Abstract:
This paper examines changes in isotopic abundances for 18O and deuterium in precipitation over the Amazon
basin based on data in the Global Network on Isotopes in Precipitation (GNIP) database from the International
Atomic Energy Agency (IAEA)/WMO. The analysis is conducted in the context of recent changes (and anticipated
future changes) to the land surface hydrology as a result of tropical deforestation. Statistically significant temporal
changes (1965–90) in selected stable isotopic signatures in the Amazon have been compared with global climate
model (GCM) predictions revealing notable differences. For example, the wet season deuterium excess differences
between Belem and Manaus, Brazil, are consistent with recent GCM simulations only if there has been a relative
increase in evaporation from nonfractionating water sources over this period. No significant change in dry season
isotopic characteristics is found despite earlier predictions that land-use change signals would be found. Results
of GCM simulations of Amazonian deforestation suggest that the recent stable isotope record is more consistent
with the predicted effects of greenhouse warming possibly combined with forest removal than with the predicted
effects of deforestation alone.
