The oxygen‐18 content of precipitation in the Amazon basin is characterized by a very small inland gradient, 0.75 × 10 −3 ‰ km −1 . This is a consequence of the large contribution of reevaporated moisture to the basin's water balance. A distinct seasonal and regional pattern of stable isotope composition has been recognized and shows the basin to be inhomogeneous from the hydrometeorological point of view. The occasional appearance of very low δ values is believed to be related to the position of the ITCZ rather than to interbasin processes.
Salati et al. (1979) studied this question.