Describing seasonal marine carbon system processes in Cambridge Bay Nunavut using an innovative sensor platform

The marine carbonate system is a critical component of global biogeochemical cycles. It determines a given marine region’s status as a source or sink for atmospheric CO2, and long-term changes (i.e. ocean acidification) that can affect key ecosystem functions. Carbonate system processes are highly-variable through space and time, which makes it difficult to fully characterize a region without either intensive sampling, or long-term deployment of high-precision instruments. Both of these are difficult in the Arctic, where challenging logistics limit sampling opportunities, and instruments must endure extreme conditions. In this work, we present the first high-resolution marine carbon system dataset covering a full Arctic cycle of sea ice growth and melt. We deployed a Satlantic SeaFET Ocean pH Sensor and a Pro-Oceanus CO2-Pro CV sensor for consecutive nearly year-long deployments onboard the Cambridge Bay Ocean Networks Canada Undersea Community Observatory from September 2015 – June 2018. The sensors measurements were compared to discrete sample references, and determined to require multipoint in situ calibration, but were representative of the greater sea surface mixed layer inside the bay through most of the year. Using a diagnostic box model approach, seasonal influencing processes on the marine carbon system at the platform were quantitatively determined. Air-sea gas exchange and biologic respiration/ remineralization were dominant in the fall, whereas following sea ice freeze-up brine rejection drove pCO2 to seasonal supersaturation with respect to the atmosphere, and the aragonite saturation state to become undersaturated. Shortly after the sun rose under the ice in the late winter, the ecosystem at the platform became net autotrophic at very low light levels, driving pCO2 to undersaturation. As sea ice melted, an under-ice phytoplankton bloom drew down a significant amount of carbon before the open water season, returning the aragonite saturation state to supersaturation at the platform. These observations show a dynamic system, where biological processes occur at times and rates previously unknown to the literature. These processes will need to be included in future biogeochemical modelling efforts, if we are to properly resolve the current, and future, role of the Arctic Ocean basin in global biogeochemical cycles.

Duke P. J., 2019. Describing seasonal marine carbon system processes in Cambridge Bay Nunavut using an innovative sensor platform. MSc thesis, University of Calgary. Article (restricted access)

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