Some features of isotopic content in rainfall in subtropical Argentina

GONZALEZ, M. A.; CERNE, B.; DAPEÑA, C.; PANARELLO, H.O.

Advances in Chemistry Research

Nova Science Publishers Inc.

Lugar: NUEVA YORK; Año: 2011; p. 299 - 317

The stable isotopes, deuterium and oxygen-18, are common components of the water molecule. The content of these isotopes in rainfall water depends on temperature, latitude, altitude, rainfall amount and source of water vapor. Its analysis allows to improve the knowledge of the water cycle and, more specifically, to determine, in a first approximation, the source of water vapor. There are several Argentine stations of the Global Network for Isotopes in Precipitation (GNIP). Some have long records like Buenos Aires (30 years) and Ushuaia (22 years) but others have discontinuous and short records. Although some records are not very long, their spatial distribution represents fairly well most of the rainfall regimes of subtropical Argentina. Therefore, the isotopic contents of meteoric water of these GNIP stations were analyzed. An important correlation between isotopic content and rainfall amount is observed in the lowest latitudes of subtropical Argentina while the relation with temperature dominates towards the south. A simple discriminant method was used to detect the probable ranges for the deuterium excess and oxygen-18 content that correspond to continental water vapor source (C) or to the Atlantic oceanic water vapor source (OA). The origin was detected by the construction of isoentropic trajectories of air mass. The source of water vapor in subtropical Argentina varies regionally and throughout the year. Two distinct patterns in the annual cycle of the water vapor source were recognized. In the south of subtropical Argentina the origin of water vapor is more likely to be continental from March to August and Atlantic from September to February. An almost anti-symmetric behavior is observed in the Northeast, where the continental source predominates in summer and early autumn, while the oceanic origin is more likely throughout the winter and early spring. The annual cycle is less clear in the other stations, where there is not a prevalent source for the meteoric water during most of the year.