Year-to-Year Variations of the Stable Isotopes in Precipitation in February at Cuiabá, Located on the Northern Fringe of Pantanal, Brazil

Abstract

Large year-to-year variations of δ18O were found in the precipitation recorded in the International Atomic Energy Agency/Global Network of Isotopes in Precipitation (IAEA/GNIP) database for February at Cuiabá, located on the northern fringe of Pantanal, Brazil. Three depleted years (1963, 1978, and 1968) and three enriched years (1966, 1984, and 1983) were chosen to investigate this phenomenon and to correlate the amount of precipitation, the occurrences of storm precipitation, and the vapor flux field. In the depleted years, precipitation exceeding the long-term mean was observed at Cuiabá, while the southward vapor flux from the Amazon basin was less than the long-term mean. Since d-excesses in these years were large in general, fast evaporation must contribute to the greater precipitation observed in these depleted years. In contrast, such common features were not found in the vapor flux field in the enriched years. The occurrences of storm precipitation are important in 1966, while the amount effect is responsible for 1984. In 1983, enriched meteoric water is attributed to both the occurrences of storm precipitation and vapor flux field.