Academic literature on the topic 'Antarctic snowfall'

The Antarctic contribution to sea-level rise has long been uncertain. While regional variability in ice dynamics has been revealed, a picture of mass changes throughout the continental ice sheet is lacking. Here, we use satellite radar altimetry to measure the elevation change of 72% of the grounded ice sheet during the period 1992–2003. Depending on the density of the snow giving rise to the observed elevation fluctuations, the ice sheet mass trend falls in the range −5–+85 Gt yr −1 . We find that data from climate model reanalyses are not able to characterise the contemporary snowfall fluctuation with useful accuracy and our best estimate of the overall mass trend—growth of 27±29 Gt yr −1 —is based on an assessment of the expected snowfall variability. Mass gains from accumulating snow, particularly on the Antarctic Peninsula and within East Antarctica, exceed the ice dynamic mass loss from West Antarctica. The result exacerbates the difficulty of explaining twentieth century sea-level rise.

The Laboratoire de Météorologie Dynamique (LMD) variable-grid atmospheric general circulation model (AGCM) was used in this study for a five-year high-resolution simulation of the Antarctic climate. The horizontal resolution is about 100 km over a large part of the ice sheet. This study focuses on the simulated surface mass balance (precipitation-evaporation sublimation-melt) and on the spatial and temporal variability of snowfall in Antarctica. The simulated annual mean surface mass balance for the whole continent is close to the observed value, and the model simulates well the spatial distribution of the surface mass balance. The annual cycle of snowfall exhibits a clear minimum in summer over the high interior plateau as well as for Antarctica as a whole, in agreement with the observations. In the interior of the continent, the model produces a permanent light background snowfall that accounts for about 5% of the total annual precipitation. The bulk of the snowfall is produced irregularly during periods that generally last only two or three days that are caused by cyclones off the coast.

The Laboratoire de Météorologie Dynamique (LMD) variable-grid atmospheric general circulation model (AGCM) was used in this study for a five-year high-resolution simulation of the Antarctic climate. The horizontal resolution is about 100 km over a large part of the ice sheet. This study focuses on the simulated surface mass balance (precipitation-evaporation sublimation-melt) and on the spatial and temporal variability of snowfall in Antarctica. The simulated annual mean surface mass balance for the whole continent is close to the observed value, and the model simulates well the spatial distribution of the surface mass balance. The annual cycle of snowfall exhibits a clear minimum in summer over the high interior plateau as well as for Antarctica as a whole, in agreement with the observations. In the interior of the continent, the model produces a permanent light background snowfall that accounts for about 5% of the total annual precipitation. The bulk of the snowfall is produced irregularly during periods that generally last only two or three days that are caused by cyclones off the coast.

Measurements of trace elements in snow and ice are frequently used to describe past atmospheric composition although there is no firm basis for assuming a direct connection. Trace-element concentrations have been measured on samples of aerosol and freshly fallen snow collected simultaneously from two sites in the Antarctic Peninsula during summer. Following improvements in contamination control, the reported concentrations and crustal enrichment factors of Cd, Cu, Pb and Zn in the aerosol are lower than any values previously reported from Antarctica. Even tighter controls will be required in the future. For a crustal element (A1) and for the marine cations (Na, Ca and K) a consistent ratio (0.48±0.31) for the concentration in air (pg m−3)/concentration in snow (pg g−1) is obtained for simultaneously collected samples. This supports a simple model of aerosol scavenging proposed by Junge which considers aerosol removal over polar ice sheets to be dominated by in-cloud processes. Averaged data for Cd, Cu, Pb and Zn from samples collected at different times appear to behave similarly. These findings suggest that there is no preferential scavenging by snowfall of either crustal or heavy metal components in contemporary aerosol. If proved more general in Antarctica this may help to simplify the interpretation of time series data from ice cores.

Measurements of trace elements in snow and ice are frequently used to describe past atmospheric composition although there is no firm basis for assuming a direct connection. Trace-element concentrations have been measured on samples of aerosol and freshly fallen snow collected simultaneously from two sites in the Antarctic Peninsula during summer. Following improvements in contamination control, the reported concentrations and crustal enrichment factors of Cd, Cu, Pb and Zn in the aerosol are lower than any values previously reported from Antarctica. Even tighter controls will be required in the future.For a crustal element (A1) and for the marine cations (Na, Ca and K) a consistent ratio (0.48±0.31) for the concentration in air (pg m−3)/concentration in snow (pg g−1) is obtained for simultaneously collected samples. This supports a simple model of aerosol scavenging proposed by Junge which considers aerosol removal over polar ice sheets to be dominated by in-cloud processes. Averaged data for Cd, Cu, Pb and Zn from samples collected at different times appear to behave similarly. These findings suggest that there is no preferential scavenging by snowfall of either crustal or heavy metal components in contemporary aerosol. If proved more general in Antarctica this may help to simplify the interpretation of time series data from ice cores.

AbstractIn this paper we first summarise major findings of recent atmospheric studies of nitrogen and sulphur species present in the boundary layer of coastal Antarctic regions. We then discuss the implications of such atmospheric data for the interpretation of nitrate, ammonium, methanesulphonate and sulphate records in deep ice cores extracted from central Antarctica in terms of past atmospheric chemistry changes.

Abstract. Climate models predict Antarctic precipitation to increase during the 21st century, but their present day Antarctic precipitation differs. A fully model-independent climatology of the Antarctic precipitation characteristics, such as snowfall rates and frequency, is needed to assess the models, but was not available so far. Satellite observation of precipitation by active spaceborne sensors has been possible in the polar regions since the launch of CloudSat in 2006. Here we use CloudSat products to build the first multi-year model-independent climatology of Antarctic precipitation. The mean snowfall rate from August 2006 to April 2011 is 171 mm yr−1 over the Antarctic ice sheet north of 82° S. The ECMWF ERA Interim dataset agrees well with the new satellite climatology.

L’Antarctique joue un rôle majeur dans le climat de la Terre, car le gradient de température entre l’équateur et les pôles contrôlent la circulation atmosphérique. L’Antarctique est également utile pour comprendre la variabilité du climat, puisque les informations préservées dans la glace peuvent complémenter les observations récentes. Cependant, l’emplacement des forages de carotte de glace sont irrégulièrement répartis sur le continent, et les reconstructions de température sur le plateau Est-Antarctique sont entravées par la faible résolution temporelle résultant d’une trop faible accumulation de neige à haute altitude. Nous présentons ici de nouvelles reconstructions de température à partir de la carotte de glace d’Aurora Basion North (ABN, 77°S, 111°E, 2700 m d’altitude). D’abord, nous utilisons le Modèle Atmosphérique Régional (MAR) pour caractériser le climat récent à ABN, et montrons que les événements de précipitation sont intermittents, et sont marqués par une température 2°C supérieure à la moyenne. Les événements de fortes précipitations sont enregistrés dans les isotopes de l’eau, avec des valeurs de δ18O avoisinant les valeurs estivales, même en hiver, comme l’attestent des mesures dans la neige et le modèle atmosphérique ECHAM5-wiso, qui est équipé avec les isotopes de l’eau. Les précipitations sont systématiquement associées avec un blocage atmosphérique sur la côte de Wilkes Land, au nord-est d’ABN, et ces blocages sont favorisés par les phases négatives du Southern Annular Mode (SAM), le principal mode de variabilité dans le climat de l’hémisphère Sud. Par conséquent, les phases positives du SAM sont marquées par des température froides à ABN, mais pas nécessairement par un δ18O faible, car les précipitations peuvent être réduites. La température reconstruite à partir de la carotte forée à ABN, qui fait 300 m et couvre 2000 ans, reste relativement stable, à ± 1°C de la température moyenne. Nous détaillons une deuxième reconstruction de température faite sur la même carotte, basée sur l’inversion de la température de trou de forage et des anciens gradients de température dans le névé, estimés avec les isotopes stables des gaz Ar et N2 piégés dans les bulles. Cette seconde reconstruction de température révèle deux périodes environ 3°C plus froides à ABN au cours des 2000 dernières années : de 300 à 550 EC, et de 1000 à 1400 EC. Cette anomalie froide médiévale est synchrone avec une phase positive du SAM, et n’a pas pu être identifiée à partir du δ18O seul. Cette étude souligne l’importance d’utiliser plusieurs indicateurs pour déterminer les variations passées de température, car le δ18O pourrait surreprésenter les événements chauds à forte précipitation<br>Antarctica is a major component in Earth’s climate system, as the equator to pole temperature gradient controls the characteristics of the general circulation of the atmosphere. Antarctica is also very useful to understand climate variability, as past climate information preserved in the ice may help extend the short observational records. However, the ice core drilling locations are unevenly spread across the glaciated continent, and the temperature reconstructions from the high elevation East Antarctic plateau suffer from poor temporal resolution, because low snow accumulation hampers our interpretation of water isotopes. Here, we present new temperature reconstructions from the Aurora Basin North (ABN, 77°S, 111°E, 2700 masl) ice core. First, we use the regional atmospheric model MAR to characterize the recent climate at ABN, and show that precipitation events are intermittent, and occur under temperature 2°C warmer than average. The large precipitation events are marked in the snow isotopes with δ18O values on par with summer levels, even during the winter, as attested by snow measurements and the isotope-enabled atmospheric model ECHAM5-wiso. Precipitations are consistently associated with a blocking on the Wilkes Land coast, North-East of ABN, and the blockings are more likely to occur during negative phases of the Southern Annular Mode (SAM), the main mode of variability in the southern hemisphere climate. Consequently, SAM positive phases are marked by cold temperatures at ABN, but not necessarily low δ18O, as precipitations may be weakened. The temperature reconstructed from the δ18O in the 300-m-deep, 2000-year ice core drilled at ABN supports stable conditions, with a temperature remaining within a ± 1°C range. We present a second temperature reconstruction from the same core, based on the inversion of borehole temperature and past firn temperature gradients, estimated with the stable isotope composition of Ar and N2 gases trapped in bubbles. This second temperature reconstruction, representative of changes in the snow, suggests that temperature at ABN was about 3°C colder during two periods of the last 2000 years: from 300 to 550 CE, and from 1000 to 1400 CE. This medieval cold anomaly is concurrent with a positive SAM phase, and could not be identified from the δ18O alone. This work highlights the importance of using multiple proxies to determine past temperature variability in Antarctica, as δ18O may be biased towards warm precipitation events

Springtime atmospheric mercury depletion events (AMDEs) lead to snow with elevated mercury concentrations (&gt;200 ng Hg/L) in the Arctic and Antarctic. During AMDEs gaseous elemental mercury (GEM) is photochemically oxidized by halogens to reactive gaseous mercury which is deposited to the snowpack. This reactive mercury is either photochemically reduced back to GEM and reemitted to the atmosphere or remains in the snowpack until spring snowmelt. GEM is also deposited to the snowpack and tundra vegetation by reactive surface uptake (dry deposition) from the atmosphere. There is little consensus on the proportion of AMDE-sourced Hg versus Hg from dry deposition that is released in spring runoff. We used mercury stable isotope measurements of GEM, snowfall, snowpack, snowmelt, surface water, vegetation, and peat from a northern Alaska coastal watershed to quantify Hg sources. Although high Hg concentrations are deposited to the snowpack during AMDEs, we estimate that ∼76 to 91% is released back to the atmosphere prior to snowmelt. Mercury deposited to the snowpack as GEM comprises the majority of snowmelt Hg and has a Hg stable isotope composition similar to Hg deposited by reactive surface uptake of GEM into the leaves of trees in temperate forests. This GEM-sourced Hg is the dominant Hg we measured in the spring snowpack and in tundra peat permafrost deposits.