Large scale meteorological phenomena, ENSO and ITCZ, define the Paraná River isotope composition

The Paraná 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 m3 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 Paraná 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, 2H and 18O showed periodic variations (δ18O between −7‰ and −3‰; δ2H 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 (δ2H − 8δ18O) also exhibited large variations (3–18‰) and showed a positive correlation with the El Niño 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 Paraná River.