O. Flora

Spatial and temporal variability of snow accumulation in East Antarctica from traverse data

Recent snow accumulation rate is a key quantity for ice-core and mass-balance studies. Several accumulation measurement methods (stake farm, fin core, snow-radar profiling, surface morphology, remote sensing) were used, compared and integrated at eight sites along a transect from Terra Nova Bay to Dome C, East Antarctica, to provide information about the spatial and temporal variability of snow accumulation. Thirty-nine cores were dated by identifying tritium/b marker levels (1965-66) and non-sea-salt (nss) SO4 2- spikes of the Tambora (Indonesia) volcanic event (1816) in order to provide information on temporal variability. Cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation. Stake-farm and ice-core accumulation rates are observed to differ significantly, but isochrones (snow radar) correlate well with ice-core derived accumulation. The accumulation/ablation pattern from stake measurements suggests that the annual local noise (metre scale) in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation, with no accumulation or ablation for a 5 year period in up to 40% of cases. The spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi-decadal/secular scale. Stake measurements and firn cores at Dome C confirm an approximate 30% increase in accumulation over the last two centuries, with respect to the average over the last 5000 years.

Chemical and isotopic snow variability along the 1998 ITASE traverse from Terra Nova Bay to Dome C (East-Antarctica)

Abstract In the framework of the PNRA–ITASE (Programma Nazionale di Ricerche in Antartide–International Trans-Antarctic Scientific Expedition) project, during the field season 1998/99, surface snow (1m cores and pits) and shallow firn cores (10–50m) were collected along a traverse from Terra Nova Bay (northern Victoria Land) to Dome C (East Antarctic ice sheet). Results of chemical, tritium and stable-isotope composition are presented here for the 1 m cores, some snow pits and the first 2 mof some shallow firn cores. the δ18O values show a regular trend with altitude, and the regression line between δ18O and surface temperature is δ18O = 0.99T (˚C) – 0.67. Primary aerosol components such as Na+, Cl–, Ca2+,Mg2+ and K+ show high concentrations decreasing with increasing altitude in the first 250–350km from the coast. At greater distances, concentrations of these species remain more constant. NO3 – concentration shows an irregular profile with a progressive decreasing trend as altitude increases. Non-sea-salt (nss) SO4 2– concentration decreases up to about 250 km from the coast, increases 250–770 km from the coast and remains relatively constant in the most remote stations. Methanesulphonate (MSA) concentration shows high variability. the MSA/nssSO4 2– ratio exhibits a decreasing trend 250–550km from the coast. With increasing distance, the ratio shows moderate oscillations. nssCl– concentration shows a progressive increase as distance from the coast increases, in agreement with the increasing influence of HCl on the Cl– budget of the inland Antarctic atmosphere. Post-depositional re-emissions of Cl– and NO3 – were found at stations characterized at the surface by long-term accumulation hiatus (wind crusts). the chemical-species distribution is consistent with the presence in the studied area of local and long-range transport processes, post-depositional effects and snow-accumulation variations observed along the traverse.

Chemical and isotopic snow variability in East Antarctica along the 2001/02 ITASE traverse

Abstract As part of the International Trans-Antarctic Scientific Expedition (ITASE) project, a traverse was carried out from November 2001 to January 2002 through Terre Adélie, George V Land, Oates Land and northern Victoria Land, for a total length of about 1875 km. The research goal is to determine the latitudinal and longitudinal variability of physical, chemical and isotopic parameters along three transects: one west–east transect (WE), following the 2150m contour line (about 400 km inland of the Adélie, George V and Oates coasts), and two north–south transects (inland Terre Adélie and Oates Coast–Talos Dome–Victoria Land). The intersection between the WE and Oates Coast–Victoria Land transects is in the Talos Dome area. Along the traverse, eight 2 m deep snow pits were dug and sampled with a 2.5 cm depth resolution. For spatial variability, 1 m deep integrated samples were collected every 5 km (363 sampling sites). In the snow-pit stratigraphy, pronounced annual cycles, with summer maxima, were observed for nssSO4 2–, MSA, NO3 – and H2O2. The seasonality of these chemical trace species was used in combination with stable-isotope stratigraphy to derive reliable and temporally representative snow-accumulation rates. The study of chemical, isotopic and accumulation-rate variability allowed the identification of a distribution pattern which is controlled not only by altitude and distance from the sea, but also by the complex circulation of air masses in the study area. In particular, although the Talos Dome area is almost equidistant from the Southern Ocean and the Ross Sea, local atmospheric circulation is such that the area is strongly affected only by the Ross Sea. Moreover, we observed a decrease in concentration of aerosol components in the central portion of the WE transect and in the southern portion of the Talos Dome transect; this decrease was linked to the higher stability of atmospheric pressure due to the channelling of katabatic winds.

Chemical characterization of the last 250 years of snow deposition at Talos Dome (East Antarctica)

High-resolution chemical records of main and trace ionic components of snow precipitation over the last 250 years were obtained by analysing the first 36 m of a firn core drilled at Talos Dome, a dome located in the ice divide between northern Victoria Land and Oates Land (East Antarctica Pacific Ocean/Ross Sea sector). The concentration/depth profiles of some relevant chemical parameters are discussed on the basis of a previous stratigraphic dating, set up following the seasonal signatures of non-sea-salt (nss) sulphate deposition and synchronised by using tritium and volcanic temporally known horizons. Particular attention is paid to the study of the temporal trends of the sea spray components (Na+, Cl−, Mg2+) and S and N cycle compounds ( ) to understand the main sources, transport mechanisms and depositional processes of these compounds at the deposition site. Good correlations between the sea spray markers show that the primary marine contribution is relevant, though Talos Dome is located at a relatively high altitude (2316 m a.s.l.) and far from the coast line (about 250 km). The study of the snow chemical composition and of the recent (for the last few centuries) atmosphere/snow relationship at Talos Dome is important as a preliminary survey at this station, which will probably be chosen for a deep ice coring project.

An oxygen isotope record from the Foscagno rock-glacier ice core, Upper Valtellina, Italian Central Alps

New high-resolution isotopic records (δ18O, δD and deuterium excess), from an ice core drilled in the Foscagno rock glacier (Italian Central Alps), are presented. The δ18O data suggest a clear division between an upper part (2.5 and 4 m), showing relatively homogeneous values, and a middle part (4—7.65 m), showing seasonal variations of this parameter. The isotopic analyses confirm previous results (crystallographic and chemical analyses) suggesting a division of this relict glacier ice body into an upper part, between 2.5 and 4 m, where melting and refreezing processes occur, and a middle part, between 4 and 7.65 m, where the isotopic signal is preserved. Larger deuterium excess variations (d = δD−8*δ 18O) are found in the massive ice (below 4 m depth) rather than in the overlying ice. These are in antiphase with the δ18O but without any clear correspondence with the presence of the debris layers. Postdepositional processes could have affected, at least partially, the isotopic content of the original precipitation. The radiocarbon dating of a leaf ( Salix spp.) found in the massive ice from another nearby borehole in the same rock glacier gave a calendar age ranging between AD 765 and 1260. The expected δ18O values of the present-day precipitation in the Foscagno valley are of the same order as those found in the massive ice (−12.4‰). This similarity would suggest climate conditions not very different from present day, in good agreement with other available palaeoclimate reconstructions for this period. However, only more abundant precipitation would make the existence of a glacier possible in a climate not very different from that of the present.

Growth processes of an inland Antarctic ice wedge, Mesa Range, northern Victoria Land

Abstract During the 16th Italian Antarctic Expedition (2000/01) a geomorphological survey of permafrost-related polygons was carried out in the Mesa Range area, upper Rennick Glacier. The investigated site is located in the uppermost reaches of Pain Mesa, which forms the northern sector of the Mesa Range. An ice wedge was found in a volcanic regolith at about 2200ma.s.l. This altitude is below a well-defined erosional trimline, located at about 2380ma.s.l. in this sector of Pain Mesa. The ice was sampled by inserting an ice screw, with an internal diameter of 14 mm, into the ice wedge in vertical sequences. Oriented block samples for thin sections were taken. A co-isotopic study was performed, measuring both oxygen (δ18O) and hydrogen (δD) isotope compositions. Tritium activity was measured, and major cations and anions were determined. The δ18O and δD obtained showed a strong divergence from the snowfalls expected to occur at this elevation, with extremely negative d excess values. Sublimation processes were taken into account to define the origin of the ice forming the wedge. The tritium data obtained suggest that the growth process of the ice wedge might still be active today.