Isotopic composition of precipitation in Portoro (Slovenia)

The stable isotopic composition of hydrogen and oxygen (δ2H and δ18O) and tritium activity (3H) have been monitored in monthly precipitation at Portoro airport meteorological station since October 2000. Here we present a complete set of numerical data and a statistical analysis for the period 2000–2006. Seasonal variations of δ2H and δ18O were observed but are much less pronounced than for continental stations of the Northern Hemisphere. The weighted mean δ2H and δ18O values are -43 ‰ and -6.6 ‰, respectively. The relation between hydrogen and oxygen isotopic composition is expressed by the orthogonal Local Meteoric Water Line as δ2H = (8.05 ± 0.22) δ18O + (9.35 ± 1.55), and the temperature coefficient of d18O is 0.13 ‰/°C. The deuterium excess weighted mean value is 9.8 ‰ and shows some seasonal variations that reflect the variable influence of air masses of different origin (either Atlantic or Mediterranean). Tritium activity in monthly precipitation also showed seasonal variations, with a weighted mean value of 6.9 TU.