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
Introduction
Mercury once emitted into the atmosphere from natural or anthropogenic sources can travel around the globe to be deposited onto soils, into waters (in liquid or solid form) and plants (United Nations Environment Program, 2018). The dominant form in the atmosphere is Hg0, which is estimated to have an atmospheric lifetime of 0.5–1.7 years (Holmes et al., 2006) allowing plenty of time to reach the Poles (Angot et al., 2016a) and the high Antarctic plateau.
The role of the Antarctic plateau in the global mercury cycle was relatively unknown until Brooks (Brooks et al., 2008) carried out the first measurements between November and December 2003 and in November 2005 at the South Pole. They found near surface atmospheric concentrations of gaseous elemental mercury (GEM) of 539 ± 189 pg (Hg) m−3, 344 ± 151 pg m−3 of reactive gaseous mercury (RGM) and mean Hg concentrations in surface snow of 198 ng L−1 that diminished to 10 ng L−1 at a depth of 25 cm. From above and below surface measurements they showed an estimated GEM surface emission flux of +8.1 ng m−2 h−1 and an RGM deposition flux of – 10.8 ng m−2 h−1. From these measurements they were able to estimate a mercury lifetime in the snow of 16 days and calculated that the entire Antarctic plateau could sequester up to 60 tonnes of Hg per year, effectively acting as a giant sink. These high concentrations of Hg in surface snow were confirmed by Angot et al. (2016c) at Concordia station, the joint French/Italian base on the East Antarctic ice sheet at Dome C. The authors reported evidence of intense oxidation of atmospheric Hg0 during the austral summer with photochemical reactions and exchanges happening at the air-snow interface. They observed multi-day to weeklong atmospheric Hg depletion events in summer that were not associated with ozone loss, indicating possible dry deposition during air mass stagnation events. These air masses then descend towards the coast with the katabatic winds (Angot et al., 2016b) provoking large variability in summer Hg0 values and elevated deposition of mercury in surface snow, suggesting that the Antarctic ice sheet can affect the mercury cycle on a continental scale.
Studies on temporal variations of Hg concentrations in the snowpack at Dome C (Spolaor et al., 2018) have shown that within 6 h after precipitation, surface snow Hg concentrations can drop from 200 pg g−1 to 20 pg g−1, showing that high concentrations can be deposited by snowfall and then be rapidly released back into the atmosphere. This is supported by concurrent atmospheric Hg0 increases from 0.5 to 1.5 ng m−3 under stable low wind speed atmospheric conditions. The converse was also found to be true, during a diamond dust deposition event. It should be noted that diamond dust is a type of precipitation composed of slowly falling, very small, unbranched crystals of ice that form under very low air temperatures such as those found at Dome C. During such an event, atmospheric Hg0 dropped from 1.5 to 0.5 ng m−3, accompanied by an increase in surface snow concentrations from 20 to 80 pg g−1, suggesting the role of diamond dust as an Hg scavenger. These combined results showed the importance of freshly deposited snow/diamond dust or frost as potential Hg atmospheric scavengers on the Antarctic plateau.
The aim of this study is to build on this work and investigate the contribution of the mercury deposition flux to mercury concentrations in surface and subsurface snow over a summer campaign. This was done by determining the Hg concentrations in wet deposition (snow, frost and diamond dust) and surface and subsurface snow on a daily basis. The effects of local meteorological conditions on variations in mercury concentrations were then studied. Since the Antarctic plateau is essentially a frozen desert, it is important to collect freshly deposited snow to investigate whether dry deposition is an important process, or whether evasion of Hg from the snowpack is dominant. This work tries to estimate whether net dry deposition occurred during the 2017–2018 sampling campaign and provides a first estimate for the snow Hg scavenging factor to help with modelling efforts in the future.
Section snippets
Concordia station
Concordia station is a research station jointly run by France and Italy. It is located at Dome C, one of the “summits” of the East Antarctic ice sheet at an elevation of 3220 m above sea level and over 1200 km from the coast (Fig. 1a). The mean annual temperature at the site is −54.5 °C (Stenni et al., 2016) but meteorological observations show a maximum of −14 °C during summer and a minimum of −85 °C during winter. Generally the weather at Dome C is dominated by a high pressure system
Surface snow mercury concentrations, temperature, and meteorological data
The results for the daily surface snow sampling can be seen in Fig. 2, showing that surface snow has mercury concentrations greater than subsurface snow until around the 28th of December, except for a spike between the 17th to 19th of December. This trend breaks with subsurface snow being more concentrated in mercury than surface snow from the 28th of December to the 8th of January. After this, to the end of the experiment, the surface and subsurface values are similar.
These results can be
Conclusions and future work
During the 2017–2018 Antarctic summer, surface and subsurface snow as well as snow deposition was sampled every day. A mean surface snow Hg concentration of 9.5 ± 13 (standard deviation (SD) n = 82) ng kg−1 was found, and the subsurface snow (3–6 cm deep) had a mean concentration of 6.7 ± 11 ng kg−1 (1 SD n = 81). These concentrations were then corrected with the snow density to make them more comparable. At the same time, atmospheric Hg (Hg0 and RM), ozone and other parameters were measured.
Funding
QAed/Qced DMC GEM data, accessible in GMOS-FR national database (https://gmos.aeris-data.fr/) and from the G-DQM central database system of GMOS/GOS4M (https://www.gmos.eu/sdi/), have been collected through fundings obtained by the European Union 7th Framework Programme project Global Mercury Observation System (GMOS, 2010–2015), LabEX OSUG@2020 (ANR10 LABX56), LEFE CNRS/INSU as well as from French Polar Institute (IPEV) via GMOStral-1028 IPEV program since 2012.
This project has received
Data
Concordia (DCC) L2 GEM data are freely available at https://gmos.aeris-data.fr/. Automatic weather station, radiosounding and sub surface temperature data are freely available at www.climantartide.it under request.
Using the mercury flux model in section 3.2, the fit intercept q represents J dry = v dry *c air while the slope m = k*c air. m has units of ng Hg g−1 of snow while q has units of ng Hg m −2 day −1.
CRediT authorship contribution statement
Clara Turetta: Investigation. Niccolò Maffezzoli: Investigation, Validation. Olivier Magand: Investigation, Writing – original draft. Beatriz Ferreira Araujo: Investigation. Hélène Angot: Writing – original draft. Delia Segato: Formal analysis. Paolo Cristofanelli: Investigation, Writing – original draft. Francesca Sprovieri: Funding acquisition. Claudio Scarchilli: Writing – original draft, Validation. Paolo Grigioni: Investigation. Virginia Ciardini: Investigation. Carlo Barbante: Project
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
These observations contribute to the GEO GOS4M (Global Observation System for Mercury (www.gos4m.org). It is aimed to support the UN Global Partnership on Mercury Fate and Transport Research (UN F&T) of the UN environment in the implementation of the Minamata Convention (www.mercuryconvention.org) by providing a Knowledge Platform on mercury in environment and the human health. It will support UN environment and Nations to assess the effectiveness of measures that will be undertaken. Data and
References (47)
- et al.
Determination of volatile mercury species at the picogram level by low-temperature gas chromatography with cold-vapour atomic fluorescence detection
Anal. Chim. Acta
(1988) - et al.
Antarctic polar plateau snow surface conversion of deposited oxidized mercury to gaseous elemental mercury with fractional long-term burial
Atmos. Environ.
(2008) - et al.
GEM fluxes and atmospheric mercury concentrations (GEM, RGM and Hgp) in the Canadian Arctic at Alert, Nunavut, Canada (February-June 2005)
Atmos. Environ.
(2007) - et al.
Analysis of multi-year near-surface ozone observations at the WMO/GAW “Concordia” station (75°06″S, 123°20″E, 3280 m a.s.l. – Antarctica)
Atmos. Environ.
(2018) - et al.
The accuracy of the vapour-injection calibration method for the determination of mercury by amalgamation/cold-vapour atomic absorption spectrometry
Anal. Chim. Acta
(1985) A climatology of wet deposition scavenging ratios for the United States
Atmos. Environ.
(2005)- et al.
Fluxes of reactive gaseous mercury measured with a newly developed method using relaxed eddy accumulation
Atmos. Environ.
(2006) - et al.
Feedback mechanisms between snow and atmospheric mercury: results and observations from field campaigns on the Antarctic plateau
Chemosphere
(2018) A theory for the scalar roughness and the scalar transfer coefficients over snow and sea ice
Boundary-Layer Meteorol.
(1987)- et al.
Chemical cycling and deposition of atmospheric mercury in polar regions: review of recent measurements and comparison with models
Atmos. Chem. Phys.
(2016)
Multi-year record of atmospheric mercury at Dumont d'Urville, East Antarctic coast: continental outflow and oceanic influences
Atmos. Chem. Phys.
New insights into the atmospheric mercury cycling in central Antarctica and implications on a continental scale
Atmos. Chem. Phys.
Snow/atmosphere coupled simulation at Dome C, Antarctica
J. Glaciol.
Parameterization of clear sky effective emissivity under surface-based temperature inversion at Dome C and South Pole, Antarctica
Antarct. Sci.
Observed and modelled convective mixing-layer height at Dome C, Antarctica
Boundary-Layer Meteorol.
Data quality through a web-based QA/QC system: implementation for atmospheric mercury data from the global mercury observation system
Environ. Sci. Process. Impacts
A review of flux-profile relationships
Boundary-Layer Meteorol.
Millennial changes in North American wildfire and soil activity over the last glacial cycle
Nat. Geosci.
Subnanogram determination of mercury by two-stage gold amalgamation and gas phase detection Applied to atmospheric analysis
Anal. Chem.
Spatial and temporal variability of snow accumulation in East Antarctica from traverse data
J. Glaciol.
Meteorological and snow accumulation gradients across Dome C, East Antarctic plateau
Int. J. Climatol.
Global lifetime of elemental mercury against oxidation by atomic bromine in the free troposphere
Geophys. Res. Lett.
Applied modeling of the nighttime surface energy balance over land
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