Abstract
Summary The Parana River, the second in discharge in South America after the Amazon River and the fifth all over the world, releases an average of more than 17 000 m 3 s −1 into the Del Plata Estuary. In order to assess the causes of variations in its stable isotope composition, 120 monthly grab samples of the Parana River, acquired on a period of 10 years at the river mouth, near Ciudad Universitaria, Buenos Aires, Argentina have been analysed for oxygen and hydrogen stable isotopes. Both, 2 H and 18 O showed periodic variations ( δ 18 O between −7‰ and −3‰; δ 2 H between −44‰ and −15‰) that follow, shifted in ca. 4 months (average transit time of the river), the southward excursions of the intertropical convergence zone (ITCZ). Deuterium excess values ( δ 2 H − 8 δ 18 O) also exhibited large variations (3–18‰) and showed a positive correlation with the El Nino South Oscillation Phenomenon (ENSO) index. ENSO affects the kinetic of the evaporation process of water and modifies the degree in which ITCZ shifts southwards capturing variable amounts of deuterium-rich recycled moisture from the Amazon’s basin, then precipitating on the catchment’s areas of the Parana River.
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