Hydrogen isotopes in lignin: a new proxy for the Amazon hydrological cycle?

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The Amazon basin is the world's largest catchment and sustains the largest continuous rainforest on Earth. Global change is affecting the Amazon climate in uncertain ways, with recent decades seeing an increase in Amazon wet season rainfall, as well as, increasing drought frequency. To better understand the drivers behind these changes, long-term accurate records of the hydrological cycle are needed. In this project we will test a new climate proxy derived from hydrogen isotopes in tree rings that can contribute towards such reconstructions. In contrast to existing oxygen isotope proxies in the Amazon, hydrogen isotopes in lignin methoxyl groups are thought to preserve the signal of hydrogen isotopes in precipitation. We will test to what degree hydrogen isotopes growing along an elevational transect from the Amazon to the Andes indeed preserve variation in hydrogen in precipitation, and apply this new method for the tropical tree species Cedrela odorata at a dry and wet site to reconstruct precipitation oxygen isotopes for the past 50 to 150 years at annual resolution. If successful this new proxy can be used to generate insights in the response of the tropical hydrological to climate change. Reconstructions of hydrogen isotopes in the source water can further be useful to interpret long-term change in plant physiology to CO2 when used in combination with oxygen and carbon isotopes from tree rings.