Despite the fact that the majority of the freshwater flux to the Arctic Ocean comes from Eurasia, there has been no comprehensive dataset of riverine nutrient and organic matter input until recently and our knowledge of the active Ntransformation processes is still limited at best. Consequently, there is no exhaustive budget estimate for N in the Laptev Sea as well as over most Eurasian Arctic shelves that cautiously takes into account internal N-cycling. We thus propose to use multiple stable isotopes to study the sources (Atlantic-derived vs Lena) and cycling (denitrification, assimilation and nitrification) of nitrogen in the Laptev Sea system. Without such investigation on the relative contribution of riverine nutrients and their cycling on the Eurasian Arctic shelves it will not be possible to precisely assess the potential impact of global change on the role of the Arctic Ocean in the carbon cycle and thus in the global climate system.