Two-dimensional impurity imaging in deep Antarctic ice cores: snapshots of three climatic periods and implications for high-resolution signal interpretation

Due to its micrometer-scale resolution and inherently micro-destructive nature, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is particularly suited to exploring the thin and closely spaced layers in the oldest sections of polar ice cores. Recent adaptions to the LA-ICP-MS instrumentation mean we have faster washout times allowing state-of-the-art 2-D imaging of an ice core. This new method has great potential especially when applied to the localization of impurities on the ice sample, something that is crucial, to avoiding misinterpretation of the ultra-fine-resolution signals. Here we present the first results of the application of LA-ICP-MS elemental imaging to the analysis of selected glacial and interglacial samples from the Talos Dome and EPICA Dome C ice cores from central Antarctica. The localization of impurities from both marine and terrestrial sources is discussed, with special emphasis on observing a connection with the network of grain boundaries and differences between different climatic periods. Scale-dependent i mage analysis shows that the spatial significance of a single line profile along the main core axis increases systematically as the imprint of the grain boundaries weakens. It is demon-strated how instrumental settings can be adapted to suit the purpose of the analysis, i.e., by either employing LA-ICP-MS to study the interplay between impurities and the ice microstructure or to investigate the extremely thin climate proxy signals in deep polar ice

On the reproducibility and repeatability of laser absorption spectroscopy measurements for δ2H and δ18O isotopic analysis

The aim of this study was to analyse the reproducibility of off-axis integrated cavity output spectroscopy (OA-ICOS)-derived δ2H and δ18O measurements on a set of 35 water samples by comparing the performance of four laser spectroscopes with the performance of a conventional mass spectrometer under typical laboratory conditions. All samples were analysed using three different schemes of standard/sample combinations and related data processing to assess the improvement of results compared with mass spectrometry. The repeatability of the four OA-ICOS instruments was further investigated by multiple analyses of a sample subset to evaluate the stability of δ2H and δ18O measurements. Results demonstrated an overall agreement between OA-ICOS-based and mass spectrometry-based measurements for the entire dataset. However, a certain degree of variability existed in precision and accuracy between the four instruments. There was no evident bias or systematic deviations from the mass spectrometer values, but random errors, which were apparently not related to external factors, significantly affected the final results. Our investigation revealed that analytical precision ranged ±from ±0.56‰ to ±1.80‰ for δ2H and from ±0.10‰ to ±0.27‰ for δ18O measurements, with a marked variability among the four instruments. The overall capability of laser instruments to reproduce stable results with repeated measurements of the same sample was acceptable, and there were general differences within the range of the analytical precision for each spectroscope. Hence, averaging the measurements of three identical samples led to a higher degree of accuracy and eliminated the potential for random deviations

Geochemical features and effects on deep-seated fluids during the May-June 2012 southern Po Valley seismic sequence

A periodic sampling of the groundwaters and dissolved and free gases in selected deep wells located in the area affected by the May-June 2012 southern Po Valley seismic sequence has provided insight into seismogenic-induced changes of the local aquifer systems. The results obtained show progressive changes in the fluid geochemistry, allowing it to be established that deep-seated fluids were mobilized during the seismic sequence and reached surface layers along faults and fractures, which generated significant geochemical anomalies. The May-June 2012 seismic swarm (mainshock on May 29, 2012, M 5.8; 7 shocks M >5, about 200 events 3 > M > 5) induced several modifications in the circulating fluids. This study reports the preliminary results obtained for the geochemical features of the waters and gases collected over the epicentral area from boreholes drilled at different depths, thus intercepting water and gases with different origins and circulation. The aim of the investigations was to improve our knowledge of the fluids circulating over the seismic area (e.g. origin, provenance, interactions, mixing of different components, temporal changes). This was achieved by collecting samples from both shallow and deep-drilled boreholes, and then, after the selection of the relevant sites, we looked for temporal changes with mid-to-long-term monitoring activity following a constant sampling rate. This allowed us to gain better insight into the relationships between the fluid circulation and the faulting activity. The sampling sites are listed in Table 1, along with the analytical results of the gas phase

Drought-induced dieback of Pinus nigra: A tale of hydraulic failure and carbon starvation

Ongoing climate change is apparently increasing tree mortality rates, and understanding mechanisms of drought-induced tree decline can improve mortality projections. Differential drought impact on conspecific individuals within a population has been reported, but no clear mechanistic explanation for this pattern has emerged. Following a severe drought (summer 2012), we monitored over a 3-year period healthy (H) and declining (D) Pinus nigra trees co-occurring in a karstic woodland to highlight eventual individual-specific physiological differences underlying differential canopy dieback. We investigated differences in water and carbon metabolism, and xylem anatomy as a function of crown health status, as well as eventual genotypic basis of contrasting drought responses. H and D trees exploited the same water pools and relied on similar hydraulic strategies to cope with drought stress. Genetic analyses did not highlight differences between groups in terms of geographical provenance. Hydraulic and anatomical analyses showed conflicting results. The hydraulic tracheid diameter and theoretical hydraulic conductivity were similar, but D trees were characterized by lower water transport efficiency, greater vulnerability to xylem conduit implosion and reduced carbohydrate stores. Our results suggest that extreme drought events can have different impacts on conspecific individuals, with differential vulnerability to xylem embolism likely playing a major role in setting the fate of trees under climate change

Volcanic synchronisation of the EPICA-DC and TALDICE ice cores for the last 42 kyr BP

The age scale synchronisation between the Talos Dome and the EPICA Dome C ice cores was carried on through the identification of several common volcanic signatures. This paper describes the rigorous method, using the signature of volcanic sulphate, which was employed for the last 42 kyr of the record. Using this tight stratigraphic link, we transferred the EDC age scale to the Talos Dome ice core, producing a new age scale for the last 12 kyr. We estimated the discrepancies between the modelled TALDICE-1 age scale and the new scale during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones. Except for a very few cases, R ranges between 0.8 and 1.2, corresponding to an uncertainty of up to 20% in the estimate of the time duration in at least one of the two ice cores. At this stage our approach does not allow us to unequivocally identify which of the models is affected by errors, but, taking into account only the historically known volcanic events, we found that discrepancies up to 200 yr appear in the last two millennia in the TALDICE-1 model, while our new age scale shows a much better agreement with the volcanic absolute horizons. Thus, we propose for the Talos Dome ice core a new age scale (covering the whole Holocene) obtained by a direct transfer, via our stratigraphic link, from the EDC modelled age scale by Lemieux-Dudon et al. (2010)

A late medieval warm period in the Southern Ocean as a delayed response to external forcing?

International audienceOn the basis of long simulations performed with a three‐dimensional climate model, we propose an interhemispheric climate lag mechanism, involving the long‐term memory of deepwater masses. Warm anomalies, formed in the North Atlantic when warm conditions prevail at surface, are transported by the deep ocean circulation towards the Southern Ocean. There, the heat is released because of large scale upwelling, maintaining warm conditions and inducing a lagged response of about 150 years compared to the Northern Hemisphere. Model results and observations covering the first half of the second millenium suggest a delay between the temperature evolution in the Northern Hemisphere and in the Southern Ocean. The mechanism described here provides a reasonable hypothesis to explain such an interhemipsheric lag

The isotopic composition of water vapor: from discrete to continuous measurements. A focus on calibration methods

The water residence time in the atmosphere is approximately nine days, the shortest residence time in any major reservoir of the whole water cycle on the planet. Nevertheless, water vapor is a key factor in climate and hydrology due to its dynamic behavior. The isotopic composition of water vapor can highlight several processes of the water cycle that link the water reservoirs to the atmosphere (Galewsky et al., 2016). In the past, the isotopic composition of water vapor was generally inferred from precipitation data, assuming isotopic equilibrium between rain and water vapor. This assumption works well when precipitation is abundant but gives misleading results when precipitation is scarce. A common method to determine the isotopic composition of water vapor is the cryotrapping technique, proposed by Craig et al., (1963). Cryotrapping consists in freezing all the moisture content of the air (to avoid fractionation) and analyze the liquid sample with the regular mass spectrometry technique. This process includes the designing of customized cold traps and usually requires several man-hours due to the long sampling time (2 - 8 hours per sample). With the advent of the laser absorption spectrometry (LAS) technique is now possible to determine the isotopic composition of water vapor with sampling time down to seconds. This novel technique increases our knowledge about the isotopic composition of water vapor and gives a substantial help in our understanding of the water cycle, both on global and local scales. However, the continuous measurement of isotopic composition of water vapor requires a specific method to calibrate the large amount of data resulting as the output of a Cavity Ring-Down Spectroscopy (CRDS) analyzer. This includes the production of vapor with known isotopic composition, determination of the response of the analyzer to different humidity levels and correction of the instrumental drift. In this work, we present a summary of potential calibration techniques for continuous measurements of the isotopic composition of water vapor. The study goes in-depth on the developing of a customized calibration unit for a commercial CRDS analyzer (Picarro L1102i). Continuous measurements will be compared to water vapor samples collected with cryotraps and several continuous measurements will be presented highlighting sub-daily processes in the atmospheric boundary layer

Atmospheric synoptic conditions of snow precipitation in East Antarctica using ice core and reanalysis data

In the framework of the International Partnerships in Ice Core Sciences (IPCS) initiatives the GV7 site (70°41’ S – 158°51’ E) in East Antarctica was chosen as the new drilling site for the Italian contribution to the understanding of the climatic variability in the last 2000 years (IPICS 2k Array). Water stable isotopes and snow accumulation (SMB) values from a shallow firn core, obtained at GV7 during the 2001-2002 International Trans-Antarctic Scientific Expedition (ITASE) traverse, are analyzed and compared with different meteorological model output in order to characterize the atmospheric synoptic conditions driving precipitation events at the site. On annual basis, ECMWF +24h forecasted snowfalls (SF) seem to well reproduce GV7 SMB values trend for the period from 1980 to 2005. Calculated air mass back-trajectories show that Eastern Indian - Western Pacific oceans represent the main moisture path toward the site during autumn - winter season. Analysis of the ECMWF 500 hPa Geopotential height field (GP500) anomalies shows that atmospheric blocking events developing between 130°E and 150°W at high latitudes drive the GV7 SMB by blocking zonal flow and conveying warm and moist deep air masses from ocean into the continental interior. On inter-annual basis, The SF variability over GV7 region follows the temporal oscillation of the third CEOF mode (CEOF3 10% of the total explained variance) of a combined complex empirical orthogonal function (CEOF) performed over GP500 and SF field. The CEOF3 highlights an oscillating feature, with wavenumber 2, in GP500 field over the Western Pacific-Eastern Indian Oceans and propagating westward. The pattern is deeply correlated with the Indian Dipole Oscillation and ENSO and their associated quasi-stationary Rossby waves propagating from the lower toward the higher latitudes

Ten years of isotopic composition of precipitation at Concordia Station, East Antarctica

Oxygen and Hydrogen isotopic composition (delta18O and deltaD) in ice cores has been widely used as a proxy for reconstructing past temperature variations. However, the atmospheric dynamics determining the precipitation isotopic composition on the Antarctic Plateau are yet to be fully understood, as well as the post-depositional processes modifying the pristine snow isotopic signal: both are fundamental for the interpretation of the isotopic records from deep Antarctic ice cores drilled in low accumulation areas in order to improve past temperature reconstructions. Since 2008, daily precipitation has been continuously collected by the winter-over personnel on raised surfaces (height: 1 m) placed in the clean area of Concordia Station on the East Antarctic plateau. Each sample has been analyzed for 18O, D and deuterium excess (d): this represents a unique record, still ongoing, for the isotopic composition of precipitation in inland Antarctica. In order to better comprehend the relationship between local temperature and the isotopic signal of precipitation, temperature data (T2m) from the Dome C Automatic Weather Station of the Programma Nazionale di Ricerche in Antartide (PNRA) were correlated with precipitation sample delta18O, deltaD and d from 2008 to 2017. A significant positive correlation between delta18O and deltaD of precipitation and T2m is observed when using both daily and monthly-averaged data. The measured precipitation isotopic data were also compared to the simulated delta18O, deltaD and d from the isotope-enabled atmospheric general circulation models ECHAM5-wiso and ECHAM6-wiso, with the latter showing significant improvement in simulating the isotopic data of precipitation

Interannual analysis of high spatially-resolved δ18O and δ2H data in precipitation across North-East Italy

Stable water isotopes are widely-used tracers to investigate hydrological processes occurring in the atmosphere and to determine the geospatial origin of water, i.e. to acquire useful information about the hydrological cycles over catchment basins and to find the origin of water recharging rivers, aquifers, and springs. Mapping the isotopic composition of precipitation provides hydrological and climate information at regional and global scales. However, the isotopic composition of precipitation is usually analyzed at large scales with a limited spatial resolution. In Italy, a few studies mapped the oxygen stable isotopes using annually-averaged data, not accounting for the strong seasonality of the isotopic composition linked to climatic and weather factors. To partially fill this gap, the present study proposes a detailed analysis of more than 2250 isotope data (δ18O, δ2H, and deuterium excess) related to precipitations collected in the Friuli Venezia Giulia (FVG) region (Italy) with monthly or seasonal frequency in 36 sites between 1984 and 2015. The FVG region lies at the north-eastern end of Italy, bordering Austria in the North and Slovenia in the East, and extends over ~7.9·103 km2. From a hydrogeological point of view, FVG is an interesting case study. Large highly-permeable carbonate aquifers are present in the Alps and Prealps, while the southern part of the region is characterized by an alluvial plain, split by the spring belt into two sectors: the High Plain in the North, characterized by an highly-permeable unconfined aquifer, and the Low Plain in the South, characterized by a system of confined and artesian aquifers. All the aquifers are recharged by the effective precipitations which in the FVG exhibits among the highest annual precipitation rates in Italy (with peaks >3000 mm/year). For the present research, the isotopic data were used: (i) to analyze the spatial and seasonal variability of isotopic composition; (ii) to relate water isotopes with orography and weather parameters collected from meteorological stations as well as using ECMWF ERA5 reanalysis; (iii) to reconstruct the local meteoric water lines across the FVG at annual and seasonal bases; (iv) to quantify interannual trends and analyze their spatial distribution; and (iv) to model the spatial distribution of isotope content in precipitation and create annual and seasonal maps