Seminar

The Arctic Ocean is a globally significant biogeochemical hub that connects the North Pacific to the North Atlantic. Yet key questions on its ecological functions and responses to climate change remain unanswered. Denitrification removes nitrate on the shallow shelves of the Bering Sea, creating a nitrogen (N) deficit that maintains anomalous nutrient ratios and constrains marine productivity downstream in the western Arctic and subarctic western Atlantic. Since the resulting surplus of phosphorus (P) is favorable to diazotrophs, N2 fixation en route to the temperate North Atlantic hypothetically restores N:P ratios toward the Global average and enables diatoms to exploit the silicon surplus. Information on rates of denitrification and N2 fixation as well as their sensitivity to environmental change is very sketchy in cold seas.

Changes in the influx of inorganic and organicnutrients from Rivers and the Bering Strait are also bound to affect productivity on High Arctic shelves. These changes will have remote consequences because the particles produced on shelves sink and the combined action of shelf-basin transport and bacterial decomposition releases nutrients into the Arctic halocline. The halocline propagates over large distances and episodically comes in contact with the euphotic zone through vertical mixing, Ekman pumping or upwelling, which may become more common under low ice conditions. Recent results dealing with all the
aforementioned aspects of biogeochemistry will be presented.

galod@locean-ipsl.upmc.fr