Antarctic Snow Research Articles

Visible and near-ultraviolet absorption spectrum of ice from transmission of solar radiation into snow

Snow is a scattering-dominated medium whose scattering is independent of wavelength at 350-600 nm. The attenuation of solar radiation in snow can be used to infer the spectral absorption coefficient of pure ice, by reference to a known value at 600 nm. The method is applied to clean Antarctic snow; the absorption minimum is at 390 nm, and the inferred absorption coefficient is lower than even the lowest values of the Antarctic Muon and Neutrino Detector Array (AMANDA) experiment on glacier ice: The absorption length is at least 700 m, by comparison with 240 m for AMANDA and 10 m from laboratory attenuation measurements.

Recent trends in Antarctic snow accumulation from Polar MM5 simulations

Polar MM5, a mesoscale atmospheric model optimized for use over polar ice sheets, is employed to simulate Antarctic accumulation in recent decades. Two sets of simulations, each with different initial and boundary conditions, are evaluated for the 17yr period spanning 1985-2001. The initial and boundary conditions for the two sets of runs are provided by the (i) European Centre for Medium-Range Weather Forecasts 40 year Reanalysis, and (ii) National Centres for Environmental Prediction-Department of Energy Atmospheric Model Intercomparison Project Reanalysis II. This approach is used so that uncertainty can be assessed by comparing the two resulting datasets. There is broad agreement between the two datasets for the annual precipitation trends for 1985-2001. These generally agree with ice core and snow stake accumulation records at various locations around the continent, indicating broad areas of both upward and downward trends. Averaged over the continent the annual trends are small and not statistically different from zero, suggesting that recent Antarctic snowfall changes do not mitigate current sea-level rise. However, this result does not suggest that Antarctica is isolated from the recent climate changes occurring elsewhere on Earth. Rather, these are expressed by strong seasonal and regional precipitation changes.

Antarctic snow accumulation mapped using polarization of 4.3‐cm wavelength microwave emission

Different parts of Antarctica receive different amounts of snowfall each year. In this paper we map the variations of the mean annual snow accumulation across the ice sheet. We also quantify the uncertainty in our estimates more objectively than has been possible for earlier maps. The new map is produced using observations from satellites and ground‐based measurements. After a logarithmic transformation, these are combined using the geostatistical method of continuous‐part universal kriging to give an estimate of the snow accumulation within each cell of a rectangular grid covering Antarctica. We also derive spatial averages over the major drainage systems of the ice sheet, along with their confidence intervals. We obtain a value of 143 ± 4 kg m−2 a−1 for the average rate of snow accumulation upon the grounded ice sheet of Antarctica.

Precipitation trapped in datable rock-forming minerals: estimating Antarctic palaeoelevations - a discussion

Meteoric water that interacted with minerals during retrogressive metamorphism and hydrothermalism in the late-stage of mountain building processes contains hydrogen and oxygen isotopes that are potential proxies for palaeoelevation reconstruction in Antarctica. The effects of temperature on meteoric isotopic signatures, meteoric crustal infiltration processes, and the mechanisms of capture and preservation of meteoric δD and δ18O values in rock-forming minerals are discussed. Special emphasis is given to Antarctica’s geographical high-latitude position and climatic fluctuations over time and to the highmountain ranges of continental Antarctica, which were tectonically active regions in the past. In this context, a new compilation of recent Antarctic snow and ice δD and δ18O data is presented, by which we demonstrate that net elevations versus isotopic depletions are positively correlated for continental Antarctica - a prime requisite when estimating palaeoelevations.

Solar power for an Antarctic rover

AbstractSensors mounted on mobile robots could serve a variety of science missions in Antarctica. Although weather conditions can be harsh, Antarctic snowfields offer unique conditions to facilitate long‐distance robot deployment: the absence of obstacles, firm snow with high albedo, and 24 h sunlight during the summer. We have developed a four‐wheel‐drive, solar‐powered rover that capitalizes on these advantages. Analyses and field measurements confirm that solar power reflected from Antarctic snow contributes 30–40% of the power available to a robot consisting of a five‐side box of solar panels. Mobility analyses indicate that the 80 kg rover can move at 0·8 m s−1 during clear sky conditions on firm snow into a 5 m s−1 headwind, twice the speed needed to achieve the design target of 500 km in 2 weeks. Local winter tests of the chassis demonstrated good grade‐climbing ability and lower than predicted rolling resistance. Tests of the completed robot occurred in Greenland in 2005. Copyright © 2006 John Wiley & Sons, Ltd.

The ocean circulation in the southern hemisphere and its climatic impacts in the Eocene

Opening of Southern Ocean gateways may have had a controlling influence on the evolution of global climate. The largest step in the history of Cenozoic climate, from an Eocene “Greenhouse” toward the modern glaciated state, is correlated with opening of a deep water connection between the Southern Indian and Southern Pacific Oceans. This study synthesizes results from previous work, assesses the possibility that ocean heat transport was much greater than modern during the globally warm Eocene, and explores the sensitivity of polar climate to large changes in ocean heat transport. The magnitudes of these sensitivities are compared with those due to greenhouse gas concentration changes. We find that ocean heat transport was unlikely to have been sufficiently greater than modern during the Eocene to explain the change in the climate. Specifically, in order to have significantly affected Antarctic climate, ocean heat transport changes would have had to change by an order of magnitude—much greater than the largest change produced in our simulations. In coupled climate model simulations, changes in CO 2 concentrations(from 1120 to 560 ppm) supported by proxy records, lead to significant Antarctic responses in the absence of ocean heat transport changes. The results show that Antarctic snow accumulation is primarily controlled by changes in summer temperature, not precipitation, and that snow did not remain on Antarctica during summer months in Eocene even at low greenhouse gas concentrations. Greenhouse gas concentration changes and subsequent processes such as ice albedo and weathering feedbacks, were more likely to have been the primary cause of Antarctic glaciation than ocean heat transport changes.

Isotopic view on nitrate loss in Antarctic surface snow

Massive post‐depositional processes alter the nitrate concentration in polar firn where the annual snow accumulation is low. This hinders a direct atmospheric interpretation of the ice core nitrate record. Fractionation of nitrate isotopes during post‐depositional nitrate loss may allow estimating the amount of nitrate loss in the past. We measured δ15N of nitrate in two Antarctic surface cores from the Dome C area. In concert with the known concentration decrease with depth we observe an increase in the isotopic signature. Assuming a Rayleigh type process we find an isotope effect of ɛ = −54‰. We measured the fractionation factor for photolysis in the laboratory and obtained ɛ = −11.7 ± 1.4‰. As the observed fractionation factor in the firn is much lower this rules out that photolysis in the surface snow is the main process leading to the dramatic nitrate loss in the top centimeters of the firn.

Sensible heat exchange at the Antarctic snow surface: a study with automatic weather stations

AbstractData of four automatic weather stations (AWSs) are used to calculate the turbulent exchange of sensible heat at the Antarctic snow surface for a 4 year period (1998–2001). The AWSs are situated on the ice shelf, in the coastal/inland katabatic wind zone and on the interior plateau in Dronning Maud Land, East Antarctica. Sensible heat flux (SHF) is calculated using the aerodynamic ‘bulk’ method between a single AWS sensor level and the surface, in combination with surface temperature derived from upwelling longwave radiation and surface roughness derived from eddy correlation measurements. Good agreement is found between calculated and directly measured SHF. All AWS sites show a downward‐directed average sensible heat transport, but otherwise the differences between the various zones are large. The surface roughness for momentum differs by an order of magnitude between the interior plateau (0.02 mm) and the katabatic wind zone (0.16 mm). On the ice shelf, frequent clouds limit surface cooling, and annual mean SHF is small (8 W m−2). In contrast, clear skies prevail on the interior plateau, but weak winds, an aerodynamically smooth surface and stability effects limit annual mean SHF to an equally low value (8 W m−2). The most favourable conditions for sensible heat exchange are found in the katabatic wind zone, where a combination of strong winds, relatively little cloud cover and a rougher surface results in annual mean SHF values of 22 to 24 W m−2. Copyright © 2005 Royal Meteorological Society

Improved analysis of volatile halogenated hydrocarbons in water by purge-and-trap with gas chromatography and mass spectrometric detection

An analytical system composed of a purge-and-trap injection system coupled to gas chromatography with mass spectrometric detection (PTI-GC–MS) specific for the analysis of volatile chlorinated hydrocarbons (VCHCs) (chloroform; 1,1,1-trichloroethane; tetrachloromethane; 1,1,2-trichloroethylene; tetrachloroethylene) and trihalomethanes (THMs) (chloroform; bromodichloromethane; dibromochloromethane; bromoform) in water was optimised. Samples were purged and trapped in a cold trap (−100 °C) fed with liquid nitrogen (cryo-concentration). In order to make this method suitable also for only slightly contaminated waters, some modifications were made to PTI sample introduction, in order to avoid any air intake into the system. PTI, GC and MS conditions were optimised for halogenated compound analysis and limits of detection (LOD) were evaluated. The proposed method allows analysis of samples whose concentrations range from μg/L to ng/L. It is, therefore, applicable to drinking waters, in analyses required by law, and to slightly contaminated aqueous matrices, such as those found in remote areas, in environmental monitoring. Moreover, by changing cold trap temperature, even sparkling mineral waters can be analysed, thus avoiding CO 2 interference during the cryo-concentration phase. Our method has been successfully used on real samples: tap water, mineral water and Antarctic snow.

Antarctic Surface and Subsurface Snow and Ice Melt Fluxes

Abstract This paper presents modeled surface and subsurface melt fluxes across near-coastal Antarctica. Simulations were performed using a physical-based energy balance model developed in conjunction with detailed field measurements in a mixed snow and blue-ice area of Dronning Maud Land, Antarctica. The model was combined with a satellite-derived map of Antarctic snow and blue-ice areas, 10 yr (1991–2000) of Antarctic meteorological station data, and a high-resolution meteorological distribution model, to provide daily simulated melt values on a 1-km grid covering Antarctica. Model simulations showed that 11.8% and 21.6% of the Antarctic continent experienced surface and subsurface melt, respectively. In addition, the simulations produced 10-yr averaged subsurface meltwater production fluxes of 316.5 and 57.4 km3 yr−1 for snow-covered and blue-ice areas, respectively. The corresponding figures for surface melt were 46.0 and 2.0 km3 yr−1, respectively, thus demonstrating the dominant role of subsurface over surface meltwater production. In total, computed surface and subsurface meltwater production values equal 31 mm yr−1 if evenly distributed over all of Antarctica. While, at any given location, meltwater production rates were highest in blue-ice areas, total annual Antarctic meltwater production was highest for snow-covered areas due to its larger spatial extent. The simulations also showed higher interannual meltwater variations for surface melt than subsurface melt. Since most of the produced meltwater refreezes near where it was produced, the simulated melt has little effect on the Antarctic mass balance. However, the melt contribution is important for the surface energy balance and in modifying surface and near-surface snow and ice properties such as density and grain size.

Stable isotope ratios of Antarctic petrel (Thalassoica antarctica) and snow petrel (Pagodroma nivea) bone collagen

This study investigated the trophic hierarchy status of the Antarctic petrel (Thalassoica antarctica) and snow petrel (Pagodroma nivea) within the Southern Ocean food-web off Dronning Maud Land, Antarctica. During 1991/92 ten Antarctic petrel and ten snow petrel carcasses were collected from Jekselen (71°59′S, 02°35′W) and Robertskollen (71°28′S, 03°15′W) respectively, in the northern Ahlmannryggen, Dronning Maud Land. Collagen from the dense bone of the humeri of these carcasses was extracted and the stable carbon and nitrogen isotope ratios of these samples determined. The snow petrel bone collagen samples displayed a mean δ13C value of −23.9±0.7 (range: −24.7 to −22.9; n=9) and a mean δ15N value of 15.2±1.6 (range: 12.9 to 18.4; n=10). The corresponding values for Antarctic petrel bone collagen were −24.8±1.0 (range: −26.2 to −22.8; n=9) and 13.2±0.6 (range: 12.5 to 13.9; n=8) respectively. The difference between the species’ δ13C values may indicate differences in their foraging habitat. It has previously been suggested that the snow petrel has a higher wing loading than other Procellariiforme species, making the snow petrel less adapted to pelagic foraging than related species and more likely to forage close to the sea ice edge. Algae growing under sea ice apparently can have comparatively high δ13C values, possibly due to growing under carbon dioxide limited conditions. If so, animals foraging close to the sea ice edge might be expected to show higher δ13C values in their body tissues than animals foraging farther out over the open ocean. However, the high δ13C of snow petrel collagen is possibly more likely to be related to the correspondingly high δ15N values found in this tissue, and hence caused by snow petrels including offal from high trophic level Antarctic mammals and birds in their diet.

Records of the δ13C of atmospheric CH4 over the last 2 centuries as recorded in Antarctic snow and ice

Methane is one of the important greenhouse gases accumulating in the atmosphere today. The increased loading over the past 2 centuries is thought to be the result of increased anthropogenic emissions. Here we present records of the δ13C of CH4 in firn air from the South Pole and in trapped bubbles in a short ice core from Siple Dome, Antarctica, that help constrain historical emissions of various sources throughout the last 2 centuries. Using two firn air samplings in 1995 and 2001 we calculate that δ13CH4 has increased by an average of 0.06 ± 0.02‰/yr over the 6 years between samplings. Our ice core results suggest the δ13C of atmospheric CH4 has increased by 1.8 ± 0.2‰ between 1820 A.D. and 2001 AD. The δ13CH4 changes in both data sets are the result of an increase in the relative proportion of CH4 sources with elevated 13C/12C isotope ratios. One explanation for observed trends involves a 16 Tg/yr increase in CH4 emissions associated with biomass burning over the past 2 centuries.

Transport and modification of humic substances present in Antarctic snow and ancient ice

We performed a study of fulvic acids extracted from fresh and aged snow, and from recent and ancient ice in Antarctica. The fresh snow samples were collected in coastal and inland sites to evaluate the influence of the distance from the sea on organic matter transport. Moreover, in a site (Melbourne Mountain) samples were collected at different heights to study the influence of altitude on transport. The obtained results showed that dissolved fulvic acid concentrations are influenced neither by distance nor by height while particulate fulvic acid concentrations are influenced by both parameters. Moreover, the results showed that fulvic acids transported for a long distance can undergo chemical modifications. Chemical modifications are better evidenced by the analysis of samples taken in trenches at different depth, which showed structural changes attributable to the loss of nitrogen-containing compounds and to an increase in aromatic character of the structures due to reduction and/or condensation processes. With ageing, the humification process proceeds with heavy carbon losses as demonstrated by results obtained from fulvic acids isolated from ice aged between twenty-five thousand and seventy thousand years.

Atmospheric Concentrations and Air−Water Flux of Organochlorine Pesticides along the Western Antarctic Peninsula

Air, seawater, sea ice, and snow were collected during the austral winter (September-October 2001) and summer (January-February 2002) along the Western Antarctic Peninsula. Hexachlorobenzene (HCB) > heptachlor > alpha- and gamma-hexachlorocyclohexane (HCH) and heptachlor epoxide, were the most frequently detected organochlorine pesticides in air. HCB and HCH levels declined over the past 20 years, with a half-life of 3 years for sigmaHCH in Antarctic air. However, heptachlor epoxide levels have not declined in Antarctic air over the past decade, possibly due to continued use of heptachlor in the southern hemisphere. Peak heptachlor concentrations in air were measured coincident with air masses moving into the region from lower latitudes. Levels of lindane were 1.2-200 times higher in annual sea ice and snow compared to alpha-HCH, likely due to greater atmospheric input of gamma-HCH. The ratio of alpha/gamma-HCH in Antarctic air, sea ice and snow was <1, illustrative of a predominance of influx of lindane versus technical HCH to the regional environment. However, alpha/gamma-HCH in seawater was >1, likely due to more rapid microbial degradation of gamma- versus alpha-HCH. Water/air fugacity ratios for HCHs demonstrate continued atmospheric influx of HCHs to coastal Antarctic seas, particularly during late summer.

Spatial characteristics of snow accumulation in Dronning Maud Land, Antarctica

An accurate knowledge of spatial variations in snow accumulation on ice sheets is vital for numerical reconstructions and future projections of ice sheet dynamics, with implications for changes in global climate and sea level. This study considers net snow accumulation in Dronning Maud Land, East Antarctica. Ground-penetrating radar (GPR) soundings were carried out along two ground traverses, 800 and 1000 km long, extending from the ice shelves to the high plateau in order to map snow accumulation rates continuously along the route. Comparisons between the net accumulation rates obtained by GPR and those obtained by stake-line measurements exhibited a close correlation. Large dissimilarities in the accumulation distribution were observed between the two traverses. The ice sheet surface topography and the regional distribution of air pressure systems and cyclone tracks can explain these differences to a large extent. Spatial trends in snow accumulation rate were determined for characteristic traverse sections. The spatial variability was calculated as the standard deviation in snow accumulation rate over 5 km, expressed as percentages of the average accumulation within the 5-km section. On ice shelves, the spatial variability was less than 10%. In grounded coastal areas, it ranged between 20% and 40%, and on the high plateau, it ranged up to 20%. In areas of intense wind erosion, the spatial variability often exceeded 50%. The generally high spatial variability demonstrates that the spatial representativeness of individual point measurements is of vital importance in Antarctic snow accumulation studies. This is a problem that is presently not properly attributed.

Photochemistry and nature of organic matter in Arctic and Antarctic snow

It has been shown that sunlit snowpacks are photochemically active, producing a number of species that can significantly impact the overlying atmosphere. Here we investigate the origin of the flux of low molecular weight carbonyl compounds (formaldehyde and acetaldehyde) from sunlit snow obtained from both Arctic (Alert, Canada, and Summit, Greenland) and Antarctic (South Pole) sources. In addition, efforts to characterize the potential snow‐phase organic matter (SPOM) precursors were undertaken. Using chemically characterized SPOM, we find that formaldehyde and acetaldehyde are produced upon irradiation, and that production is enhanced with the addition of nitrate (a precursor to OH radicals). SPOM from both Alert and Summit is found to be derived from a variety of sources, including vascular plants. This indicates deposition of atmospheric particulate matter containing vascular tissue to high‐altitude Arctic snow. These findings open a potential window for a rich record of variations in terrestrial vegetation‐derived aerosol signals that could be preserved in ice cores.

Estimation of snow water equivalent using microwave radiometry over Arctic first‐year sea ice

AbstractThe magnitude and spatial distribution of snow on sea ice are both integral components of the ocean–sea‐ice–atmosphere system. Although there exists a number of algorithms to estimate the snow water equivalent (SWE) on terrestrial surfaces, to date there is no precise method to estimate SWE on sea ice. Physical snow properties and in situ microwave radiometry at 19, 37 and 85 GHz, V and H polarization were collected for a 10‐day period over 20 first‐year sea ice sites.We present and compare the in situ physical, electrical and microwave emission properties of snow over smooth Arctic first‐year sea ice for 19 of the 20 sites sampled. Physical processes creating the observed vertical patterns in the physical and electrical properties are discussed. An algorithm is then developed from the relationship between the SWE and the brightness temperature measured at 37 GHz (55°) H polarization and the air temperature. The multiple regression between these variables is able to account for over 90% of the variability in the measured SWE. This algorithm is validated with a small in situ data set collected during the 1999 field experiment. We then compare our data against the NASA snow thickness algorithm, designed as part of the NASA Earth Enterprise Program. The results indicated a lack of agreement between the NASA algorithm and the algorithm developed here. This lack of agreement is attributed to differences in scale between the Special Sensor Microwave/Imager and surface radiometers and to differences in the Antarctic versus Arctic snow physical and electrical properties. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Variability and Trends of the Summer Melt Period of Antarctic Ice Margins since 1980 from Microwave Sensors

Abstract The density and range of observations made by meteorological stations is insufficient to fully characterize decadal climate variability in Antarctica. Satellite-borne instruments, which offer a high spatial and temporal density of information, can contribute complementary data for characterizing Antarctic climate change. Here, partial melting of Antarctic snow, which significantly affects the microwave emissivity of the surface, is identified and counted over 18 yr in the 20-yr period 1980–99. The cumulated product of the surface area affected by melting and the duration of the melting event, called cumulative melting surface (CMS), is one of the three melt indices defined and discussed here. On average over the last 20 yr, the Antarctic CMS has decreased by 1.8% ± 1% yr−1, a result that is consistent with a mean January cooling of the continent recently identified from infrared satellite data. In addition, the interannual signatures of the Antarctic Oscillation, and possibly of the Southern Osci...

What controls photochemical NO and NO2 production from Antarctic snow? Laboratory investigation assessing the wavelength and temperature dependence

Laboratory experiments were conducted to determine the wavelength and temperature dependence of NO and NO2 release from Antarctic snow. This photochemically driven process has been observed during recent field measurements in polar regions. In this work the photochemical production of NO and NO2 was reproduced under laboratory conditions with NO2 dominating the production. The wavelength of incident light was varied over the range 295–385 nm. We observed a λ dependence where NO and NO2 release ceases when the snow was illuminated with λ &gt; 345 nm. Comparing these data with the aqueous absorption cross section of the nitrate ion (NO3−) indicates that NO3− is the precursor N‐oxide species, which is photolyzed in snow. The temperature of the experimental system was varied over the range 253–243 K with no effect on NO and NO2 production. The occurrence of these photochemical processes followed by release to the atmosphere will impact the chemistry of the boundary layer over any snow‐covered region. In addition, understanding these processes is essential for accurate ice core interpretation.

One hundred fifty–year record of lead isotopes in Antarctic snow from Coats Land

A record of the concentrations of Pb and Ba and the isotopic composition of Pb has been established for a remote, low accumulation site in the Atlantic sector of Antarctica (Coats Land) by means of thermal ionization mass spectrometry. The snow samples cover the period ∼1840 to 1990. They were taken from the walls of a pit to a depth of 7.8 m and as a core to 16 m; ultraclean procedures were used. Detailed laboratory subsampling provided both long-term (secular scale) and short-term (intra-annual) Pb, Ba, and Pb isotope variations. The results show that there have been significant variations in Pb concentrations (range, 0.1 to 9.3 pg/g) and isotopic composition (range, 1.096 to 1.208 for 206Pb/ 207Pb ratio) since the 1840s. The data show evidence of pollution for this metal in Antarctica as early as the 1880s. Several Pb maxima were observed: the first at the beginning of the 20th century and the last in the 1970s to 1980s, with a clear decrease during recent years. Although the last maximum is clearly linked to the rise and fall in the use of leaded gasoline in the Southern Hemisphere, especially in South America, the reason for the first remains uncertain. The pattern of changing isotopic composition of Pb reveals the changing origin and character of the anthropogenic inputs to Antarctica. An interesting feature in this pattern is the relatively large contribution of unradiogenic Pb in the ∼1890s, possibly originating from Australia. Another interesting feature is the pronounced intra-annual variation in the isotopic composition of Pb, which illustrates the complexity of the changing inputs of Pb to Antarctica.