The German ICOS community gathered aloft and surrounded by snow-capped mountain peaks for a scientific exchange on the activities of the ICOS-D network. The meeting was held from Nov 30 to Dec 01 in the environmental research station Schneefernerhaus, which houses the ICOS atmosphere station "Zugspitze" operated by the Federal Environment Agency (UBA) - in addition to a large number of other measurement laboratories. Beside status reports from the three domains (atmosphere, terrestrial ecosystems, oceans) and the central laboratories, current scientific studies were presented and discussed.

Network status

With a large number of measurement stations, the German network makes a significant contribution to the entire ICOS research infrastructure, which currently comprises almost 150 stations throughout Europe. ICOS Germany currently operates 12 stations in the atmosphere domain (tall towers, mountain and coastal stations), 5 ocean stations (ship lines, fixed stations) and 20 eddy-covariance sites over the most important land use types (forest, grassland, cropland, peatland) in the area of terrestrial ecosystems. In order to get an accurate picture of the most important sources and sinks for greenhouse gases, targeted expansions in regions that have not yet been examined or are underrepresented are also planned for the coming years. For example, the first estuary station at the mouth of the Elbe near Cuxhaven will join the ICOS network in 2023. This will bring together important information on the so far little studied carbon transport between land and ocean. Due to the high contribution to the nationwide CO2 emissions, the different forms of peatland ecosystems are also in the focus of potential further observation sites. An eddy-covariance site recently set up by the University of Münster in the Amtsvenn-Hündfelder Moor is considered a promising candidate for accession.

New format – Domain-specific focal topics

One goal of the annual meeting was to focus on previously set domain-specific topics. In addition to presenting the scientific status quo and the German network contribution, issues and relevance for research and society and potential areas of development were asked to be identified for the German and European ICOS network.

Methane in the atmosphere

Beside CO2, methane (CH4) is the second most important anthropogenic greenhouse gas in the atmosphere and has a 28-fold higher global warming potential than CO2 over a period of 100 years. In 2021, the United States and the European Union launched the Global Methane Pledge (GMP). The initiative aims to reduce global methane emissions by at least 30% by 2030 (compared to 2020) in order to make a significant contribution to curbing global temperature rise. Since the beginning of measurements, the highest increases in global CH4 concentrations were observed in 2020 and 2021. Case studies dealing with the isotopic signature of methane were presented. The signature provides information on the specific emitters or source regions, for example whether the methane comes from biogenic sources (e.g. from wetlands or from livestock farming) or from natural gas or coal production. However, the determination of the CH4 isotope signature is currently not an integral part of the ICOS observation network. Furthermore, the high variability of the atmospheric methane concentrations at the German ICOS stations was illustrated in the lecture series. Particular attention was paid to the coastal station in Westerland on Sylt. Up to now, the periodically increased concentrations could be linked to a prevailing westerly wind direction, but the actual cause or source of the methane was unclear. A new study now provides evidence of methane release from beach nourishment, which serves to protect the dunes and the coastal strip and is carried out a few kilometers offshore. The atmospheric observations from ICOS were also able to analyze the leaks discovered in the Nord Stream pipelines in September 2022 by providing estimates of the source strength and the spread of the methane cloud. In a next step, an emission verification is carried out using inverse modelling.

Integration of ICOS Ocean data with other infrastructures

The Ocean domain focused on networking and integration with data from other infrastructures. Among other things, the possibility of merging the surface data of ICOS SOOP lines (Ship of Opportunity) with vertical profiles from the BGC-Argo program was demonstrated using examples from the North Atlantic and the Baltic Sea. The embedding in major climate research efforts in the Arctic region was highlighted using the example of the unique surface pCO2 data collected by the research vessel Polarstern during the MOSAiC expedition. A combination of different data with a focus on the upper water column and lower atmosphere in connection with the leaks at the two Nord Stream pipelines in the Bornholm Basin (Baltic Sea) showed the high potential of integration within different domains of ICOS. The presentation of the Cuxhaven station (mouth of the Elbe), which was newly included in the ocean component, and its obtained data, demonstrates the extension of the ICOS research question to include land-sea greenhouse gas fluxes, and the high potential of interaction with other European research infrastructures in this field (Danubius , JERICO).

Carbon balances in agricultural ecosystems

Studies from the terrestrial ecosystems set their focus on crop sites and grasslands. Based on the CO2 flux measurements, balances of carbon gain or loss of the ecosystem were presented. A critical look was directed at the accounting methodology. A recognized parameter is the so-called net biome production (NBP), in which the measured CO2 fluxes are offset against the lateral carbon additions (e.g. through organic fertilizers and seeds) and losses through harvesting. Preliminary results show that the grasslands on mineral soils are more or less carbon neutral, i.e. the carbon sequestered through photosynthesis and added through fertilization is approximately in equilibrium with the C content of the harvest losses. On the other hand, arable land and grassland on organic soils (here drained raised bogs) clearly show an alarming tendency. The C loss of the area under consideration, i.e. the sum of the C content of the harvest plus soil respiration, exceeds the carbon input into the system (uptake through photosynthesis plus remaining biomass such as roots and stubble) on average at all stations. This means that current land management leads to a long-term loss of carbon. In order to check the reliability of the results, the components with the largest uncertainties were discussed. While the potential error in the eddy covariance measurements is well documented and can be thoroughly estimated, the overall balances are subject to considerable uncertainties, especially due to the determination of the C content in the biomass - primarily due to variable remaining moisture. During the meeting, it was agreed that a sensitivity study needs to be carried out in order to make more reliable statements and confirm the trends found so far. Furthermore, it was pointed out that with continuing negative net biome productions, a loss in soil carbon should become visible. So far, this cannot be clearly proven, since on the one hand soil C inventories themselves show high uncertainties due to small-scale variability and, depending on the location, the loss does not necessarily come from the organic C substance, but could also stem from inorganic origin, e.g. in soils with high carbonate content. Another point of discussion included the fundamentally promising catch crop cultivation, in which the grown biomass (e.g. from oilseed radish) is completely incorporated into the soil in order to keep the sequestered carbon in the system. However, due to the very small number of years with cover crop cultivation at the observation sites, there is currently no reliable information or conclusions that can be derived from this management option. While initial estimates at the Klingenberg arable site show that the C release from catch crop cultivation can be halved compared to fallow land, the measure proved to be impractical at the Gebesee arable site due to the excessive water requirement. Finally, the importance of good and trustworthy communication with the farmers was pointed out in order to be able to accurately include all important steps of agricultural management in the creation of the carbon balance and to ensure the long-term operation, which is so important for ICOS.

ICOS-Links:

Website of the ICOS Research Infrastructure: https://www.icos-cp.eu/

Website of the German contribution (ICOS-D): https://www.icos-infrastruktur.de/

ICOS brochure: https://www.icos-cp.eu/sites/default/files/2022-03/ICOS_brochure_2022_web.pdf

ICOS Hand book: https://www.icos-cp.eu/sites/default/files/2022-03/ICOS_Handbook_2022_web.pdf

ICOS Strategy: https://www.icos-cp.eu/sites/default/files/cmis/ICOS%20Strategy.pdf

ICOS FLUXES Bulletin: https://www.icos-cp.eu/fluxes