Enricomaria Selmo

A late-glacial high-resolution site and source temperature record derived from the EPICA Dome C isotope records (East Antarctica)

The timing and synchronisation of Greenland and Antarctic climate events that occurred during the last glacial period are still under debate, as is the magnitude of temperature change associated with these events. Here we present detailed records of local and moisture-source temperature changes spanning the period 27-45 kyr BP from water stable isotope measurements (deltaD and delta(18)O) in the recently drilled EPICA Dome C ice core, East Antarctic plateau. Using a simple isotopic model, site (DeltaT(site)) and source (DeltaT(source)) temperatures are extracted from the initial 50-yr high-resolution isotopic records, taking into account the changes in seawater isotopic composition. The deuterium isotope variability is very similar to the less precise deltaD record from the Vostok ice core, and the site temperature inversion leads to a temperature profile similar to the classical palaeothermometry method, due to compensations between source and ocean water corrections. The reconstructed DeltaT(site) and DeltaT(source) profiles show different trends during the glacial: the former shows a decreasing trend from the warm Al event (38 kyr BP) toward the Last Glacial Maximum, while the latter shows increasing values from 41 to 28 kyr BP. The low-frequency deuterium excess fluctuations are strongly influenced by obliquity fluctuations, controlling the low- to high-latitude temperature gradients, and show a remarkable similarity with a high-resolution southeast Atlantic sea surface temperature record. A comparison of the temperature profiles (site and source) and temperature gradient (DeltaT(source)-DeltaT(site)) with the non-sea-salt calcium and sodium records suggests a secondary influence of atmospheric transport changes on aerosol variations.

Abrupt change of Antarctic moisture origin at the end of Termination II

The deuterium excess of polar ice cores documents past changes in evaporation conditions and moisture origin. New data obtained from the European Project for Ice Coring in Antarctica Dome C East Antarctic ice core provide new insights on the sequence of events involved in Termination II, the transition between the penultimate glacial and interglacial periods. This termination is marked by a north–south seesaw behavior, with first a slow methane concentration rise associated with a strong Antarctic temperature warming and a slow deuterium excess rise. This first step is followed by an abrupt north Atlantic warming, an abrupt resumption of the East Asian summer monsoon, a sharp methane rise, and a CO2 overshoot, which coincide within dating uncertainties with the end of Antarctic optimum. Here, we show that this second phase is marked by a very sharp Dome C centennial deuterium excess rise, revealing abrupt reorganization of atmospheric circulation in the southern Indian Ocean sector.

Atmospheric CO2 concentrations and δ13C values across the Antarctic Circumpolar Current between New Zealand and Antarctica

Measurements of atmospheric CO2 concentrations were repeatedly carried out on the vessel ‘Italica’ of the Italian National Research Program in Antarctica, during cruises from Italy to Antarctica. Discrete air samples were also collected in 4-L Pyrex flasks during these cruises in order to carry out δ13C analyses on atmospheric CO2. The results acquired between New Zealand and Antarctica are reported here. The mean growth rate of the CO2 concentration from 1996 to 2003 in this area of the Southern Oceans is of about 1.8 ppmv yr-1, in good agreement with NOAA/CMDL measurements. The rates of increase from cruise to cruise are rather variable. From 1996.1997 to 1998.1999 cruise the yearly growth rate is 2.75 ppmv yr-1, close to the large growth rates measured in several areas and mainly related to the most severe El Ni.no event of the last years. The other yearly growth rates are of about 1.3 and 2 ppmv for the periods 1998.1999 to 2001.2002 and 2001.2002 to 2003.2004, respectively. The large difference between these two values is probably related to the uncertainty on the only two 2001.2002 discrete measurements of CO2 concentration in this area. The measured δ13C values show two completely different distributions and a large interannual variability. The 1998.1999, 2002.2003, and 2003.2004 results obtained between about 55.S and 65.S across the Antarctic Polar Front show a marked negativization of up to more than 2° when compared to the background values. The results are related to local source regions of CO2, as frequently found in the Southern Ocean by several authors; the negative δ13C values are tentatively related to the possible contribution of different causes. Among them, the southward negative gradient of δ13C of the dissolved inorganic carbon, the contribution from upwelling deep waters and from subsurface processes between the Northern SubAntarctic Front and the Polar Front, and, partly, the contribution of CO2 of biogenic origin, e.g. from heterotrophic activity. The 2001.2002 results are very homogeneous and almost constant, close to .8.5% showing only minor deviations from the oceanic background values. This behaviour may be related to differences in the frontal structure along the 2001.2002 track.

Chemical and Oxygen Isotopic Composition of Roman and Late Antique Glass from Northern Greece

The present paper emphasizes the importance of measuring the oxygen isotopic and chemical compositions of ancient glass, in order to constrain some features such as age, raw materials, and production technologies and to identify the “fingerprint“ of local productions. In this context, thirty-nine Roman and late Antique glass samples and eight chert samples from northern Greece were selected and analysed for their oxygen isotopic and chemical compositions. Results show that the majority of glass samples are produced using natron as flux and have 18O values of about 15.5, plus or minus a few tenths of one per mil, suggesting that raw materials probably come from Levantine area. Four samples are heavily enriched in 18O, and their chemical composition clearly shows that they were made with soda plant ash as flux. Isotopic and chemical data of Greek chert samples support the hypothesis of local production of the above samples. About half of the glass samples have chemical compositions, which allow their age to be constrained to the late Antique period. For the remaining glass, similarities with literature compositional groups are reported and discussed.

Oxygen isotopic composition of fulgurites from the Egyptian Sahara and other locations.

RATIONALE Fulgurites are glassy crusts or hollow glassy tubes formed by the impact of a lightning strike on a target material on the Earths surface. The oxygen isotopic composition of fulgurites has never been measured and, consequently, it is unknown whether or not isotopic fractionations take place between the target material and the fulgurite glass during the lightning event which is an excellent natural example of extremely fast melting process. METHODS Following well-established procedures (high-temperature reaction of the fulgurite material with BrF(5), conversion into CO(2) of the evolved O(2) and measurement of the(18)O/(16)O ratio on a Finnigan Delta S mass spectrometer) we measured for the first time the oxygen isotopic composition of sets of fulgurites coming from various locations on the Earths surface. RESULTS The range of isotopic values is quite large, probably reflecting the oxygen isotopic values of the target materials. In the case of fulgurites from the Sahara Desert the isotopic values obtained from the bulk material, quartz crystals sticking to the fulgurite body, tiny samples of loose sand coming from fulgurite bubbles, and sand samples collected near the fulgurites, are very close to one another. CONCLUSIONS Although we do not have indisputable evidence, we conclude that, at least in the case of oxygen, the fusion process of the material struck by lightning, as well as all the extremely fast high-temperature fusion processes, probably take place without any isotopic fractionation effect.

Atmospheric CO 2 concentrations and δ 13 C values between New Zealand and Antarctica, 1998 to 2010: some puzzling results

ABSTRACT From 1998 to 2010, during eight cruises of the M/V Italica between New Zealand and Antarctica, sets of flask air samples were collected and atmospheric CO2 concentrations were recorded. The δ13C of CO2 from the 1998 to 2003 air samples have already been published and show large interannual variability and an increasing frequency of 13C-depleted samples. These results were related to a mosaic of areas with positive air–sea fluxes. We report here δ13C results from air samples collected from four further cruises. δ13C values obtained during the 2004/2005 cruise show an inexplicable saw-toothed distribution. Air samples from the 2005/2006 cruise have δ13C values which match previous sets of samples (1998 to 2004) and show more frequent and more negative isotopic events. From 2006 until 2009, further samples could not be collected. However, during December 2009 and January 2010, two more sets of air samples were collected, the δ13C values of which greatly differ from previous results, being absolutely homogeneous and paralleled by flat CO2 concentrations. The results of these last two sets of air samples may be due either to fortuitous environmental conditions or to an improbable and substantial change in oceanic and atmospheric conditions in this section of the circumpolar area.

CO2 concentrations and δ13C (CO2) values in monthly sets of air samples from downtown Parma and the Parma and Taro river valleys, Emilia-Romagna, Italy

Monthly sets of discrete air samples were collected from September 2004 to June 2005 in the town of Parma, along North-South and East-West runs (8 plus 8 samples), using four-litre Pyrex flasks. The CO2 concentrations and δ13C values were determined on these samples with the aim of evaluating quantitatively the contribution of domestic heating to the winter atmospheric CO2 pollution in downtown Parma by comparing autumn and spring atmospheric values with winter values. After separation of CO2 from the other air gases in the laboratory, the CO2 concentrations were calculated from the intensity of the 12C16O ion beam in the mass spectrometer, after calibration with artificial air samples whose CO2 concentration was very carefully determined by the Monte Cimone Observatory (Sestola, Modena, Italy). The reproducibility of these measurements was of ∼±0.4 % and, consequently, the most probable error is not higher than±2–3 ppmv and does not affect the magnitude of the gradients between different samples. The standard deviation of δ13C measurements ranges from±0.02 to ±0.04 ‰ (1σ). The results suggest that the contribution of domestic heating to atmospheric CO2 pollution is almost negligible in the case of ground level atmosphere, where the main CO2 pollution is essentially related to the heavy car traffic. This is probably because of the fact that the gases from the domestic heating systems are discharged tens of metres above ground level at a relatively high temperature so that they rise quickly to the upper atmospheric layers and are then displaced by air masses dynamics. Revised version of a paper presented at the VIII IsotopeWorkshop of the European Society for Isotope Research (ESIR), 25–30 June, 2005, Leipzig-Halle, Germany. Monthly sets of discrete air samples were also collected from October 2004 to June 2005 along North-South runs from the town of Parma to the Apennine ridge following the Parma and the Taro river valleys (8 samples and 7 samples per set, respectively) and measured using the same technique. The aim of this study was the comparison between the town samples, the plain country samples and the samples collected on the northern slope of the Apennines. The results reveal huge variations of both CO2 concentration and δ13C through space and time, some of which can be reasonably explained whereas others are rather difficult to understand. The sets of values are discussed and various hypotheses are suggested.

Oxygen, Hydrogen, Boron and Lithium Isotope Data of a Natural Spring Water with an Extreme Composition: A Fluid from the Dehydrating Slab?

The chemical and isotope compositions of slab dehydration fluids from convergent margins have been theorized by many authors who have adopted several approaches. A direct collection of natural water is possible only in an oceanic environment, despite several difficulties in estimating the deepest component due to the mixing with seawater or hydrothermal fluids from the ridge. Accordingly, the study of melt inclusions is a valuable alternative. However, the latter mainly represents high temperature/pressure conditions in deep magmatic or metamorphic settings. Here, we present new H, O, Li and B isotope along with a revision of previously published chemical data from a potential natural example of slab dehydration water, sampled in a forearc region and affected by low-temperature metamorphism and serpentinization processes (Aqua de Ney, Northern California). Its extreme composition challenges the understanding of its origin and deep temperature, but this work is a further step on a topic of increasing interest for several scientists from different academic disciplines.