Ecological drivers of nitrogen cycling and primary productivity in changing Arctic and sub-arctic seas.

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The marine ecosystems bordering Canada provide numerous benefits of economic, societal and environmental value, including maintenance of the diversity of species and habitats that support food webs, culture, coastal livelihoods, resource extraction, carbon storage and climate regulation. Climate-driven pressures on those services are fastest and deepest in the Arctic Ocean (AO), where the ocean is impacted in different concurrent ways by warming, acidification, the demise of sea ice and ensuing changes in freshwater loading and upper ocean dynamics. Because these changes necessarily impact primary production, which sets an upper limit to the amount of harvestable resources produced by the sea and its impact on carbon storage and climate regulation, the long-term objective of my Discovery research is to quantify this primary biological productivity and its sensitivity to environmental variability and change in Arctic and sub-arctic seas. Having recently established that the availability of nitrogen (N), and not light, is the most critical factor regulating the magnitude of annual PP in northern seas, I will focus the next 5-year program on a thorough assessment of N cycling and the microbial processes that affect its oceanic inventory and availability to algae. Due to its geographical location, the AO is a planetary conduit that drains water from the Subarctic Pacific and channels it across the Canadian Archipelago into Baffin Bay, the Labrador Sea and ultimately the northwest Atlantic, where fisheries abound. This connectivity is crucial: it makes all affected regions sensitive to the cumulated effect of imbalanced N cycling in upstream areas. In one of three proposed tasks, these cumulated impacts will be diagnosed from spatial patterns in the relative concentrations of different nutrients and in the atomic structure of major N substrates, which integrates dominant N cycling pathways. This work will connect the dots between comprehensive survey sites, where a full suite of N cycling rates will be assessed using incubations with stable isotopic tracers. This second tasks aims to better understand how N cycling is affected by spatially and seasonally changing environmental conditions (e.g. sea-ice cover, light availability, temperature, pH). These two tasks will be complemented by a third, which takes an experimental approach to evaluating the short-term impacts of ocean acidification and warming on nitrogen dynamics and primary production. In keeping with recent achievements, the proposed program will train highly qualified personnel and provide them with the expertise required to undertake scientific careers in academia, government or the private sector. Beyond its confirmed transformative impact on the field of AO ecology, this work will help to refine predictive models, inform the public and assist decision makers in managing the risks and opportunities that abrupt change brings.