Relevant Degree Programs
Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Nov 2019)
This PhD thesis describes some of the first distributions of lead, iron and manganese in the Canadian Arctic Ocean and other multiple trace metals in remote rivers in the Canadian Arctic Archipelago (CAA), unraveling the processes which modulate their distributions. A clear spatial variability in the distributions of dissolved aluminum, iron, manganese, nickel, copper, zinc, cadmium and lead was observed in small CAA rivers, which reflects differences in bedrock geology and South-North environmental gradients (e.g., solar radiation, precipitation, temperature) in the Archipelago. The concentrations of many trace metals from these small CAA rivers are considerably higher than those measured in Canada Basin waters, and therefore they have the potential to be a significant source of metals to transiting waters to adjacent coastal areas. Dissolved lead concentrations in the Canadian Arctic Ocean were among the lowest reported concentrations in ocean waters, attributed to the isolation of this region from anthropogenic inputs. Nonetheless, distinctive high and anthropogenically derived lead features, advected from the northeast Subarctic Pacific and the Labrador Sea, were observed in this study. The natural cycling of lead in the Canadian Arctic Ocean is primarily controlled by an interaction of glacial and sea ice melt water inputs, and scavenging throughout the water column and especially at the sediment water interface. Contrary to lead distributions, dissolved iron and manganese (DFe and DMn) concentrations measured in the Canadian Arctic Ocean were within the range of those reported for major basins. In our study the highest DFe and DMn concentrations were generally found in surface and subsurface waters. This is attributed to large riverine inputs present in this region and to continental shelf sediment fluxes. A dynamic interplay between removal processes and inputs of these trace metals largely control their vertical distribution below 300 m. Advective sources are predominant in the low productivity Canada Basin, contrasting with the important role of regenerated DFe and DMn in the productive Baffin Bay and Labrador Sea. The findings presented in this thesis shed light on important biogeochemical processes and water masses circulation taking place in this unique and underexplored environment.
The biogeochemical cycling of manganese (Mn) in the ocean is regulated by the complex interaction between external sources, removal processes and its redox sensitive chemistry. The goal of this research was to expand our knowledge about the relative importance of each process, to assess the major controls on annual variability in Mn distributions, and to explore interaction between particulate and dissolved phases of Mn. To address these questions, the distribution of suspended particulate Mn (pMn) and dissolved Mn (dMn) in the northeast Pacific Ocean across the Line-P transect and the Beaufort Sea of the Arctic Ocean was evaluated in the context of the regional physical and chemical processes. Within the Summer Mixing Layer (SML) of the Line-P transect, it was found that eolian dust input and photo-reduction elevate dMn and the annual variability in dMn at the station nearest the shore is driven by variations in the strength of Ekman transport, which brings Mn-rich coastal water to this area. Below the SML, where UV ration is no longer available for photo-reduction, rapid oxidation is identified as the main process responsible for elevated pMn. Based on a simple advection/mixing model, it was identified that the horizontal distribution of dMn at intermediate depths is influenced either by eastward advection of NPIW or by northward advection of low dMn water, depending on the position of the boundary between the Pacific subarctic and subtropical gyres. Within the Oxygen Minimum Zone (OMZ), Mn is regulated by increased reduction across the transect. The decreasing concentration of dMn from the continent to the open ocean, and the low lithogenic pMn near the continental margin in the OMZ, are the combined result of reduction of re-suspended particles and addition of dMn from the sediments. This work also evaluated the biogeochemical cycling of dMn in the Beaufort Sea. Mn in this area is controlled more by external sources rather than internal cycling. River water, sea ice melt water, and photo-reduction dominate in the surface, while advection of water mass and the mixing with remobilized dMn from the continental margin are the dominant influences at the mid-depth in this region.
This thesis presents novel applications of dissolved Ga and Pb isotope ratios as oceanographic tracers of biogeochemical cycling and trace metal input mechanisms in the northeast Pacific Ocean, the Columbia River plume, and the Western Arctic Ocean. Conclusions of this thesis are based on the first multi-year transect of dissolved Ga in the northeast Pacific Ocean along Line P, the first dissolved Ga concentrations reported in the Arctic Ocean, and the first Line P transect of Pb isotope ratios. This thesis introduces 5 new tracer applications contributing to oceanographic research, dissolved Ga traces: 1) advective inputs of trace metals in the northeast Pacific, 2) Pacific and Atlantic source waters in the western Arctic, and 3) plume transport of the Columbia River, Ga/Pb traces: 4) fluvial freshwater inputs, and Pb isotope ratios trace: 5) geographically and temporally distinct trace metal inputs to the northeast Pacific. Dissolved Ga is positively correlated with the variable spice, interpreted to trace advective trace metal inputs from the California Undercurrent and North Pacific Intermediate Waters bisecting the Line P transect. This thesis identifies the Ga/Pb ratio as a tracer of an interface along Line P of fluvial trace metal inputs. Isotopic ratios of Pb trace eolian Asiatic and fluvial North American sources, identifying a front of differential trace metal inputs along Line P. Dissolved Ga is identified as a conservative tracer of Pacific waters in the Arctic and applies the conservative nature of dissolved Ga to interpretation of calculated rates of nitrogen fixation within shallow waters of the Beaufort Gyre, impacting phosphate concentrations and ecosystems in both the Arctic and North Atlantic Oceans. Finally, dissolved Ga traces conservative and non-conservative behaviour under upwelling and downwelling conditions associated with the dynamic Columbia River plume. This thesis contributes the five tracer applications described above to interpretation of trace metal inputs and advection in the northeast Pacific Ocean and source waters and nitrogen and phosphate coupling in the western Arctic Ocean.
Environmental monitoring and remediation require techniques to identify the source and fate of metals emissions. In this study, Cd and Zn isotopes were evaluated as tools for the identification of metal sources through (1) the assessment of metallurgical processing as a source of Cd and Zn isotopic fractionation and (2) the measurement of isotopic compositions in bivalves from sites receiving variable metal contributions from natural and anthropogenic sources. This study was facilitated by the successful development of a technique to measure Cd and Zn isotopes (MC-ICP-MS) in environmental and anthropogenic samples.Cadmium, Zn and Pb isotopic ratios were measured for samples from an integrated Zn–Pb smelting/refining complex in B.C. (British Columbia, Canada). Significant fractionation of Cd and Zn isotopes during processing is demonstrated by the total isotopic variation in δ¹¹⁴/¹¹⁰Cd (1.04‰) and δ⁶⁶/⁶⁴Zn (0.42‰) among smelter samples. Characterization of Cd and Zn isotopic compositions in emissions as fractionated relative to ores demonstrates the tracing capability of this new tool. Moreover, Pb isotopic signatures may be used to identify sources contributing metals to environmental samples. Combined Cd, Zn and Pb isotope systematics were used to trace the source and distribution of these metals in bivalves from western Canada (B.C.), the USA and France. Variability in δ¹¹⁴/¹¹⁰Cd of bivalves (-1.20 to -0.09‰) is attributed to differences in the relative contributions of Cd from natural and anthropogenic (e.g., smelting) sources between sites. High Cd levels in B.C. oysters are identified as primarily natural, with some additional variability attributed to anthropogenic sources. In contrast, high Cd levels in French bivalves (Gironde estuary and Marennes-Oléron basin) are primarily anthropogenic. Variability in δ⁶⁶/⁶⁴Zn values exhibited by bivalve samples is small (0.28 to 0.46‰), with the exception of oysters from the polluted Gironde estuary (1.03 to 1.15‰). Lead isotopes are used to identify emissions from industrial processes and the consumption of unleaded gasoline and diesel fuel as metal sources to bivalve samples.This study demonstrates the effective use of Cd and Zn isotopes to trace anthropogenic sources in the environment and the benefit of combining these tools with Pb “fingerprinting” techniques.
Master's Student Supervision (2010 - 2018)
Aluminum dynamics in the ocean are unique given its rapid removal from the surface through adsorption onto sinking particles and its high abundance in the earth's crust. We optimized a flow injection analysis method to allow detection of the extremely low concentrations of dissolved aluminum found in the study region. Samples from the northeast Pacific have the lowest concentrations of dissolved Al found anywhere in the world’s ocean. We present dissolved aluminum data from a transect along Line P in the northeast Pacific in 2010 and 2011. Stations extend from near coastal waters, going through areas of potential eddy influence, and terminate at the historic Ocean Station Papa. Open ocean data shows concentrations an order of magnitude lower than extensive work performed in the Atlantic but overall similar trends with higher aluminum in the surface layer. The concentrations can go as low as 0.06 nmol/kg at depth and 0.36 nmol/kg in the surface. Coastal stations show elevated aluminum levels relative to the open ocean, and eddy influence inputs high aluminum concentrations from coastal shelf water.In the western Arctic, we present a transect from the 2009 Canadian GEOTRACES program. Here we see concentrations that increase with depth, from below 1.0 nmol/kg at the surface up to 11.6 nmol/kg at depth. This is inconsistent with previous measurements in the region, which showed an increase in the surface, proposed to be due to sea ice melt supplying dissolved aluminum to the surface. The high concentration of dissolved aluminum at depth indicate a bottom source of dissolved aluminum in this region. This is also observed in the north Atlantic near Labrador. Lastly, we present dust input data from both of these regions and compare them to previous modelled data, showing that models in the Pacific over-represent the amount of dust input. Arctic data is relatively less well known for dust.
Using a method which simultaneously concentrates and isolates Pb from seawater, a total of 208 samplescollected using trace-metal clean techniques were determined for dissolved Pb concentration in the subarcticNortheast Pacific and the Canada Basin of the southwestern Arctic Ocean. The analytical method found goodagreement between determined values and consensus values of several seawater standards. Concentration inseawater was generally dictated by proximity to pollution sources which appeared to provide Pb via aeoliandeposition and by proximity to primary productivity or freshly precipitated mineral phases which scavenged Pbto lower levels than expected based on previous research. Over the entire dataset, concentration ranged from 1.8pmol/kg to 81.3 pmol/kg, with the highest values occurring just below the permanent mixed layer in thenortheast Pacific and was of unknown origin. The lowest level was found in the Pacific water mass of thesouthern Beaufort Sea, which may be the result of interactions with sediment during transit through the Beringand Chukchi Seas. When samples that were expected to be contaminated are discounted, Pb levels weregenerally lowest in the Arctic, below 30 pmol/kg. Samples taken from three eddies along the British Columbianand southern Alaskan coasts found low [Pb] within the eddy relative to reference stations, though in two of theeddies a phytoplankton bloom had not occurred, suggesting that either the source water was low in Pb orscavenging had occurred by sorption onto precipitated mineral phases during estuarine processes. A low-resolution time series between 1992 and 2010 at Ocean Station Papa (OSP; 50°N, 145°W) found that Pbconcentration at this location has remained quite steady over time, in contrast with the North Atlantic Oceanwhich showed a drastic decrease in concentration over the same time period. The difference may be attributed toformation of the water mass in the Sea of Okhotsk during the winter when atmospheric conditions wouldtransport most Asian pollution away from the region where the water mass subducts and advects towards OSP,along with a different history of Pb pollution upwind of the Atlantic and Pacific Oceans.