Mercury in precipitated and surface snow at Dome C and a first estimate of mercury depositional fluxes during the Austral summer on the high Antarctic plateau.

Abstract. Surface mass balances of polar ice sheets are essential to estimate the contribution of ice sheets to sea level rise. Uncertain snow and firn densities lead to significant uncertainties in surface mass balances, especially in the interior regions of the ice sheets, such as the East Antarctic Plateau (EAP). Robust field measurements of surface snow density are sparse and challenging due to local noise. Here, we present a snow density dataset from an overland traverse in austral summer 2016/17 on the Dronning Maud Land plateau. The sampling strategy using 1 m carbon fiber tubes covered various spatial scales, as well as a high-resolution study in a trench at 79∘ S, 30∘ E. The 1 m snow density has been derived volumetrically, and vertical snow profiles have been measured using a core-scale microfocus X-ray computer tomograph. With an error of less than 2 %, our method provides higher precision than other sampling devices of smaller volume. With four spatially independent snow profiles per location, we reduce the local noise and derive a representative 1 m snow density with an error of the mean of less than 1.5 %. Assessing sampling methods used in previous studies, we find the highest horizontal variability in density in the upper 0.3 m and therefore recommend the 1 m snow density as a robust measure of surface snow density in future studies. The average 1 m snow density across the EAP is 355 kg m−3, which we identify as representative surface snow density between Kohnen Station and Dome Fuji. We cannot detect a temporal trend caused by the temperature increase over the last 2 decades. A difference of more than 10 % to the density of 320 kg m−3 suggested by a semiempirical firn model for the same region indicates the necessity for further calibration of surface snow density parameterizations. Our data provide a solid baseline for tuning the surface snow density parameterizations for regions with low accumulation and low temperatures like the EAP.

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Large mixing ratios of atmospheric nitrous acid (HONO) at Concordia (East Antarctic Plateau) in summer: a strong source from surface snow?

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-9963-2014 ◽

2014 ◽

Vol 14 (18) ◽

pp. 9963-9976 ◽

Cited By ~ 30

Author(s):

M. Legrand ◽

S. Preunkert ◽

M. Frey ◽

Th. Bartels-Rausch ◽

A. Kukui ◽

...

Keyword(s):

Nitrous Acid ◽

Austral Summer ◽

Vertical Gradient ◽

No Oxidation ◽

Local Source ◽

Mixing Ratio ◽

Model Calculations ◽

Antarctic Plateau ◽

Mixing Ratios ◽

Surface Snow

Abstract. During the austral summer 2011/2012 atmospheric nitrous acid (HONO) was investigated for the second time at the Concordia site (75°06' S, 123°33' E), located on the East Antarctic Plateau, by deploying a long-path absorption photometer (LOPAP). Hourly mixing ratios of HONO measured in December 2011/January 2012 (35 ± 5.0 pptv) were similar to those measured in December 2010/January 2011 (30.4 ± 3.5 pptv). The large value of the HONO mixing ratio at the remote Concordia site suggests a local source of HONO in addition to weak production from oxidation of NO by the OH radical. Laboratory experiments demonstrate that surface snow removed from Concordia can produce gas-phase HONO at mixing ratios half that of the NOx mixing ratio produced in the same experiment at typical temperatures encountered at Concordia in summer. Using these lab data and the emission flux of NOx from snow estimated from the vertical gradient of atmospheric concentrations measured during the campaign, a mean diurnal HONO snow emission ranging between 0.5 and 0.8 × 109 molecules cm−2 s−1 is calculated. Model calculations indicate that, in addition to around 1.2 pptv of HONO produced by the NO oxidation, these HONO snow emissions can only explain 6.5 to 10.5 pptv of HONO in the atmosphere at Concordia. To explain the difference between observed and simulated HONO mixing ratios, tests were done both in the field and at lab to explore the possibility that the presence of HNO4 had biased the measurements of HONO.

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Large mixing ratios of atmospheric nitrous acid (HONO) at Concordia (East Antarctic plateau) in summer: a strong source from surface snow?

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-11749-2014 ◽

2014 ◽

Vol 14 (8) ◽

pp. 11749-11785 ◽

Cited By ~ 1

Author(s):

M. Legrand ◽

S. Preunkert ◽

M. Frey ◽

T. Bartels-Rausch ◽

A. Kukui ◽

...

Keyword(s):

Nitrous Acid ◽

Austral Summer ◽

Vertical Gradient ◽

No Oxidation ◽

Local Source ◽

Mixing Ratio ◽

Model Calculations ◽

Antarctic Plateau ◽

Mixing Ratios ◽

Surface Snow

Abstract. During the austral summer 2011/2012 atmospheric nitrous acid was investigated for the second time at the Concordia site (75°06' S, 123°33' E) located on the East Antarctic plateau by deploying a long path absorption photometer (LOPAP). Hourly mixing ratios of HONO measured in December 2011/January 2012 (35 ± 5.0 pptv) were similar to those measured in December 2010/January 2011 (30.4 ± 3.5 pptv). The large value of the HONO mixing ratio at the remote Concordia site suggests a local source of HONO in addition to weak production from oxidation of NO by the OH radical. Laboratory experiments demonstrate that surface snow removed from Concordia can produce gas phase HONO at mixing ratios half that of NOx mixing ratio produced in the same experiment at typical temperatures encountered at Concordia in summer. Using these lab data and the emission flux of NOx from snow estimated from the vertical gradient of atmospheric concentrations measured during the campaign, a mean diurnal HONO snow emission ranging between 0.5 and 0.8 × 109 molecules cm−2 s−1 is calculated. Model calculations indicate that, in addition to around 1.2 pptv of HONO produced by the NO oxidation, these HONO snow emissions can only explain 6.5 to 10.5 pptv of HONO in the atmosphere at Concordia. To explain the difference between observed and simulated HONO mixing ratios, tests were done both in the field and at lab to explore the possibility that the presence of HNO4 had biased the measurements of HONO.

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Comparison of Ventilated and Unventilated Air Temperature Measurements in Inland Dronning Maud Land on the East Antarctic Plateau

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-21-0107.1 ◽

2021 ◽

Vol 38 (12) ◽

pp. 2061-2070

Keyword(s):

Austral Summer ◽

Radiative Heating ◽

Temperature Measurements ◽

Shortwave Radiation ◽

Relay Station ◽

Antarctic Plateau ◽

Temperature Bias ◽

Dronning Maud Land ◽

Weak Winds ◽

Temperature Errors

Abstract Surface temperature measurements with naturally ventilated (NV) sensors over the Antarctic Plateau are largely subject to systematic errors caused by solar radiative heating. Here we examined the radiative heating error in Dronning Maud Land on the East Antarctic Plateau using both the newly installed automatic weather stations (AWSs) at NDF and Relay Station and the existing AWSs at Relay Station and Dome Fuji. Two types of NV shields were used in these AWSs: a multiplate radiation shield and a simple cylinder-shaped shield. In austral summer, the temperature bias between the force-ventilated (FV) sensor and the NV sensor never reached zero because of continuous sunlight. The hourly mean temperature errors reached up to 8°C at noon on a sunny day with weak wind conditions. The errors increased linearly with increasing reflected shortwave radiation and decreased nonlinearly with increasing wind speed. These features were observed in both the multiplate and the cylinder-shaped shields. The magnitude of the errors of the multiplate shield was much larger than that of the cylinder-shaped shield. To quantify the radiative errors, we applied an existing correction model based on the regression approach and successfully reduced the errors by more than 70% after the correction. This indicates that we can use the corrected temperature data instead of quality controlled data, which removed warm bias during weak winds in inland Dronning Maud Land.

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The Weddell Sea region: an important precipitation channel to the interior of the Antarctic ice sheet as revealed by glaciochemical investigation of surface snow along the longest trans-Antarctic route

Annals of Glaciology ◽

10.3189/172756499781821012 ◽

1999 ◽

Vol 29 ◽

pp. 55-60 ◽

Cited By ~ 5

Author(s):

Qin Dahe ◽

Paul A. Mayewski ◽

Ren Jiawen ◽

Xiao Cunde ◽

Sun Junying

Keyword(s):

Ice Sheet ◽

Weddell Sea ◽

Sea Salt ◽

East Antarctica ◽

Antarctic Ice Sheet ◽

Air Masses ◽

Antarctic Plateau ◽

Salt Ions ◽

Surface Snow ◽

The Antarctic

AbstractGlaciochemical analysis of surface snow samples, collected along a profile crossing the Antarctic ice sheet from the Larsen Ice Shelf, Antarctic Peninsula, via the Antarctic Plateau through South Pole, Vostok and Komsomolskaya to Mirny station (at the east margin of East Antarctica), shows that the Weddell Sea region is an important channel for air masses to the high plateau of the Antarctic ice sheet (>2000 m a.s.l.). This opinion is supported by the following. (1) The fluxes of sea-salt ions such as Na+, Mg2 + and CF display a decreasing trend from the west to the east of interior Antarctica. In |eneral, as sea-salt aerosols are injected into the atmosphere over the Antarctic ice sheet from the Weddell Sea, large aerosols tend to decrease. For the inland plateau, few large particles of sea-salt aerosol reach the area, and the sea-salt concentration levels are low (2) The high altitude of the East Antarctic plateau, as well as the polar cold high-pressure system, obstruct the intrusive air masses mainly from the South Indian Ocean sector. (3) For the coastal regions of the East Antarctic ice sheet, the elevation rises to 2000 m over a distance from several to several tens of km. High concentrations of sea salt exist in snow in East Antarctica but are limited to a narrow coastal zone. (4) Fluxes of calcium and non-sea-salt sulfate in snow from the interior plateau do not display an eastward-decreasing trend. Since calcium is mainly derived from crustal sources, and nssSO42- is a secondary aerosol, this again confirms that the eastward-declining tendency of sea-salt ions indicates the transfer direction of precipitation vapor.

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Spatial variability of surface snow isotopic composition on the East Antarctic Plateau and implications for climate reconstructions

10.5194/egusphere-egu2020-13653 ◽

2020 ◽

Author(s):

Maria Hörhold ◽

Alexander Weinhart ◽

Sepp Kipfstuhl ◽

Johannes Freitag ◽

Georgia Micha ◽

...

Keyword(s):

Isotopic Composition ◽

Ice Core ◽

Empirical Relationship ◽

Ice Cores ◽

Stable Water Isotopes ◽

Antarctic Plateau ◽

Mean Temperature ◽

Spatial Coverage ◽

Surface Snow ◽

Relationship Of

<p>The reconstruction of past temperatures based on ice core records relies on the quantitative but empirical relationship of stable water isotopes and annual mean temperature. However, its relation varies through space and time. On the East Antarctic Plateau, temperature reconstructions from ice cores are poorly constrained or even fail on decadal and smaller time scales. The observed discrepancy between annual mean temperature and isotopic composition partly relies on surface processes altering the signal after deposition but also, to a great deal, on spatially coherent processes prior to or during deposition. However, spatial coverage over larger areas on the East Antarctic Plateau is challenging. We here present in-situ measurements of the isotopic composition of surface snow with unprecedented statistical quality and coverage. 1m surface snow profiles were collected during an overland traverse between Kohnen station and Plateau Station, covering a 1200km long transect. We explore regional differences of the temperature-isotope relationship and discuss possible mechanisms affecting the isotopic composition in areas with accumulation rates lower than 60mmWEa^-1.</p>

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Air–snow transfer of nitrate on the East Antarctic Plateau – Part 2: An isotopic model for the interpretation of deep ice-core records

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-12079-2015 ◽

2015 ◽

Vol 15 (20) ◽

pp. 12079-12113 ◽

Cited By ~ 17

Author(s):

J. Erbland ◽

J. Savarino ◽

S. Morin ◽

J. L. France ◽

M. M. Frey ◽

...

Keyword(s):

Mass Fraction ◽

Ice Core ◽

Ice Cores ◽

Reactive Nitrogen ◽

Antarctic Plateau ◽

Surface Snow ◽

Rate Building ◽

The Antarctic ◽

The Impact ◽

Ice Core Records

Abstract. Unraveling the modern budget of reactive nitrogen on the Antarctic Plateau is critical for the interpretation of ice-core records of nitrate. This requires accounting for nitrate recycling processes occurring in near-surface snow and the overlying atmospheric boundary layer. Not only concentration measurements but also isotopic ratios of nitrogen and oxygen in nitrate provide constraints on the processes at play. However, due to the large number of intertwined chemical and physical phenomena involved, numerical modeling is required to test hypotheses in a quantitative manner. Here we introduce the model TRANSITS (TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow), a novel conceptual, multi-layer and one-dimensional model representing the impact of processes operating on nitrate at the air–snow interface on the East Antarctic Plateau, in terms of concentrations (mass fraction) and nitrogen (δ15N) and oxygen isotopic composition (17O excess, Δ17O) in nitrate. At the air–snow interface at Dome C (DC; 75° 06' S, 123° 19' E), the model reproduces well the values of δ15N in atmospheric and surface snow (skin layer) nitrate as well as in the δ15N profile in DC snow, including the observed extraordinary high positive values (around +300 ‰) below 2 cm. The model also captures the observed variability in nitrate mass fraction in the snow. While oxygen data are qualitatively reproduced at the air–snow interface at DC and in East Antarctica, the simulated Δ17O values underestimate the observed Δ17O values by several per mill. This is explained by the simplifications made in the description of the atmospheric cycling and oxidation of NO2 as well as by our lack of understanding of the NOx chemistry at Dome C. The model reproduces well the sensitivity of δ15N, Δ17O and the apparent fractionation constants (15&varepsilon;app, 17Eapp) to the snow accumulation rate. Building on this development, we propose a framework for the interpretation of nitrate records measured from ice cores. Measurement of nitrate mass fractions and δ15N in the nitrate archived in an ice core may be used to derive information about past variations in the total ozone column and/or the primary inputs of nitrate above Antarctica as well as in nitrate trapping efficiency (defined as the ratio between the archived nitrate flux and the primary nitrate input flux). The Δ17O of nitrate could then be corrected from the impact of cage recombination effects associated with the photolysis of nitrate in snow. Past changes in the relative contributions of the Δ17O in the primary inputs of nitrate and the Δ17O in the locally cycled NO2 and that inherited from the additional O atom in the oxidation of NO2 could then be determined. Therefore, information about the past variations in the local and long-range processes operating on reactive nitrogen species could be obtained from ice cores collected in low-accumulation regions such as the Antarctic Plateau.

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Spatial Distribution of Crusts in Antarctic and Greenland Snowpacks and Implications for Snow and Firn Studies

Frontiers in Earth Science ◽

10.3389/feart.2021.630070 ◽

2021 ◽

Vol 9 ◽

Author(s):

Alexander H. Weinhart ◽

Sepp Kipfstuhl ◽

Maria Hörhold ◽

Olaf Eisen ◽

Johannes Freitag

Keyword(s):

Spatial Distribution ◽

Large Scale ◽

Accumulation Rate ◽

Sampling Site ◽

Stable Water Isotopes ◽

High Accumulation ◽

Surface Mass ◽

Antarctic Plateau ◽

Wide Range ◽

Surface Snow

The occurrence of snowpack features has been used in the past to classify environmental regimes on the polar ice sheets. Among these features are thin crusts with high density, which contribute to firn stratigraphy and can have significant impact on firn ventilation as well as on remotely inferred properties like accumulation rate or surface mass balance. The importance of crusts in polar snowpack has been acknowledged, but nonetheless little is known about their large-scale distribution. From snow profiles measured by means of microfocus X-ray computer tomography we created a unique dataset showing the spatial distribution of crusts in snow on the East Antarctic Plateau as well as in northern Greenland including a measure for their local variability. With this method, we are able to find also weak and oblique crusts, to count their frequency of occurrence and to measure the high-resolution density. Crusts are local features with a small spatial extent in the range of tens of meters. From several profiles per sampling site we are able to show a decreasing number of crusts in surface snow along a traverse on the East Antarctic Plateau. Combining samples from Antarctica and Greenland with a wide range of annual accumulation rate, we find a positive correlation (R2 = 0.89) between the logarithmic accumulation rate and crusts per annual layer in surface snow. By counting crusts in two Antarctic firn cores, we can show the preservation of crusts with depth and discuss their temporal variability as well as the sensitivity to accumulation rate. In local applications we test the robustness of crusts as a seasonal proxy in comparison to chemical records like impurities or stable water isotopes. While in regions with high accumulation rates the occurrence of crusts shows signs of seasonality, in low accumulation areas dating of the snowpack should be done using a combination of volumetric and stratigraphic elements. Our data can bring new insights for the study of firn permeability, improving of remote sensing signals or the development of new proxies in snow and firn core research.

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The multi-seasonal NO<sub>y</sub> budget in coastal Antarctica and its link with surface snow and ice core nitrate: results from the CHABLIS campaign

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-4127-2007 ◽

2007 ◽

Vol 7 (2) ◽

pp. 4127-4163 ◽

Cited By ~ 27

Author(s):

A. E. Jones ◽

E. W. Wolff ◽

D. Ames ◽

S. J.-B. Bauguitte ◽

K. C. Clemitshaw ◽

...

Keyword(s):

Boundary Layer ◽

Ice Core ◽

Austral Summer ◽

Polar Regions ◽

Low Concentrations ◽

Surface Snow ◽

Consistent Picture ◽

Antarctic Boundary Layer ◽

The Antarctic

Abstract. Measurements of individual NOy components were carried out at Halley station in coastal Antarctica. The measurements were made as part of the CHABLIS campaign (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) and cover over half a year, from austral winter 2004 through to austral summer 2005. They are the longest duration and most extensive NOy budget study carried out to date in polar regions. Results show clear dominance of organic NOy compounds (PAN and MeONO2) during the winter months, with low concentrations of inorganic NOy, but a reversal of this situation towards summer when the balance shifts in favour of inorganic NOy. Multi-seasonal measurements of surface snow nitrate correlate strongly with inorganic NOy species. One case study in August suggested that particulate nitrate was the dominant source of nitrate to the snowpack, but this was not the consistent picture throughout the measurement period. An analysis of NOx production rates showed that emissions of NOx from the snowpack dominate over gas-phase sources of "new NOx", suggesting that, for certain periods in the past, the flux of NOx into the boundary layer can be calculated from ice core nitrate data.

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Archival processes of the water stable isotope signal in East Antarctic ice cores

10.5194/tc-2017-243 ◽

2017 ◽

Cited By ~ 1

Author(s):

Mathieu Casado ◽

Amaelle Landais ◽

Ghislain Picard ◽

Thomas Münch ◽

Thomas Laepple ◽

...

Keyword(s):

Isotopic Composition ◽

Climate Models ◽

Ice Core ◽

Ice Cores ◽

Climatic Conditions ◽

Antarctic Plateau ◽

Surface Snow ◽

Rayleigh Distillation ◽

The Difference ◽

Ice Core Records

Abstract. The oldest ice core records are obtained from the East Antarctic plateau. Water isotopes records are key to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all the processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in Rayleigh distillation and isotope enabled climate models. However, a quantitative understanding of processes potentially altering the snow isotopic composition after the deposition is still missing. In low accumulation sites, such as those found in Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretation of isotopic composition. Here, we combine observations of isotopic composition in the vapour, the precipitation, the surface snow and the buried snow from Dome C, a deep ice core site on the East Antarctic Plateau. At the seasonal scale, we suggest a significant impact of metamorphism on surface snow isotopic signal compared to the initial precipitation signal. Particularly, in summer, exchanges of water molecules between vapour and snow are driven by the sublimation/condensation cycles at the diurnal scale. Using highly resolved isotopic composition profiles from pits in five Antarctic sites, we identify common patterns, despite different accumulation rates, which cannot be attributed to the seasonal variability of precipitation. Altogether, the difference in the signals observed in the precipitation, surface snow and buried snow isotopic composition constitute evidences of post-deposition processes affecting ice core records in low accumulation areas.

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