Natural and Anthropogenic Impacts on Mercury Cycling and Distribution in the Sub-Arctic Hudson Bay Marine Environment

This thesis provides information on how mercury moves to and from Hudson Bay, and how it is distributed within the system. The first comprehensive survey of total mercury concentrations in river and marine waters and in marine sediments permits a compilation of mercury mass budgets that are used to model the modern and preindustrial mercury cycles in Hudson Bay. This model demonstrates that an internal process of sediment recycling provides the largest amount of mercury to the burial flux offshore. It further reveals that most modern mercury fluxes to Hudson Bay have increased by large amounts over the preindustrial era. Histories of sediment mercury deposition determined at 12 locations reveal that mercury originating from anthropogenic activities contributes to the increased sediment fluxes in most areas. However, underlying natural processes have also increased mercury concentrations in some areas, and natural variability of mercury within the sediments is similar in magnitude to the enrichments observed during the industrialized era. Consistent with the large role of recycled sediment in Hudson Bay, the distribution of mercury appears to be largely governed by oxidized, reworked marine carbon, rather than labile or residual carbon fractions. In areas demonstrating naturally increasing sediment mercury enrichments, greater proportions of marine carbon appear to drive the higher mercury concentrations.