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

亚马逊盆地是世界上最大的集水区，拥有地球上最大的连续雨林。全球变化正在以不确定的方式影响亚马逊气候，近几十年来，亚马逊雨季降雨量增加，干旱频率增加。为了更好地了解这些变化背后的驱动因素，需要对水文循环进行长期准确的记录。在这个项目中，我们将测试一种新的气候指标，该指标来自树木年轮中的氢同位素，它可以促进这种重建。与亚马逊地区现有的氧同位素替代物不同，木质素甲氧基中的氢同位素被认为保留了降水中氢同位素的信号。我们将测试从亚马逊到安第斯山脉沿海拔方向生长的氢同位素在多大程度上确实保留了降水中氢的变化，并将这种新方法应用于干燥和潮湿地点的热带树种香柏，以重建过去50至150年的年分辨率降水氧同位素。如果成功，这一新的指标可用于深入了解热带水文学对气候变化的反应。当与树木年轮中的氧和碳同位素结合使用时，源水中氢同位素的重建可以进一步有助于解释植物生理对二氧化碳的长期变化。

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.