Robie W. Macdonald

PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition

Abstract Parent and alkyl PAHs (51 compounds and alkyl homologues) have been quantified in suspended particulates and sediments (345 samples) from the Fraser River system, British Columbia, Canada. The best potential to distinguish natural and anthropogenic sources is exhibited by ratios of the principal mass 178, 202, 228 and 276 parent PAHs, 1,7/2,6+1,7-DMP (dimethylphenanthrene), the phenanthrene/anthracene and fluoranthene/pyrene alkyl PAH series and several less commonly applied PAHs (e.g. acephenanthrylene and pentaphene). Using these ratios we infer sources of PAH to the Fraser basin and evaluate the consistency of these source assignments and the suitability of various commonly applied PAH ratios as indicators. PAH ratios and total concentration data reveal a basin lightly impacted by a variety of sources in its remote regions, especially near roads, but heavily impacted in urban areas, particularly near Vancouver. Contamination sources shift from biomass (e.g. wood and grass) burning to vehicle emissions between remote and urban locations. Stormwater and wastewater discharges appear to collect PAH from urban areas and release them as point sources. In contaminated areas ratios are specific for combustion vs. petroleum sources, and some ratios (202 and 276) distinguish biomass or coal from liquid fossil fuel combustion. At lower concentrations multiple sources at times make interpretations based on a single ratio misleading and the higher mass ratios (228 and 276) may be most applicable to urban areas. In all cases the examination of a variety of PAH indicator ratios that encompass a range of masses is necessary for a robust interpretation.

Sensitivity of the carbon cycle in the Arctic to climate change

The recent warming in the Arctic is affecting a broad spectrum of physical, ecological, and human/cultural systems that may be irreversible on century time scales and have the potential to cause rapid changes in the earth system. The response of the carbon cycle of the Arctic to changes in climate is a major issue of global concern, yet there has not been a comprehensive review of the status of the contemporary carbon cycle of the Arctic and its response to climate change. This review is designed to clarify key uncertainties and vulnerabilities in the response of the carbon cycle of the Arctic to ongoing climatic change. While it is clear that there are substantial stocks of carbon in the Arctic, there are also significant uncertainties associated with the magnitude of organic matter stocks contained in permafrost and the storage of methane hydrates beneath both subterranean and submerged permafrost of the Arctic. In the context of the global carbon cycle, this review demonstrates that the Arctic plays an important role in the global dynamics of both CO2 and CH4. Studies suggest that the Arctic has been a sink for atmospheric CO2 of between 0 and 0.8 Pg C/yr in recent decades, which is between 0% and 25% of the global net land/ocean flux during the 1990s. The Arctic is a substantial source of CH4 to the atmosphere (between 32 and 112 Tg CH4/yr), primarily because of the large area of wetlands throughout the region. Analyses to date indicate that the sensitivity of the carbon cycle of the Arctic during the remainder of the 21st century is highly uncertain. To improve the capability to assess the sensitivity of the carbon cycle of the Arctic to projected climate change, we recommend that (1) integrated regional studies be conducted to link observations of carbon dynamics to the processes that are likely to influence those dynamics, and (2) the understanding gained from these integrated studies be incorporated into both uncoupled and fully coupled carbon-climate modeling efforts. (Less)

Contaminants in the Canadian Arctic: 5 years of progress in understanding sources, occurrence and pathways

Recent studies of contaminants under the Canadian Northern Contaminants Program (NCP) have substantially enhanced our understanding of the pathways by which contaminants enter Canadas Arctic and move through terrestrial and marine ecosystems there. Building on a previous review (Barrie et al., Arctic contaminants: sources, occurrence and pathways. Sci Total Environ 1992:1-74), we highlight new knowledge developed under the NCP on the sources, occurrence and pathways of contaminants (organochlorines, Hg, Pb and Cd, PAHs, artificial radionuclides). Starting from the global scale, we examine emission histories and sources for selected contaminants focussing especially on the organochlorines. Physical and chemical properties, transport processes in the environment (e.g. winds, currents, partitioning), and models are then used to identify, understand and illustrate the connection between the contaminant sources in industrial and agricultural regions to the south and the eventual arrival of contaminants in remote regions of the Arctic. Within the Arctic, we examine how contaminants impinge on marine and terrestrial pathways and how they are subsequently either removed to sinks or remain where they can enter the biosphere. As a way to focus this synthesis on key concerns of northern residents, a number of special topics are examined including: a mass balance for HCH and toxaphene (CHBs) in the Arctic Ocean; a comparison of PCB sources within Canadas Arctic (Dew Line Sites) with PCBs imported through long-range transport; an evaluation of concerns posed by three priority metals--Hg, Pb and Cd; an evaluation of the risks from artificial radionuclides in the ocean; a review of what is known about new-generation pesticides that are replacing the organochlorines; and a comparison of natural vs. anthropogenic sources of PAH in the Arctic. The research and syntheses provide compelling evidence for close connectivity between the global emission of contaminants from industrial and agricultural activities and the Arctic. For semi-volatile compounds that partition strongly into cold water (e.g. HCH) we have seen an inevitable loading of Arctic aquatic reservoirs. Drastic HCH emission reductions have been rapidly followed by reduced atmospheric burdens with the result that the major reservoir and transport agent has become the ocean. In the Arctic, it will take decades for the upper ocean to clear itself of HCH. For compounds that partition strongly onto particles, and for which the soil reservoir is most important (e.g. PCBs), we have seen a delay in their arrival in the Arctic and some fractionation toward more volatile compounds (e.g. lower-chlorinated PCBs). Despite banning the production of PCB in the 1970s, and despite decreases of PCBs in environmental compartments in temperate regions, the Arctic presently shows little evidence of reduced PCB loadings. We anticipate a delay in PCB reductions in the Arctic and environmental lifetimes measured in decades. Although artificial radionuclides have caused great concern due to their direct disposal on Russian Shelves, they are found to pose little threat to Canadian waters and, indeed, much of the radionuclide inventory can be explained as remnant global fallout, which was sharply curtailed in the 1960s, and waste emissions released under license by the European reprocessing plants. Although Cd poses a human dietary concern both for terrestrial and marine mammals, we find little evidence that Cd in marine systems has been impacted by human activities. There is evidence of contaminant Pb in the Arctic, but loadings appear presently to be decreasing due to source controls (e.g. removal of Pb from gasoline) in Europe and North America. Of the metals, Hg provokes the greatest concern; loadings appear to be increasing in the Arctic due to global human activities, but such loadings are not evenly distributed nor are the pathways by which they enter and move within the Arctic well understood.

A SEDIMENT AND ORGANIC CARBON BUDGET FOR THE CANADIAN BEAUFORT SHELF

Abstract The Arctic Ocean accounts for 20% of the worlds continental shelves. Because the Arctic is sensitive to global change, budgets of organic carbon for its shelves are of immediate interest. The Mackenzie Shelf of the Canadian Beaufort Sea is the best North American proxy for the enormous Eurasian Shelves (large area, large river input), and the only site for which a complete organic carbon budget can be attempted, due to an extensive data base. A mass balance for the Mackenzie Shelf has been constructed for sediments, terrestrial organic carbon, and primary produced carbon. We have considered allochthonous inputs from the Mackenzie River, from coastal erosion, from smaller rivers, from groundwater, from the atmosphere and import by ice. The Mackenzie River dominates the supply to the Beaufort shelf of inorganic sediment (127 Mt a −1 ) and paniculate and dissolved terrestrial carbon (2.1 Mt a −1 POC, 1.3 Mt a −1 DOC). The combined input from all other sources contributes only about 5% of the Mackenzie load. Using sediment accumulation data we estimate that about half of the sediment supply is trapped in the delta, about 40% on the shelf and the remainder escapes the shelf edge by various processes. Autochthonous primary production in the delta and on the shelf adds a further 3.3 Mt a −1 of particulate organic carbon. A box model has been constructed to account for sediment, terrestrial organic carbon and primary produced carbon. Whereas about 60% of the terrestrial POC is preserved in delta and shelf sediments, it appears that most (97%) of the primary produced carbon is recycled and not preserved in sediments. Confidence in the budget should be improved by focusing future research on the determination of modern sedimentation rates on the delta and shelf, measurement of organic carbon content of deltaic sediments, determination of primary production on the shelf, and determination of the relative proportions of terrestrial and marine organic carbon preserved in sediments.

Physical and geochemical properties across the Atlantic/Pacific water mass front in the southern Canadian Basin

Temperature, salinity, nutrients, oxygen, and halocarbon data collected in the Arctic Ocean reveal a frontal structure previously unrecognized in the hydrography of the Canadian Basin. Samples were collected on a 1300-km section extending from the Beaufort Sea in the Canada Basin to the East Siberian Sea in the Makarov Basin. These data, collected in 1993 aboard the CCGS Henry Larsen, reveal a lateral boundary between water masses of Atlantic and Pacific origin. The term “water mass assembly” is introduced to describe the basic arrangement or vertical stacking of water masses found in the Arctic Ocean, recognizing that water mass components within each assembly may differ from basin to basin. Using historical data, two primary water mass assemblies are defined, each consisting of three layers: an upper layer, an Atlantic layer, and a deep layer. These two assemblies are marked by important differences. One assembly, here defined as the Western Arctic (WA) assembly, is characterized by an upper layer of relatively fresh, high-nutrient water of Pacific origin; below this, by an Atlantic layer with a core temperature generally below 0.5°C; and, finally, by a deep layer of higher salinities and colder temperatures (about −0.5°C) than found in the overlying Atlantic layer. The second assembly, here defined as Eastern Arctic (EA) assembly, is characterized by the absence of Pacific water in the upper layer; below this, by an Atlantic layer core as warm as 2° to 3°C; and by a colder (about −0.9°C) deep layer. Because the presence or absence of Pacific origin water is a key characteristic distinguishing the two assemblies, we will refer to the water mass boundary between the two assemblies as the Atlantic/Pacific front. Earlier research indicated that water masses in the Arctic Ocean were separated by a front above the Lomonosov Ridge into the Canadian and Eurasian basins. Although all Larsen-93 stations from the Canada Basin (A1–D1) display classic WA assembly characteristics, the Makarov Basin station (E1) shows EA assembly characteristics in the upper and Atlantic layers and a WA assembly deep layer. This suggests a relocation in the position of the Atlantic/Pacific boundary away from the Lomonosov Ridge. Further, Larsen-93 data show the transition region between the Atlantic and deep layers is fresher in the Makarov Basin than corresponding water in either the Canada or Eurasian basins, implying a source of cold, low-salinity water, perhaps from the Laptev and East Siberian shelves. The front separating these two assemblies lies above the Mendeleyev Ridge and is marked by large lateral gradients in all measured properties. In particular, the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the Makarov Basin than in the Canada Basin, implying enhanced rates of ventilation. This suggests that direct exchange between the Canadian and Eurasian basins has occurred recently near the perimeter and that physical and chemical properties, including contaminants, may have been transported by boundary currents more quickly from one basin to the other.

Terrestrial and marine biomarkers in a seasonally ice-covered Arctic estuary — integration of multivariate and biomarker approaches

Hydrocarbons, including alkanes, alkenes, hopane triterpenes and polycyclic aromatic hydrocarbons (PAHs), plus sterols, n-alcohols and a number of higher plant triterpenoids have been determined for suspended particulate, sediment trap and sediment samples taken from the Mackenzie River and the adjacent Mackenzie shelf in the Beaufort Sea. These biomarkers are valuable tracers of terrigenous and petrogenic inputs from the river to the shelf water column and are also useful for assessing marine production in the Mackenzie River estuary. We use Principal Component Analysis (PCA) to provide a robust classification of biomarkers according to their primary source (e.g. terrigenous, marine) and to identify which biomarkers covary. The Mackenzie River is the dominant source for n-alkanes, n-alcohols, sterols and triterpenoids from higher plants, diagenetic hopanes, petrogenic isoprenoids and parent (unsubstituted) PAHs to the Mackenzie shelf. The riverine hydrocarbon signature of these markers is modified by preferential settling out of lithic material relative to less dense higher plant debris. Seasonal marine production of a suite of alkenes, sterols and alcohols from phytoplankton and Zooplankton is evident in water column and sediment trap samples, but these labile compounds tend not to be preserved in surficial sediments. Although few individual sterols provide unambiguous markers of terrestrial or marine organic matter, PCA successfully classifies sterols as either principally marine or principally terrestrial. n-Alcohols are often overlooked as biomarkers, but we find that they too reflect the relative contributions of Zooplankton and terrigenous inputs in the Mackenzie estuary. To quantify dispersal of riverine material on the adjacent shelf in the context of dilution by marine production, we develop a multivariate Partial Least Squares (PLS) path model. We find that the PLS results strengthen geochemical interpretations based on individual biomarkers by providing a quantitative representation of the differences among samples. PLS successfully models the increases in terrigenous particulate on the shelf with river flow and the effect of autochthonous production.

Distribution and sources of organic biomarkers in arctic sediments from the Mackenzie River and Beaufort Shelf

Abstract Suspended sediments from the Mackenzie River Delta and surface sediments from the Beaufort Shelf were analyzed by alkaline CuO oxidation. In addition, elemental (percentage total organic carbon, inorganic carbon and silica) and stable carbon isotope compositions were determined for all samples. The carbon-normalized yields of over 60 different compounds derived from the oxidative hydrolysis of several biochemicals, including lignin, cutin, proteins, polysaccharides and lipids were quantified and subjected to principal component analyses (PCA). The results of these investigations indicate that most lignin and cutin products originate from non-woody angiosperm vascular vegetation such as that present in the tundra. For example, lignin-derived product compositions are characterized by relatively high syringyl:vanillyl and cinnamyl:vanillyl phenol ratios (exceeding 0.4 and 0.15, respectively). The compositions of these biomarkers, especially the elevated (0.5 to 1.5) acid:aldehyde ratios for vanillyl and syringyl phenols, also suggest that the land-derived organic matter (OM) exported by the Mackenzie River is highly degraded. Non-lignin CuO reaction products derived from proteins, polysaccharides and lipids display distributions that are consistent with a predominant marine (autochthonous) source. The composition of lipid-derived fatty acid products, which is in shelf sediments are dominated by hexanedecenoic acid, suggests a planktonic origin, likely from diatoms. The distribution of these biomarkers across the shelf indicates the presence of relatively fresh algal remains in at least one sample. The relationships between terrigenous biomarker concentrations and bulk 13 C/ 12 C ratios in surface sediments indicate that terrestrial organic carbon dominates in abundance (80% to 50% of total organic carbon) over much of the shelf. Marine/algal-derived carbon represents 20% to 50% of the total carbon in shelf sediments, with the largest fraction being present in the outer mid-shelf. The large variability in the yields of CuO biomarkers from the river suspended sediment samples highlights the heterogeneous nature of the particle load exported by the Mackenzie River. Such variability must be taken into account during the development of quantitative carbon budgets for the Beaufort Shelf.

Waters of the Makarov and Canada basins

Abstract Hydrographic measurements from the 1994 Arctic Ocean Section show how the Makarov and Canada basins of the Arctic Ocean are related, and demonstrate their oceanographic connections to the Eurasian Basin. The inflow into the Makarov Basin consists largely of well-ventilated water within a broad band of densities from a boundary flow over the Siberian end of the Lomonosov Ridge. The boundary flow contains a significant component of dense shelf water likely originating in the Barents, Kara, and Laptev Seas. Earlier ice camp data show that the Canada Basin is relatively more isolated from this ventilation source. In the Canada Basin shelf sources influenced by Bering Sea water appear to add cold waters with high silicate concentrations to the halocline and deeper. In 1994 the halocline silicate maximum over the central Makarov Basin was absent, evidence of the recent displacement of the upper (S∼ 33.1) halocline water from the Chukchi-East Siberian Sea region by water from the Eurasian Basin. Much of the Makarov Basin water in and below the halocline is in fact from the Eurasian Basin, with admixture of waters from the Canada Basin suggested by their higher silicate concentrations. Mid-depth eddies may transport anomalous properties into the central Arctic and create property gradients or fronts in mid-depth and deep waters. The complex topography of the Mendeleyev Ridge-Chukchi Plateau region also may assist spreading of water from the boundary into the interior. Atlantic layer characteristics in 1994 differed from previous general depictions. In particular the core temperatures at the Chukchi-Mendeleyev boundary were at least 0.2°C warmer on average than indicated in earlier work. The recent warming at intermediate depth has resulted from inflow of Atlantic waters that have been cooled relatively little during their transit of the Norwegian Sea.

Evidence for warming of Atlantic water in the Southern Canadian Basin of the Arctic Ocean: Results from the Larsen‐93 Expedition

Potential temperature (θ) and salinity (S) data obtained along the perimeter of the southern Canadian Basin north of the East Siberian Sea in 1993 aboard the CCGS Henry Larsen show higher temperatures in waters of Atlantic origin than in available climatological data for the Canadian Basin. In particular, a front is observed near the Mendeleyev Ridge which separates the cooler Atlantic waters of the Canada Basin from the warmer Atlantic waters observed in the Makarov Basin. The front is further characterized by a change in the θ/S slope of Arctic thermocline water, and by thermohaline intrusions (θ and S reversals) within the Atlantic layer. The idea that this warm variety of Atlantic water has come recently from the Eurasian Basin is supported by its higher level of the tracer CFC-11.

Changes in temperature and tracer distributions within the Arctic Ocean: results from the 1994 Arctic Ocean section

Abstract Major changes in temperature and tracer properties within the Arctic Ocean are evident in a comparison of data obtained during the 1994 Arctic Ocean Section to earlier measurements. (1) Anomalously warm and well-ventilated waters are now found in the Nansen, Amundsen and Makarov basins, with the largest temperature differences, as much as 1 °C, in the core of the Atlantic layer (200–400 m). Thus thermohaline transition appears to follow from two distinct mechanisms: narrow (order 100 km), topographically-steered cyclonic flows that rapidly carry new water around the perimeters of the basins; and multiple intrusions, 40–60 m thick, which extend laterally into the basin interiors. (2) Altered nutrient distributions that within the halocline distinguish water masses of Pacific and Atlantic origins likewise point to a basin-wide redistribution of properties. (3) Distributions of CFCs associated with inflows from adjacent shelf regions and from the Atlantic demonstrate recent ventilation to depths exceeding 1800 m. (4) Concentrations of the pesticide HCH in the surface and halocline layers are supersaturated with respect to present atmospheric concentrations and show that the ice-capped Arctic Ocean is now a source to the global atmosphere of this contaminant. (5) The radionuclide 129I is now widespread throughout the Arctic Ocean. Although the current level of 129I level poses no significant radiological threat, its rapid arrival and wide distribution illustrate the speed and extent to which waterborne contaminants are dispersed within the Arctic Ocean on pathways along which other contaminants can travel from western European or Russian sources.