As the isotopic composition of chemical compounds changes during natural biogeochemical processes, isotopes represent a unique tool in biogeochemical research to learn more about the sources of such compounds and their exchange processes between the biosphere, ocean and atmosphere. This technique is for example extensively used in ice core research in our working group at the University of Bern to study greenhouse gas cycles. The trace gas ammonia (NH3) is also produced and emitted during nutrient cycling in the ocean and in soils, but is then incorporated into acidic aerosol in the atmosphere as ammonium (NH4+), which can also be found in the ice. Within AeroTope we will develop a novel mass spectrometric method that will also allow us to measure the nitrogen isotopic composition of NH4+ in polar ice cores.

Lay summary

NH3 is a key intermediate species of the nutrient turnover in the Southern Ocean. After emission from the surface ocean it is incorporated into acidic atmospheric aerosol and partly transported to the Antarctic Ice Sheet, where it is deposited onto the snow surface. In the middle and high latitude northern hemisphere, NH4+ stems from both marine biological as well as soil nitrogen turnover and part of the NH4 bearing aerosol is transported to the Greenland ice sheet.

Using a unique contamination-free Continuous Flow Analysis (CFA) developed in our working group at the University of Bern, we are able to precisely quantify the concentration of NH4+ in the ice. However, quantitative information about the efficiency of nutrient turnover in the Southern Ocean and a quantitative attribution of terrestrial and marine sources in high northern latitudes could be accomplished, if the nitrogen isotopic composition of NH4+ could be measured as well.

To develop such a high precision isotopic measurement technique for NH4+, which is present in the ice only at the parts-per-billion level and which is prone to lab contamination, is the ultimate goal of AeroTope. To this end we combine our extensive experience in coupled gas chromatography-mass spectrometry techniques for isotopic trace gas studies with our unique CFA system for online measurements of chemical aerosol species. The R’Equip project AeroTope will provide part of the funds to purchase a new mass spectrometer for this application and to couple it to our CFA system.