The Changing Amazon Hydrological Cycle—Inferences From Over 200 Years of Tree-Ring Oxygen Isotope Data

Abstract:

Changes to the Amazon hydrological cycle have important consequences for world's largest tropical forest, and the biodiversity it contains. However, a scarcity of long-term climate data in the region makes it hard to contextualize recent observed changes in Amazon hydrology. Here, we explore to what extent tree-ring oxygen isotope (δ¹⁸O<inf>TR</inf>) chronologies can inform us about hydrological changes in the Amazon over the past two centuries. Two δ¹⁸O<inf>TR</inf> records from northern Bolivia and the Ecuadorian Andes are presented. The Ecuador record spans 1799–2012 (n = 16 trees) and the Bolivia record spans 1860–2014 (n = 32 trees), making them the longest δ¹⁸O<inf>TR</inf> records from the Amazon, and among the most highly-replicated δ¹⁸O<inf>TR</inf> records from the tropics to date. The two chronologies correlate well at interannual and decadal timescales, despite coming from sites more than 1,500 km apart. Both δ¹⁸O<inf>TR</inf> records are strongly related to interannual variation in Amazon River discharge measured at Óbidos, and accumulated upwind precipitation, suggesting a common climatic driver. In both records a strong increase in δ¹⁸O<inf>TR</inf> was observed up until approximately 1950, consistent with positive trends in the few other existing δ¹⁸O proxy records from across the Amazon. Considering all possible drivers of this long-term increase, a reduction in rainout fraction over the basin driven by rising sea surface temperatures in the North Atlantic is suggested as the most likely cause. The upward trend in δ¹⁸O<inf>TR</inf> reverses over the past 1–2 decades, consistent with the observed strengthening of the Amazon hydrological cycle since approximately 1990.

Año de publicación:

2022

Keywords:

• tropical
• Water cycle
• Palaeoclimate
• climate reconstruction
• proxy
• δ18O

Fuente:

scopus