Coastal ocean inorganic carbon cycling is influenced by cycles and seasonal variations in inland waters: a case study from Cambridge Bay (Iqaluktuuttiaq), Nunavut, Canada

Changes to inland waters (e.g. lakes, ponds, and streams) have the potential to impact carbon cycling in coastal marine environments. Terrestrial and marine settings are linked by features including rivers and streams, thus variations in streamflow and water chemistry may alter the timing and amount of carbon delivered to the coastal ocean from adjacent watersheds. This research focuses on inorganic carbon cycling in a lake – river – coastal ocean continuum (Greiner Lake, Freshwater Creek, and Cambridge Bay) and includes time-series data collected during field campaigns in the years 2017 – 2019. Understanding present-day inorganic carbon fluxes is important for identification of vulnerabilities such as susceptibility of coastal Arctic settings to ocean acidification. This requires quantification of dissolved inorganic carbon (DIC) discharge to the coastal ocean and CO₂ exchange between water bodies and the atmosphere. Preliminary results show variations in inorganic carbon concentrations and stream characteristics at multiple scales (e.g. daily, seasonal, and annual/inter-annual). A pulse of high-DIC, high-alkalinity water is released from the Greiner Lake watershed via Freshwater Creek during spring melt when the lake ice breaks up and the river begins to flow. The river plume can be mapped under the sea ice during spring melt using stable water isotopes as tracers and the associated elevated DIC concentrations can be detected in the center of Cambridge Bay. A detailed understanding of the temporally heterogeneous inorganic carbon inputs from the terrestrial environment to the ocean is critical for the calculation of carbon fluxes and the development of carbon budgets and models. Studies focused on inorganic carbon cycling in the coastal ocean should consider connected watersheds and careful design of field campaigns and sampling plans is needed to capture the full range of variations in the carbonate system parameters required to estimate fluxes.