ALBERT

Description: On three transects, in October, November and December 2018 with RV Uthörn dissolved methane was determined continuously . We used a degassing unit which was using surface water from the ship's water supply in an overflowing bucket. The gas mixture was subsequently analyzed with a Greenhouse Gas Analyzer from LosGatos. Conversion to methane concentration was performed with water samples, from which the methane content was determined with gas chromatography. Atmospheric methane was measured in certain intervals, by disconnecting the degasser, and connecting the Greenhouse Gas Analyzer with a tubing attached at about 6 m above the water surface at the ships upper deck. For basic hydrographic parameters were determined with a CTD (SSDA Sea and Sun Technology, Trappenkamp, Germany ) was placed in the same bucket as described above.

Description: Rivers are suspected to be a main source of greenhouse gases (methane and carbon dioxide) for coastal seas, while the role of the interjacent tidal flats is still ambiguous. In this study we investigated the role of the river Elbe and the Elbe estuary as source of methane to the North Sea. With high spatial resolution by an underway degassing system and subsequent analysis by cavity ring down spectroscopy a high resolution picture of the methane distribution in surface waters and hydrographic parameters was obtained in autumn to spring 2018/19. For most areas, riverine methane was simply diluted by seawater, overlain by a strong tidal influence. However at several occasions unexpected high methane concentrations were observed. By further detailed analysis we will elucidate the role of riverine versus tidal impact on the methane flux from the coastal North Sea

Description: Estuaries are complex systems, which are expected to hold a big share of global oceanic methane emissions to the atmosphere. Rivers are considered to be the main contributors of methane for coastal seas, whereas both the role and impact of tidal flats are still unclear. The river Elbe being one of the major waterways in central Europe, makes the selected site in the southern North Sea a highly relevant case study. In the conducted research the role of the Elbe Estuary as a source of methane in the North Sea was investigated and the effect of environmental parameters on the methane distribution was explored. With high spatial and temporal resolution, the methane distribution in surface waters was obtained in autumn 2018 with a new system comprising of a degassing unit followed by analysis with off-axis integrated cavity output spectroscopy. Shipborne analysis and measurements at a fixed station were performed. For the measurements close to the shore, a dilution process of methane enriched riverine water and lateral input from tidal flats with methane depleted seawater was observed, affected by a strong tidal influence. The water showed a tidally impacted methane pattern with maximum concentrations up to 5 times higher during low tide than concentrations during high tide. The Elbe Estuary was shown to be a source of methane to the atmosphere. Future studies should consider tidal variations to reduce uncertainties of dissolved methane measurements and methane flux estimations of estuarine systems, hence improve the global methane budget calculations. The role of estuaries as methane sources and their influence on the climate highlight the importance of eradicating these uncertainties.