Time series analysis of the δ 2 H, δ 18 O and d excess values in correlation with monthly temperature, relative humidity and precipitation in Râmnicu Vâlcea, Romania: 2012–2018

Abstract

Abstract To investigate the influence of local climate and transboundary circulation of moisture on the stable isotope of precipitation in Ramnicu Valcea, Romania, monthly values of δ 2 H, δ 18 O, deuterium excess (d excess ), temperature, relative humidity and precipitation were determined between January 2012 and December 2018. Monthly analysis showed differences in d excess varying between 24.2‰ (October 2015) and −23.7‰ (July 2013) with a multi-annual average of 6.1 ± 5.9‰, suggesting an Atlantic origin of moisture with episodic Mediterranean transport. Also a significant correlation between the North Atlantic Oscillation on the local temperature during winter season was noticed. The local meteoric water line (LMWL) for the entire period showed slope and intercept values similar to those for neighbouring localities with the same altitude. When the analysis was extended to summer (April–October) and winter (November–March) seasons, the LMWL slope and intercept were different, reflecting the summer–winter difference in temperatures and air circulation. The monthly values of all parameters formed equal-spaced time series whose detailed analysis confirmed at p < 0.01 that δ 2 H, δ 18 O, temperature and relative humidity show a well-evidenced one-year periodicity. In contrast, precipitation and d excess seasonality were almost unrecognizable, most probably owing to the reduced number of observations.