Studies of rainfall isotopic composition in the Iberian Peninsula are scarce, and to date, none of them have provided analyses of the triple oxygen isotopes, preventing from the complete understanding of current atmospheric processes in this region. We investigate the rainwater δ17O, δ18O, and δD and derived parameters 17O-excess and d-excess in a mountain site in the Central South Pyrenees (Villanúa, Huesca, Spain) to identify the main factors (regional and local) controlling the isotopic composition of precipitation at event scale. The samples were collected on a rainfall-event basis during 2 years (from July 2017 to June 2019), and meteorological variables [temperature, relative humidity (RH), and rainfall amount] were monitored at the sampling site. The δ17O, δ18O, and δD values were higher during summer and lower during the rest of the year. In contrast, the 17O-excess and d-excess were lower during summer and higher during the remaining months. We found that the isotopic parameters are weakly correlated with rainfall amount during each event, but they strongly depend on changes in air temperature and moderately on RH. We consider other factors affecting the isotopic composition of rainfall events that resulted to have an important role, such as the influence of the moisture source and trajectory throughout the variations in the synoptic pattern during rainfall events. This dataset can be useful for further comprehensive atmospheric and hydrological studies, with application to paleoclimatic investigations.
<p>Few studies of rainfall isotopic composition are available in the northern Iberian Peninsula, and up to now none of them has provided detailed analyses of the triple oxygen isotopes (d<sup>17</sup>O, <sub>&#160;</sub>d<sup>18</sup>O and derived parameter <sup>17</sup>O<sub>excess</sub>), preventing from the complete understanding of some atmospheric processes and their relationship with the current climate in this region. This information, together with the characterization of dripwater isotopic composition once transferred throughout the epikarst, is essential to the correct interpretation of paleoclimate records based on speleothem isotopic data.</p><p>We provide the first database of triple oxygen and hydrogen stable isotopes of rainwater in Central-South Pyrenees. We characterize local rainfall isotopic variability in a high altitude site and identify the main factors controlling the isotopic composition of rainwater. The samples were collected on a rainfall-event basis from July 2017 to June 2019 (n=216) at the interpretation center of &#8220;Las G&#252;ixas&#8221; touristic cave in Villan&#250;a (Huesca, Spain), where other monitoring surveys are in progress. This site (42&#186;40&#8217;59&#8217;&#8217;N; 0&#186;31&#8217;55&#8217;&#8217;W; 957 m a.s.l.) is characterized by a transitional Mediterranean &#8211; Oceanic climate with a highly contrasted seasonality, mean annual temperature of 10&#186;C and mean annual precipitation of 1100 mm. We analyzed d<sup>17</sup>O, d<sup>18</sup>O and dD, and derived parameters <sup>17</sup>O<sub>excess</sub> and d-excess in rainwaters using a Picarro L2140-i analyzer at the University of Almer&#237;a (Spain), with mean precisions (1-standard error) of 5 per meg for <sup>17</sup>O<sub>excess </sub>and 0.1&#8240; for d-excess. Meteorological variables (temperature, RH and rainfall amount) were monitored (every 10 min) at the sampling site during the length of this study.</p><p>During the two-years monitoring period, d<sup>18</sup>O ranged from -21.7 to 8.7&#8240; and dD did from -170.8 to 34.1&#8240;, with average values of -7.4&#8240; and -52.3&#8240;, respectively. The <sup>17</sup>O<sub>excess</sub> averaged 21&#177;24 per meg and the mean d-excess was 7.1&#177;7.7&#8240;. The local meteoric water line is defined by dD= 7.3&#183;d<sup>18</sup>O+1.9 (R<sup>2</sup>=0.96) and d&#180;<sup>17</sup>O= 0.524&#183;d&#180;<sup>18</sup>O+0.0088 (R<sup>2</sup>=1). The d<sup>17</sup>O, d<sup>18</sup>O and dD values were higher during summer (June to September; -2.1, -3.9 and -26.6&#8240;, respectively; n=68) and were lower during the rest of the year (-4.7, -9.0 and -63.8&#8240;, respectively; n=164). In contrast, the <sup>17</sup>O<sub>excess</sub> and d-excess were lower during summer (3 per meg and 4.6&#8240;, respectively) and higher (29 per meg and 8.2&#8240;, respectively) during the remaining months. We found that the isotopic parameters are weakly correlated with rainfall amount during each event, but they strongly depend on seasonal changes in air temperature and relative humidity. The extremely low <sup>17</sup>O<sub>excess</sub> and d-excess values observed in summer (down to -75 per meg and -35.6&#8240;, respectively), cannot be explained by particular conditions at the source of moisture during water vapor formation, but by local meteorological parameters and rain drops re-evaporation during rainfall events.</p><p>Further processing of this database will consider other influencing factors in the isotopic composition of rainfall events, such as changes in the source moisture, synoptic pattern and type of rainfall, to further understand the complexity of atmospheric processes through the information stored in the triple oxygen isotopes of rainfall, with application to future <sup>17</sup>O<sub>excess</sub> studies in speleothems.</p>
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