The long-term fate of saturates and biomarkers within crude oil spilled during the Baffin Island Oil Spill (BIOS) Project.

The Baffin Island Oil Spill (BIOS) Project is a long-term monitoring field study conducted in the early 1980s, seeking to examine the physical and chemical fate of crude oil released into a pristine Arctic setting. During the present study, sites of the BIOS Project were revisited in 2019 for the collection of oiled intertidal and backshore sediments. These samples were analyzed for several groups of petroleum hydrocarbons including saturates (n-alkanes, branched alkanes, and alkylcycloalkanes), hopane and sterane biomarkers, and alkylbenzenes. These hydrocarbon groups were present in concentrations ranging from 1.77-1210, 0.224-51.7, 0.0643-16.9, 0.00-11.7, and 0.0171-8.60 mg/kg within individual samples, respectively. When comparing current to limited results from past BIOS studies, a representative branched alkane (phytane), and medium-chain (nC18) and long-chain (nC30) n-alkanes demonstrate extensive weathering processes, exhibiting up to 90 %, 98 %, and 77 % loss since the penultimate BIOS revisitation in 2001, respectively.

The recalcitrance and potential toxicity of polycyclic aromatic hydrocarbons within crude oil residues in beach sediments at the BIOS site, nearly forty years later.

The Arctic is a unique environment characterized by extreme conditions, including daylight patterns, sea ice cover, and some of the lowest temperatures on Earth. Such characteristics in tandem present challenges when extrapolating information from oil spill research within warmer, more temperate regions. Consequently, oil spill studies must be conducted within the Arctic to yield accurate and reliable results. Sites of the Baffin Island Oil Spill (BIOS) project (Cape Hatt, Baffin Island, Canadian Arctic) were revisited nearly 40 years after the original oil application to provide long-term monitoring data for Arctic oil spill research. Surface and subsurface sediment samples were collected from the intertidal zone of the 1981 nearshore oil spill experiment (Bay 11), from 1980 supratidal control plots (Crude Oil Point) and 1982 supratidal treatment plots (Bay 106). Samples were analyzed for Polycyclic Aromatic Hydrocarbons (PAHs) and alkylated homologues via Gas Chromatography - Mass Spectrometry (GC-MS). Our results suggest that total mean concentrations of all measured PAHs range from 0.049 to 14 mg/kg, whereas total mean concentrations of the 16 US EPA priority PAHs range from 0.02 to 2.1 mg/kg. The relative proportions of individual PAHs were compared between sampling sites and with the original technical mixture. Where available, percent loss of individual PAHs was compared with data from samples collected at the BIOS site, in 2001. All three sites featured samples where concentrations of various priority PAHs exceeded the established Interim Marine Sediment Quality Guidelines. All supratidal samples contained potentially toxic levels of PAHs. Even after nearly four decades of weathering, the recalcitrant crude oil residues remain a potential hazard for the native organisms. Continued monitoring of this unique study site is crucial for establishing a timeline for oil degradation, and to observe a reduction in toxicity over time.

Baseline levels and characterization of hydrocarbons in surface marine sediments along the transportation corridor in Hudson Bay: A multivariate analysis of n-alkanes, PAHs and biomarkers.

Hudson Bay is a small arctic inland shelf sea which receives large amounts of freshwater from riverine discharges, with marine flow from the north and the Atlantic. A warming climate has resulted in an expanded open water season which will result in an increase in shipping of fuel oil and petroleum to communities and mines on the western shore, increasing the risk of hydrocarbon releases. To evaluate the status of hydrocarbons, surface sediments were collected at 34 locations in the transportation route and offshore and analysed for several types of hydrocarbons. Total hydrocarbons varied by over 25 times between sites, reaching a maximum of 1116 µg/g OC (organic carbon basis) in Hudson Strait due to low molecular weight n-alkanes from marine primary production. The gross mean for all sites was 344 µg/g OC (GSD = 173-682), roughly equivalent to other remote sites in the Canadian Arctic with no known local hydrocarbon source. n-alkanes accounted for >90 % of residues. Diagnostic ratios (e.g., Carbon Preference Index (CPI), Odd-Even Predominance (OEP)) indicated mixed sources of n-alkanes, likely due to the input from vascular plants and ombrotrophic peat in northern and western watersheds, and primary production within the Bay. The elevated proportion of high molecular weight n-alkanes at deep water sites is consistent with lotic particulate organic matter deposited in the nearshore environment and redeposited offshore. Æ©36PAHs were a small fraction (1.9 %) of hydrocarbons, with a gross mean of 5.68 µg/g OC (GSD = 3.30-9.79). PCA separated deep water sediments from nearshore and community samples due to 4 alkylated naphthalenes which usually indicate a petrogenic source but probably indicates a natural source due to the lack of other petrogenic markers. Priority PAHs (i.e., Æ©16PAH) varied from 31.5 % to 56.6 % of the Æ©36PAH residues. The concentrations of individual PAHs were well below the Interim Sediment Quality Guidelines recommended by the Canadian Council of Ministers of the Environment.

Methods for Interpreting the Partitioning and Fate of Petroleum Hydrocarbons in a Sea Ice Environment.

Decreases in Arctic Sea ice extent and thickness have led to more open ice conditions, encouraging both shipping traffic and oil exploration within the northern Arctic. As a result, the increased potential for accidental releases of crude oil or fuel into the Arctic environment threatens the pristine marine environment, its ecosystem, and local inhabitants. Thus, there is a need to develop a better understanding of oil behavior in a sea ice environment on a microscopic level. Computational quantum chemistry was used to simulate the effects of evaporation, dissolution, and partitioning within sea ice. Vapor pressures, solubilities, octanol-water partition coefficients, and molecular volumes were calculated using quantum chemistry and thermodynamics for pure liquid solutes (oil constituents) of interest. These calculations incorporated experimentally measured temperatures and salinities taken throughout an oil-in-ice mesocosm experiment conducted at the University of Manitoba in 2017. Their potential for interpreting the relative movements of oil constituents was assessed. Our results suggest that the relative movement of oil constituents is influenced by differences in physical properties. Lighter molecules showed a greater tendency to be controlled by brine advection processes due to their greater solubility. Molecules which are more hydrophobic were found to concentrate in areas of lower salt concentration.

Investigation into the geometry and distribution of oil inclusions in sea ice using non-destructive X-ray microtomography and its implications for remote sensing and mitigation potential.

As climate change brings reduced sea ice cover and longer ice-free summers to the Arctic, northern Canada is experiencing an increase in shipping and industrial activity in this sensitive region. Disappearing sea ice, therefore, makes the Arctic region susceptible to accidental releases of different types of oil and fuel pollution resulting in a pressing need for the development of appropriate scientific knowledge necessary to inform regulatory policy formulation. In this study, we examine the microstructure of the surficial layers of sea ice exposed to oil using X-ray microtomography. Through analysis, 3D imaging of the spatial distribution of the ice's components (brine, air, and oil) were made. Additional quantitative information regarding the size, proximity, orientation, and geometry of oil inclusions were computed to ascertain discernable relationships between oil and the other components of the ice. Our results indicate implications for airborne remote sensing and bioremediation of the upper sea ice layers.

High mercury accumulation in deep-ocean hadal sediments.

Ocean sediments are the largest sink for mercury (Hg) sequestration and hence an important part of the global Hg cycle1. Yet accepted global average Hg flux data for deep-ocean sediments (> 200 m depth) are not based on measurements on sediments but are inferred from sinking particulates2. Mercury fluxes have never been reported from the deepest zone, the hadal (> 6 km depth). Here we report the first measurements of Hg fluxes from two hadal trenches (Atacama and Kermadec) and adjacent abyssal areas (2-6 km). Mercury concentrations of up to 400 ng g-1 were the highest recorded in marine sediments remote from anthropogenic or hydrothermal sources. The two trench systems differed significantly in Hg concentrations and fluxes, but hadal and abyssal areas within each system did not. The relatively low recent mean flux at Kermadec was 6-15 times higher than the inferred deep-ocean average1,3, while the median flux across all cores was 22-56 times higher. Thus, some hadal and abyssal sediments are Hg accumulation hot-spots. The hadal zone comprises only ~ 1% of the deep-ocean area, yet a preliminary estimate based on sediment Hg and particulate organic carbon (POC) fluxes suggests total hadal Hg accumulation may be 12-30% of the estimate for the entire deep-ocean. The few abyssal data show equally high Hg fluxes near trench systems. These results highlight a need for further research into deep-ocean Hg fluxes to better constrain global Hg models.

Photooxidation and biodegradation potential of a light crude oil in first-year sea ice.

Disappearing sea ice in the Arctic region results in a pressing need to develop oil spill mitigation techniques suitable for ice-covered waters. The uncertainty around the nature of an oil spill in the Arctic arises from the ice-covered waters and sub-zero temperatures, and how they may influence natural attenuation efficiency. The Sea-ice Environmental Research Facility was used to create a simulated Arctic marine setting. This paper focuses on the potential for biodegradation of the bulk crude oil content (encapsulated in the upper regions of the ice), to provide insight regarding the possible fate of crude oil in an Arctic marine setting. Cheaper and faster methods of chemical composition analysis were applied to the samples to assess for weathering and transformation effects. Results suggest that brine volume in ice may not be sufficient at low temperatures to encompass biodegradation and that seawater is more suitable for biodegradation.

Effect of dissolution, evaporation, and photooxidation on crude oil chemical composition, dielectric properties and its radar signature in the Arctic environment.

Accidental release of petroleum in the Arctic is of growing concern owing to increases in ship traffic and possible future oil exploration. A crude oil-in-sea ice mesocosm experiment was conducted to identify oil-partitioning trends in sea ice and determine the effect of weathering on crude oil permittivity. The dissolution of the lighter fractions increased with decreasing bulk oil-concentration because of greater oil-brine interface area. Movement of the oil towards the ice surface predominated over dissolution process when oil concentrations exceeded 1 mg/mL. Evaporation decreased oil permittivity due to losses of low molecular weight alkanes and increased asphaltene-resin interactions. Photooxidation increased the permittivity of the crude oil due to the transformation of branched aromatics to esters and ketones. Overall, the weathering processes influenced crude oil permittivity by up to 15%, which may produce sufficient quantifiable differences in the measured normalized radar cross-section of the ice.

Oil behavior in sea ice: Changes in chemical composition and resultant effect on sea ice dielectrics.

There has been increasing urgency to develop methods for detecting oil in sea ice owing to the effects of climate change in the Arctic. A multidisciplinary study of crude oil behavior in a sea ice environment was conducted at the University of Manitoba during the winter of 2016. In the experiment, medium-light crude oil was injected underneath young sea ice in a mesocosm. The physical and thermodynamic properties of the oil-infiltrated sea ice were monitored over a three-week time span, with concomitant analysis of the oil composition using analytical instrumentation. A resonant perturbation technique was used to measure the oil dielectric properties, and the contaminated sea ice dielectric properties were modeled using a mixture model approach. Results showed that the interactions between the oil and sea ice altered their physical and thermodynamic properties. These changes led to an overall decrease in sea ice dielectrics, potentially detectable by remote sensing systems.

Examining the physical processes of corn oil (medium crude oil surrogate) in sea ice and its resultant effect on complex permittivity and normalized radar cross-section.

Due to the effects of heightened warming in the Arctic, there has been an urgency to develop methods for detecting oil in (or under) sea ice, owing to increasing potential for oil exploration and ship traffic in the more accessible Arctic regions. To test the potential for radar utilizing the normalized radar cross section (NRCS) of the sea ice, an oil-in-ice mesocosm experiment was performed. Throughout the experiment, corn oil was used as a surrogate for medium crude oil, to assess oil movement tendencies in sea ice, and the resultant impact on the complex permittivity through measurement and modelling techniques. We performed a modelling study to establish the effects of corn oil on the NRCS of sea ice. The oil presence in the sea ice increased the temperature and reduced the salinity of the sea ice, thereby lowering its complex permittivity and modeled NRCS when compared to control sea ice.

Current use pesticide and legacy organochlorine pesticide dynamics at the ocean-sea ice-atmosphere interface in resolute passage, Canadian Arctic, during winter-summer transition.

Here, we present the first detailed analysis of processes by which various current use pesticides (CUPs) and legacy organochlorine pesticides (OCPs) are concentrated in melt ponds that form on Arctic sea ice in the summer, when surface snow is melting and ice eventually breaks up. Four current use pesticides (dacthal, chlorpyrifos, trifluralin, and pentachloronitrobenzene) and one legacy organochlorine pesticide (α-hexachlorocyclohexane) were detected in ponds in Resolute Passage, Canadian Arctic, in 2012. Melt-pond concentrations changed over time as a function of gas exchange, precipitation, and dilution with melting sea ice. Observed increases in melt-pond concentrations for all detected pesticides were associated with precipitation events. Dacthal reached the highest concentration of all current use pesticides in ponds (95±71pgL-1), a value exceeding measured concentrations in the under-ice (0m) and 5m seawater by >10 and >16 times, respectively. Drainage of dacthal-enriched pond water to the ocean during ice break-up provides an important ice-mediated annual delivery route, adding ~30% of inventory in the summer Mixed Layer (ML; 10m) in the Resolute Passage, and a concentrating mechanism with potential implications for exposures to organisms such as ice algae, and phytoplankton.

Pan-Arctic concentrations of mercury and stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N) in marine zooplankton.

Zooplankton play a central role in marine food webs, dictating the quantity and quality of energy available to upper trophic levels. They act as "keystone" species in transfer of mercury (Hg) up through the marine food chain. Here, we present the first Pan-Arctic overview of total and monomethylmercury concentrations (THg and MMHg) and stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N) in selected zooplankton species by assembling data collected between 1998 and 2012 from six arctic regions (Laptev Sea, Chukchi Sea, southeastern Beaufort Sea, Canadian Arctic Archipelago, Hudson Bay and northern Baffin Bay). MMHg concentrations in Calanus spp., Themisto spp. and Paraeuchaeta spp. were found to increase with higher δ(15)N and lower δ(13)C. The southern Beaufort Sea exhibited both the highest THg and MMHg concentrations. Biomagnification of MMHg between Calanus spp. and two of its known predators, Themisto spp. and Paraeuchaeta spp., was greatest in the southern Beaufort Sea. Our results show large geographical variations in Hg concentrations and isotopic signatures for individual species related to regional ecosystem features, such as varying water masses and freshwater inputs, and highlight the increased exposure to Hg in the marine food chain of the southern Beaufort Sea.

20 Years of Air-Water Gas Exchange Observations for Pesticides in the Western Arctic Ocean.

The Arctic has been contaminated by legacy organochlorine pesticides (OCPs) and currently used pesticides (CUPs) through atmospheric transport and oceanic currents. Here we report the time trends and air-water exchange of OCPs and CUPs from research expeditions conducted between 1993 and 2013. Compounds determined in both air and water were trans- and cis-chlordanes (TC, CC), trans- and cis-nonachlors (TN, CN), heptachlor exo-epoxide (HEPX), dieldrin (DIEL), chlorobornanes (ΣCHBs and toxaphene), dacthal (DAC), endosulfans and metabolite endosulfan sulfate (ENDO-I, ENDO-II, and ENDO SUL), chlorothalonil (CHT), chlorpyrifos (CPF), and trifluralin (TFN). Pentachloronitrobenzene (PCNB and quintozene) and its soil metabolite pentachlorothianisole (PCTA) were also found in air. Concentrations of most OCPs declined in surface water, whereas some CUPs increased (ENDO-I, CHT, and TFN) or showed no significant change (CPF and DAC), and most compounds declined in air. Chlordane compound fractions TC/(TC + CC) and TC/(TC + CC + TN) decreased in water and air, while CC/(TC + CC + TN) increased. TN/(TC + CC + TN) also increased in air and slightly, but not significantly, in water. These changes suggest selective removal of more labile TC and/or a shift in chlordane sources. Water-air fugacity ratios indicated net volatilization (FR > 1.0) or near equilibrium (FR not significantly different from 1.0) for most OCPs but net deposition (FR < 1.0) for ΣCHBs. Net deposition was shown for ENDO-I on all expeditions, while the net exchange direction of other CUPs varied. Understanding the processes and current state of air-surface exchange helps to interpret environmental exposure and evaluate the effectiveness of international protocols and provides insights for the environmental fate of new and emerging chemicals.

The delivery of organic contaminants to the Arctic food web: why sea ice matters.

For decades sea ice has been perceived as a physical barrier for the loading of contaminants to the Arctic Ocean. We show that sea ice, in fact, facilitates the delivery of organic contaminants to the Arctic marine food web through processes that: 1) are independent of contaminant physical-chemical properties (e.g. 2-3-fold increase in exposure to brine-associated biota), and 2) depend on physical-chemical properties and, therefore, differentiate between contaminants (e.g. atmospheric loading of contaminants to melt ponds over the summer, and their subsequent leakage to the ocean). We estimate the concentrations of legacy organochlorine pesticides (OCPs) and current-use pesticides (CUPs) in melt pond water in the Beaufort Sea, Canadian High Arctic, in 2008, at near-gas exchange equilibrium based on Henry's law constants (HLCs), air concentrations and exchange dynamics. CUPs currently present the highest risk of increased exposures through melt pond loading and drainage due to the high ratio of melt pond water to seawater concentration (Melt pond Enrichment Factor, MEF), which ranges from 2 for dacthal to 10 for endosulfan I. Melt pond contaminant enrichment can be perceived as a hypothetical 'pump' delivering contaminants from the atmosphere to the ocean under ice-covered conditions, with 2-10% of CUPs annually entering the Beaufort Sea via this input route compared to the standing stock in the Polar Mixed Layer of the ocean. The abovementioned processes are strongly favored in first-year ice compared to multi-year ice and, therefore, the dynamic balance between contaminant inventories and contaminant deposition to the surface ocean is being widely affected by the large-scale icescape transition taking place in the Arctic.

Spatial, temporal, and source variations of hydrocarbons in marine sediments from Baffin Bay, Eastern Canadian Arctic.

With declining sea ice conditions in Arctic regions owing to changing climate, the large prospective reservoirs of oil and gas in Baffin Bay and Davis Strait are increasingly accessible, and the interest in offshore exploration and shipping through these regions has increased. Both of these activities are associated with the risk of hydrocarbon releases into the marine ecosystem. However, hydrocarbons are also present naturally in marine environments, in some cases deriving from oil seeps. We have analyzed hydrocarbon concentrations in eleven sediment cores collected from northern Baffin Bay during 2008 and 2009 Amundsen expeditions and have examined the hydrocarbon compositions in both pre- and post-industrial periods (i.e., before and after 1900) to assess the sources of hydrocarbons, and their temporal and spatial variabilities. Concentrations of ΣPAHs ranged from 341 to 2693 ng g(-1) dw, with concentrations in cores from sites within the North Water (NOW) Polynya generally higher. Individual PAH concentrations did not exceed concentrations of concern for marine aquatic life, with one exception found in a core collected within the NOW (one of the seven sediment core samples). Hydrocarbon biomarkers, including alkane profiles, OEP (odd-to-even preference), and TAR (terrigenous/aquatic ratios) values indicated that organic carbon at all sites is derived from both terrigenous higher plants and marine algae, the former being of greater significance at coastal sites, and the latter at the deepest sites at the southern boundary of the NOW. Biomarker ratios and chemical profiles indicate that petrogenic sources dominate over combustion sources, and thus long-range atmospheric transport is less significant than inputs from weathering. Present-day and historic pre-1900 hydrocarbon concentrations exhibited less than an order of magnitude difference for most compounds at all sites. The dataset presented here provides a baseline record of hydrocarbon concentrations in Baffin Bay sediments in advance of offshore exploration and increased shipping activities.

Scavenging amphipods: sentinels for penetration of mercury and persistent organic chemicals into food webs of the deep Arctic Ocean.

Archived specimens of the scavenging amphipod Eurythenes gryllus, collected from 2075 to 4250 m below the surface on five expeditions to the western and central Arctic Ocean between 1983 and 1998, were analyzed for total mercury (∑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 ∑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 ∑Hg. ∑Hg and MeHg were positively and significantly correlated with ww (∑Hg r(2) = 0.18, p = 0.0004, n = 63; MeHg r(2) = 0.42, p = 0.0004, n = 25), but not significantly with δ(13)C nor δ(15)N. Median concentrations of total persistent organic pollutants (POPs) ranged from 9750 to 156,000 ng g(-1) lipid weight, with order of abundance: ∑TOX (chlorobornanes quantified as technical toxaphene) > ∑PCBs > ∑DDTs > ∑chlordanes > ∑mirex compounds > ∑BDEs ∼ ∑chlorobenzenes ∼ octachlorostyrene > α-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 homologues, whereas profiles of other compound classes were more related to specific stations rather than central-west differences.

Mercury distribution and speciation in different brain regions of beluga whales (Delphinapterus leucas).

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 (6.0 mg kg(-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 1.05 mg kg(-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.

Mercury biomagnification in marine zooplankton food webs in Hudson Bay.

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.

Total and methylated mercury in the Beaufort Sea: the role of local and recent organic remineralization.

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.