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Determination of nitrogen fixation and denitrification in the Baltic Sea by N2 partial pressure measurements (DFG)



Annekatrin Löffler

A new approach for the quantification of nitrogen fixation and denitrification in the Baltic Sea will be developed. The method is based on measurements of the total pressure of gases dissolved in seawater (total gas tension). Nitrogen fixation and denitrification cause changes in the N2 concentrations and thus affect the total gas tension which is detected by a high sensitivity pressure gauge (GTD – gas tension device). Simultaneous measurements of the O2 and CO2 partial pressures and calculation of the water vapour and argon saturation allow the determination of the N2 partial pressure. Based on the N2 solubility constant, N2 concentrations are calculated and its changes are used to estimate the efficiency of nitrogen fixation and denitrification. The investigations of the denitrification will be performed during research cruises in the Baltic Sea using a pump CTD for supplying seawater to the gas tension device. For the determination of the nitrogen fixation it is planned to integrate the GTD into a fully automated pCO2 and pO2 measurement system that is deployed on a cargo ship (Project FINNMAID).

Abb. 1: Nitrogen cycle