Carbonyl sulfide, fluxes and isotopic signatures measured in Finnish forest and wetland

Abstract

Carbonyl sulfide (COS) can be used to increase our understanding of the atmospheric carbon cycle and its responses to climate change as it can serve as proxy for gross primary production (GPP) calculations. However, the utility of COS is difficult as knowledge about the global COS budget is incomplete. In this project we aim to reduce this knowledge gap. We are the first to investigate COS fluxes measured with Eddy Covariance (EC) on a Northern latitude fen and we analyze COS fluxes at a boreal forest. Furthermore, by date, this is the first study identifying the isotopic signature of COS (34S, 33S and 13C) at these ecosystems at various heights, light availability and seasons. The most important finding is that the fen is a stable sink for the studied period (May-September 2019) with a median COS flux of -9.15 pmol/m-2s-1 (-16.2 and -4.42 pmol/m-2s-1 25%-75% range). The diurnal cycle is primarily driven by photosynthesis active radiation. Upscaling this sink for all Northern latitude wetlands, results in little but significant increase of the Northern Hemisphere COS sink. Finally, we successfully used the data as a proxy for the GPP estimations on the fen. The isotopic signatures have a mean falling within literature ranges and show little difference between the sites, seasons and among the vertical gradient suggesting non fully active ecosystems during our sampling period (February-April 2022). Herewith, we prove the practical utility of the pre-concentration chromatography - isotope ratio mass spectrometer developed at IMAU which gives rise to new study opportunities. In summary, we show the importance of COS measurements on Northern latitude wetlands as we suspect them to be a stable sink and we report a new dataset of COS isotopic signatures. All this is done to improve the understanding of COS and the atmospheric carbon cycle.