Izotopska sestava padavin na postaji Portorož, Slovenija – obdobje 2007–2010

The stable isotopic composition of oxygen and hydrogen (δ18O and δ2H) and the tritium activity (A) were monitored in precipitation at synoptic station Portorož (Slovenia) during the period 2007–2010. Monthly and yearly isotope variations are discussed and compared with those observed over the period 2001–2006 and with the basic meteorological parameters. The mean values for δ18O and δ2H, weighted by precipitation, are –6.28 ‰ and –41.6 ‰, and these values are 0.35 ‰ and 1.6 ‰ higher but not significantly different than for the period 2001–2006. The reduced major axis (RMA) local meteoric water line (LMWLRMA) for the period 2007–2010 is δ2H = (8.14 ± 0.25)×δ18O + (8.28 ± 1.64), while the precipitation weighted least square regression (PWLSR) results in LMWLPWLSR δ2H = (7.87 ± 0.28)×δ18O + (7.97 ± 1.87). The deuterium excess (d) weighted mean value is 8.6 ‰ and is 1.2 ‰ lower than in 2001–2006, while the temperature coefficient of δ18O is 0.21 ‰/ºC and is for 0.02 ‰/ºC higher than for the previous period. The mean Mediterranean precipitation index (MI) for the period 2007–2010 is 2.3. Lower values of MI and deuterium excess than in the preceding period indicate stronger continental climatic character during observation period, however the differences are not statistically significant. The weighted mean tritium activity is 6.4 TU, which is 0.5 TU lower but not significantly different than in 2001–2006.V prispevku obravnavamo izotopsko sestavo kisika in vodika (δ18O in δ2H) ter aktivnosti tricija (A) v mesečnih vzorcih padavin, ki smo jo spremljali na sinoptični postaji Portorož (Slovenija) v obdobju 2007–2010. Analizirali smo mesečne in letne spremembe izotopske sestave padavin in jih primerjali z nizom podatkov za obdobje 2001–2006 ter z osnovnimi meteorološkimi parametri. Srednje tehtane vrednosti δ18O in δ2H določene ob upoštevanju izmerjene količine padavin znašajo –6,28 ‰ in –41,6 ‰ in so za 0,35 ‰ oziroma 1,6 ‰ višje kot v obdobju 2001–2006, vendar so razlike statistično neznačilne. Lokalno padavinsko premico (LMWLRMA) za obdobje 2007–2010 zapišemo kot δ2H = (8,14 ± 0,25)×δ18O + (8,28 ± 1,64), ob upoštevanju količine padavin pa kot LMWLPWLSR δ2H = (7,87 ± 0,28)×δ18O + (7,97 ± 1,87). Srednja tehtana vrednost devterijevega presežka (δ) znaša 8,6 ‰ in je za 1,2 ‰ nižja kot v obdobju 2001–2006, medtem ko je temperaturni koeficient za δ18O za 0,02 ‰/°C višji kot v primerjalnem obdobju in znaša 0,21 ‰/°C. Srednja vrednost indeksa mediteranskosti padavin (MI) znaša 2,3. Nižje vrednosti MI in devterijevega presežka nakazujejo v opazovanem obdobju bolj kontinentalni značaj podnebja, vendar so razlike statistično neznačilne. Srednja tehtana vrednost tricijeve aktivnosti znaša 6,4 TU in je za 0,5 TU nižja kot v obdobju 2001–2006, a je tudi ta razlika statistično neznačilna

Distribution of authigenic and allogenic fractions in recent lake sediment: Isotopic and chemical compositions

Recent sediments in Lake Kozjak, in the Plitvice Lakes National Park, Croatia, were used to study the impact of the material delivered to the lake sediment via Rječica Brook. Sediment cores, top 40 cm, were taken near the mouth of the Rječica Brook at three locations in the lake at different distances from the shore, water depth 2-9 m and analyzed using different isotopic and chemical methods. Sediment depth profiles of the following parameters were obtained: organic and carbonate fraction, C/N analyses of organic fraction, 14C activity (a14C) and d13C values of carbonate (d13Ccarb) and organic fraction (d13Corg) and d15N of total nitrogen. The results were compared with sediment core collected in the middle of Lake Kozjak, water depth 21 m. Distribution of organic matter, C/N values, d13Corg and d13Ccarb in sediment profiles showed strong influence of terrestrial organic and carbonate fraction run-off via Rječica Brook which decreased rapidly in the direction of the open lake. The sedimentation rate as well as the ratio of allogenic and authigenic fraction in sediments was estimated. Lower d13Corg values in surface sediments might be a consequence of the increase in algal productivity but might also be a contribution of fossil fuel combustion. The anthropogenicaly induced 14C in the atmosphere in 1963/64 is visible though shadowed in sediments

Long-Term Isotope Records of Precipitation in Zagreb, Croatia

The isotope composition of precipitation has been monitored in monthly precipitation at Zagreb, Croatia, since 1976. Here, we present a statistical analysis of available long-term isotope data (3H activity concentration, delta2H, delta18O, and deuterium excess) and compare them to basic meteorological data. The aim was to see whether isotope composition reflected observed climate changes in Zagreb: a significant increase in the annual air temperature and larger variations in the precipitation amount. Annual mean delta18O and delta2H values showed an increase of 0.017 ‰ and 0.14 ‰ per year, respectively, with larger differences in monthly mean values in the first half of the year than in the second half. Mean annual d-excess remained constant over the whole long-term period, with a tendency for monthly mean d-excess values to decrease in the first half of the year and increase in the second half due to the influence of air masses originating from the eastern Mediterranean. Changes in the stable isotope composition of precipitation thus resembled changes in the temperature, the circulation pattern of air masses, and the precipitation regime. A local meteoric water line was obtained using different regression methods, which did not result in significant differences between nonweighted and precipitation-weighted slope and intercept values. Deviations from the Global Meteoric Water Line GMWL (lower slopes and intercepts) were observed in two recent periods and could be explained by changes in climate parameters. The temperature gradient of delta18O was 0.33 ‰/°C. The tritium activity concentrations in precipitation showed slight decreases during the last two decades, and the mean A in the most recent period, 2012–2018, was 7.6 ± 0.8 Tritium Units (TU)

Analysis of the Spatial Distribution of Stable Oxygen and Hydrogen Isotopes in Precipitation across the Iberian Peninsula

The isotopic composition of precipitation provides insight into the origin of water vapor, and the conditions attained during condensation and precipitation. Thus, the spatial variation of oxygen and hydrogen stable isotope composition (δp) and d-excess of precipitation was explored across the Iberian Peninsula for October 2002–September 2003 with 24 monitoring stations of the Global Network of Isotopes in Precipitation (GNIP), and for October 2004–June 2006, in which 13 GNIP stations were merged with 21 monitoring stations from a regional network in NW Iberia. Spatial autocorrelation structure of monthly and amount weighted seasonal/annual mean δp values was modelled, and two isoscapes were derived for stable oxygen and hydrogen isotopes in precipitation with regression kriging. Only using the GNIP sampling network, no spatial autocorrelation structure of δp could have been determined due to the scarcity of the network. However, in the case of the merged GNIP and NW dataset, for δp a spatial sampling range of ~450 km in planar distance (corresponding to ~340 km in geodetic distance) was determined. The range of δp, which also broadly corresponds to the range of the d-excess, probably refers to the spatially variable moisture contribution of the western, Atlantic-dominated, and eastern, Mediterranean-dominated domain of the Iberian Peninsula. The estimation error of the presented Iberian precipitation isoscapes, both for oxygen and hydrogen, is smaller than the ones that were reported for the regional subset of one of the most widely used global model, suggesting that the current regional model provides a higher predictive power