Summary of the project
We currently witness in the Arctic:
- a decrease in summer ice cover that exposes sea surface to solar radiation and physical forcings,
- permafrost thawing and increased river runoff, both leading to an increase in the export to ocean of organic carbon previously sequestered in the Tundra,
- 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.
The general objective of the proposed study is to determine the impact of climate change on the fate of terrestrial carbon exported to the Arctic Ocean, microbial diversity, and the photosynthetic production of organic carbon. More specifically, we will attempt to answer the following 10 questions :
- What is the importance and form (particulate vs. dissolved) of the terrestrial organic material transported to the Arctic Ocean by rivers ?
- What are the transport pathways of this material in the coastal zone and offshore ?
- What is the chemical composition of the terrestrial organic material exported and what transformations occur during transport from rivers → coast → open ocean ?
- What is the importance of photo-oxidation of organic material in the pelagic environment (production of CO and CO2) ?
- What is the impact of photodegradation on the chemical composition of terrestrial organic material ?
- What is the importance of bacterial activity in the pelagic environment and its impact on the fate of terrestrial organic material ?
- What is the impact of the photodegradation of organic material on bacterial activity ?
- What is the importance of primary productivity and how is it affected by nutrients and light ?
- How will these processes evolve in response to climate change (principally ice and UV) ?
- What will the impact be of these changes on the biodiversity of bacteria and marine phytoplankton ?
Area of study
The geographic region of the Arctic Ocean that is of particular interest in this study is the continental shelf of the Mackenzie River in the Beaufort Sea. The Mackenzie is the river in the Arctic that exports the most organic particulate matter, and the third most important for the export of total organic carbon (dissolved and particulate) of terrestrial origin (Rachold et al. 2004). During recent decades, this region has experienced a significant reduction in summertime ice cover (Barber and Hanesiak 2004) and an increase in ultraviolet radiation (Bélanger et al. 2006), and the study by Arora & Boer (2001) predicts a strong increase of freshwater inputs if the anthropogenic emissions of CO2 were to double. The choice of this study area is also motivated by the particularly intensive research efforts between 2002 and 2004 in this region carried out by Canada, the United States, Japan, and other countries (including France) within the framework of the international CASES project (Canadian Arctic Shelf Exchange Study, website). The results of this work as well as other research projects during the last two decades in this region form an excellent foundation for the more focused study that we propose here. Related Canadian research activities in the Arctic include the Arcticnet project (Canadian Network of Centers of Excellence) and the Circumpolar Flaw Lead Study (Canadian IPY). Our ultimate goal is to extend our modeling effort to the whole Arctic basin.
TimeTable for activities
1/7/2007 – 30/6/2011