Physical and biological controls on ocean acidification in the Southampton Island region, Hudson Bay

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Yezhova, Yekaterina
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Located in northwestern Hudson Bay, the Southampton Island region was identified as an Ecologically and Biologically Significant Area by Fisheries and Oceans Canada, and most recently distinguished as an Area of Interest in 2019 to become a Marine Protected Area. The region is undergoing climate-related changes; however, its oceanography has received little attention until recently. The main goal of this thesis was to provide a baseline evaluation of the state of ocean acidification of these waters, and to identify key factors driving changes in both pH and calcium carbonate saturation state. Twenty-two stations were sampled around the Island in August of 2019 for salinity, stable oxygen isotope ratio of seawater, total alkalinity, dissolved inorganic carbon (DIC), and stable carbon isotope ratio of DIC (δ13CDIC), providing comprehensive water column coverage. High fractions of sea-ice melt were found in surface waters in Foxe Basin/Channel, which had experienced the most recent loss of sea ice. High fractions of meteoric water were found in near-surface waters in Roes Welcome Sound, likely from Wager Bay outflow, and south of the Island, likely from both rivers local to the Island and from Hudson Bay’s northwestern rivers. Regionally high pH, low pCO2, dissolved oxygen (O2) oversaturation, and enriched values of δ13CDIC, and thus likely areas of net primary production, were generally observed in the top ~50 m in Foxe Basin/Channel and Roes Welcome Sound, and near surface in Repulse Bay and Frozen Strait. More acidic and aragonite-undersaturated waters, potentially corrosive to marine calcifying organisms, were found below ~60 to 250 m at stations in Foxe Basin/Channel, and in bottom waters of South Bay and Evans Strait. These areas were high in pCO2 and undersaturated in O2, signifying net respiration had likely produced the observed values. It was concluded that while primary production and respiration appeared to be the dominant processes controlling the concentration of DIC in the Southampton Island region, the data could not be explained by any single process alone, highlighting the importance of metabolic processes, freshwater inputs, and air-sea gas exchange in governing the DIC pool in the region.
Southampton Island, Hudson Bay, Ocean acidification, Carbon, Stable isotopes