UBC Theses and Dissertations

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UBC Theses and Dissertations

Tracing ocean pathways : modelling manganese and lead in the Canadian Arctic Rogalla, Birgit


Human-induced climate change is rapidly altering the Arctic sea ice regime, ocean dynamics, and freshwater cycle. These changes impact biogeochemical cycling, including the cycling of trace elements, but the exact manifestations remain unclear. Over the past decade, the international GEOTRACES program has greatly expanded the coverage of trace element observations in the Arctic Ocean, capturing the current state of the system. These observations, in conjunction with improvements in model representations, allow the development of trace element models to investigate drivers of the spatial distribution and seasonal variability of trace element concentrations, and to estimate sensitivity of trace element cycling to climate change. This dissertation describes some of the first three-dimensional models of the dissolved micronutrient manganese (Mn) and pollutant lead (Pb) in the Canadian Arctic Ocean, including the Canada Basin, the Canadian Arctic Archipelago (CAA), and Baffin Bay. I highlight sources that control the distributions of Mn and Pb in this region, and use Mn and Pb to trace sea ice sediments and river runoff, and Atlantic Water. The Mn model highlights the significance of the long-range transport of sediments by sea ice for micronutrients such as Mn in the Canada Basin. The disruption of the transpolar sea ice drift could reduce Mn supply to the Canada Basin and downstream. Sensitivity experiments varying the Mn content in runoff identify distinct continental and glacial runoff fingerprints of influence in the southwestern and northern CAA, respectively. Glacial runoff carries micronutrients southward from Nares Strait in the late summer and may help support longer phytoplankton blooms in the Pikialasorsuaq Polynya. The Pb model illustrates the continued impact of anthropogenic pollution on Pb concentrations in the Arctic through aerosol deposition, boundary transport, and, likely, river runoff and sediment resuspension. The Labrador Sea is a net source of Pb to Baffin Bay via the West Greenland Current and Pb highlights pathways of Atlantic Water in Baffin Bay. The model results presented in this thesis highlight trace element concentrations and supply mechanisms in the Arctic Ocean and their sensitivity to climatic changes, and illustrates the use of trace element models in extending knowledge gained from observations.

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