Variable d15N in volcanic gases are typically interpreted as proxies for the contribution of mantle versus slab-derived nitrogen. However, air lies between the mantle and the crust. Hence d15N values alone are blind to air contributions to geological fluids. In order to disambiguate the nitrogen cycle in volcanoes, we determined the N content, d15N and 15N15N excess measured on the Panorama mass spectrometer of 35 N2 samples from a wide variety of crustal and volcanic settings. We find that the low d15N observed in volcanic gases are not mantle contributions but instead must result from isotope fractionation of air-derived N2 in hydrothermal systems. This observation implies that volcanic N2 is dominated by crustal components and air, thus redefining the geodynamic nitrogen sources to the atmosphere.
Leibniz Institut für Ostseeforschung Warnemünde an der Universität Rostock
The Baltic Sea, one of the largest brackish water systems on earth, with various sub-basins characterized by horizontal and vertical salinity gradients, is a unique system to investigate the marine cycling of carbon dioxide and methane. Since 2003, IOW is operating gas analytical instrumentation on the Voluntary Observation Ship (VOS) Finnmaid, commuting between Lübeck and Helsinki and back roughly every three days. The system, which began as an amendment to the Finnish Alg@line project, has originally been set up for the measurement of pCO2 in surface waters, but has since then been extended by continuous measurements of oxygen and methane partial pressure. Further extension in the framework of the Integrated Carbon Observation System (ICOS) is planned for mid-2018. The presentation highlights the potential of continuous surface measurements to depict seasonal cycles as well as interannual variability of trace gas patterns, and to get insights into the underlying processes, including production, mineralization, upwelling, and mixed layer dynamics. In particular, the use for a quantitative assessment of primary production is given. The talk also seeks to communicate the vision of a network of VOS lines across the Baltic for a better monitoring of acidification and eutrophication in the Baltic Sea.