Hydroclimate changes across the Amazon lowlands over the past 45,000 years

Oxygen isotope records derived from stalagmites in the eastern Amazon reveal that rainfall was about half of today’s during the Last Glacial Maximum but half again as much during the mid-Holocene, broadly coinciding with global changes in temperature and carbon dioxide. Amazon Basin resilience to hydroclimate variation The Amazon forest both responds to and drives much of the variability in climate and biogeochemistry from annual to millennial time scales. But highly resolved records of past climate variability in the region are hard to come by, and until now it has not been clear whether the Amazon forest was wetter or drier during the Last Glacial Maximum (LGM). Xianfeng Wang et al . have now collected oxygen isotope data covering the past 45,000 years from stalagmite calcite deposits in the Paraíso Cave in eastern Amazonia. Their data show that rainfall was about half that of today during the LGM (around 21,000 years ago) but was some 50% greater during the mid-Holocene (6,000 years ago), broadly coinciding with global changes in temperature and carbon dioxide. Although the Amazon was drier during the glacial period, the rainforest persisted throughout. Whether or not it can be sustained in the future, however, remains an open question. Reconstructing the history of tropical hydroclimates has been difficult, particularly for the Amazon basin—one of Earth’s major centres of deep atmospheric convection 1 , 2 . For example, whether the Amazon basin was substantially drier 3 , 4 or remained wet 1 , 5 during glacial times has been controversial, largely because most study sites have been located on the periphery of the basin, and because interpretations can be complicated by sediment preservation, uncertainties in chronology, and topographical setting 6 . Here we show that rainfall in the basin responds closely to changes in glacial boundary conditions in terms of temperature and atmospheric concentrations of carbon dioxide 7 . Our results are based on a decadally resolved, uranium/thorium-dated, oxygen isotopic record for much of the past 45,000 years, obtained using speleothems from Paraíso Cave in eastern Amazonia; we interpret the record as being broadly related to precipitation. Relative to modern levels, precipitation in the region was about 58% during the Last Glacial Maximum (around 21,000 years ago) and 142% during the mid-Holocene epoch (about 6,000 years ago). We find that, as compared with cave records from the western edge of the lowlands, the A