Zooplankton assoziierte Methanproduktion
Zusammenfassung der Projektergebnisse
Oxic methane production in aquatic systems places the methane source close to the wateratmosphere interface, thereby allowing a nearly direct emission into the atmosphere. Several processes that produce methane in oxic waters have been recently identified and it is assumed that climate change will impact their source strength, with far reaching consequences for methane flux and climate feedback. However, mechanisms and magnitudes of this source remain ephemeral. Our own studies in the central Baltic Sea show a recurring CH4 accumulation immediately below the thermocline that emerges during the summer months. This anomaly, together with stable carbon isotope signatures of CH4, indicates an in situ biogenic origin. Isotope values and clonal sequences obtained from water column samples suggest also methanogenic Archaea as potential producers of CH4 in the oxic water column. To elucidate the particular contribution of zooplankton to sub-thermocline CH4 production, we conducted community and food-specific grazing experiments during a cruise in August 2016. Our experimental results suggest that CH4 enrichment in the eastern basin of the central Baltic Sea may involve diet-consumer relationship between DMSP-rich dinoflagellates and the copepod T. longicornis. This assumption is further supported (1) by characteristic biomarkers in the neutral (storage-) lipids of T. longicornis dominated community, and (2) by sequence analyses, which show that methanogens were present on particles and inside T. longicornis, rather than in the free water column. However, microbial analyses as well as our mass balance established for the upper water column of the central Baltic Sea indicate that zooplankton CH4 production rates alone are not sufficient to fully explain the observed CH4 enrichment. These calculations also verify that CH4 is consumed below the thermocline and not transported into the upper water column, suggesting that other, yet unknown sources in the mixed layer are needed to maintain the observed CH4 sea-air flux. Further investigations are needed to identify the methanogenic pathways that are not related to zooplankton activity and that appear to have an important influence on methane emissions into the atmosphere in the central Baltic Sea. Within the last phase of the project run time, the project members developed a network that integrates the expertise from marine (IOW), brackish (IOW), limnic (Hans-Peter Grossart, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, IGB), and terrestrial systems (Frank Keppler, University of Heidelberg). In a workshop that took place at the IOW the working group leaders decided to coordinate future activities to achieve a comprehensive understanding of the control of oxic methane production in ocean and lake system.
Projektbezogene Publikationen (Auswahl)
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(2018). The contribution of zooplankton to methane supersaturation in the oxygenated upper waters of the central Baltic Sea. Limnology and Oceanography, 63(1), 412-430
Schmale, O., Wäge, J., Mohrholz, V., Wasmund, N., Gräwe, U., Rehder, G., Labrenz, M. and Loick‐Wilde, N.
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(2019). Controls on zooplankton methane production in the central Baltic Sea, Biogeosciences, 16(1), 1-16
Stawiarski, B., Otto, S., Thiel, V., Gräwe, U., Loick-Wilde, N., Wittenborn, A. K., Schloemer, S., Wäge, J., Rehder, G., Labrenz, M., Wasmund, N., and Schmale, O.
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(2019). Microcapillary sampling of Baltic Sea copepod gut microbiomes indicates high variability between individuals and the potential for methane production. FEMS Microbiology Ecology
Wäge, J., Strassert, J.F.H., Landsberger, A., Loick-Wilde, N., Schmale, O., Stawiarski, B., Kreikemeyer, B., Michel, G., Labrenz, M.
