Article pubs.acs.org/est
Seasonal Study of Mercury Species in the Antarctic Sea Ice Environment Michelle G. Nerentorp Mastromonaco,*,† Katarina Gårdfeldt,† Sarka Langer,‡ and Aurélien Dommergue§ †
Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden IVL Swedish Environmental Research Institute, P.O. Box 53021, SE-400 14 Göteborg, Sweden § Laboratoire de Glaciologie et Géophysique de l’Environnement, CNRS, UMR 5183 − Université Joseph Fourier Grenoble, 54 Rue Molière, 38400 St Martin d’Hères, France ‡
S Supporting Information *
ABSTRACT: Limited studies have been conducted on mercury concentrations in the polar cryosphere and the factors affecting the distribution of mercury within sea ice and snow are poorly understood. Here we present the first comprehensive seasonal study of elemental and total mercury concentrations in the Antarctic sea ice environment covering data from measurements in air, sea ice, seawater, snow, frost flowers, and brine. The average concentration of total mercury in sea ice decreased from winter (9.7 ng L−1) to spring (4.7 ng L−1) while the average elemental mercury concentration increased from winter (0.07 ng L−1) to summer (0.105 ng L−1). The opposite trends suggest potential photoor dark oxidation/reduction processes within the ice and an eventual loss of mercury via brine drainage or gas evasion of elemental mercury. Our results indicate a seasonal variation of mercury species in the polar sea ice environment probably due to varying factors such as solar radiation, temperature, brine volume, and atmospheric deposition. This study shows that the sea ice environment is a significant interphase between the polar ocean and the atmosphere and should be accounted for when studying how climate change may affect the mercury cycle in polar regions.
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dissolved gaseous mercury (DGM),21−23 which during super saturated conditions partly re-emits back into the atmosphere as GEM.24 Despite reduction, re-emission, and demethylation processes, around 40 tons of MeHg is estimated to accumulate in Arctic marine food chains annually and the trend is increasing,17,18,25. Even though Antarctica is more remote, high levels of MeHg have been observed in Antarctic biota.26 Sea ice consists of frozen seawater, brine, gases, minerals, particles, and biota.6,7 Three major processes by which Hg can enter sea ice are suggested by Chaulk et al.6: freeze rejection from underlying seawater, scavenging of Hg in air (by noncovered ice surfaces), and leaching from an overlaying snow cover. Freeze rejection is due to dissolved species within the ice being rejected during the freezing process, forming a crystal matrix. This process leads to an enrichment of dissolved species in brine pockets,6 which can connect to each other to form brine channels within the ice.27 Scavenging of atmospheric Hg occurs when frost flowers are formed or when the top layer of newly formed sea ice is exposed to the atmosphere.6 During AMDEs, a large portion of deposited Hg(II) on surface snow has been found to generally be photoreduced to elemental
INTRODUCTION Because of climate change, the sea ice extents in the Arctic and in Antarctica experience rapid changes.1,2 The role of sea ice for the cycling of the toxic pollutant mercury (Hg) in polar regions has in recent global models been acknowledged to be important due to its capacity to reduce re-evasion of Hg from sea surfaces and its potential to be a Hg reservoir.3−5 However, only limited studies have been performed on Hg in the sea ice environment, which results in insufficient data contributions for future modeling.6,7 The environmental cycling of Hg is dynamic and complex8 and gaseous elemental mercury (GEM) emitted to air can reach polar regions within days. Oxidized Hg in air is quickly dry and wet deposited onto nearby surfaces and is an important source of mercury input into polar oceans.9−12 Events of enhanced atmospheric oxidation are frequent during springtime in polar regions during atmospheric mercury depletion events (AMDEs) when photoproduced halogen radicals oxidize GEM in air, causing increased deposition.10,11,13−15 Other sources of Hg to polar oceans are oceanic transportation, lake and riverine inputs, costal sediment erosion, movement of biota, and melting ice, snow, and permafrost.5,16−19 Dissolved oxidized Hg in seawater can be transformed by microorganisms into the neurotoxic and bio-accumulative organic form methylmercury (MeHg).20 Divalent mercury (Hg(II)) can be reduced by biotic and abiotic processes to © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
May 30, October October October
2016 20, 2016 25, 2016 26, 2016 DOI: 10.1021/acs.est.6b02700 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
calculated by Poissant et al.34 to be 0.06 ng m−3 and regular calibrations were performed by using the internal calibration source and by manual injections from an external calibration source. Maintenance of the instrument was performed following the recommendations and directives of the standard operational procedure (SOP) developed by the GMOS project (Global Mercury Observation System (www.gmos.eu)). Field Sampling. During the winter and spring campaigns, a Mark II coring system from Kovacs Enterprise (http:// kovacsicedrillingequipment.com/) was used to sample ice cores. The bore core had a diameter of 9 cm and consisted of an aluminum cutting shoe and cutting teeth in stainless steel (SI Figure S1). During the summer expedition a stainless steel ice corer with a diameter of 12 cm was used. All ice cores were sampled in a clean area and overlaying snow was sampled using an acid-rinsed plastic shovel. The ice and snow samples for Hg(0) analysis were immediately put in blank-tested LDPE bags for transportation to the lab onboard (SI, S3). The temperature and the salinity of the ice was measured in reference ice cores, see SI, S3. A few sample cores that were not immediately prepared for analysis were stored for a short period (
