Deep Snow Pit Research Articles

Variations in lead isotopes in Antarctic snow from northern Victoria Land during 2012–2015

To evaluate recent changes in anthropogenic Pb pollution and its sources and origins in Antarctica, Pb and Ba concentrations and Pb isotopic compositions were determined in a continuous series of 40 snow samples from a 2-m deep snow pit, covering 4 full years from 2011/12 summer to 2015/16 summer, at the Hercules Névé plateau in Victoria Land, Antarctica. The results show that more than 90% of the atmospheric Pb deposited in Victoria Land was of noncrustal origin. This result implies the persistence of a significant human impact on the atmospheric cycle of Pb in the most remote places on Earth, despite a substantial reduction in anthropogenic Pb emissions in the Southern Hemisphere during recent years. The Pb isotopic fingerprints indicate that South America, particularly Brazil and Chile, has become a major source of anthropogenic Pb reaching Victoria Land. Our data highlight the need for both national and international measures to further reduce Pb emissions.

Investigation on the Sources and Impact of Trace Elements in the Annual Snowpack and the Firn in the Hansbreen (Southwest Spitsbergen)

We present a thorough evaluation of the water soluble fraction of the trace element composition (Ca, Sr, Mg, Na, K, Li, B, Rb, U, Ni, Co, As, Cs, Cd, Mo, Se, Eu, Ba, V, Ge, Ga, Cr, Cr, P, Ti, Mn, Zr, Ce, Zn, Fe, Gd, Y, Pb, Bi, Yb, Al, Nb, Er, Nd, Dy, Sm, Ho, Th, La, Lu, Tm, Pr, Tb, Fe, In, Tl) and their fluxes in the annual snowpack and the firn of the Hansbreen (a tidewater glacier terminating in the Hornsund fjord, southwest Spitsbergen). The trace element samples were obtained from a 3 m deep snow pit dug at the plateau of the glacier (450 m a.s.l.), and from a 2 m deep firn core collected from the bottom of the snow pit. The comparison of elemental fluxes and enrichment factors allowed us to constrain specific summer and wintertime deposition patterns of water soluble trace elements in the southern part of the Svalbard archipelago. Our results suggest that the chemical composition of the Hansbreen (and likely other glaciers where the summit is close to the equilibrium line) is mainly affected by summertime deposition of trace elements from local sources and some volatile elements, which may be transported into the Arctic when polar vortex is weak. The melting of the annual snowpack seems to have a minor influence on the overall chemical signature of the glacier ice.

Uranium record from a 3 m snow pit at Dome Argus, East Antarctica.

Understanding the distribution and transport of Uranium is important because it can lead to both chemical and radiological toxicity. This study presents the Uranium concentrations time series from 1964 to 2009 obtained from a 3 m deep snow pit at Dome Argus, East Antarctic Plateau. The data shows that Uranium concentrations vary from 0.0067 pg g-1 to 0.12 pg g-1, with a mean concentration of 0.044 pg g-1. Its mean concentration is 2–3 folds lower than at West Antarctica study sites, such as the Antarctic Peninsula (mean 0.12 pg g-1), IC-6 (Ice Core-6) (mean 0.11 pg g-1) and a suite of ice cores from the US ITASE traverse. Before the mid-1980s, the varieties of Uranium concentrations are relatively stable, with a very low mean concentration of 0.016 pg g-1and its main source is sea salt deposition, while a small number of anthropogenic sources are likely to be caused by Uranium mining operations in South Africa. A remarkable increase of Uranium concentrations has occurred since the mid-1980s (by a factor of ~ 9) compared with the amount before the mid-1980s. This increase coincides with the Uranium records at IC-6 and Antarctic Peninsula (DP-07-01) during the same period, and are mostly attributed to Uranium mining operations in Australia as a potential primary anthropogenic Uranium source. Our observations suggest that Uranium pollution in the atmosphere might have already become a global phenomenon.

Light-absorption of dust and elemental carbon in snow in the Indian Himalayas and the Finnish Arctic

Abstract. Light-absorbing impurities (LAIs) deposited in snow have the potential to substantially affect the snow radiation budget, with subsequent implications for snow melt. To more accurately quantify the snow albedo, the contribution from different LAIs needs to be assessed. Here we estimate the main LAI components, elemental carbon (EC) (as a proxy for black carbon) and mineral dust in snow from the Indian Himalayas and paired the results with snow samples from Arctic Finland. The impurities are collected onto quartz filters and are analyzed thermal–optically for EC, as well as with an additional optical measurement to estimate the light-absorption of dust separately on the filters. Laboratory tests were conducted using substrates containing soot and mineral particles, especially prepared to test the experimental setup. Analyzed ambient snow samples show EC concentrations that are in the same range as presented by previous research, for each respective region. In terms of the mass absorption cross section (MAC) our ambient EC surprisingly had about half of the MAC value compared to our laboratory standard EC (chimney soot), suggesting a less light absorptive EC in the snow, which has consequences for the snow albedo reduction caused by EC. In the Himalayan samples, larger contributions by dust (in the range of 50 % or greater for the light absorption caused by the LAI) highlighted the importance of dust acting as a light absorber in the snow. Moreover, EC concentrations in the Indian samples, acquired from a 120 cm deep snow pit (possibly covering the last five years of snow fall), suggest an increase in both EC and dust deposition. This work emphasizes the complexity in determining the snow albedo, showing that LAI concentrations alone might not be sufficient, but additional transient effects on the light-absorbing properties of the EC need to be considered and studied in the snow. Equally as imperative is the confirmation of the spatial and temporal representativeness of these data by comparing data from several and deeper pits explored at the same time.

Application of a Markov Chain Monte Carlo algorithm for snow water equivalent retrieval from passive microwave measurements

Recent applications of passive microwave remote sensing techniques to estimate snow water equivalent (SWE) increasingly rely on the comprehension of microwave emission theories, instead of traditional empirical fitting approaches. In this study, an advanced SWE retrieval algorithm based on the Markov Chain Monte Carlo method was developed. This method samples the posterior multiple-layer snow properties according to the likelihood of the brightness temperature (TB) simulation with the actual TB observations. The Microwave Emission Model of Layered Snowpacks with improved Born approximation (MEMLS-IBA) was used as the observation model. Using a globally applicable method to produce prior estimates of snow properties, the retrieval approach is called the Bayesian Algorithm for SWE Estimation with Passive Microwave measurements (BASE-PM), and was applied on 48 snowpits at Sodankylä, Finland; Churchill, Canada and Colorado, US. The result shows that the root mean squared (RMS) error of the retrieved SWE is 42.7mm excluding two outliers, and is 30.8mm if the outliers as well as six deep snowpits from Colorado are excluded. This accuracy approximately meets the 30-mm requirement of Integrated Global Observing Strategy for shallow snow. The poor performance for the outlier and deep snowpits is explained. Additional experiments using more accurate priors show that SWE retrieval accuracy can be improved with local snowcover knowledge, e.g. if historical snowpit measurements or snow process model simulations are available.

Evidence of air-snow mercury exchange recorded in the snowpack at Dome Fuji, Antarctica

Measuring the mercury content in shallow Antarctic snow pits is useful for understanding the mercury dynamics of the Antarctic Plateau and the global mercury cycle and for interpreting ice core data. We determined the total mercury concentration (HgT) in snow samples successively collected at 5 cm intervals from two 4m deep snow pits at Dome Fuji. The measured mercury concentration varied between 0.32 (the detection limit) and 2.93 pg g−1 (n = 160) with depth and was lower than that of summertime surface snow that was sampled simultaneously. This finding is consistent with previous observations that a bidirectional exchange of mercury between the snowpack and the atmosphere led to an increase in HgT in the surface snow during the summer. However, the contribution of the air-snow Hg exchange to the net Hg sequestration was offset by the intense re-emission of deposited mercury over the past ∼50 years. Our results demonstrate that the Antarctic Plateau snowpack is a temporary reservoir of mercury rather than a permanent sink.

Eolian deposition of trace elements onto Taylor Valley Antarctic glaciers

Abstract The major ion and trace element chemistry in four 60–110 cm deep snow pits was examined from three Antarctic Taylor Valley glaciers (Commonwealth, Canada and Howard), all located within 20 km of the Ross Sea. Taylor Valley (TV) (77°30′S, 163°15′E) is part of the McMurdo Dry Valleys (MDV), the largest ice-free area in Antarctica. Snow chemistry of these glaciers is strongly influenced by cross-valley (SW–NE and NE–SW) winds that deposit eolian materials, including mineral dust and soluble salts. Arsenic, Cd, Cu, Mo, Pb, Sb and Sn in recent TV glacier snow are almost exclusively derived from eolian dust. The relative magnitude of element variations with depth relate to the exposure of snow sites to prevalent winds. Eolian deposition is a primary source of these elements to Canada Glacier snow and supra and proglacial streams. Eolian processes are likely very important to the delivery and availability of nutrients and, potentially toxic elements to dry valley Antarctic ecosystems.

Seasonal features of aerosol particles recorded in snow from Mt. Qomolangma (Everest) and their environmental implications

To assess the seasonality of aerosol deposition and anthropogenic effects on central Himalayas, a 1.85-m deep snow pit was dug on the northern slope of Mt. Qomolangma (Everest). Based on the morphology and energy dispersive X-ray (EDX) signal, totally 1500 particles were classed into 7 groups: soot; aluminosilicates; fly ash; calcium sulfates; Ca/Mg carbonates; metal oxides; and biological particles and carbon fragments. The size distribution and number fractions of different particle groups exhibited distinct seasonal variations between non-monsoon and monsoon periods, which are clearly related to the differences in air mass pathways. Specifically, the relative abundance of soot in non-monsoon period (25%) was much higher than that in monsoon period (14%), indicating Mt. Qomolangma region received more anthropogenic influence in non-monsoon than monsoon period.

Increasing atmospheric antimony contamination in the northern hemisphere: snow and ice evidence from Devon Island, Arctic Canada

Adopting recently developed clean laboratory techniques, antimony (Sb) and scandium (Sc) deposition were measured in a 63.72 m-long ice core (1842-1996) and a 5 m deep snow pit (1994-2004) collected on Devon Island, Canadian High Arctic. Antimony concentrations ranged from 0.07 to 108 pg g(-1) with a median of 0.98 pg g(-1)(N= 510). Scandium, used as a conservative reference element, revealed that dust inputs were effectively constant during the last 160 years. The atmospheric Sb signal preserved in the ice core reflects contamination from industrialisation, the economic boom which followed WWII, as well as the comparatively recent introduction of flue gas filter technologies and emission reduction efforts. Natural contributions to the total Sb inventory are negligible, meaning that anthropogenic emissions have dominated atmospheric Sb deposition throughout the entire period. The seasonal resolution of the snow pit showed that aerosols deposited during the Arctic winter, when air masses are derived mainly from Eurasia, show the greatest Sb concentrations. Deposition during summer, when air masses come mainly from North America, is still enriched in Sb, but less so. Snow and ice provide unambiguous evidence that enrichments of Sb in Arctic air have increased 50% during the past three decades, with two-thirds being deposited during winter. Most Sb is produced in Asia, primarily from Sb sulfides such as stibnite (Sb2S3), but also as a by-product of lead and copper smelting. In addition there is a growing worldwide use of Sb in automobile brake pads, plastics and flame retardants. In contrast to Pb which has gone into decline during the same interval because of the gradual elimination of gasoline lead additives, the enrichments of Sb have been increasing and today clearly exceed those of Pb. Given that the toxicity of Sb is comparable to that of Pb, Sb has now replaced Pb in the rank of potentially toxic trace metals in the Arctic atmosphere.

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

AbstractAs 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 nssSO42–, 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.

The changes in isotope composition and accumulation of snow at Vostok station, East Antarctica, over the past 200 years

AbstractHigh-resolution records of isotope composition (δD) and accumulation of snow have been obtained from 10–12m deep snow pits dug in the vicinity of Vostok station during the 1979/80 and 1999/2000 Antarctic field seasons. We employ meteorological, balloon-sounding and snow-stake data to interpret the isotope record in terms of past temperature changes. Our reconstruction suggests that snow accumulation rate and the near-surface air temperature at Vostok have varied during the past 200 years between 15 and 30 kg m–2 a–1, and between –56 and –55˚C, respectively, with a slight general tendency to increase from the past to the present. Both parameters reveal a 50 year periodicity that correlates with the Pacific Decadal Oscillation index, implying a climatic teleconnection between central Antarctica and the tropical Pacific.

Ice core chemistry of Vestfonna Ice Cap in Svalbard, Norway

Chemical analyses were done on samples from a 2.2‐m deep snow pit and a 211‐m deep ice core that came from the top of the Vestfonna Ice Cap in Nordaustlandet, Svalbard, Norway. The snow pit samples showed that the temperature increased during the winter owing to advection of warm air from the south, and δ18O did not show a seasonal cycle. Chronology of the ice core was determined by tritium analysis and comparison to the signal from the volcanic eruption of Laki; the resulting accumulation rate was 0.34–0.35 m water eq. · yr−1 for the last 400 years. The δ18O profile in the ice core revealed a warm period from 1920 up to the present in Svalbard. According to nonseasalt (nss) SO42− and NO3− concentrations, anthropogenic substances had increased from 1940s but declined from 1970s to the present. The variation of nss SO42− and the increase of NO3− can be explained by an increase of SO2 and NOx emissions from Eurasia. The decline of NO3− is assumed to be caused either by a change in the transport process or by a change of NOx emissions from Europe.

Spatial variability of snow chemistry in western Dronning Maud Land, Antarctica

During the austral summer of 1993-94 a number of 1-2 m deep snow pits were sampled in connection with firn-coring in western Dronning Maud Land, Antarctica. The traverse went from 800 to about 3000 m a.s.l. upon the high-altitude plateau. Profiles of cations (Na+, K+, Mg2+, Ca2+), anions (Cl−, NO3-, SO4 2- , CH3SO3 −) and stable oxygen isotopes (δ18O) from 11 snow pils are presented here. Close to the coast 2 m of snow accumulates in about 2-3 years, whilst at sites on the high-altitude plateau 2 m of snow accumulates in 10—14 years. The spatial variation in ion concentrations shows that the ions can be divided into two groups, one with sea-salt elements and methane sulfonate and the other with nitrate and sulfate. For the sca-salt elements and methane sulfonate the concentrations decrease with increasing altitude and increasing distance from the coast, as well as with decreasing temperature and decreasing accumulation rate. For nitrate and sulfate the concentrations are constant or increase with respect to these parameters. This pattern suggests that the sources for sca-salt elements and methane sulfonate are local, whereas the sources for nitrate and sulfate are a mixture of local and long-range transport.

Recent climate anomalies and their impact on snow chemistry at South Pole, 1987‐1994

Three 2‐m deep snowpits sampled at South Pole in 1994 provide detailed (2‐cm resolution) profiles of the concentrations of soluble ionic species for the period 1987–1994. The most prominent feature is a large concentration spike of SO4= in snow deposited in 1992 reflecting fallout from the eruptions of Pinatubo and Hudson in 1991. Concentrations of MSA and values of the MSA/(non‐sea‐salt SO4=) ratio are elevated for about three years centered on the prominent volcanic signal. These changes appear to be due to the extended 1991–1993 El Nino. The overlapping effects of the volcanic eruptions and El Nino circulation preclude partitioning the enhanced deposition of SO4= into volcanic and biogenic fractions. Nitrate concentration profiles show no relation to the severity of O3 depletion in the Antarctic stratosphere during the period of record. Rather, the profiles show a progressive decline of the annual peak concentrations over the top 0.5–1.0 m of each pit. This behavior is attributed to post‐deposition loss of NO3−, presumably by reemission of HNO3 into the atmosphere.