We currently witness in the Arctic: 1) a decrease in summer ice cover that exposes sea surface to solar radiation and physical forcings, 2) permafrost thawing and increased river runoff, both leading to an increase in the export to ocean of organic carbon previously sequestered in the Tundra, 3) an increase in ultraviolet radiation. These three phenomena favour a growing mineralization of organic carbon through photo-oxidation and bacterial activity, resulting in an amplification of the increase in atmospheric CO2. At the same time, the exposure of a larger fraction of ocean surface to sun light and the increase in nutrients brought by rivers lead to larger autotrophic production and sequestration of organic carbon.
To determine and monitor the balance of these processes, we will conduct an extensive study in the Mackenzie River / Beaufort Sea system in July and August 2008 onboard the Canadian research ice-breaker CCGS Amundsen. The spatial distribution of organic carbon stocks (living and detrital) in the water column and sediments will be determined on the shelf and beyond. The magnitude and variability of ... organic carbon mineralization through photo-oxidation and bacterial activity, and production through photosynthesis will be determined. These targeted studies will allow the monitoring of these processes using remote sensing in the coming years and decades. A detailed study of microbial biodiversity will be conducted to describe the different typical communities and eventually anticipate their response to climate change. Diagnostic models of the studied processes (primary production, bacterial activity and light-driven mineralization of organic matter) will be combined with Global Climate Model outputs to assess the fate of the associated carbon fluxes during the next decades under different climate change scenarios.