S4 Mercury in the Arctic

Thursday, 28 July, 2011

RS4-P1 — 11:00-12:00 and 17:30-18:30
Authors: AMYOT, Marc1, GIRARD, Catherine 1, LAURION, Isabelle2, LECLERC, Maxime1
(1) Université de Montréal, m.amyot@umontreal.ca; (2) INRS-ETE;

Some Arctic freshwater systems have high levels of aqueous monomethylmercury (MMHg), and our recent survey of 27 thaw ponds and 7 lakes reported levels ranging from 0.02 to 18.2 ng/L for MMHg. The highest concentrations of MMHg were mostly found in runnels (ponds formed over melting ice wedges) and are considered extreme compared to levels in natural aquatic systems. Photodemethylation of MMHg into inorganic mercury (Hg) has been shown to represent a major degradation pathway for this contaminant in Arctic freshwater ecosystems. In 2008-2010, in situ incubation experiments were performed in selected lakes and runnel ponds on Cornwallis and Bylot Islands (Nunavut) to assess photodemethylation potential in these natural waters. Natural water exposed to continuous sunlight for 7 days during the Arctic summer presented considerably lower concentrations of MMHg (losses of 34-63% of MMHg after one week) than water incubated in the dark. The process was shown to be abiotic, being unaffected by filtration, and appeared to be mediated more effectively by short wavelengths of solar radiation (UV-A, UV-B). Moreover, MMHg has been previously shown to interact closely with sulfur-containing compounds and reactive oxygen species, these molecules potentially playing an important role in photodemethylation. Sulfur compounds (glutathione) and reactive oxygen species (singlet oxygen, radical OH) were added both in field and laboratory incubations of natural waters to investigate their role in mediating photodemethylation, and seemed to accelerate it in all cases. We conclude that photodemethylation in Arctic freshwater ecosystems is most effectively mediated by wavelengths <410nm, and that sulfur-rich compounds and reactive oxygen species play an important role in chemical exchanges leading to in situ loss of MMHg through solar irradiation.

RS4-P2 — 11:00-12:00 and 17:30-18:30
Authors: TOYOTA, Kenjiro1, DASTOOR, Ashu2, MCCONNELL, John C.3
(1) Air Quality Research Division, Environment Canada, Toronto, Ontario, Canada, kenjiro.toyota@ec.gc.ca; (2) Air Quality Research Division, Environment Canada, Dorval, Quebec, Canada; (3) Department of Earth and Space Science and Engineering, York University, Toronto, Ontario, Canada.

Snowpack on sea ice and coastal land surface in the polar region is an active source of reactive halogen species to the overlying atmosphere, particularly during the spring when substantial decrease in the mixing ratios of ozone and gaseous elemental mercury (GEM) occurs frequently in the near-surface air via photochemical loss involving halogen radicals. During such episodes, GEM is transformed to oxidized forms, collectively called “reactive gaseous mercury” (RGM), followed by rapid deposition to the sea/land surface directly or after taken up by particulate matters. However, it is not well understood how much of these mercury species actually pose a threat to the ecosystem and indigenous people in the polar region, because mercury in the snow and the surface water is reduced photochemically (as well as biologically) and released back to the atmosphere as GEM on the timescale of hours to weeks. In the snow, chloride and bromide appear to stabilize oxidized mercury via mercury-halide complex formation, whereas dissolved organic matters (DOMs) appear to facilitate the reduction of oxidized mercury. But exact reaction mechanisms are not fully elucidated.

We have developed a one-dimensional model, which describes the transport of trace gases between the snowpack and the overlying atmosphere as well as their photochemical reactions in the gas phase and in the condensed phase of aerosols and snowpack. Vertical diffusivity in the lowest hundred meters of the atmosphere is diagnosed empirically from surface wind speed and heat flux. Gas transport in the snowpack interstitial air is represented by a combination of molecular diffusivity and wind-pumping advection. Model runs are performed to show that a strong surface wind promotes turbulent mixing in the boundary layer and the pumping of air in the snowpack and, consequently, reactive halogen release from the snowpack. Ozone and GEM are both lost rapidly via reactions with bromine atoms in the atmospheric boundary layer and, depending on the assumed fate of key radical species against gas-to-snow uptake, in the snowpack interstitial air as well. The effect of DOMs is represented by a combination of one-step, first-order photolysis reactions of mercury-DOM complexes of varying complexation stability. Model sensitivity is explored with regard to concentration profiles of halides and DOMs in the snow as well as the type of DOMs interacting with mercury, in order to provide insights into the fate of mercury after its deposition to the polar snow.

RS4-P3 — 11:00-12:00 and 17:30-18:30
Authors: KADING, Tristan1, ANDERSSON, Maria2
(1)WHOI, tkading@whoi.edu; (2) University of Gothenburg.

During the 2005 Beringia expedition, sediment samples were collected from 10 sampling locations transecting the Arctic Ocean encompassing coastal, basin, and ridge sites using a multi core. The upper 20 centimeters of sediment was collected and analyzed for total mercury and methyl mercury. The distribution of mercury in Arctic Ocean surface sediments shows a large degree of geographic variability. The measured total mercury concentrations ranged from 6 to 136 ng g-1. There was also variability in the total mercury concentrations within each core. All sites except two showed a decrease in total mercury from the sediment water interface downwards. Five sites show a significant peak in concentration at depths ranging from 6 to 20 cm. Results for methyl mercury will also be presented.

RS4-P4 — 11:00-12:00 and 17:30-18:30
Authors: COLE, Amanda1, STEFFEN, Alexandra1, POISSANT, Laurier1, PILOTE, Martin1, PFAFFHUBER, Katrine Aspmo2, BERG, Torunn3
(1) Environment Canada, amanda.cole@ec.gc.ca; (2) 3. Norwegian Institute for Air Research; (3) Norwegian Institute of Science and Technology.

As emissions of mercury throughout the world continue to change and the Arctic undergoes changes in the landscape such as shrinking permanent sea ice, continuous monitoring of mercury provides important information about long-term changes in the transport, chemistry, and deposition of this atmospheric pollutant in the Arctic environment. Ten-year records of gaseous elemental mercury were analyzed from two Arctic sites – Alert, Nunavut, Canada (82.5oN, 62.3oW) and Zeppelin Station, Svalbard, Norway (78.9oN, 11.9oE); one sub-Arctic site – Kuujjuarapik, Québec, Canada (55.3oN, 77.7oW); and one temperate site – St. Anicet, Québec, Canada (45.1oN, 74.3oW). Trends over the period 2000-2009 were calculated using the seasonal Kendall test for trend and Sen’s estimator of slope. Overall trends based on the entire data set were: -0.4% to -1.6% per year at Alert, -0.4% to +0.8% per year at Zeppelin, -1.0% to -2.8% per year at Kuujjuarapik, and -1.8% to -2.1% per year at St. Anicet. Trends at the lower-latitude Québec sites agree well with the reported decrease in background GEM concentration at Mace Head, Ireland of -1.6% to -2.0% per year over the period 1996-2009 (Ebinghaus et al., 2011). The rate of decrease at Alert is faster over this 10-year period than was found for 1995-2007, but is still slower than the lower latitude sites. Finally, there was no significant trend at Zeppelin Station. Possible reasons for differences in seasonal and overall trends at the Arctic sites compared to those at lower latitudes are discussed, as well as implications for the Arctic mercury cycle.

RS4-P5 — 11:00-12:00 and 17:30-18:30
Authors: LESCORD, Gretchen L.1, KIDD, Karen A.1, MUIR, Derek C.G.2, KIRK, Jane2, O’DRISCOLL, Nelson3
(1) University of New Brunswick/Canadian Rivers Institute, gretchen.lescord@unb.ca; (2) Environment Canada/CCIW; (3) Acaidia University.

Mercury (Hg) concentrations in landlocked Arctic char (Salvelinus alpinus) in the Canadian High Arctic can vary up to 4-fold between neighboring populations. In lower latitude systems, physical and chemical features such as catchment area, dissolved organic carbon (DOC), pH, surface area, and wetland inputs affect Hg uptake and transfer through lake food webs. Despite the many contaminant studies done on high latitude systems, it is not well known how differences in abiotic characteristics or food web structure in these lakes affects Hg concentrations in char. Arctic lakes receive most of their Hg from wet deposition and the input of summer snowmelt, which are affected by the system’s catchment and surface areas. It is also possible that food chain length or feeding ecology (i.e. benthic versus pelagic) affect Hg uptake and biomagnification through these food webs, as in more southerly systems. This study is comparing Hg concentrations in the food webs of six lakes on Cornwallis Island, Nunavut, each with differing physical and chemical features. For example, lake areas, DOC, and chlorophyll a concentrations range between 0.13-1.3 km2, 0.59 -2.08 mg/L, and 0.05-1.10 µg/L, respectively. The lakes were sampled repeatedly (~ 3 times over the field season) for sediments and biota during and after the annual spring melt in 2010. Water samples were collected weekly to assess temporal changes in Hg concentrations in relation to snowmelt. All samples are being analyzed for methyl Hg (MeHg; and total Hg in fish) and the food web will be characterized using stable isotopes; nitrogen isotopes are used to assess trophic level and carbon and sulfur isotopes are used to assess energy source (benthic, pelagic, profundal, terrestrial). Preliminary results show significant differences in mean total Hg concentrations (µg/g, wet wt.) in char between these lakes (Kruskal-Wallis p<0.001). Stable isotope analyses of the organisms and MeHg of the lower-trophic-level biota and abiotic samples are ongoing. Rates of Hg biomagnification through the food web will be quantified by regressing log MeHg versus nitrogen isotopes and these relationships will be compared against results from other studies. Multivariate analyses will also be performed to determine the factors that best predict Hg concentrations in char. Results from this study will improve our understanding of the variability in fish Hg in High Arctic lakes and critical baseline information for future studies on how these systems are changing in response to climate change.

RS4-P6 — 11:00-12:00 and 17:30-18:30
Authors: VOGEL, Nicolas1, DOMMERGUE, Aurelien1, FERRARI, Christophe1, PREUNKERT, Susanne1, JOURDAIN, Bruno1
(1) Laboratoire de Glaciologie et Géophysique de l’Environnement, Université Joseph Fourier Grenoble/CNRS,

While the tropospheric reactivity of mercury in the Arctic is more and more documented only a few attempts were made to study the Hg cycle in the Southern Polar Regions. Following Schroeder et al. (1998) study, AMDEs were observed in Coastal Antarctica after polar sunrise at Neumayer and Terra Nova Bay (Ebinghaus et al., 2002b; Sprovieri et al., 2002). The study of the Hg cycling in Antarctica is first necessary to understand and follow the extent of the contamination within these ecosystems. Mercury concentrations in biota of some Arctic areas are known to have increased with time (Dietz et al., 2009) and to be rather high. In Antarctica, available data on Hg concentrations in water, sediments, phytoplankton, macroalgae, krill and several species of benthic invertebrates compiled by Bargagli et al. (2008) indicate that there is no enhanced bioavailability of Hg in the Southern Ocean food web. However, recent studies showed an enhanced Hg bioaccumulation in terrestrial ecosystem samples collected close to Terra Nova Bay (Bargagli et al., 2005), suggesting that local deposition events of Hg may impact these ecosystems. There is a clear lack of long-term data in Antarctica.

In February 2010, we initiated continuous gaseous elemental mercury (GEM) measurements at Dumont D’Urville in Antarctica (66°40’S - 140°01’E, 40 masl). DDU is mainly influenced by oceanic air masses, continental air masses from South America, and air masses from the central Antarctic Plateau, where a strong Hg reactivity has already been observed. Here we present 1 year record of GEM, ozone, met data at DDU. We found that the Hg reactivity was significantly different from that observed at Neumayer. An intense reactivity was observed during summer time with daily cycling of GEM and short depletion events of short duration were daily observed.

RS4-P8 — 11:00-12:00 and 17:30-18:30
Authors: KIRK, Jane1, ST. LOUIS, Vincent2, MUIR, Derek1, LEHNHERR, Igor2, LAMOUREUX, Scott3, LEWIS, Ted 3, STEWART, Kailey3, IQALUK, Debbie4, TUNKS, Carolyn1, LAWSON, Greg1
(1) Environment Canada, Jane.Kirk@ec.gc.ca; (2) University of Alberta; (3) Queen’s University; (4) Resolute Bay;

We are examining the impact of climate change on the release of terrestrial mercury (Hg) to two adjacent Canadian Arctic lakes (West and East) on Melville Island, Nunavut, which are undergoing climate-related changes at different rates. The West catchment, for example, experienced numerous active layer detachments during the summers of 2007 and 2008 due to record 2007 summer temperatures and rainfall while the East catchment experienced only minor disturbances. To assess the impacts of climate-induced changes on the release of Hg from the lake catchments and on the subsequent bioaccumulation of this Hg through aquatic foodwebs, water from the lake and its inflows, arctic char (Salvelinus alpinus), and invertebrates were collected for analysis of total Hg (THg) and MeHg between 2007-2010. Sediment cores were also obtained from 10 locations in each lake to quantify changes to sedimentation and THg deposition rates over time. Preliminary calculation of total Hg exports to the lakes from their major inflows indicate that 2008-2010 West River exports are on average ~20% higher than those from East River (76±12 and 63±5 g/year, respectively). Exports of methyl Hg (MeHg), were low and similar among the two rivers in all three years (0.4±0.2 and 0.4±0.2 g/year for West and East rivers, respectively). Detailed lake Hg profiles were obtained in 2010 and demonstrated that unfiltered THg concentrations in West Lake are almost double those in East Lake (1.3±0.6 and 0.8±0.4 ng/g, respectively), while filtered THg concentrations are similar (0.5±0.5 and 0.4±0.2 ng/g, respectively), indicative of greater terrestrial Hg inputs from climate-induced erosion of the West catchment. Interestingly, Hg concentrations in West Lake Arctic char were significantly higher than those in East Lake (0.15 and 0.10 ug/g, respectively, p=0.03). We currently hypothesize that differences in char growth rates and/or feeding patterns are resulting in char Hg concentrations differences among the two lakes as char in West Lake were larger (N=26; 447±147 g versus N=17; 327±80 g), had less depleted d13C (-25.0±1.6 versus -27.2±0.53‰, p<0.001) and lower d15N (9.99±0.79 versus 10.98±0.35‰, p<0.001). In fact, after adjusting char Hg concentrations for d15N, the Hg concentration difference among char of the two lakes became more significant (adjusted means = 0.174 and 0.081 ug/g, for West and East respectively, p<0.001). Analysis of food web samples and lake MeHg samples should provide further insights and will be presented along with results from sediment core analyses.

Thursday, 28 July, 2011