G A Stern

University of Manitoba, Winnipeg, Manitoba, Canada

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Publications (157)414.65 Total impact

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    ABSTRACT: The Canadian Arctic has vast freshwater resources, and fish are important in the diet of many Northerners. Mercury is a contaminant of concern because of its potential toxicity and elevated bioaccumulation in some fish populations. Over the last decade, significant advances have been made in characterizing the cycling and fate of mercury in these freshwater environments. Large amounts of new data on concentrations, speciation and fluxes of Hg are provided and summarized for water and sediment, which were virtually absent for the Canadian Arctic a decade ago. The biogeochemical processes that control the speciation of mercury remain poorly resolved, including the sites and controls of methylmercury production. Food web studies have examined the roles of Hg uptake, trophic transfer, and diet for Hg bioaccumulation in fish, and, in particular, advances have been made in identifying determinants of mercury levels in lake-dwelling and sea-run forms of Arctic char. In a comparison of common freshwater fish species that were sampled across the Canadian Arctic between 2002 and 2009, no geographic patterns or regional hotspots were evident. Over the last two to four decades, Hg concentrations have increased in some monitored populations of fish in the Mackenzie River Basin while other populations from the Yukon and Nunavut showed no change or a slight decline. The different Hg trends indicate that the drivers of temporal change may be regional or habitat-specific. The Canadian Arctic is undergoing profound environmental change, and preliminary evidence suggests that it may be impacting the cycling and bioaccumulation of mercury. Further research is needed to investigate climate change impacts on the Hg cycle as well as biogeochemical controls of methylmercury production and the processes leading to increasing Hg levels in some fish populations in the Canadian Arctic.
    Science of The Total Environment 06/2014; · 3.26 Impact Factor
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    ABSTRACT: This review summarizes data and information which have been generated on mercury (Hg) in the marine environment of the Canadian Arctic since the previous Canadian Arctic Contaminants Assessment Report (CACAR) was released in 2003. Much new information has been collected on Hg concentrations in marine water, snow and ice in the Canadian Arctic. The first measurements of methylation rates in Arctic seawater indicate that the water column is an important site for Hg methylation. Arctic marine waters were also found to be a substantial source of gaseous Hg to the atmosphere during the ice-free season. High Hg concentrations have been found in marine snow as a result of deposition following atmospheric mercury depletion events, although much of this Hg is photoreduced and re-emitted back to the atmosphere. The most extensive sampling of marine sediments in the Canadian Arctic was carried out in Hudson Bay where sediment total Hg (THg) concentrations were low compared with other marine regions in the circumpolar Arctic. Mass balance models have been developed to provide quantitative estimates of THg fluxes into and out of the Arctic Ocean and Hudson Bay. Several recent studies on Hg biomagnification have improved our understanding of trophic transfer of Hg through marine food webs. Over the past several decades, Hg concentrations have increased in some marine biota, while other populations showed no temporal change. Marine biota also exhibited considerable geographic variation in Hg concentrations with ringed seals, beluga and polar bears from the Beaufort Sea region having higher Hg concentrations compared with other parts of the Canadian Arctic. The drivers of these variable patterns of Hg bioaccumulation, both regionally and temporally, within the Canadian Arctic remain unclear. Further research is needed to identify the underlying processes including the interplay between biogeochemical and food web processes and climate change.
    Science of The Total Environment 06/2014; · 3.26 Impact Factor
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    ABSTRACT: We show 2008 seasonal trends of total and mono-methyl mercury (THg and MeHg, respectively) in herbivorous (Calanus hyperboreus) and predatory (Chaetognaths, Paraeuchaeta glacialis and Themisto abyssorum) zooplankton species from the Canadian High Arctic (Amundsen Gulf and the Canadian Beaufort Sea) in relation to ambient seawater and diet. It has recently been postulated that the Arctic marine environment may be exceptionally vulnerable to toxic MeHg contamination through post-depositional processes leading to mercury transformation and methylation. Here, we show that C. hyperboreus plays a hitherto unrecognized central role in mercury transformation while, itself, not manifesting inordinately high levels of THg compared to its prey (pelagic particulate organic matter (POM)). Calanus hyperboreus shifts Hg from mainly inorganic forms in pelagic POM (> 99.5%) or ambient seawater (> 90%) to primarily organic forms (> 50%) in their tissue. We calculate that annual dietary intake of MeHg could supply only ~30% of the MeHg body burden in C. hyperboreus and, thus, transformation within the species, perhaps mediated by gut microbial communities, or bioconcentration from ambient seawater likely play overriding roles. Seasonal THg trends in C. hyperboreus are variable and directly controlled by species-specific physiology, e.g. egg laying and grazing. Zooplankton that prey on species such as C. hyperboreus provide a further biomagnification of MeHg and reflect seasonal trends observed in their prey.
    Environmental science & technology. 06/2014;
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    ABSTRACT: This paper synthesizes the sediment geochemistry data for 19 sediment cores from 16 lakes from various regions of Canada to describe general relationships between mercury (Hg) and the relative amount of labile organic matter (OM) as a proportion of total organic carbon. These relationships form the basis for proposing a general classification scheme of the capacity of a lake system to bind Hg to OM, which provides a first order screening of lakes to quickly assess them before further detailed analytical methods are employed. Mercury is known to have a strong affinity to OM before entering the lakes (binding with soil OM in the watershed) and also within the lakes (scavenging by autochthonous OM). Association of Hg with particulate OM, irrespective of the source, effectively captures available Hg (II) and ultimately sequesters it in bottom sediments. Relationships between total Hg concentration and the relative amount of labile OM in the sediments of a given system reveal important geochemical information; for example, the overall capacity of the system to effectively scavenge and fix available Hg, or its vulnerability to be overwhelmed by excess inputs of Hg in organic-poor or Hg contaminated systems.
    Chemical Geology. 01/2014;
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    ABSTRACT: A combination of Rock-Eval pyrolysis and isotopic analyses is used to characterize the sources and distribution of organic matter in modern marine sediments from the subarctic Hudson Bay (including Hudson Strait and Foxe Basin), Canada. This approach reveals organic matter contributions from both marine and terrigenous sources, with spatial patterns and varying degrees of degradation that are consistent with inferences from traditional geochemical tracers for modern organic matter. Rock-Eval parameters characterize Hudson Bay organic matter with low hydrogen index, high oxygen index and a high degree of residual carbon that suggests heavily reworked materials. Locations of higher primary productivity in Hudson Strait, Foxe Basin, the northeast and far west of Hudson Bay, and the concentration of watershed runoff in the southern part of Hudson Bay can be delineated using the ratios between hydrogen and oxygen indices and from the distribution of labile organic carbon. Relatively high temperatures of peak hydrocarbon yield identify an advanced state of OM degradation or humic substances as important classes of organic carbon compounds in the majority of the sediment. Such highly degraded and oxygenated organic matter is unusual compared to that typically observed in other Arctic shelf seas and is consistent with a strong role for sediment and organic matter recycling in Hudson Bay. In the offshore region, the source of highly oxidized and labile organic matter identified by Rock-Eval parameters is resolved with δ13C and biomarker information that also permit examination of the sediment biogeochemical regime. This approach suggests that a distinct association with Mn enriched sediment contributes to the oxidization signal by abiotic or biological Mn related processes. These interpretations extend the limited information available on using Rock-Eval analyses to characterize organic matter in recently deposited marine sediments and describe an important consideration to using this method in Mn enriched environments.
    Organic Geochemistry 01/2014; · 2.52 Impact Factor
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    ABSTRACT: Surface sediment samples from the Hudson Bay system were analysed in order to examine the role of key regulators of arctic marine productivity—light and nutrients as affected by freshwater stratification and sea-ice cover—on the spatial distribution and production of dinoflagellate cysts. Total cyst fluxes vary from 0.2 × 106 to 30.6 × 106 cysts m- 2 a- 1, with the highest values observed in eastern Hudson Bay. A total of 24 cyst taxa, representing 11 genera of five orders, were identified and distribution maps of the most common taxa have been produced. This is the first record of Echinidinium aculeatum, Echinidinium karaense, cf. Echinidinium delicatum, Islandinium brevispinosum, Selenopemphix quanta, cysts of Protoperidinium americanum, cysts of cf. Biecheleria sp. and Polarella glacialis in the Hudson Bay system. Dinoflagellate cyst assemblages show distinct spatial patterns revealing three compositional domains: eastern Hudson Bay, western-central Hudson Bay and Hudson Strait. The eastern domain is characterised by a dominance of autotrophic cysts of Pentapharsodinium dalei whereas the western-central domain is characterized by autotrophic Operculodinium centrocarpum with some contribution by heterotrophic Polykrikos sp. var. arctic morphotype and Polykrikos spp. Sites from Hudson Strait are distinguished by an overwhelming prevalence of heterotrophic Protoperidiniaceae cysts, mainly Islandinium minutum, and have the highest values of sedimentary biogenic silica, used as a proxy for diatom productivity. Sediment geochemical tracers are used as proxies for freshwater inputs (lignin and its biomarkers) and nitrate availability (nitrogen isotopes), and sea-ice concentrations derived from passive microwave data as a proxy for light availability. Sea-ice regulated length of the dark season has a negligible influence on the proportion and production of heterotrophic (dark-adapted) versus autotrophic (light-dependent) dinoflagellate cysts, perhaps due to the location of our study area on the southern fringe of the Arctic. Instead, cyst populations in Hudson Bay are primarily regulated by vertical stratification and nitrate availability, while in Hudson Strait the pivotal mechanism constitutes food availability.
    Marine Micropaleontology 01/2014; · 1.93 Impact Factor
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    ABSTRACT: In this study, we examine mercury bioaccumulation by a first-year sea-ice (FYI) algal community in the western Canadian Arctic during the spring of 2008. Total mercury concentration in bottom sea-ice particulate ([PHg]T) ranged 0.004–0.022 mg/g dw and was limited by the amount of mercury available for uptake when the spring bloom commenced. Mercury in ice algae originated from a combination of brine and seawater as sources, while atmospheric mercury depletion events did not appear to significantly contribute as a source in a coupled manner. We show that the bottom sea-ice brine presents a chemically and biologically unique niche from which inorganic Hg makes its way into the food web. Once incorporated into algae, mercury can be transported spatially and trophically within the ecosystem by a range of processes including grazing, resuspension, remineralization, and sedimentation. Ice algae contribute 10–60% of the annual primary production in the Arctic and are thought to become even more productive and abundant under a mild climate change scenario. Replacement of multiyear ice with FYI in the Beaufort Sea alone could result in an additional influx of 48 kg/yr of particle bound Hg. Further studies are thus warranted to elucidate mechanisms by which mercury transformation processes and transfer into the Arctic marine food web are impacted by the interaction between sea ice, brine, and seawater.
    Journal of Geophysical Research 10/2013; 118:1-9. · 3.17 Impact Factor
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    ABSTRACT: Archived specimens of the scavenging amphipod Eurythenes gryllus, collected from 2075-4250 m below the surface on five expeditions to the western and central Arctic Ocean between 1983-1998, were analyzed for total mercury (sum-Hg), methyl mercury (MeHg), polychlorinated biphenyls (PCBs) and other industrial or byproduct organochlorines (chlorobenzenes, pentachloroanisole, octachlorostyrene), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs). Median sum-Hg concentrations ranged from 70 to 366 ng g-1 wet weight (ww). MeHg concentrations (3.55 to 23.5 ng g-1 ww) accounted for 1.7 to 20.1% (median 3.7%) of sum-Hg. Sum-Hg and MeHg were positively and significantly correlated with ww (sum-Hg r2 = 0.18, p = 0.0004, n=63; MeHg r2 = 0.42, p = 0.0004, n=25), but not significantly with δ13C nor δ15N. Median concentrations of total persistent organic pollutants (POPs) ranged from 9750-156000 ng g-1 lipid weight, with order of abundance: sum-TOX (chlorobornanes quantified as technical toxaphene) > sum-PCBs > sum-DDTs > sum-chlordanes > sum-mirex compounds > sum-PBDEs ~ sum-chlorobenzenes ~ octachlorostyrene > alpha-hexachlorocyclohexane ~ hexachlorobenzene ~ pentachloroanisole. Enantioselective accumulation was found for the chiral OCPs o,p'-DDT, cis- and trans-chlordane, nonachlor MC6 and oxychlordane. Lipid-normalized POPs concentrations were elevated in amphipods with lipid percentages ≤10%, suggesting that utilization of lipids resulted in concentration of POPs in the remaining lipid pool. Multidimensional Scaling (MDS) analysis using log-transformed physiological variables and lipid-normalized organochlorine concentrations distinguished amphipods from the central vs. western arctic stations. This distinction was also seen for PCB homologs, while profiles of other compound classes were more related to specific stations rather than central-west differences.
    Environmental Science & Technology 04/2013; · 5.26 Impact Factor
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    ABSTRACT: The toxicokinetics of mercury (Hg) in key species of Arctic ecosystem are poorly understood. We sampled five brain regions (frontal lobe, temporal lobe, cerebellum, brain stem and spinal cord) from beluga whales (Delphinapterus leucas) harvested in 2006, 2008, and 2010 from the eastern Beaufort Sea, Canada, and measured total Hg (HgT) and total selenium (SeT) by inductively coupled plasma mass spectrometry (ICP-MS), mercury analyzer or cold vapor atomic absorption spectrometry, and the chemical forms using a high performance liquid chromatography ICP-MS. At least 14% of the beluga whales had HgT concentrations higher than the levels of observable adverse effect (6.0mgkg(-1) wet weight (ww)) in primates. The concentrations of HgT differed between brain regions; median concentrations (mgkg(-1) ww) were 2.34 (0.06 to 22.6, 81) (range, n) in temporal lobe, 1.84 (0.12 to 21.9, 77) in frontal lobe, 1.84 (0.05 to 16.9, 83) in cerebellum, 1.25 (0.02 to 11.1, 77) in spinal cord and 1.32 (0.13 to 15.2, 39) in brain stem. Total Hg concentrations in the cerebellum increased with age (p<0.05). Between 35 and 45% of HgT was water-soluble, of which, 32 to 41% was methyl mercury (MeHg) and 59 to 68% was labile inorganic Hg. The concentration of MeHg (range: 0.03 to 1.05mgkg(-1) ww) was positively associated with HgT concentration, and the percent MeHg (4 to 109%) decreased exponentially with increasing HgT concentration in the spinal cord, cerebellum, frontal lobe and temporal lobe. There was a positive association between SeT and HgT in all brain regions (p<0.05) suggesting that Se may play a role in the detoxification of Hg in the brain. The concentration of HgT in the cerebellum was significantly associated with HgT in other organs. Therefore, HgT concentrations in organs that are frequently sampled in bio-monitoring studies could be used to estimate HgT concentrations in the cerebellum, which is the target organ of MeHg toxicity.
    Science of The Total Environment 04/2013; 456-457C:278-286. · 3.26 Impact Factor
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    ABSTRACT: Like most zooplankton, Calanus hyperboreus undergoes seasonal migration spending late spring and summer grazing at the surface and the rest of the year in diapause at depth. As a result, in the Arctic Ocean this copepod resides for part of the year in the hexachlorocyclohexane (HCH) enriched surface water and for part of the year at depth where HCH undergoes significant microbial degradation resulting in far lower concentrations (∼3 times for α-HCH). We collected C. hyperboreus from summer and winter from the Amundsen Gulf and measured their α-HCH concentrations, enantiomeric compositions, and bioaccumulation factors (BAFs) to investigate how this copepod responds to the change in exposure to α-HCH. C. hyperboreus collected in winter were also cultured for 5 weeks under surface water conditions without feeding to investigate bioconcentration dynamics following spring ascent. Concentration of α-HCH was 2-3 times higher in individuals from the summer than those from the winter. Log BAF from the summer (feeding period) does not exceed log BCF (bioconcentration factor) from the culturing experiment (no feeding) suggesting that α-HCH concentration in C. hyperboreus is maintained through equilibration rather than feeding. After the spring ascent from deep waters, C. hyperboreus approach equilibrium partitioning with the higher surface water concentrations of α-HCH within 3-4 weeks with about 60% of bioconcentration taking place in the first week. The C. hyperboreus α-HCH chiral signature also reflects ambient seawater and can therefore be used as a determinant of residence depth. Even though a single cycle of seasonal migration does not result in a significant redistribution of α-HCH in the water column, this process could have a significant cumulative effect over longer time scales with particular local importance where the zooplankton biomass is high and the ocean depth is great enough to provide substantial vertical concentration gradients.
    Environmental Science & Technology 04/2013; · 5.26 Impact Factor
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    ABSTRACT: Water column concentrations of α-HCH were measured in the southern Beaufort Sea as part of the Canadian Arctic Shelf Exchange Study (CASES; 2003–04), the Circumpolar Flaw Lead System Study (CFL; 2007–08), and in the Mackenzie River during the 2008 NAHIDIK program. Atmospheric α-HCH concentrations were measured during CASES program. Inventories of α-HCH in the Polar Mixed Layer (PML) and the Pacific Mode Layer (PL) of the Beaufort Sea were calculated between 1986 and 2007 based on the available data. Between 1986 and 1993, there was a significant loading of α-HCH to the Beaufort Sea via the ocean currents. About 12% of the loading to the PML could be explained by the combined effect of the air–water gas exchange and the river runoff. After 1993, α-HCH inventories started decreasing, and could be well predicted exclusively by degradation. Ice formation was shown to be a solvent depleting process leading to a significant increase in the α-HCH concentration in the water just beneath the ice. Associated low α-HCH concentrations in the ice and relatively low ice export from the Beaufort Sea resulted in negligible influence of this output route on the inventories in the PML. The majority of α-HCH in the Beaufort Sea could be eliminated due to degradation by 2020, with concentrations in 2040 dropping to
    Journal of Marine Systems 01/2013; · 2.66 Impact Factor
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    ABSTRACT: Elimination of persistent organic pollutants (POPs) under national and international regulations reduces "primary" emissions, but "secondary" emissions continue from residues deposited in soil, water, ice and vegetation during former years of usage. In a future, secondary source controlled world, POPs will follow the carbon cycle and biogeochemical processes will determine their transport, accumulation and fate. Climate change is likely to affect mobilisation of POPs through e.g., increased temperature, altered precipitation and wind patterns, flooding, loss of ice cover in polar regions, melting glaciers, and changes in soil and water microbiology which affect degradation and transformation. Chiral compounds offer advantages for following transport and fate pathways because of their ability to distinguish racemic (newly released or protected from microbial attack) and nonracemic (microbially degraded) sources. This paper discusses the rationale for this approach and suggests applications where chiral POPs could aid investigation of climate-mediated exchange and degradation processes. Multiyear measurements of two chiral POPs, trans-chlordane and α-HCH, at a Canadian Arctic air monitoring station show enantiomer compositions which cycle seasonally, suggesting varying source contributions which may be under climatic control. Large-scale shifts in the enantioselective metabolism of chiral POPs in soil and water might influence the enantiomer composition of atmospheric residues, and it would be advantageous to include enantiospecific analysis in POPs monitoring programs.
    Mass spectrometry (Tokyo, Japan). 01/2013; 2(Spec Iss):S0019.
  • 01/2013: pages pp. 273-422;
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    ABSTRACT: This review critically evaluates the available mercury (Hg) data in Arctic marine biota and the Inuit population against toxicity threshold values. In particular marine top predators exhibit concentrations of mercury in their tissues and organs that are believed to exceed thresholds for biological effects. Species whose concentrations exceed threshold values include the polar bears (Ursus maritimus), beluga whale (Delphinapterus leucas), pilot whale (Globicephala melas), hooded seal (Cystophora cristata), a few seabird species, and landlocked Arctic char (Salvelinus alpinus). Toothed whales appear to be one of the most vulnerable groups, with high concentrations of mercury recorded in brain tissue with associated signs of neurochemical effects. Evidence of increasing concentrations in mercury in some biota in Arctic Canada and Greenland is therefore a concern with respect to ecosystem health.
    Science of The Total Environment 12/2012; 443C:775-790. · 3.26 Impact Factor
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    ABSTRACT: Declines in 6 organochlorine (OC) contaminant groups; chlordane (CHL), DDT, HCH, toxaphene (CHB), PCB and chlorinated benzenes (CBz) were measured in biota of a sub-Arctic lake (Lake Laberge, YT) following the closure of a commercial fishery in 1991. This study examined morphological (length, weight, age), biochemical (lipid content, δ(13)C, δ(15)N), population and OC data for 9 fishes and zooplankton between 1993 and 2003 (2010 for lake trout) to investigate causes for the OC declines. Growth dilution was a major factor influencing the decrease of OCs in lake trout, round whitefish and possibly zooplankton most notably in the early 2000s. A decline in lipids of most fish species also contributed to OC declines, although no such change was evident for zooplankton. It is suspected that increases in fish populations or climate variations over the 1990s, may have contributed towards a shift in plankton community composition. From 1991 to 1999, CPUE increased for 7 of the fish species and declined for 2 others. Concurrently, the zooplankton community shifted from an abundance of C. scutifer in 1993 to dominance by D. pribilofensis in 2001. Nitrogen and carbon stable isotope data suggested that food web interactions for most fish species have not changed over time. Although concentrations of OCs have declined in many fishes, the "rate" of OC transfer (using slopes of log OC vs. nitrogen isotope ratios) through the food web was greater in 2001 than in 1993. Overall, the declines in OC concentrations in the fish from Lake Laberge occurred concurrently with changes in their growth, lipid, and abundance, suggesting that ecosystem responses to the closure of the fishery were in part responsible for the lower contaminants in these fishes. As a result of this study, the Yukon government rescinded the health advisory for limiting the consumption of fish from Lake Laberge.
    Science of The Total Environment 11/2012; 443C:80-92. · 3.26 Impact Factor
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    ABSTRACT: While much research has been carried out on mercury in large marine mammals and associated food webs in northern regions, comparatively less has been conducted on lower trophic levels including zooplankton and the subsequent transfer to predators, which marks the entry of mercury into northern marine food webs. We present here the first database for mercury uptake and transfer exclusively within zooplankton food webs in northern marine waters. We have investigated both total (THg) and monomethylmercury (MMHg) concentrations, and isotopic signatures (δ(15)N and δ(13)C) in individual zooplankton taxa collected over a period of eight years (2003-2010) from across Hudson Bay (including Hudson Strait and Foxe Basin) as part of research icebreaker cruises. δ(15)N values ranged from 3.4 to 14.0‰, implying trophic levels ranging from 1 to 4, and THg concentrations ranged from 5 to 242 ng g(-1) dw. Food web linkages were identified within the data set, and mercury biomagnification was evident both with THg and MMHg concentrations increasing from prey to predator, and with trophic magnification factors (TMFs). Total mercury and MMHg transfer in a unique prey-predator linkage (Limacina helicina-Clione limacina) are investigated and discussed with regard to known physiological and biochemical characteristics. The results suggest that exposure to mercury at higher trophic levels including humans can be affected by processes at the bottom of Arctic marine food webs.
    Environmental Science & Technology 11/2012; · 5.26 Impact Factor
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    ABSTRACT: During the summer of 2009, we sampled 14 partially refrozen melt ponds and the top 1 m of old ice in the pond vicinity for α-hexachlorocyclohexane (α-HCH) concentrations and enantiomer fractions (EFs) in the Beaufort Sea. α-HCH concentrations were 3 - 9 times higher in melt ponds than in the old ice. We identify two routes of α-HCH enrichment in the ice over the summer. First, atmospheric gas deposition results in an increase of α-HCH concentration from 0.07 ± 0.02 ng/L (old ice) to 0.34 ± 0.08 ng/L, or ∼20% less than the atmosphere-water equilibrium partitioning concentration (0.43 ng/L). Second, late-season ice permeability and/or complete ice thawing at the bottom of ponds permit α-HCH rich seawater (∼0.88 ng/L) to replenish pond water, bringing concentrations up to 0.75 ± 0.06 ng/L. α-HCH pond enrichment may lead to substantial concentration patchiness in old ice floes, and changed exposures to biota as the surface meltwater eventually reaches the ocean through various drainage mechanisms. Melt pond concentrations of α-HCH were relatively high prior to the late 1980-s, with a Melt pond Enrichment Factor >1 (MEF; a ratio of concentration in surface meltwater to surface seawater), providing for the potential of increased biological exposures.
    Environmental Science & Technology 10/2012; · 5.26 Impact Factor
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    ABSTRACT: Mercury is a major contaminant in the Arctic marine ecosystem. While extensive studies have been conducted on mercury in the Arctic's atmosphere and biota, far less is known about the distribution and dynamics of mercury species in the Arctic Ocean. Here, we present vertical profiles for total mercury (Hg(T)) and total methylated mercury (MeHg(T), sum of monomethylmercury and dimethylmercury) from the Beaufort Sea of the Arctic Ocean at locations with differing sea ice conditions. The concentration of Hg(T) ranged from 0.40 to 2.9 pM, with a surface enrichment that can be attributed to a combination of sea ice-modified atmospheric deposition and riverine input. The concentration of MeHg(T) ranged from <0.04 to 0.59 pM, with a subsurface peak occurring at the same depth as a nutrient maximum with lower dissolved oxygen, which is consistent with the recent findings in the Pacific Ocean, Southern Ocean, and Mediterranean Sea. However, unlike the interior ocean regions, the nutrient maximum in the Beaufort Sea is predominantly an advective feature produced over the Chukchi Shelf. On the basis of the short lifetime of monomethylmercury in seawater, we propose that the MeHg(T) profile in the Beaufort Sea reflects the local, short-term remineralization of labile organic matter, and not the larger signal of organic remineralization advected from the Chukchi Sea in the halocline. The finding that MeHg(T) is produced locally, reflecting recent strength of organic matter cycling, not only explains wide variance in MeHg(T) in seawater and biota over time and space, but also implies that MeHg(T) could be used as an indicator of the recent export flux of labile organic matter.
    Environmental Science & Technology 10/2012; · 5.26 Impact Factor
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    ABSTRACT: Recent drastic reduction of the older perennial sea ice in the Arctic Ocean has resulted in a vast expansion of younger and saltier seasonal sea ice. This increase in the salinity of the overall ice cover could impact tropospheric chemical processes. Springtime perennial ice extent in 2008 and 2009 broke the half-century record minimum in 2007 by about one million km2. In both years seasonal ice was dominant across the Beaufort Sea extending to the Amundsen Gulf, where significant field and satellite observations of sea ice, temperature, and atmospheric chemicals have been made. Measurements at the site of the Canadian Coast Guard Ship Amundsen ice breaker in the Amundsen Gulf showed events of increased bromine monoxide (BrO), coupled with decreases of ozone (O3) and gaseous elemental mercury (GEM), during cold periods in March 2008. The timing of the main event of BrO, O3, and GEM changes was found to be consistent with BrO observed by satellites over an extensive area around the site. Furthermore, satellite sensors detected a doubling of atmospheric BrO in a vortex associated with a spiral rising air pattern. In spring 2009, excessive and widespread bromine explosions occurred in the same region while the regional air temperature was low and the extent of perennial ice was significantly reduced compared to the case in 2008. Using satellite observations together with a Rising-Air-Parcel model, we discover a topographic control on BrO distribution such that the Alaskan North Slope and the Canadian Shield region were exposed to elevated BrO, whereas the surrounding mountains isolated the Alaskan interior from bromine intrusion.
    Journal of Geophysical Research 09/2012; 117(D17). · 3.17 Impact Factor
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    ABSTRACT: α-HCH (hexachlorocyclohexane) and the enantiomeric fraction (EF) of its mirror-image isomers have been determined for water column profiles in the southern Beaufort Sea in 2004 and 2007. Using estimated rates of metabolic degradation, we have applied a simple kinetic model to convert the observed EFs to apparent ventilation ages of the water masses in the study region. We found an age of 1.7 ± 0.1 years for the Polar Mixed Layer (PML), 6.6 ± 0.6 for the core of the Pacific Layer centered at salinity 33.1, and 21.7 ± 0.5 years for the core of the Atlantic Layer identified by a Tmax of ˜0.5°C. These ages are in reasonable accord with other methods used to date water masses in the Arctic Ocean suggesting that α-HCH has an unexploited potential as a dating tool.
    Journal of Geophysical Research (Oceans). 08/2012; 117(C8):8038-.

Publication Stats

3k Citations
414.65 Total Impact Points

Institutions

  • 2003–2014
    • University of Manitoba
      • • Centre for Earth Observation Science
      • • Department of Environment and Geography
      Winnipeg, Manitoba, Canada
  • 1993–2013
    • Fisheries and Oceans Canada
      • Institute of Ocean Sciences
      Ottawa, Ontario, Canada
    • University of South Carolina
      • Marine Science
      Columbia, SC, United States
  • 1993–2012
    • The University of Winnipeg
      Winnipeg, Manitoba, Canada
  • 2003–2005
    • Lancaster University
      • Lancaster Environment Centre
      Lancaster, ENG, United Kingdom
  • 2004
    • University of Toronto
      • Department of Geography
      Toronto, Ontario, Canada
  • 2001–2004
    • Environment Canada
      • Science and Technology Branch
      Gatineau, Quebec, Canada
  • 2000
    • National Water Research Institute
      Fountain Valley, California, United States