Distant drivers or local signals: where do mercury trends in western Arctic belugas originate?

Temporal trends of contaminants are monitored in Arctic higher trophic level species to inform us on the fate, transport and risk of contaminants as well as advise on global emissions. However, monitoring mercury (Hg) trends in species such as belugas challenge us, as their tissue concentrations reflect complex interactions among Hg deposition and methylation, whale physiology, dietary exposure and foraging patterns. The Beaufort Sea beluga population showed significant increases in Hg during the 1990 s; since that time an additional 10 years of data have been collected. During this time of data collection, changes in the Arctic have affected many processes that underlie the Hg cycle. Here, we examine Hg in beluga tissues and investigate factors that could contribute to the observed trends after removing the effect of age and size on Hg concentrations and dietary factors. Finally, we examine available indicators of climate variability (Arctic Oscillation (AO), the Pacific Decadal Oscillation (PDO) and sea-ice minimum (SIM) concentration) to evaluate their potential to explain beluga Hg trends. Results reveal a decline in Hg concentrations from 2002 to 2012 in the liver of older whales and the muscle of large whales. The temporal increases in Hg in the 1990 s followed by recent declines do not follow trends in Hg emission, and are not easily explained by diet markers highlighting the complexity of feeding, food web dynamics and Hg uptake. Among the regional-scale climate variables the PDO exhibited the most significant relationship with beluga Hg at an eight year lag time. This distant signal points us to consider beluga winter feeding areas. Given that changes in climate will impact ecosystems; it is plausible that these climate variables are important in explaining beluga Hg trends. Such relationships require further investigation of the multiple connections between climate variables and beluga Hg.

Transformation of mercury at the bottom of the Arctic food web: an overlooked puzzle in the mercury exposure narrative.

We show 2008 seasonal trends of total and monomethyl 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 postdepositional 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.

Importance of Arctic zooplankton seasonal migrations for α-hexachlorocyclohexane bioaccumulation dynamics.

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.

Mechanisms and implications of α-HCH enrichment in melt pond water on Arctic sea ice.

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.

There is no 1954 in that core! Interpreting sedimentation rates and contaminant trends in marine sediment cores.

Marine sediment preserves a useful archive for contaminants and other properties that associate with particles. However, biomixing of sediments can smear the record on a scale of years to thousands of years, depending on sedimentation rate and on the depth and vigour of mixing within a particular sediment. Where such mixing occurs, dates can no longer be associated with discrete sediment depths. Nevertheless, much can still be learned from biomixed profiles, provided that mixing is accounted for. With no modelling at all, it is possible to calculate an inventory of a contaminant at a site and a maximum possible sedimentation rate, and to determine whether the contaminant has increased or decreased over time. Radiodating the core with (210)Pb permits the estimation of sedimentation and mixing rates, which can be combined with the surface contaminant concentration to estimate an approximate flux of the contaminant. Numerical models that incorporate sedimentation and mixing rates (determined using (210)Pb and other transient signals with known deposition histories) can provide the basis to propose plausible histories for contaminant fluxes.

α- and γ-Hexachlorocyclohexane measurements in the brine fraction of sea ice in the Canadian High Arctic using a sump-hole technique.

We used holes augered partially into first-year sea ice (sumps) to determine α- and γ-HCH concentrations in sea-ice brine. The overwintering of the CCGS Amundsen in the Canadian western Arctic, as part of the Circumpolar Flaw Lead (CFL) System Study, provided the circumstances to allow brine to accumulate in sumps sufficiently to test the methodology. We show, for the first time, that as much as 50% of total HCHs in seawater can become entrapped within the ice crystal matrix. On average, in the winter first-year sea ice HCH brine concentrations reached 4.013 ± 0.307 ng/L and 0.423 ± 0.013 ng/L for the α- and γ-isomer, respectively. In the spring, HCHs decreased gradually with time, with increasing brine volume fraction and decreasing brine salinity. These decreasing concentrations could be accounted for by both the dilution with the ice crystal matrix and under-ice seawater. We propose that the former process plays a more significant role considering brine volume fractions calculated in this study were below 20%. Levels of HCHs in the brine exceed under-ice water concentrations by approximately a factor of 3, a circumstance suggesting that the brine ecosystem has been, and continues to be, the most exposed to HCHs.

Increasing contaminant burdens in an arctic fish, Burbot ( Lota lota ), in a warming climate.

The temporal patterns of mercury (Hg), polychlorinated biphenyls (PCBs), and other contaminants in Arctic aquatic biota are usually attributed to changing atmospheric sources. However, climate variability and change is another means of altering contaminant fate and bioavailability. We show here that the concentrations of Hg and PCBs in Mackenzie River burbot ( Lota lota ), a top predator fish and important staple food for northern Canadian communities, have increased significantly over the last 25 years despite falling or stable atmospheric concentrations, suggesting that environmental processes subsequent to atmospheric transport are responsible. Using a dated sediment core from a tributary lake near the Mackenzie River sampling site, we show that variations in Hg concentrations downcore are strongly associated with labile, algal-derived organic matter (OM). Strong temporal correlations between increasing primary productivity and biotic Hg and PCBs as reflected by burbot suggest that warming temperatures and reduced ice cover may lead to increased exposure to these contaminants in high trophic level Arctic freshwater biota.

Natural rates of sediment containment of PAH, PCB and metal inventories in Sydney Harbour, Nova Scotia.

Analyses of metal and organic contaminants were carried out on 41 sediment cores, dated using (210)Pb and (137)Cs, from the heavily industrialized region of Sydney Harbour, N.S. to evaluate the history of contamination and to predict the rates of natural containment of the harbour by sediment burial. Geochronologies for metals (eg. Pb, As) and polycyclic aromatic hydrocarbons (PAHs) are correlated with the development of the steel and coke industries in the Sydney region while polychlorinated biphenyl (PCB) geochronologies reflect the disposal of electrical equipment used in the steel mill/coking operations. Pb was derived mainly from atmospheric emissions and its concentration has declined exponentially with time in harbour sediments since the closure of the steel mill/coke ovens in the 1980s with a time constant of about 15 years. This represents the time scale for the circulation of this particle-associated contaminant in transient catchment basins prior to permanent deposition in the sediments. PAH and PCB sediment concentrations have also declined exponentially with time since the 1980s, but with a smaller time constant of 10 years owing to the fact that they enter the harbour directly with steel mill and coke oven effluent rather than through atmospheric pathways. Since the time dependence for the burial of metal and organic inventories can be modeled by first order processes, future contaminant levels can be predicted for surface sediments in Sydney Harbour. Mean sediment concentrations of metal and organic contaminants in the upper 5 cm throughout most of the harbour are predicted to decline to levels below the effects range-medium (above which organisms are very likely to be negatively affected by the presence of a contaminant) by 2030.

Biogeochemical cycling in the Strait of Georgia.

The papers in this special issue present the results of a five-year project to study sedimentary biogeochemical processes in the Strait of Georgia, with special emphasis on the near-field of a large municipal outfall. Included in this special issue are overviews of the sedimentology, benthic biology, status of siliceous sponge reefs and distribution of organic carbon in the water column. Other papers address the cycling of contaminants (PCBs, PBDEs) and redox metals in the sediment, a method to map the extent of the influence of municipal effluent from staining on benthic bivalves, and the relationships among geochemical conditions and benthic abundance and diversity. The latter set of papers addresses the role of municipal effluent as a pathway of organic carbon and other contaminants into the Strait of Georgia and the effect of the effluent on benthic geochemistry and biology.

Responses of subtidal benthos of the Strait of Georgia, British Columbia, Canada to ambient sediment conditions and natural and anthropogenic depositions.

Patterns in infaunal biota in the Strait of Georgia are explored relative to water depth, substrate type, organic content of sediments and sedimentation characteristics. The analyses are based on geographically-diverse grab and core data collected over a 19-year period. Infaunal abundance and biomass were not predictable by sediment particle size, organic content or water depth. While organic flux was a reasonable predictor of biotic factors, quality of organic material, relative proportions of organic and inorganic input and source of inputs were also important in this regard. Areas with high accumulation of sediment and high organic flux rates from terrestrial (riverine) sources supported the highest macro-infaunal abundance and biomass found to date in the Strait of Georgia, and were dominated by bivalves. Polychaetes dominated in low organic deposition conditions, and where anthropogenic organic deposition was high. However, biota were severely impoverished in sediments with high organic content from marine deposition, due to low fluxes and poor quality of organic material. Taxa number was related to percent total nitrogen and to the ratio of organic/inorganic flux, both in background conditions and where there was labile organic enrichment. Faunal communities from the Fraser River delta, which experiences considerable bottom-transported riverine material, were very different in composition from those that proliferate in habitats with high deposition and organic flux from the water column.

Water column organic carbon in a Pacific marginal sea (Strait of Georgia, Canada).

Marginal seas provide a globally important interface between land and interior ocean where organic carbon is metabolized, buried or exported. The trophic status of these seas varies seasonally, depending on river flow, primary production, the proportion of dissolved to particulate organic carbon and other factors. In the Strait of Georgia, about 80% of the organic carbon in the water column is dissolved. Organic carbon enters at the surface, with river discharge and primary production, particularly during spring and summer. The amount of organic carbon passing through the Strait (approximately 16x10(8) kg C yr(-1)) is almost twice the standing inventory (approximately 9.4x10(8) kg C). The organic carbon that is oxidized within the Strait (approximately 5.6x10(8) kg yr(-1)) presumably supports microbial food webs or participates in chemical or photochemical reactions, while that which is exported (7.2x10(8) kg yr(-1)) represents a local source of organic carbon to the open ocean.

Sediment redox tracers in Strait of Georgia sediments--can they inform us of the loadings of organic carbon from municipal wastewater?

Organic carbon composition and redox element (Mn, Cd, U, Re, Mo, SigmaS, AVS) distributions are examined in seven 210Pb-dated box cores collected from the Strait of Georgia, British Columbia to evaluate the potential for redox elements to reveal impacts of anthropogenic loadings of labile organic carbon to sediments. In particular, the cores have been collected widely including regions far from local anthropogenic inputs and from locations within the zone of influence of two municipal outfalls where sediments are exposed to enhanced organic loadings from outfalls. We find a wide natural range in organic carbon forcing within the basin sediments generally reflected as Mn enrichments near the surface in cores exhibiting slow organic oxidation and sulphide, Cd, Mo, U and Re enrichments in cores exhibiting higher organic oxidation rates. Concentration profiles for redox elements or organic carbon are misleading by themselves, as they are influenced strongly by sediment porosity and sedimentation rate, and the organic matter remaining in sediment cores is predominantly recalcitrant. Fluxes of redox elements together with rates of organic metabolism estimated from sedimentation rates provide a better picture of the organic forcing. One core, GVRD-3, collected within the zone of influence of the Iona municipal outfall (0.5 km away), exhibits the highest organic carbon oxidation rates, enhanced Ag fluxes in the sediment surface mixed layer and altered delta15N composition, all of which implicate outfall particulates. Cd is also elevated in the GVRD-3 surface sediments, but evidence points to contamination and not redox forcing supporting this observation. Uranium also shows enrichment at sites near the outfalls, possibly in response to enhanced microbial metabolism. Predominantly these cores exhibit a wide natural range of organic carbon fluxes and organic carbon oxidation rates, supported by fluxes of marine and terrigenous organic carbon, within which it is difficult to identify any significant impact from municipal outfall organic carbon.

Joined by geochemistry, divided by history: PCBs and PBDEs in Strait of Georgia sediments.

Polychlorinated biphenyls (PCBs) are relict contaminants, while polybrominated diphenyl ethers (PBDEs) are in increasing use. Using sediment cores collected in the Strait of Georgia, we demonstrate that the surface sediment concentration of PCBs is largely determined by environmental processes, such as sediment accumulation and mixing rates, while that of PBDEs is strongly influenced by proximity to source. The Iona Island wastewater outfall appears to be a primary pathway for PBDEs. As well, Vancouver Harbour is highly contaminated with both classes of chemical. BDE-209, the main component of deca-BDE, is the dominant PBDE congener. Environmental debromination is not evident. Currently, the ranges of the surface concentration of PCBs and PBDEs are similar to one another, but that will change in the future, as the concentration of PBDEs continues to rise. The experience with PCBs suggests that if PBDEs were banned today, it would take decades for inorganic sediment to bury them.

Hexachlorocyclohexanes in the Canadian archipelago. 1. Spatial distribution and pathways of alpha-, beta- and gamma-HCHS in surface water.

Hexachlorocyclohexanes (HCHs) in the surface water of the Canadian Archipelago and south Beaufort Sea were measured in summer, 1999. Overall concentrations of HCH isomers were in order of abundance: alpha-HCH (3.5 +/- 1.2 ng L(-1)) > gamma-HCH (0.31 +/- 0.07 ng L(-1)) > beta-HCH (0.10 +/- 0.03 ng L(-1)). Concentrations and ratios of alpha-HCH/gamma-HCH decreased significantly (p < 0.001 to 0.003) from west to east, but there was no significant variation in alpha-HCH/ beta-HCH. The (+) enantiomer of alpha-HCH was preferentially degraded, with enantiomer fractions (EFs) ranging from 0.432-0.463 and increasing significantly (p < 0.001) from west to east. Concentrations also varied latitudinally for alpha-HCH and gamma-HCH (p < 0.002) but not for beta-HCH. Principal component analysis with variables alpha-HCH and gamma-HCH concentrations, EF, latitude, and longitude accounted for 71% (PC 1) and 16% (PC 2) of the variance. Mixing in the eastern Archipelago was modeled by assuming three end members with characteristic concentrations of alpha-HCH and gamma-HCH. The model accounted for the observed concentrations and higher EFs of alpha-HCH at the eastern stations.

Trifluoroacetate profiles in the Arctic, Atlantic, and Pacific Oceans.

A series of depth profiles was collected at 22 sites in the Arctic, North and South Atlantic, and Pacific Oceans to determine spatial patterns for trifluoroacetate (TFA) concentrations in the marine environment and to investigate possible natural sources of TFA. Profiles were also taken over underwater vents in the North and South Pacific and the Mediterranean Sea. At the profile sites, TFA values ranged from <10 ng/L in the Pacific Ocean to greater than 150 ng/L in the Atlantic Ocean. Samples from the Canada Basin of the Arctic Ocean exhibited variable TFA concentrations (60-160 ng/L) down to 700 m. Below this depth, in water having 14C ages exceeding 1000 years, the TFA concentrations were constant (150 ng/L). Water returning to the Atlantic through the Canadian Arctic Archipelago had constant high TFA values. Profiles from the Northern Atlantic exhibited high values at all depths but were more consistent in the Western Atlantic. The northwestern Pacific Ocean surface profile sites exhibited low TFA concentrations in the top 100 m increasing to a maximum of 60 ng/L with depth. Samples from the South Pacific Ocean site had generally low values with a few depths (>800 m) having concentrations of 50 ng/L or more. To determine if underwater vents could contribute to the TFA concentrations in the oceans, profiles were taken over three vents in the Pacific and Mediterranean Oceans. The results suggest that some deep-sea vents may be natural sources of TFA.

Biogeographic provinces of total and methyl mercury in zooplankton and fish from the Beaufort and Chukchi seas: results from the SHEBA drift.

Samples of copepods (Calanus hyperboreus) and arctic cod (Boreogadus saida) were collected along the SHEBA (Surface HEat Budget of the Arctic) drift track, which commenced in the Canada Basin (October 1997) and finished in the Mendeleev Basin (October 1998). Here, we report total mercury (HgT) and CH3Hg concentrations in these biological samples and examine concentration variability along the drift track in the context of trophic variation, inputs from land, spring mercury depletion events (MDEs), and oceanographic provinces. We find background concentrations of HgT in C. hyperboreus as low as 0.02 microg/g (dw), with the Canada Basin samples exhibiting approximately 2-fold higher mercury concentrations than those from the Chukchi Plateau and Mendeleev Abyssal Plain. This east-to-west trend in mercury concentration is punctuated by two and possibly three intervals of elevated mercury (HgT, 0.10-0.12 microg/g (dw); CH3Hg, 0.023-0.028 microg/g (dw)) along the drift track. One interval of elevated HgT and CH3-Hg levels occurred during and shortly after melt. %CH3Hg reached a maximum of 60% during this time period, three times higher than any other time during the drift. This transient rise in C. hyperboreus CH3Hg concentration seems to strongly point to mercury accumulated in snow during MDEs. However, the alignment of elevated mercury samples with oceanographic fronts and the observed regional differences between basins suggest that variation of mercury concentration is primarily a consequence of ocean structure. Given that large animals such as whales selectively forage in regions of higher food concentration such as fronts, recent change in the ice climate of the western Arctic Ocean, perhaps mediated by changes in heat storage, may provide the means to change their exposure to mercury thus explaining observed increases in mercury concentrations in western beluga whales during the 1990s.

Recent climate change in the Arctic and its impact on contaminant pathways and interpretation of temporal trend data.

The Arctic has undergone dramatic change during the past decade. The observed changes include atmospheric sea-level pressure, wind fields, sea-ice drift, ice cover, length of melt season, change in precipitation patterns, change in hydrology and change in ocean currents and watermass distribution. It is likely that these primary changes have altered the carbon cycle and biological systems, but the difficulty of observing these together with sporadic, incomplete time series makes it difficult to evaluate what the changes have been. Because contaminants enter global systems and transport through air and water, the changes listed above will clearly alter contaminant pathways. Here, we review what is known about recent changes using the Arctic Oscillation as a proxy to help us understand the forms under which global change will be manifest in the Arctic. For Pb, Cd and Zn, the Arctic is likely to become a more effective trap because precipitation is likely to increase. In the case of Cd, the natural cycle in the ocean appears to have a much greater potential to alter exposure than do human releases of this metal. Mercury has an especially complex cycle in the Arctic including a unique scavenging process (mercury depletion events), biomagnifying foodwebs, and chemical transformations such as methylation. The observation that mercury seems to be increasing in a number of aquatic species whereas atmospheric gaseous mercury shows little sign of change suggests that factors related to change in the physical system (ice cover, permafrost degradation, organic carbon cycling) may be more important than human activities. Organochlorine contaminants offer a surprising array of possibilities for changed pathways. To change in precipitation patterns can be added change in ice cover (air-water exchange), change in food webs either from the top down or from the bottom up (biomagnification), change in the organic carbon cycle and change in diets. Perhaps the most interesting possibility, presently difficult to predict, is combination of immune suppression together with expanding ranges of disease vectors. Finally, biotransport through migratory species is exceptionally vulnerable to changes in migration strength or in migration pathway-in the Arctic, change in the distribution of ice and temperature may already have caused such changes. Hydrocarbons, which tend to impact surfaces, will be mostly affected by change in the ice climate (distribution and drift tracks). Perhaps the most dramatic changes will occur because our view of the Arctic Ocean will change as it becomes more amenable to transport, tourism and mineral exploration on the shelves. Radionuclides have tended not to produce a radiological problem in the Arctic; nevertheless one pathway, the ice, remains a risk because it can accrue, concentrate and transport radio-contaminated sediments. This pathway is sensitive to where ice is produced, what the transport pathways of ice are, and where ice is finally melted-all strong candidates for change during the coming century. The changes that have already occurred in the Arctic and those that are projected to occur have an effect on contaminant time series including direct measurements (air, water, biota) or proxies (sediment cores, ice cores, archive material). Although these 'system' changes can alter the flux and concentrations at given sites in a number of obvious ways, they have been all but ignored in the interpretation of such time series. To understand properly what trends mean, especially in complex 'recorders' such as seals, walrus and polar bears, demands a more thorough approach to time series by collecting data in a number of media coherently. Presently, a major reservoir for contaminants and the one most directly connected to biological uptake in species at greatest risk-the ocean-practically lacks such time series.

Sources and pathways of selected organochlorine pesticides to the Arctic and the effect of pathway divergence on HCH trends in biota: a review.

Historical global usage and emissions for organochlorine pesticides (OCPs), including hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethane (DDT), toxaphene and endosulfan, are presented. Relationships between the air concentrations of these OCPs and their global emissions are also discussed. Differences between the pathways of alpha- and beta-HCH to the Arctic Ocean are described in the context of environmental concentrating and diluting processes. These concentrating and diluting processes are shown to control the temporal and spatial loading of northern oceans and that the HCH burdens in marine biota from these oceans respond accordingly. The HCHs provide an elegant example of how hemispheric-scale solvent switching processes can alter the ocean into which an HCH congener partitions, how air-water partitioning controls the pathway for HCHs entering the Arctic, and how the various pathways impact spatial and temporal trends of HCH residues in arctic animals feeding out of marine and terrestrial foodwebs.