amazon forest in ATTO, Brazil.

 

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