Water isotopic variability in Mallorca: a path to understanding past changes in hydroclimate

This paper reports the first results on δ18O and δ2H analysis of precipitations, cave drip waters, and groundwaters from sites in Mallorca (Balearic Islands, western Mediterranean), a key region for paleoclimate studies. Understanding the isotopic variability and the sources of moisture in modern climate systems is required to develop speleothem isotope-based climate reconstructions. The stable isotopic composition of precipitation was analyzed in samples collected between March 2012 and March 2013. The values are in the range reported by GNIP Palma station. Based on these results, the local meteoric water line δ2H = 7.9 (±0.3) δ18O + 10.8 (±2.5) was derived, with slightly lower slope than GMWL. The results help tracking two main sources of air masses affecting the study sites: rain events with the highest δ18O values (> –5 ‰) originate over the Mediterranean Sea, whereas the more depleted samples ( 50 m) limestone cap (Arta) exhibit more negative values. A well-homogenized aquifer supplied by rainwaters of both origins is clearly indicated by groundwater δ18O values, which show to be within 2.4 ‰ of the unweighted arithmetic mean of –7.4 ‰. Although limited, the isotopic data presented here constitute the baseline for future studies using speleothem δ18O records for western Mediterranean paleoclimate reconstructions.