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

Area of Science:

• Paleoclimatology
• Tropical hydroclimate dynamics
• Speleothem-based climate reconstructions

Background:

• Reconstructing past tropical hydroclimates, especially in the Amazon, is challenging due to limited data and complex interpretations.
• Previous studies on Amazonian glacial-era climate have yielded controversial results regarding moisture levels.

Observation:

• A high-resolution oxygen isotope record from speleothems in Paraíso Cave, eastern Amazonia, spanning 45,000 years was analyzed.
• The speleothem record, dated using uranium-thorium, is interpreted as a proxy for regional precipitation.

Findings:

• Amazonian precipitation closely tracks changes in glacial boundary conditions, including temperature and atmospheric CO2 levels.
• During the Last Glacial Maximum (approx. 21,000 years ago), precipitation was 58% of modern levels, indicating a significantly drier Amazon.
• Mid-Holocene precipitation (approx. 6,000 years ago) was 142% of modern levels, suggesting a wetter period.

Implications:

• The Amazon basin was generally drier during the last glacial period compared to western lowland records, with reduced water recycling and plant transpiration.
• Despite drier conditions, the Amazon rainforest likely persisted throughout the last glacial period.
• This study provides crucial insights into the sensitivity of Amazonian hydroclimate to global climate variability.