1,721,323 research outputs found
Stable isotope study of water, gypsum and carbonate samples from the Bannock and Tyro Basins, Eastern Mediterranean.
No full textSeawater and brine samples collected along vertical profiles above the Bannock and Tyro Basins (eastern Mediterranean), and gypsum samples collected by dredging and coring the anoxic section of the Bannock Basin, have been studied for their δ18O values. The following conclusions may be drawn from these data: (1) The water of the deep brines is isotopically slightly different from modern Mediterranean bottom water and might be a 'fossil water' possibly formed during a recent, climatically cooler stage or when the evaporation was slightly higher than nowadays. (2) The similarity between the δ18O values of the brine samples from the Bannock and Tyro Basins supports the possibility that the ages of the two basins are very close to each other. (3) Gypsum crystals on the bottom of the Bannock Basin are probably being formed by the dissolution and reprecipitation of sub-bottom (or outcropping) Messinian evaporites. This hypothesis is supported by the oxygen isotopic values exhibited by the gypsum crystallization water and by the oxygen and sulphur isotopic composition of gypsum. (4) The shells of pelagic organisms included in gypsum are probably very recent, but not contemporary, and may be referred to cooler environmental conditions. © 1990
Oxygen isotopic composition of ice samples from the Hells Gate and Backstairs Passage Ice Shelves (Victoria Land, Antarctica): evidence of bottom freezing.
No full textIsotopic composition of Holocene shells from raised beaches and ice shelves of Terra Nova Bay (Victoria Land, Antarctica).
No full textIsotopic composition of water vapor near the air-water interface
Full text linkEvaporation is a key process in water cycle that links liquid water to the atmosphere. In the last fifty years stable
isotopes of hydrogen and oxygen have been intensively used to describe climate processes related to evaporation
and precipitation, ranging in different spatial and temporal scales. Evaporation introduces large isotopic effects
in the phases involved. The well known Craig-Gordon model (Craig & Gordon, 1965) describes those isotopic
effects involving several steps and different processes, moving from the air-water interface to the free atmosphere.
However, very few works in literature have tested the vertical behavior of the Craig-Gordon model in natural
conditions on both fresh and marine waters. In this work we present the results from four field experiments aimed
to describe the vertical variability of δ18O and δD in the first few meters over a large water body (the coastal
lagoon of Venice, northern Italy) and to test the Craig-Gordon model in such conditions. Each experiment involved
cryotrapping of water vapor at different height over the water surface (0.1m, 2m and 4m) and the sampling of the
liquid water at two depth (surface and 0.5m). During the experiments, water vapor was also sampled in the nearest
mainland (~2.5 km from gradient measurements) to determine the isotopic composition of background water vapor.
Liquid samples were then analyzed with a Picarro L1102-i and Thermo-Fisher Delta Plus Advantage for water
vapor and lagoon water, respectively. The last two experiments have also involved simultaneous measurements
of relative humidity using commercially-available humidity probes at each height. This approach was used to
determine a reference scale in order to compare observations to modeled estimates. Despite the coarse time
resolution due to cryotrapping method (measurements are averaged over 1.5 hours), preliminary results show
measurable differences in the isotopic composition of water vapor along the vertical gradient and good agreement
between observations and predicted values from the model. Even if this work is an exploratory phase it shows an
interesting potential to grow our understanding of the processes involved as well as a useful implementation for
future studies focused on fractionation of water isotopes due to evaporation in natural conditions
Characterization of a customized calibration unit for continuous measurements of the isotopic composition of water vapor
Full text linkThe objective of this work is the development, standardization and creation of a method to carry out continuous
measurement of oxygen and hydrogen isotopic composition of the atmospheric water vapor using a wavelengthscanned cavity ring down spectroscopy (WS-CRDS) instrument produced by Picarro, L1102-i model.
Some technical improvements of the standard instrument configuration have been made to create three different
inlet gas lines: a “standard” line, a calibration line and a line connected with the external sampler.
The calibration line is composed of a syringe-pump that continuously injects standard water into a steel tee
heated at the temperature of 170◦C and flushed with dry nitrogen gas. In this way, instantaneous and complete
vaporization of the standard water takes place. The resulting steam is characterized by a well-defined composition
in δD e δ18O values.
To allow comparison with other international data, we have characterized the individual instrumental response to
variation of the isotopic composition of the water vapor. Several humidity-isotope response functions (6000-26000
ppmv) have been estimated with three different internal standards (0.35h -8.75h -29.11h and -40.28h for
δ18O; 2.31h -58.91h -222.19h and -317.78h for δD).
Moreover, we have measured the instrumental drift at regular time intervals to apply the opportune corrections to
instrument data.
The setup has been tested using a 3.5 day continuous measurements carried out with the Picarro sampling the
water vapor outside our campus in Venice and parallel sampling using the classical cryogenic trapping procedure,
obtaining excellent results. Furthermore, our analysis technique has given good results for the standards with
values which are similar to those obtained with the isotope ratio mass spectrometry (IRMS) technique
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