A tale of two cave records from the Amazon lowlands
Abstract
We present here a comparison between two high-resolved, U/Th-dated, speleothem d18O records through the last ~45,000 years from caves located in the eastern and western Amazon lowlands. The record from Paraiso Cave (04o04'S, 55o27'W) shows higher d18O values during the glacial period, but lower values in Holocene, with a shift of 7 per mil. On the other hand, the d18O values recorded at Diamante cave (05o44'S, 77o30'W) stay low with similar late glacial and Holocene values, varying within ~2 per mil through the whole profile. Both records register millennial-scale variations, which are anti-phased with the Hulu-Dongge speleothem record, consistent with the previously observed meridional shift of the tropical rainfall belt. However, d18O values in two records have a large offset during the glacial, but not in Holocene. We suggest the Amazon Basin was relatively dry in the glacial time. Therefore, rainfall d18O in the Basin was dominated by a typical continental fractionation along a moisture trajectory. During the Holocene, higher rainfall and denser rainforest in the lowlands may have resulted in more water recycling through transpiration. Therefore, moisture d18O gradient would be reduced between the two sites. Despite the drier conditions inferred for the glacial Amazon lowlands, d13C values in the Paraiso record never reach high values; thus ruling out vegetation dominated by C4 plants.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMPP33C1944W
- Keywords:
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- 1605 GLOBAL CHANGE Abrupt/rapid climate change;
- 1655 GLOBAL CHANGE Water cycles