Search results for "Oxygen-18"
showing 5 items of 5 documents
Stable isotopes of water as a tool to study groundwater–seawater interactions in coastal south-eastern Sicily
2009
Summary Stable isotopes of hydrogen (δD) and oxygen (δ 18 O) in groundwater, submarine springs and seawater collected in coastal south-eastern Sicily were investigated. While the spatial distribution of δ 18 O in groundwater showed that most of the heavy-isotope-depleted samples (from −5.7‰ to −6.9‰) were located in the higher portion of the Hyblean Mountains, more positive values (from −3.4‰ to −5.6‰) were found in the marginal areas. The isotope composition of submarine springs was characterized by significant variability (δ 18 O between −5.6‰ and +1.0‰ and δD between −30‰ and +5.0‰) reflecting seasonal variations and different seawater contributions. The isotopic and chemical composition…
Geochemical monitoring of groundwaters (1998-2001) at Vesuvius volcano (Italy)
2004
This work presents the results of hydrogeochemical studies carried out at Vesuvius during the period May 1998-December 2001, mostly focusing on compositional time variations observed during this time. Based on their chemistry, groundwater samples are distinguished into two groups, 1 and 2, representative of water circulation in the southern and northern sectors of the volcano, respectively. Waters from group 1 are typically more acidic, warmer, and more saline than those of group 2. They also have higher CO2 and CH4 contents, attributed to enhanced input of deep-rising volatiles and prolonged water-rock interactions. Time-series highlight the fairly constant chemical composition of the enti…
Stable isotope fractionation in speleothems: Laboratory experiments
2010
Abstract In recent years, stalagmites have become important archives for paleoclimate. Several studies applying carbon and oxygen isotopes of stalagmites show a simultaneous increase of δ 13 C and δ 18 O along individual growth layers, which is interpreted as being indicative of isotope fractionation under disequilibrium conditions. In order to obtain robust paleoclimatic information from calcite precipitated under these non-equilibrium conditions it is important to improve the quantitative understanding of the corresponding isotope fractionation processes. Here we present laboratory experiments simulating calcite precipitation under cave-analogue conditions. The major focus was the investi…
δ2H, δ13C and δ18O from whole wood,α-cellulose and lignin methoxyl groups inPinus sylvestris: a multi-parameter approach
2015
Novel tree ring parameters – δ13C and δ2H from methoxyl groups – have been developed to reconstruct palaeoclimate. Tests with δ13C and δ18O derived from whole wood and cellulose samples, however, indicated differences in the isotopic composition and climate signal, depending on the extracted wood component. We assess this signal dependency by analysing (i) δ13C and δ18O from whole wood and cellulose and (ii) δ13C and δ2H from methoxyl groups, using Pinus sylvestris L. growing near Altenkirchen (Germany). Results indicate significant correlations among the time series derived from whole wood, cellulose, and lignin methoxyl groups. Compared with the whole wood samples, δ13C from methoxyl grou…
Nuclear potentials for sub-barrier fusion and cluster decay inC14,O18+Pb208systems
2007
Near-barrier fusion excitation functions for the $^{14}\mathrm{C}$ and $^{18}\mathrm{O}+^{208}\mathrm{Pb}$ reactions have been analyzed in the framework of the barrier-passing model using different forms of the nuclear potential and the phenomenology of a fluctuating barrier. The best-fit fusion potentials were used to estimate cluster decay probabilities from the corresponding ground states of Ra and Th (i.e., for the inverse decay process). The analysis supports the ``\ensuremath{\alpha}-decay-like'' scenario for carbon and oxygen emission from these nuclei.