Reconstruction of the Record of Tritium in Precipitation in the Temperate Zone of South America

Abstract

Tritium, a radioisotope of hydrogen, is an ideal tracer for groundwater and surface dating and tracking since it is part of the water molecule. The knowledge of the history of tritium in precipitation and recharge is the key link for the calculation of groundwater tritium age. However, records of tritium in precipitation are usually sparse and discontinuous, especially in regions like South America, and often need to be reconstructed. To solve this problem, different reconstruction methods of the tritium input function have been analysed and compared. Clustering of Global Network of Isotopes in Precipitation stations by regions and the correlation with the complete and continuous data recorded in Kaitoke (New Zealand) proved to be the most effective approach, having low relative errors and a much more extended coverage in time compared to other interpolation or reference curves methods. Thus, tritium time series for five different regions of the temperate zone of South America were obtained. These curves can be used as representative tritium input curves in future studies for these regions. The results obtained also allow a quick qualitative analysis of groundwater ages in these areas, based on their current or past tritium concentrations. In addition, they contributed to the understanding of the patterns and characteristics of tritium distribution in the atmosphere of the southern sector of South America.