GEOTRACES: Multi-tracer investigation of the effect of climate change on nutrient and carbon cycles in the Arctic Ocean

Significant environmental changes are under way in the Arctic, in particular, a large reduction in sea ice extent and thickness, as well as increasing river discharge. Primary production in the Arctic Ocean is highly seasonal and highest on the shelf and at the receding ice edge. As the summer ice cover shrinks and river input increases, the physical and biogeochemical processes that control both the productivity and the structure of the marine ecosystems it supports are bound to be affected. Yet, our limited understanding of the factors that control the supply and cycling of organic carbon and essential nutrients in Arctic waters prevents us from predicting the longer term consequences of such changes. A better understanding of carbon and nutrient cycling, and their evolution in response to changes in ice cover and river discharge is clearly important to better predict the impact of climate change on the socio-economic sustainability of northern Canadians communities, the carbon sequestration capacity of the Arctic Ocean, and the oceanic sources/sinks of climatologically active gases (CO2, CH4, N2O, DMS). To this end, our proposal aims to: (i) elucidate the mode of addition, removal and cycling of key trace elements which act as micronutrients (Fe, Cu, Zn, Cd) or tracers of sources or processes (Al, Ba, Ga, Mn, Cr, Th, Pa) impacting the carbon and nutrient cycles in the Beaufort Sea and Canada Basin; (ii) use this information to elucidate the effect of climate change on the productivity, carbon sequestration and trace gas emission in the Arctic Ocean; (iii) develop geochemical tracers (alkenone, delta 53C, uranium isotopes, 231Pa/230Th) that will provide a sedimentary record yielding insight into the past evolution of these processes in relation to past climate changes. This project is a contribution to an emerging international program called 'GEOTRACES' whose goals are to document the processes that control the oceanic distribution of trace elements and their isotopes (chemical elements found at very low concentration in seawater) and establish their role as regulators or recorders of processes that affect the structure and productivity of marine ecosystems, the dispersion of contaminants in the ocean, the level of greenhouse gases in the atmosphere, and global climate.